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Showing papers on "Intramolecular force published in 2012"


Journal ArticleDOI
Gang He1, Yingsheng Zhao1, Shu-Yu Zhang1, Chengxi Lu1, Gong Chen1 
TL;DR: Efficient methods have been developed to synthesize azetidine, pyrrolidine, and indoline compounds via palladium-catalyzed intramolecular amination of C-H bonds at the γ and δ positions of picolinamide (PA) protected amine substrates, highlighting the use of unactivated C- H bond, especially the C(sp(3))-H bond of methyl groups, as functional groups in organic synthesis.
Abstract: Efficient methods have been developed to synthesize azetidine, pyrrolidine, and indoline compounds via palladium-catalyzed intramolecular amination of C–H bonds at the γ and δ positions of picolinamide (PA) protected amine substrates. These methods feature relatively a low catalyst loading, use of inexpensive reagents, and convenient operating conditions. Their selectivities are predictable. These methods highlight the use of unactivated C–H bond, especially the C(sp3)–H bond of methyl groups, as functional groups in organic synthesis.

417 citations


Journal ArticleDOI
TL;DR: An ab initio molecular dynamics study is presented that reveals, for the first time, the microscopic mechanism of this high proton conductivity ineat liquid phosphoric acid.
Abstract: Neat liquid phosphoric acid (H(3)PO(4)) has the highest intrinsic proton conductivity of any known substance and is a useful model for understanding proton transport in other phosphate-based systems in biology and clean energy technologies. Here, we present an ab initio molecular dynamics study that reveals, for the first time, the microscopic mechanism of this high proton conductivity. Anomalously fast proton transport in hydrogen-bonded systems involves a structural diffusion mechanism in which intramolecular proton transfer is driven by specific hydrogen bond rearrangements in the surrounding environment. Aqueous media transport excess charge defects through local hydrogen bond rearrangements that drive individual proton transfer reactions. In contrast, strong, polarizable hydrogen bonds in phosphoric acid produce coupled proton motion and a pronounced protic dielectric response of the medium, leading to the formation of extended, polarized hydrogen-bonded chains. The interplay between these chains and a frustrated hydrogen-bond network gives rise to the high proton conductivity.

404 citations


Journal ArticleDOI
TL;DR: The photoredox-catalyzed coupling of N-aryltetrahydroisoquinoline and Michael acceptors was achieved using Ru(bpy)(3)Cl(2) or [Ir(ppy)(2)(dtb-bpy)]PF(6) in combination with irradiation at 455 nm generated by a blue LED, demonstrating the trapping of visible light generated α-amino radicals.

283 citations


Journal ArticleDOI
TL;DR: The mild, efficient, and practical intramolecular rhodium-catalyzed C-H/N-H bond functionalization reaction provides isoquinolones with a reverse regioselectivity compared to the reported intermolecular version.
Abstract: The mild, efficient, and practical intramolecular rhodium-catalyzed C—H/N—H bond functionalization reaction provides isoquinolones with a reverse regioselectivity compared to the reported intermolecular version.

254 citations


Journal ArticleDOI
TL;DR: These compounds were stable toward air, water, and amines, despite the absence of steric protection in the vertical direction with respect to the B atoms, and showed characteristic structural, electronic, and photophysical properties.
Abstract: Triphenylborane and 9,10-diphenyl-9,10-dihydro-9,10-diboraanthracene, constrained to a planar arrangement with methylene tethers, were synthesized by intramolecular multi-fold Friedel-Crafts cyclization. These compounds were stable toward air, water, and amines, despite the absence of steric protection in the vertical direction with respect to the B atoms, and showed characteristic structural, electronic, and photophysical properties. In addition, upon treatment with a fluoride ion, these compounds underwent a plane-to-bowl conversion in a controlled manner.

246 citations


Journal ArticleDOI
TL;DR: The recently synthesized 2-hydroxy-substituted isomer (OHBDI) shows an entirely different photochemical behavior experimentally, since it mainly undergoes ultrafast intramolecular excited-state proton transfer, followed by S(1) → S(0) decay and ground-state reverse hydrogen transfer.
Abstract: In commonly studied GFP chromophore analogues such as 4-(4-hydroxybenzylidene)-1,2-dimethyl-1H-imidazol-5(4H)-one (PHBDI), the dominant photoinduced processes are cis-trans isomerization and subsequent S-1 -> S-0 decay via a conical intersection characterized by a highly twisted double bond. The recently synthesized 2-hydroxy-substituted isomer (OHBDI) shows an entirely different photochemical behavior experimentally, since it mainly undergoes ultrafast intramolecular excited-state proton transfer, followed by S-1 -> S-0 decay and ground-state reverse hydrogen transfer. We have chosen 4-(2-hydroxybenzylidene)-1H-imidazol-5(4H)-one (OHBI) to model the gas-phase photodynamics of such 2-hydroxy-substituted chromophores. We first use various electronic structure methods (DFT, TDDFT, CC2, DFT/MRCI, OM2/MRCI) to explore the S-0 and S-1 potential energy surfaces of OHBI and to locate the relevant minima, transition state, and minimum-energy conical intersection. These static calculations suggest the following decay mechanism: upon photoexcitation to the S-1 state, an ultrafast adiabatic charge-transfer induced excited-state intramolecular proton transfer (ESIPT) occurs that leads to the S-1 minimum-energy structure. Nearby, there is a S-1/S-0 minimum-energy conical intersection that allows for an efficient nonadiabatic S-1 -> S-0 internal conversion, which is followed by a fast ground-state reverse hydrogen transfer (GSHT). This mechanism is verified by semiempirical OM2/MRCI surface-hopping dynamics simulations, in which the successive ESIPT-GSTH processes are observed, but without cis-trans isomerization (which is a minor path experimentally with less than 5% yield). These gas-phase simulations of OHM give an estimated first-order decay time of 476 Is for the S-1 state, which is larger but of the same order as the experimental values measured for OHBDI in solution: 270 Is in CH3CN and 230 fs in CH2Cl2. The differences between the photoinduced processes of the 2- and 4-hydroxy-substituted chromophores are attributed to the presence or absence of intramolecular hydrogen bonding between the two rings.

188 citations


Journal ArticleDOI
TL;DR: A linear correlation is found between the branching ratio of intramolecular charge transfer and the charge separation of hole-electron pairs in isolated polymers versus the device fill factor and PCE.
Abstract: Record-setting organic photovoltaic cells with PTB polymers have recently achieved ∼8% power conversion efficiencies (PCE). A subset of these polymers, the PTBF series, has a common conjugated backbone with alternating thieno[3,4-b]thiophene and benzodithiophene moieties but differs by the number and position of pendant fluorine atoms attached to the backbone. These electron-withdrawing pendant fluorine atoms fine tune the energetics of the polymers and result in device PCE variations of 2–8%. Using near-IR, ultrafast optical transient absorption (TA) spectroscopy combined with steady-state electrochemical methods we were able to obtain TA signatures not only for the exciton and charge-separated states but also for an intramolecular (“pseudo”) charge-transfer state in isolated PTBF polymers in solution, in the absence of the acceptor phenyl-C61-butyric acid methyl ester (PCBM) molecules. This led to the discovery of branched pathways for intramolecular, ultrafast exciton splitting to populate (a) the char...

174 citations


Journal ArticleDOI
TL;DR: It is found that both electron-rich and electron-poor aryl azides are efficient sources for the metal nitrene reactive intermediate.
Abstract: Rhodium(II) dicarboxylate complexes were discovered to catalyze the intramolecular amination of unactivated primary, secondary, or tertiary aliphatic C–H bonds using aryl azides as the N-atom precursor. While a strong electron-withdrawing group on the nitrogen atom is typically required to achieve this reaction, we found that both electron-rich and electron-poor aryl azides are efficient sources for the metal nitrene reactive intermediate.

165 citations


Journal ArticleDOI
TL;DR: The metal-induced coupling of tertiary diamondoid bromides gave highly sterically congested hydrocarbon (hetero)dimers with exceptionally long central C-C bonds of up to 1.71 A in 2-(1-diamantyl) tetramantane as mentioned in this paper.
Abstract: The metal-induced coupling of tertiary diamondoid bromides gave highly sterically congested hydrocarbon (hetero)dimers with exceptionally long central C–C bonds of up to 1.71 A in 2-(1-diamantyl)[121]tetramantane. Yet, these dimers are thermally very stable even at temperatures above 200 °C, which is not in line with common C–C bond length versus bond strengths correlations. We suggest that the extraordinary stabilization arises from numerous intramolecular van der Waals attractions between the neighboring H-terminated diamond-like surfaces. The C–C bond rotational dynamics of 1-(1-adamantyl)diamantane, 1-(1-diamantyl)diamantane, 2-(1-adamantyl)triamantane, 2-(1-diamantyl)triamantane, and 2-(1-diamantyl)[121]tetramantane were studied through variable-temperature 1H- and 13C NMR spectroscopies. The shapes of the inward (endo) CH surfaces determine the dynamic behavior, changing the central C–C bond rotation barriers from 7 to 33 kcal mol–1. We probe the ability of popular density functional theory (DFT) ap...

162 citations


Journal ArticleDOI
TL;DR: In this paper, the gold-and palladium-catalysed cross-coupling reactions were investigated on two substrates containing an aryl iodide and an allenoate ester.
Abstract: Two substrates containing an aryl iodide and an allenoate ester were prepared and the gold-induced cycloisomerisation to vinylgold(I) species and their proto-deauration as well as the intramolecular palladium-catalysed cross-coupling reactions were investigated. Switching to catalytic amounts of gold and palladium and stoichiometric amounts of silver did indeed furnish the product of a cycloisomerisation/intramolecular cross-coupling. Control experiments revealed that silver cannot substitute for gold or palladium in these reactions, but a different palladium catalyst in a different oxidation state also afforded the cycloisomerisation/intramolecular cross-coupling products in only slightly reduced yields. By ICP analysis the palladium was shown to contain gold only at the sub-ppm level. This shows how carefully results obtained with such systems have to be interpreted. Then a series of allylic and benzylic o-alkynylbenzoates were investigated in gold- and palladium-catalysed reactions. For esters of benzyl alcohol and cinnamyl alcohol no palladium co-catalyst was needed for the conversion. All reagents were thoroughly checked for palladium traces by ICP analysis in order to thoroughly exclude a gold/palladium co-catalysis. Optimisation of the gold complex, counter ion and solvent showed that gold(I) isonitrile pre-catalysts and silver triflate as activator in dioxane are suitable to convert a number of substrates with aryl, alkyl and even cyclopropyl substituents. Crossover experiments proved an intermolecular allyl transfer.

156 citations


Journal ArticleDOI
TL;DR: The design of a synthetic strategy for coupling such powerful intramolecular redox transformations with a subsequent, intermolecular functionalization step, a number of relevant preliminary mechanistic studies, and an application of the method to a short total synthesis of a naturally occuring indolizidine alkaloid are reported.
Abstract: C H functionalization strategies have made tremendous progress over the past decades. The fast-paced development of this vibrant area is likely due to the recognition by the chemical community of the potential that such methodologies possess to streamline synthetic routes. Indeed, the ability to selectively manipulate targeted C H bonds precludes substrate prefunctionalization prior to the desired key steps and, therefore, represents a shift in the logical rationale of organic synthesis. Particularly appealing for functionalization are C H linkages located immediately adjacent to a heteroatom: the contemporary development of cross-dehydrogenativecoupling (CDC) reactions, where the elegant functionalization of certain classes of amine substrates is achieved at the expense of an external oxidant, attests to this fact. In this context, the family of redox processes involving the intramolecular functionalization of one of the a,a’-positions of certain tertiary amines has witnessed a recent vigorous revival. This transformation is based on the propensity of these amines to undergo a 1,5-hydride shift to an electrophilic moiety followed by cyclization of the zwitterionic intermediate formed (originally called the “tert-amino effect”). Interestingly, the majority of the research described is dominated by Michael acceptors as electropositive fragments (Scheme 1a). Only a limited number of reports have dealt with aldehydes or iminium ions. 9] We became interested in the design of a synthetic strategy for coupling such powerful intramolecular redox transformations with a subsequent, intermolecular functionalization step. The conversion of readily available, 2-substituted aminobenzaldehydes 1 to functionalized derivatives 2 was selected as a model platform to implement this plan (Scheme 1b). This conversion would amount to a redoxtriggered C H functionalization through the sacrificial reduction of the neighboring carboxaldehyde group. We report herein our results on the development of this strategy, a number of relevant preliminary mechanistic studies, and an application of the method to a short total synthesis of a naturally occuring indolizidine alkaloid. We screened different solvents and Brønsted/Lewis acids as catalysts for the envisaged redox process and found the use of 10 mol% of Sc(OTf)3 in 1,2-DCE at 80 8C to be the optimal conditions. We then combined this step with the key C C bond-forming nucleophilic addition (Scheme 1b). To this end, a variety of commercially available Grignard reagents could be successfully employed (Scheme 2). The corresponding a-functionalized amine products, bearing a wide range of appendages, could be obtained in generally good to excellent yields. It was possible to introduce alkyl, allyl, branched alkyl, vinyl, and aryl moieties with only marginal variations in yield (5a–i). The procedure proved nonetheless to be sensitive to the nature of the secondary amine moiety. Upon the change from a pyrrolidine to a piperidine ring, the yield for the corresponding redox product dropped significantly (requiring increased catalyst loading, 5j), whilst the nucleophilic capture step still proceeded smoothly. Importantly, substitution at the aryl ring was also fully compatible with this sequence (5k–s). Given the intrinsic versatility and synthetic usefulness of the alkyne functional group, we became intrigued by the possibility of achieving C(sp)–C(sp) bond formation and eagerly probed lithium alkynyl trifluoroborates as nucleophiles. In the event (Scheme 3), addition of excess lithium alkynyl borates following the redox transformation delivered the desired substituted amines 6 directly in good to very good yields for this one-pot operation. As indicates in Scheme 3, acetylides carrying alkyl, tert-butyl, silyl, and aryl moieties were generally well tolerated (6a–d). Functionalized alkyl moieties (6 e) and densely substituted aryl residues (6 f–h) were also tolerated by this process, as well as substitution at the aromatic ring of the substrate (6 i–o). It is noteworthy that products 5 and 6 result from the overall addition of a strong Scheme 1. a) Prior intramolecular redox methodologies based on the tert-amino effect. b) Proposed design for intermolecular redox-triggered C H functionalization.

Journal ArticleDOI
TL;DR: Application of copper-catalyzed cyclization of γ-alkenylsulfonamides and a δ-alkene C-H functionalization to the concise synthesis of a 5-HT(7) receptor antagonist is demonstrated.
Abstract: Enantioselective copper-catalyzed cyclization of γ-alkenylsulfonamides and a δ-alkenylsulfonamide in the presence of a range of vinyl arenes results in variously functionalized 2-substituted chiral nitrogen heterocycles via a formal alkene C–H functionalization process. Application of this reaction to the concise synthesis of a 5-HT7 receptor antagonist is demonstrated.

Journal ArticleDOI
20 Apr 2012-Science
TL;DR: The data indicate that only the first two water molecules induce a substantial change of the gramicidin S structure by breaking two intramolecular noncovalent bonds, and the peptide structure remains largely intact upon further solvation, reflecting the interplay between the strong intramolescular and weaker intermolecular hydrogen bonds.
Abstract: Studying solvation of a large molecule on an atomic level is challenging because of the transient character and inhomogeneity of hydrogen bonding in liquid water. We studied water clusters of a protonated macrocyclic decapeptide, gramicidin S, which were prepared in the gas phase and then cooled to cryogenic temperatures. The experiment spectroscopically tracked fine structural changes of the clusters upon increasing the number of attached water molecules from 1 to 50 and distinguished vibrational fingerprints of different conformers. The data indicate that only the first two water molecules induce a substantial change of the gramicidin S structure by breaking two intramolecular noncovalent bonds. The peptide structure remains largely intact upon further solvation, reflecting the interplay between the strong intramolecular and weaker intermolecular hydrogen bonds.

Journal ArticleDOI
TL;DR: Mechanistic investigation of gold(I)-catalyzed intramolecular allene hydroalkoxylation established a mechanism involving rapid and reversible C-O bond formation followed by turnover-limiting protodeauration from a mono(gold) vinyl complex.
Abstract: Mechanistic investigation of gold(I)-catalyzed intramolecular allene hydroalkoxylation established a mechanism involving rapid and reversible C–O bond formation followed by turnover-limiting protodeauration from a mono(gold) vinyl complex. This on-cycle pathway competes with catalyst aggregation and formation of an off-cycle bis(gold) vinyl complex.

Journal ArticleDOI
TL;DR: A subtle relationship exists between the output of intramolecular oxidative coupling and the nature of the second aromatic moiety, cation in the porphyrin cavity, oxidant, and type of remaining meso-substituent.

Journal ArticleDOI
TL;DR: By integrating N,N-dimethyl (donor, D) and fumaronitrile (acceptor, A) groups with the biphenyl fluorogen, which has an aggregation-induced emission (AIE) property, Wang et al. as mentioned in this paper obtained the target molecule 2-(4-bromophenyl)-3-(4′-(dimethylamino)-biphenyl-4-yl) fumaritrile, which is a red-to-near-infrared-emitting fluorogen with emission peaks at 653 and 710 nm
Abstract: By integrating N,N-dimethyl (donor, D) and fumaronitrile (acceptor, A) groups with the biphenyl fluorogen, which has an aggregation-induced emission (AIE) property, we have obtained the target molecule 2-(4-bromophenyl)-3-(4′-(dimethylamino)-biphenyl-4-yl) fumaronitrile (BDABFN). BDABFN is a red-to-near-infrared-emitting fluorogen with emission peaks at 653 and 710 nm for its amorphous and crystal solids, respectively. BDABFN shows an evident aggregation-induced emission property, and the fluorescence quantum efficiency of its solid is 26.5%. Cystallographic data indicate that there is no π–π stacking, and neither J- nor H-aggregates are observed between the adjacent molecules. The existence of multiple C–H···π bonds between the adjacent molecules restricts the intramolecular rotation of the D and A moieties and enables the fluorogen to emit intensely in the solid states. Meanwhile, because of strong intramolecular D–A interaction, BDABFN exhibits pronounced solvatochromism, and the fluorescence peak red-...

Journal ArticleDOI
TL;DR: Preliminary catalytic enantioselective reactions are promising and provide evidence that copper is involved in the alkene addition step, likely through a cis-oxycupration mechanism.
Abstract: Fused-ring and bridged-ring tetrahydrofuran scaffolds are found in a number of natural products and biologically active compounds. A new copper-catalyzed intramolecular carboetherification of alkenes for the synthesis of bicyclic tetrahydrofurans is reported herein. The reaction involves Cu-catalyzed intramolecular addition of alcohols to unactivated alkenes and subsequent aryl C–H functionalization provides the C–C bond. Mechanistic studies indicate a primary carbon radical intermediate is involved and radical addition to the aryl ring is the likely C–C bond-forming mechanism. Preliminary catalytic enantioselective reactions are promising (up to 75% ee) and provide evidence that copper is involved in the alkene addition step, likely through a cis-oxycupration mechanism. Catalytic enantioselective alkene carboetherification reactions are rare and future development of this new method into a highly enantioselective process is promising. During the course of the mechanistic studies a protocol for alkene hyd...

Journal ArticleDOI
TL;DR: An efficient method has been developed for the synthesis of indoline compounds from picolinamide (PA)-protected β-arylethylamine substrates via palladium-catalyzed intramolecular amination of ortho-C(sp(2))-H bonds.

Journal ArticleDOI
TL;DR: The synthesis and characterization of symmetric BODIPY dyads where the chromophores are attached at the meso position, using either a phenylene bridge or direct linkage are reported.

Journal ArticleDOI
TL;DR: It has been shown that XHY iHBs with red-shift values over 40 cm(-1) are characterized by the following minimal values of the XHY angle, ρ(cp) and nubla(2)ρ(cp): 112°, 0.005 e a(0)(-3) and 0.016 e a.(-5), respectively.
Abstract: Physical properties of over 8000 intramolecular hydrogen bonds (iHBs), including 2901 ones of the types OH⋯O, OH⋯N, NH⋯O and OH⋯C, in 4244 conformers of the DNA-related molecules (four canonical 2′-deoxyribonucleotides, 1,2-dideoxyribose-5-phosphate, and 2-deoxy-D-ribose in its furanose, pyranose and linear forms) have been investigated using quantum theory of atoms in molecules (QTAIM) and vibrational analysis. It has been found that for all iHBs with positive red-shift of the proton donating group stretching frequency the shift value correlates with ρcp—the electron charge density at the (3,−1)-type bond critical point. Combining QTAIM and spectroscopic data new relationships for estimation of OH⋯O, OH⋯N, NH⋯O and OH⋯C iHB enthalpy of formation (kcal mol−1) with RMS error below 0.8 kcal mol−1 have been established: EOH⋯O = −3.09 + 239·ρcp, EOH⋯N = 1.72 + 142·ρcp, ENH⋯O = −2.03 + 225·ρcp, EOH⋯C = −0.29 + 288·ρcp, where ρcp is in e a0−3 (a0 – the Bohr radius). It has been shown that XH⋯Y iHBs with red-shift values over 40 cm−1 are characterized by the following minimal values of the XHY angle, ρcp and ∇2ρcp: 112°, 0.005 e a0−3 and 0.016 e a0−5, respectively. New relationships have been used to reveal the strongest iHBs in canonical 2′-deoxy- and ribonucleosides and the O5′H⋯N3 H-bond in ribonucleoside guanosine was found to have the maximum energy (8.1 kcal mol−1).

Journal ArticleDOI
TL;DR: An excited-state intramolecular proton transfer (ESIPT) mechanism based two reactive probes HBTCo and HBTCu is reported for the selective detection of Co(2+) and Cu(+) respectively in a reducing aqueous environment.

Journal ArticleDOI
TL;DR: These results represent the first general examples of aryl chloride/C-H coupling under transition-metal-free conditions and only 10 mol % of simple and inexpensive ethylene glycol is required.

Journal ArticleDOI
TL;DR: The intermolecular amination of unactivated α-olefins and bicycloalkenes with arylamides and sulfonamides is reported to generate synthetically useful protected amine products in high yield.
Abstract: The intermolecular addition of N-H bonds to unactivated alkenes remains a challenging, but desirable, strategy for the synthesis of N-alkylamines. We report the intermolecular amination of unactivated α-olefins and bicycloalkenes with arylamides and sulfonamides to generate synthetically useful protected amine products in high yield. Mechanistic studies on this rare catalytic reaction revealed a resting state that is the product of N-H bond oxidative addition and coordination of the amide. Rapid, reversible dissociation of the amide precedes reaction with the alkene, but an intramolecular, kinetically significant rearrangement of the species occurs before this reaction with alkene.

Journal ArticleDOI
TL;DR: Spectral investigations on novel N,O-chelated naphthyridine-BF(2) complexes with push-pull structures reveal that photoinduced intramolecular charge transfer occurs and results in a large Stokes shift, which is further supported by density functional theory based theoretical calculations.

Journal ArticleDOI
TL;DR: Analysis of the alkyne-insertion transition states revealed that the serious steric repulsion between the substituents in theAlkyne moiety of the substrates and the rigid H(8)-BINAP backbone is responsible for not generating the disfavored [3 + 2] cycloadducts.
Abstract: A highly enantioselective Rh(I)-catalyzed intramolecular [3 + 2] cycloaddition of 1-yne-VCPs to bicyclo[3.3.0] compounds with an all-carbon chiral quaternary stereocenter at the bridgehead carbon was developed. DFT calculations of the energy surface of the catalytic cycle (complexation, cyclopropane cleavage, alkyne insertion, and reductive elimination) of the asymmetric [3 + 2] cycloaddition reaction indicated that the rate- and stereo-determining step is the alkyne-insertion step. Analysis of the alkyne-insertion transition states revealed that the serious steric repulsion between the substituents in the alkyne moiety of the substrates and the rigid H(8)-BINAP backbone is responsible for not generating the disfavored [3 + 2] cycloadducts.

Journal ArticleDOI
TL;DR: The total synthesis of the terpene indole alkaloid (+)-ibophyllidine is performed through a pathway involving asymmetric phosphine catalysis, with the novel l-4-hydroxyproline-derived chiral phosphine mediating the key [3 + 2] annulation.
Abstract: In this study we performed the total synthesis of the terpene indole alkaloid (+)-ibophyllidine through a pathway involving asymmetric phosphine catalysis, with our novel L-4-hydroxyproline-derived chiral phosphine mediating the key [3 + 2] annulation. Hydrogenation of the [3 + 2] adduct allowed the rapid formation of the stereochemically dense pyrrolidine ring of (+)-ibophyllidine in excellent yield with exceptionally high levels of both diastereo- and enantioselectivity. We constructed the remainder of the pentacyclic skeleton through an intramolecular alkylation and an intramolecular aza-Morita–Baylis–Hillman reaction.

Journal ArticleDOI
TL;DR: Combining information from X-ray emission spectroscopy and scattering, the excitation fraction as well as the temperature and density changes of the solvent can be closely followed on the subnanosecond time scale of the HS lifetime, allowing the detection of an ultrafast change in bulk solvent density.
Abstract: We have studied the photoinduced low spin (LS) to high spin (HS) conversion of [Fe(bipy)(3)](2+) in aqueous solution. In a laser pump/X-ray probe synchrotron setup permitting simultaneous, time-resolved X-ray diffuse scattering (XDS) and X-ray spectroscopic measurements at a 3.26 MHz repetition rate, we observed the interplay between intramolecular dynamics and the intermolecular caging solvent response with better than 100 ps time resolution. On this time scale, the initial ultrafast spin transition and the associated intramolecular geometric structure changes are long completed, as is the solvent heating due to the initial energy dissipation from the excited HS molecule. Combining information from X-ray emission spectroscopy and scattering, the excitation fraction as well as the temperature and density changes of the solvent can be closely followed on the subnanosecond time scale of the HS lifetime, allowing the detection of an ultrafast change in bulk solvent density. An analysis approach directly utilizing the spectroscopic data in the XDS analysis effectively reduces the number of free parameters, and both combined permit extraction of information about the ultrafast structural dynamics of the caging solvent, in particular, a decrease in the number of water molecules in the first solvation shell is inferred, as predicted by recent theoretical work.

Journal ArticleDOI
TL;DR: In solution, the binding is weak, and NMR spectroscopy reveals a rapid exchange of the NHC between the two boron centers, and DFT calculations reveal that the exchange involves dissociation and reassociation of NHC rather than an intramolecular process.
Abstract: The Lewis base adduct of B2pin2 and the NHC (1,3-bis(cyclohexyl)imidazol-2-ylidene), which was proposed to act as a source of nucleophilic boryl groups in the β-borylation of α,β-unsaturated ketones, has been isolated, and its solid state structure and solution behavior was studied. In solution, the binding is weak, and NMR spectroscopy reveals a rapid exchange of the NHC between the two boron centers. DFT calculations reveal that the exchange involves dissociation and reassociation of NHC rather than an intramolecular process.

Journal ArticleDOI
TL;DR: A transition-metal-free intramolecular dehydrohalide coupling via intramolescular homolytic aromatic substitution (HAS) with aryl radicals has been developed in the presence of potassium tert-butoxide and an organic molecule as the catalyst.

Journal ArticleDOI
TL;DR: A rational explanation for the formation of contiguous stereogenic centers is given and a nickel-mediated intermolecular reductive cross-coupling reaction of unactivated alkyl bromides and aryl iodides at room temperature is developed and successfully extended.
Abstract: A nickel-mediated intermolecular reductive cross-coupling reaction of unactivated alkyl bromides and aryl iodides at room temperature has been developed and successfully extended to less explored intramolecular versions and tandem cyclization-intermolecular cross-coupling. Highly stereoselective (or stereospecific) synthesis of linear-fused perhydrofuro[2,3-b]furan (pyran) and spiroketal skeletons allows rapid access to these useful building blocks, which would be potentially valuable in the synthesis of relevant natural products. A rational explanation for the formation of contiguous stereogenic centers is given.