Showing papers on "Annulation published in 2015"
TL;DR: This review summarizes research directed towards the formation of carbocyclic adducts from donor-acceptor cyclopropanes and focuses on annulation and cycloaddition reactions mediated by Lewis or protic acid, bases, or thermal conditions.
Abstract: This review summarizes research directed towards the formation of carbocyclic adducts from donor–acceptor cyclopropanes. The focus of the review is on annulation and cycloaddition reactions (both inter- and intramolecularly) mediated by Lewis or protic acid, bases, or thermal conditions. Rearrangements resulting in carbocycles and those reactions mediated by transition metal catalysis have been excluded.
366 citations
316 citations
TL;DR: In the presence of a chiral Cp/Rh catalyst and combined oxidants of Cu(OAc)2 and air, various highly enantioenriched spirocyclic enones bearing an all-carbon quaternary stereogenic center could be synthesized in 33-98% yields with up to 97:3 er.
Abstract: A Rh-catalyzed enantioselective dearomatization of 1-aryl-2-naphthols with internal alkynes via C–H functionalization reaction was achieved. In the presence of a chiral Cp/Rh catalyst and combined oxidants of Cu(OAc)2 and air (oxygen), various highly enantioenriched spirocyclic enones bearing an all-carbon quaternary stereogenic center could be synthesized in 33–98% yields with up to 97:3 er.
232 citations
TL;DR: Mechanistic studies identified the key factors controlling the elementary step of the oxidation of the ruthenium(0) complex.
Abstract: Aerobic oxidative CH functionalizations of weakly coordinating benzoic acids have been accomplished with versatile ruthenium(II) biscarboxylates under ambient oxygen or air. Mechanistic studies identified the key factors controlling the elementary step of the oxidation of the ruthenium(0) complex.
226 citations
TL;DR: This tutorial review will describe Lewis base-promoted annulation reactions with MBHADs, with a special emphasis on recent work regarding diverse reactivities of MBH ADs.
Abstract: Lewis base-promoted annulation reactions with MBHADs have emerged as a key platform for the construction of functionalized carbo- and heterocycles. MBHADs, which are economical and readily available, exert diverse and amazing reactivity when reacted with a wide range of electrophiles. A variety of carbo- and heterocycles, most of which are predominant in natural products and pharmaceuticals, could be constructed with high efficiency. This tutorial review will describe these annulation reactions, with a special emphasis on recent work regarding diverse reactivities of MBHADs.
211 citations
TL;DR: Efficient, scalable cobalt-catalyzed redox-neutral [4+2] annulation of readily available oximes and alkyne is reported, which progresses smoothly by way of a reversible cyclometallation without any external oxidizing agent, and produces only water as the side product.
Abstract: Efficient, scalable cobalt-catalyzed redox-neutral [4+2] annulation of readily available oximes and alkyne is reported. The developed synthetic methodology is widely applicable and tolerates various functional groups including heterocycles. A stable Cp*Co(III) neutral complex is employed as the catalyst for this redox-neutral [4+2] annulation reaction, which progresses smoothly by way of a reversible cyclometallation without any external oxidizing agent, and produces only water as the side product.
173 citations
TL;DR: C-H/N-O functionalizations by cobalt(III) catalysis allowed the expedient synthesis of a broad range of isoquinolines and internal and challenging terminal alkynes proved to be viable substrates for an isohypsic annulation.
Abstract: C-H/N-O functionalizations by cobalt(III) catalysis allowed the expedient synthesis of a broad range of isoquinolines. Thus, internal and challenging terminal alkynes proved to be viable substrates for an isohypsic annulation, which was shown to proceed by a facile C-H cobaltation.
160 citations
TL;DR: The synthetic value of the dihydropyran motif was demonstrated by a concise preparation of an anti-hypercholesterolemic agent by employing allene ketones as C2 synthons and β,γ-unsaturated α-keto esters as C4 synthons.
Abstract: A phosphine-catalyzed novel [4+2] annulation process was devised employing allene ketones as C2 synthons and β,γ-unsaturated α-keto esters as C4 synthons. In the presence of an l-threonine-derived bifunctional phosphine, 3,4-dihydropyrans were obtained in high yields and with virtually perfect enantioselectivities. The synthetic value of the dihydropyran motif was demonstrated by a concise preparation of an anti-hypercholesterolemic agent.
158 citations
TL;DR: This method achieves two C(sp(3))-H oxidative functionalizations and an annulation, thus providing efficient and general access to a variety of fused five-membered carbocyclic hydrocarbons.
Abstract: A new metal-free oxidative radical [2+2+1] carbocyclization of benzene-linked 1,n-enynes with two C(sp(3))H bonds adjacent to the same heteroatom is described. This method achieves two C(sp(3))H oxidative functionalizations and an annulation, thus providing efficient and general access to a variety of fused five-membered carbocyclic hydrocarbons.
156 citations
TL;DR: An efficient [4 + 3] cycloaddition reaction of D-A cyclopropanes with dienes has been successfully developed, delivering a variety of cycloheptenes and [n,5,0]carbobicycles with excellent stereoselectivity.
Abstract: An efficient [4 + 3] cycloaddition reaction of D–A cyclopropanes with dienes has been successfully developed. The reaction proceeds well with various dienolsilyl ethers in the presence of Lewis acid, delivering a variety of cycloheptenes and [n,5,0]carbobicycles with excellent stereoselectivity. The asymmetric version of this reaction is also realized using a newly designed chiral Cy-TOX ligand, providing a new approach to access optically active cycloheptenes and [n,5,0]carbobicycles. Mechanisic study reveals that the reaction involves a stepwise pathway, which undergoes an unusual ring opening of five-membered [3 + 2] intermediate and sequential intramolecular cyclization to afford the thermodynamically stable [4 + 3] annulation product.
155 citations
TL;DR: A highly efficient cobalt(II)-catalyzed alkynylation/annulation of terminal alkynes assisted by an N,O-bidentate directing group is described, and offers a new approach to 3-methyleneisoindolin-1-one, which can be converted into an oxadiazine salt in one step.
Abstract: A highly efficient cobalt(II)-catalyzed alkynylation/annulation of terminal alkynes assisted by an N,O-bidentate directing group is described. This protocol is characterized by wide substrate scope utilizing cheap cobalt catalysts, and offers a new approach to 3-methyleneisoindolin-1-one, which can be converted into an oxadiazine salt in one step. Moreover, the directing group could be removed in three steps.
TL;DR: In this article, Isoindolinone derivatives were prepared in a step-economical fashion by a C-H/N-H functionalization process with a catalytic system composed of Co(OAc)2 and Mn(OAC)2 or AgOPiv.
Abstract: Isoindolinone derivatives were prepared in a step-economical fashion by a C–H/N–H functionalization process with a catalytic system composed of Co(OAc)2 and Mn(OAc)2 or AgOPiv. The oxidative annulation by benzamides occurred efficiently with differently substituted electron-deficient alkenes. Mechanistic studies were indicative of a kinetically relevant, carboxylate-assisted C–H cobaltation.
TL;DR: Rhodium-catalyzed directed carbene insertions into aromatic CH bonds of S-aryl sulfoximines lead to intermediates, which upon dehydration provide 1,2-benzothiazines in excellent yields.
Abstract: Rhodium-catalyzed directed carbene insertions into aromatic CH bonds of S-aryl sulfoximines lead to intermediates, which upon dehydration provide 1,2-benzothiazines in excellent yields. The domino-type process is regioselective and shows a high functional-group tolerance. It is scalable, and the only by-products are dinitrogen and water. Three illustrative transformations underscore the synthetic value of the products.
TL;DR: Through iodine catalysis, the direct oxidative coupling/annulation of β-keto esters or 2-pyridinyl-β-esters with alkenes was achieved and provides a simple and selective way for the synthesis of dihydrofurans and indolizines in one step.
TL;DR: A switchable catalytic activation of enals with aromatic azomethine imines that provides high selectivity using NHC organocatalysts is shown to afford different products with high regio- and stereoselectivity.
Abstract: The development of general catalytic methods for the regio- and stereoselective construction of chiral N-heterocycles in a diversity-oriented fashion remains a formidable challenge in organic synthesis. N-heterocyclic carbene (NHC) catalysis has been shown to produce a variety of outcomes, but control of the reactivity has rarely been demonstrated. Here we report a switchable catalytic activation of enals with aromatic azomethine imines that provides high selectivity using NHC organocatalysts. The original selectivity corresponds to the acidity of the base used in the reaction. The catalytically generated chiral homoenolate or enol intermediate undergoes enantioselective annulation with electrophiles such as N-iminoquinolinium ylides, N-iminoisoquinolinium ylides and β-N-iminocarboline ylides. The good-to-high overall yields, high regioselectivities and excellent enantioselectivities observed are controlled by the catalyst and reaction conditions.
TL;DR: The first examples of the synthesis of pyrroloindolines by means of (3 + 2) dearomative annulation reactions between 3-substituted indoles and highly reactive azaoxyallyl cations are reported.
Abstract: Herein, we report the first examples of the synthesis of pyrroloindolines by means of (3 + 2) dearomative annulation reactions between 3-substituted indoles and highly reactive azaoxyallyl cations. Computational studies using density functional theory (DFT) (B3LYP-D3/6-311G**++) support a stepwise reaction pathway in which initial C–C bond formation takes place at C3 of indole, followed by ring closure to give the observed products. Insights gleaned from these calculations indicate that the solvent, either TFE or HFIP, can stabilize the transition state through H-bonding interactions with oxygen of the azaoxyallyl cation and other relevant intermediates, thereby increasing the rates of these reactions.
TL;DR: Chelate assisted cobalt catalyzed C-H and N-H annulation of aryl sulfonamide with terminal and internal alkynes with very high regioselectivity and excellent functional group tolerance were achieved using oxygen as a co-oxidant.
TL;DR: In the absence of substrates, donor-acceptor cyclopropanes can undergo dimerization reactions in quite various ways which are summarized in this article, which is an excellent review.
TL;DR: This transformation provides straightforward access to indeno[1,7-cd]azepine architectures through a sequence involving the formation of a rhodium(III) azavinyl carbene, dual C(sp(2))-H functionalization, and [3+2]/[5-2] annulation.
Abstract: A rhodium(III)-catalyzed [3+2]/[5+2] annulation of 4-aryl 1-tosyl-1,2,3-triazoles with internal alkynes is presented. This transformation provides straightforward access to indeno[1,7-cd]azepine architectures through a sequence involving the formation of a rhodium(III) azavinyl carbene, dual C(sp(2))-H functionalization, and [3+2]/[5+2] annulation.
TL;DR: A novel and efficient Rh-catalyzed carbonylation and annulation of simple anilines with CO and alkynes through N-H and C-H bond activation for the direct synthesis of quinolin-2(1H)-ones has been developed.
Abstract: A novel and efficient Rh-catalyzed carbonylation and annulation of simple anilines with CO and alkynes through N–H and C–H bond activation for the direct synthesis of quinolin-2(1H)-ones has been developed. Simple anilines without preactivation, broad substrate scope with hetero/polycycles, and high-value products make this protocol very practical and attractive. A key rhodacycle complex was isolated and well-characterized.
TL;DR: A formal 1,6-conjugated addition-mediated [2+1] annulation to synthesize spiro[2.5]octa-4,7-dien-6-one with p-quinone methides and sulfur ylides has been described and exhibited good functional group tolerance and scalability without the use of metals and bases.
Abstract: A formal 1,6-conjugated addition-mediated [2+1] annulation to synthesize spiro[2.5]octa-4,7-dien-6-one with p-quinone methides and sulfur ylides has been described. This domino-type process was highly diastereoselective and exhibited good functional group tolerance and scalability without the use of metals and bases.
TL;DR: The first successful example of a visible-light-induced copper-catalyzed process for C-H annulation of arylamines with terminal alkynes and benzoquinone is described, which represents a sustainable and atom-economical approach for the preparation of complex indoles from easily accessible starting materials under visible- light irradiation.
Abstract: The first successful example of a visible-light-induced copper-catalyzed process for C-H annulation of arylamines with terminal alkynes and benzoquinone is described. This three-component reaction allows use of a variety of commercial terminal alkynes as coupling partners for the one-step regioselective synthesis of functionalized indoles. Moreover, the current process represents a sustainable and atom-economical approach for the preparation of complex indoles from easily accessible starting materials under visible-light irradiation, without the need for expensive metals and harsh reaction conditions.
TL;DR: An unprecedented rhodium(III)-catalyzed regioselective redox-neutral annulation reaction of 1-naphthylamine N-oxides with diazo compounds was developed to afford various biologically important 1H-benzo[g]indolines.
Abstract: An unprecedented rhodium(III)-catalyzed regioselective redox-neutral annulation reaction of 1-naphthylamine N-oxides with diazo compounds was developed to afford various biologically important 1H-benzo[g]indolines. This coupling reaction proceeds under mild reaction conditions and does not require external oxidants. The only by-products are dinitrogen and water. More significantly, this reaction represents the first example of dual functiaonalization of unactivated a primary C(sp(3) )H bond and C(sp(2) )H bond with diazocarbonyl compounds. DFT calculations revealed that an intermediate iminium is most likely involved in the catalytic cycle. Moreover, a rhodium(III)-catalyzed coupling of readily available tertiary aniline N-oxides with α-diazomalonates was also developed under external oxidant-free conditions to access various aminomandelic acid derivatives by an O-atom-transfer reaction.
TL;DR: High selectivity between two possible directing groups, as well as control of the direction of rotation in the isomerization of an O-bound rhodium enolate into the C-bound isomer, appear to be critical for high enantiomeric excesses.
Abstract: Chiral cyclopentadienyl rhodium complexes promote highly enantioselective enol-directed C(sp2)-H functionalization and oxidative annulation with alkynes to give spiroindenes containing all-carbon quaternary stereocenters. High selectivity between two possible directing groups, as well as control of the direction of rotation in the isomerization of an O-bound rhodium enolate into the C-bound isomer, appear to be critical for high enantiomeric excesses.
01 Jan 2015
TL;DR: In this paper, the Suzuki-Miyaura cross-coupling of borocations has been used for boron-containing polymers, including alkenyl/ alkyl and allylboron compounds.
Abstract: Boryl anions.- Fundamental and applied properties of borocations.- Asymmetric catalytic borylation reactions.- Metal-catalyzed annulation of alkynylboronates.- Improving transformation through organotrifluoroborates.- Principles on dehydrocoupling of phosphine-boranes and amine-boranes Stereoselective Suzuki-Miyaura cross-coupling including alkenyl / alkyl and allylboron compounds.- Boronic acid catalysed reactions.- Stereospecific coupling throughout Lithiation/Borylation.- Boron-containing polymers.
TL;DR: A mild and efficient Rh(III)-catalyzed regioselective synthesis of isoquinolones and pyridones and derivatives containing various functional groups has been developed.
TL;DR: The rhodium(III)-catalyzed C-H annulation of nitrones with symmetrical diaryl alkynes is reported as an alternative method to prepare 2,3-diaryl-substituted N-unprotected indoles with two different aryl groups, providing the indole products with exclusive regioselectivity.
Abstract: The direct CH annulation of anilines or related compounds with internal alkynes provides straightforward access to 2,3-disubstituted indole products. However, this transformation proceeds with poor regioselectivity in the synthesis of unsymmetrically 2,3-diaryl substituted indoles. Herein, we report the rhodium(III)-catalyzed CH annulation of nitrones with symmetrical diaryl alkynes as an alternative method to prepare 2,3-diaryl-substituted N-unprotected indoles with two different aryl groups. One of the aryl substituents is derived from NC-aryl ring of the nitrone and the other from the alkyne substrate, thus providing the indole products with exclusive regioselectivity.
TL;DR: This work has developed, with the aid of a new chiral spirophosphine catalyst, a method with increased utility, specifically, improved yield, enhanced scope, and good ee.
Abstract: Due in part to the common occurrence of five-membered nitrogen heterocycles in bioactive molecules, the discovery of methods for the enantioselective synthesis of such structures is a useful endeavor. Building on a single example by Tong of a phosphine-catalyzed [4 + 1] annulation of an amine with an allene that furnished an achiral dihydropyrrole in 22% yield, we have developed, with the aid of a new chiral spirophosphine catalyst, a method with increased utility, specifically, improved yield, enhanced scope (the use of γ-substituted allenes), and good ee. The enantioenriched dihydropyrrole products can be transformed into other interesting families of compounds with very good stereoselectivity.
TL;DR: Rh(III)-catalyzed C-H activation of 2-phenylimidazo[1,2-a]pyridines in divergent oxidative coupling with alkynes has been achieved and a rhodacyclic intermediate has been isolated.
Abstract: Rh(III)-catalyzed C–H activation of 2-phenylimidazo[1,2-a]pyridines in divergent oxidative coupling with alkynes has been achieved. Selective mono versus 2-fold C–H activation has been attained under condition control. When AgOAc was used as an oxidant, the coupling afforded 5,6-disubstituted naphtho[1′,2′:4,5]imidazo[1,2-a]pyridines as a result of initial nitrogen chelation-assisted C–H activation at the benzene ring followed by rollover C–H activation. In contrast, the reaction afforded a fused isoquinolinium salt as a result of C–C and C–N coupling when AgBF4 was employed as a co-oxidant. A rhodacyclic intermediate has been isolated.
TL;DR: Evaluation of the antiviral activity of these compounds revealed that xiamycin A is a potent agent against herpes simplex virus–1 (HSV-1) in vitro and the dimeric congener dixiamYcin C has been synthesized for the first time.
Abstract: Indolosesquiterpenoids are a growing class of natural products that exhibit a wide range of biological activities. Here, we report the total syntheses of xiamycin A and oridamycins A and B, indolosesquiterpenoids isolated from Streptomyces. Two parallel strategies were exploited to forge the carbazole core: 6π-electrocyclization/aromatization and indole C2-H bond activation/Heck annulation. The construction of their trans-decalin motifs relied on two diastereochemically complementary radical cyclization reactions mediated by Ti(III) and Mn(III), respectively. The C23 hydroxyl of oridamycin B was introduced by an sp(3) C-H bond oxidation at a late stage. On the basis of the chemistry developed, the dimeric congener dixiamycin C has been synthesized for the first time. Evaluation of the antiviral activity of these compounds revealed that xiamycin A is a potent agent against herpes simplex virus-1 (HSV-1) in vitro.