Showing papers on "Intramolecular reaction published in 2013"

Gold-Catalyzed Intramolecular Regio- and Enantioselective Cycloisomerization of 1,1-Bis(indolyl)-5-alkynes

Abstract: ticularly abundant in marine sponges. In bis(indole) alkaloids, two indole moieties are connected to various heterocyclic units. Compounds with this structural motif exhibit a wide spectrum of pharmacological activities, including antibacterial, antiviral, and cytotoxic activities, which make bis(indole) alkaloids and their analogues attractive targets for biomedical and synthetic studies. Gold catalysis, which is currently a hot topic in homogeneous catalysis, can be well understood with the concept of carbophilic p-acids, which are widely employed in the activation of alkynes, allenes, and alkenes. However, in contrast to gold-catalyzed enantioselective transformations involving allenes, there are relatively few examples involving alkynes. Echavarren and co-workers reported an elegant gold-catalyzed intramolecular reaction of indoles with alkynes, which proceeded through 6-endo-dig, 6-exo-dig, 7exo-dig, and 8-endo-dig cyclizations and were highly dependent on the oxidation state of the gold catalyst. Further investigations by this group indicated that similar spirocyclic intermediates were probably involved in cyclizations of various other substrates [Scheme 2, Eq. (1)]. Recently,

Mild Metal-Free Intramolecular Oxidative Alkylation of a Csp3H Bond Adjacent to a Nitrogen Atom: A Versatile Approach to Ring-Fused Tetrahydroquinolines

Abstract: A metal-free intramolecular oxidative cross-coupling reaction for the constructing Csp3Csp3 bonds mediated by 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) under mild conditions was realized for the first time. This novel strategy provides a simple, efficient, and environmentally friendly access to diverse ring-fused tetrahydroquinoline derivatives.

Synthesis of 1‐Arylnaphthalenes by Gold‐Catalyzed One‐Pot Sequential Epoxide to Carbonyl Rearrangement and Cyclization with Arylalkynes

Abstract: Intermolecular and intramolecular reactions of a one-pot gold-catalyzed epoxide rearrangement followed by an electrophilic addition to arylalkynes to synthesize 1-arylnaphthalenes have been reported. The intramolecular reaction has been applied to synthesize 1-arylnaphthalenes fused with saturated furan, pyran, pyrrole, and cyclopentane ring systems.

Enantiospecific total synthesis of (+)-tanikolide via a key [2,3]-Meisenheimer rearrangement with an allylic amine N-oxide-directed epoxidation and a one-pot trichloroisocyanuric acid N-debenzylation and N-chlorination.

Abstract: The enantiospecific total synthesis of the δ-lactonic marine natural product (+)-tanikolide (1), isolated from Lyngbya majuscula , was achieved using a [2,3]-Meisenheimer rearrangement as the key reaction. During this rearrangement, we discovered that the allylic amine N-oxide could direct the m-CPBA double-bond epoxidation to the syn position. The resulting syn product 8 underwent epoxide ring opening under the m-CBA conditions to give the five- and six-membered cyclic ether amine N-oxides, which we further treated with Zn and conc. HCl to obtain the reduced bisbenzyl tertiary amines 23 and 22, respectively. When 23 and 22 were treated with trichloroisocyanuric acid (TCCA) in dichloromethane, oxidation at the benzyl position occurred, forming iminium ions. These intermediates were trapped by intramolecular reaction with the hydroxyls, and the resulting intermediates were then oxidized or shifted to afford 25 and 24, respectively. The entire one-pot process involves N-debenzylation, N-chlorination, and hemiacetal oxidation. The amine N-oxide-directed epoxidation complements Davies' ammonium-directed epoxidation. Thus, TCCA N-debenzylation is described for the first time and might be a useful N-debenzylation technique.

Access to 2,6-Disubstituted Piperidines: Control of the Diastereoselectivity, Scope, and Limitations. Applications to the Stereoselective Synthesis of (−)-Solenopsine A and Alkaloid (+)-241D

Abstract: Scope and limitations in the diastereoselective preparation of 2,6-cis or 2,6-trans disubstituted piperidines are described, through intramolecular reaction of chiral β′-carbamate-α,β-unsaturated ketone. This methodology has been applied to the total synthesis of a few well chosen examples, such as (−)-solenopsine A and alkaloid (+)-241D.

Intramolecular trapping of allenylzincs by carbonyl groups.

Abstract: Allenylzinc formed via oxygen-promoted zinc/iodine exchange between propargyl iodides and diethylzinc can be trapped by intramolecular reaction with various electrophiles such as aldehydes, ketones, esters, carbamates, and imides. Potentially useful building blocks were obtained in high yields.

Formation of the cage-like phosphoranes with the P-C and P-N bonds in the reactions of 2-(2-benzylidenamino)phenoxy-4- tert -butylbenzo-1,3,2-dioxaphosphol with ethyl mesoxalate and ethyl trifluoropyruvate

Abstract: The reaction of 2-(2-benzylidenamino)phenoxy-4-tert-butylbenzo-1,3,2-dioxaphosphol with ethyl mesoxalate and ethyl trifluoropyruvate resulted in the formation of tricyclic phosphoranes with the P-C and P-N bonds. The adduct emerged from the initial reaction of the PIII derivative with the activated ketone (1: 1), further underwent the transformation via the intramolecular reaction involving the benzylideniminoaryl substituent, which resulted in the formation of the cage-like phosphoranes.

Organo-di-Lithio Reagents: Cooperative Effect and Synthetic Applications

Abstract: The development of organometallic reagents remains one of the most important frontiers in synthetic chemistry. In this review, we summarize our research on the structures, reactions, and synthetic applications of 1,4-dilithio-1,3-butadienes as organo-di-lithio reagents. The 1,4-dilithio-1,3-butadienes bearing a wide variety of substitution patterns on the butadienyl skeleton can be readily prepared in high efficiency. The configuration has been predicted and demonstrated to favor a double dilithium bridging structure in both solution and solid states. The two Li atoms are bridged by a butadiene moiety and are in close proximity. By taking advantage of this unique configuration, we have developed useful and interesting synthetic methodologies. Three types of reactions of 1,4-dilithio-1,3-butadienes have been developed and are discussed: intramolecular reaction, intermolecular reaction, and transmetallation. First, intramolecular reaction is introduced as a result of the intra-cooperative effect among the two C–Li moieties, the butadienyl bridge, and the substituents. A useful transformation from silylated 1,4-dilithio-1,3-butadienes to α-lithio siloles is described. Second, we discuss an intermolecular reaction that results from the inter-cooperative effect of the two C–Li moieties toward substrates. The intermolecular reactions are featured with formation of oxy-cyclopentadienyl dilithium via the reaction of di-lithio reagents with CO and formation of a series of N-heterocycles via the reaction of di-lithio reagents with nitriles. Third, we discuss transmetallation of di-lithio reagents with aluminum, copper, iron, zinc, or barium salts to generate diversified organo-di-metallic or metallacyclic compounds. The dimetallic 1,4-dilithio-1,3-butadienes and their transmetallated derivatives provide unique synthetic organometallic reagents that are different from monometallic reagents, both in terms of reactivity and in synthetic application. These organo-di-metallic reagents provide the access to interesting and useful compounds that are not available by other means, such as N-, O-, and Si-containing heterocycles, strained ring systems, metal-containing macrocycles, and metal complexes bearing new types of ligand.

Reactivity of the Pyrimidine Nitrogen Atom toward an Acetal Moiety: Formation­ of 3-Ethoxy-2,3-dihydroimidazo[1,2-c]pyrimidines by Intramolecular Cyclization of N-(2,2-Diethoxyethyl)pyrimidine-4-amines

Abstract: A new protocol was developed for the synthesis of 2,3-dihydroimidazo[1,2-c]pyrimidines, based on an intramolecular reaction between a pyrimidine nitrogen atom and an acetal moiety in the presence of boron trifluoride etherate. The method was expanded to permit the synthesis of the triheterocyclic imidazo[1,2-c]pyrazolo[4,3-e]pyrimidine system.

Access to 2,6-Disubstituted Piperidines: Control of the Diastereoselectivity, Scope, and Limitations. Applications to the Stereoselective Synthesis of (—)-Solenopsine A and Alkaloid (+)-241D.

Abstract: Scope and limitations in the diastereoselective preparation of 2,6-cis or 2,6-trans disubstituted piperidines are described, through intramolecular reaction of chiral β′-carbamate-α,β-unsaturated ketone. This methodology has been applied to the total synthesis of a few well chosen examples, such as (−)-solenopsine A and alkaloid (+)-241D.

Intramolecular Aza-Anti-Michael Addition for the Synthesis of 2-Iminothiazolidines

Abstract: The reaction of allylic bromides 1 with Nsubstituted thioureas 2a in acetonitrile furnished isothiuronium salts 3 (66-97%, Scheme 1). Subsequent acetylation reactions of N-substituted salts 4 with acetic anhydride under basic medium at low temperature furnished a mixture of monoacetylated isomers 3b where 4 was the major product (60-80%, conversion, determined by 1 H NMR 400 MHz, CDCl3, Scheme 1). Monoacetylated isomer 4a (R1 = C6H5, R2 = CH3) was purified by column chromatography. Subsequent treatment of 4a with base (DABCO) in acetonitrile allowed the unexpected formation of 2iminothiazolidine 6a through the conjugate addition at the α-position of the alkenoate acceptor known as the anti-Michael reaction (91% yield). Complete structural elucidation of compound 6a was achieved by X-ray crystallography analysis (Scheme 1, Table 1). Cyclization reaction of crude mixtures of Nacetylated products 4 in basic medium without prior purification also furnished the corresponding 2iminothiazolidines 6 in reasonable yields (Scheme 1, Table 1). In a more convergent synthetic approach, 2iminothiazolidines 6 could also be obtained in good yields from a one-step reaction of N-benzoyl-N'substituted thioureas 2b with allylic bromides 1 in the presence of DBU (Scheme 1, Table 2). S N N O MeO R1

Divergent Reactivity of Allene‐Containing α‐Diazoesters Using Cu and Rh Catalysis.

Abstract: A versatile intramolecular reaction of allene-containing diazomalonates that exhibits excellent chemoselectivity for either C—H insertion or cyclopropanation is demonstrated.