Intramolecular 1,3-Dipolar Cycloaddition of Geminal Difluoro Azomethine Ylides at Multiple Carbon-Carbon Bonds

N-Alkyl- and N-arylimines derived from o-allyl-, o-allyloxy-, and o-(2-propynyloxy)arenecarbaldehydes react with difluorocarbene to give indeno[1,2-b]pyrrole and chromeno[4,3-b]pyrrole derivatives. The reaction involves intermediate formation of difluoro-substituted azomethine ylides which undergo regio- and stereoselective intramolecular ring closure at the multiple bond.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 3, 2005, pp. 372–380.Original Russian Text Copyright © 2005 by Novikov, Khlebnikov, Voznyi, Besedina, Kostikov.Dedicated to Full Member of the Russian Academy of Sciences V.I. Minkin on his 70th Anniversary     

Intramolecular 1,3-Dipolar Cycloaddition of Azomethine Ylides Leading to Pyrido[2,3-b]quinolines

A convenient six-step route to the previously unknown 1H-pyrrolo[2,3-f]benzo[b][1,8]naphthyridine ring system using an intramolecular 1,3-dipolar cycloaddition of nonstabilized azomethine ylides has been described.     

Intramolecular 1,3-Dipolar Cycloaddition of Azomethine Ylides Generated from Ethoxycarbonylcarbenoids and Schiff Bases

Decomposition of ethyl diazoacetate in the presence of copper, copper acetylacetonate, or copper trifluoroacetylacetonate and ethyl 4-[2-(R-imino)phenoxymethyl]-2-butenoate leads to formation of chromeno-[4,3-b]pyrrole-2,3-dicarboxylic acid derivatives. The reactions involve intermediate formation of azomethine ylides which undergo regio- and stereoselective intramolecular cycloaddition at the C=C bond to afford chromeno[4,3-b]pyrroles. The steric structure of the product depends on the configuration of intermediate ylide and nature of the substituent at the ylide nitrogen atom.     

N-杂环卡宾金属配合物的制备及其在碳-碳多重键硅氢加成反应中的新进展

综述了N-杂环卡宾金属配合物的制备方法,并总结了N-杂环卡宾金属配合物在碳-碳硅氢加成反应中的新进展.     

First Example of 1,3-Dipolar Cycloaddition of Carbonyl Ylides to Cyclopropenes

Carbonyl ylide generated from 1-diazo-5-phenylpentane-2,5-dione in the presence of Rh₂(OAc)₄ reacts with 3-substituted cyclopropenes following the 1,3-dipolar cycloaddition pattern to afford substituted 9-oxatricyclo[3.3.1.0^2,4]nonan-6-ones.     

Intramolecular 1,3-Dipolar Cycloaddition Reactions

The intramolecular 1,3-dipolar cycloaddition reaction of suitably functionalized 1,3-dipoles represents a general scheme for the synthesis of novel fused ring heterocycles. Such reactions of a number of 1,3-dipoles are summarized and the general outline and potential analogies for these reactions noted. While the immediate aim of this review is to survey and correlate published work, it is hoped that general and specific points in need of study will be revealed and will stimulate further work in this fertile field.     

Strength of Intramolecular Hydrogen Bonds

The concept of resonance-assisted hydrogen bonds(RAHBs)highlights the synergistic interplay between theπ-resonance and hydrogen bonding interactions.This concept has been well-accepted in academia and is widely used in practice.However,it has been argued that the seemingly enhanced intramolecular hydrogen bonding(IMHB)in unsaturated compounds may simply be a result of the constraints imposed by theσ-skeleton framework.Thus,it is crucial to estimate the strength of IMHBs.In this work,we used two approaches to probe the resonance effect and estimate the strength of the IMHBs in the two exemplary cases of the enol forms of acetylacetone and o-hydroxyacetophenone.One approach is the block-localized wavefunction(BLW)method,which is a variant of the ab initio valence bond(VB)theory.Using this approach,it is possible to derive the geometries and energetics with resonance shut down.The other approach is Edmiston’s truncated localized molecular orbital(TLMO)technique,which monitors the energy changes by removing the delocalization tails from localized molecular orbitals.The integrated BLW and TLMO studies confirmed that the hydrogen bonding in these two molecules is indeed enhanced byπ-resonance,and that this enhancement is not a result ofσconstraints.     

分子内环加成的甾体全合成

近年来,分子内环加成反应已广泛用于甾体化合物全合成,其主要一步是由取代的苯并环丁烯热裂而成的5,6-二亚甲基-1,3-环己二烯发生区域专一和立体选择性的环加成反应,构成甾体骨架。现在用此法已合成了一系列消旋和光学活性的甾体化合物。     

Intramolecular Resonance-assisted Hydrogen Bonds in N-Salicylidene-anilines

In the crystal structures of N-salicylidene-anilines, the ortho-OH group with the central N atom forms a planar six-membered ring through intramolecular hydrogen bonds (Fig. 1). The pseudo-aromatic ring is coplanar with its attached phenyl ring. The resonance strengthens the H-bond through proton transfer between the O and N atoms (Fig.1,Ⅰ←→Ⅱ): dco and dcc become shorter and dCN longer significantly. The d1～d6 are also changed regularly. According to the geometries obtained from X-ray analysis and retrieved from the Cambridge Structural Database (CSD, version 5.21), we believe that the main resonance, at least in solid state, is the molecular keto form (Ⅱ, Fig. 1) instead of the zwitterionic one (Ⅲ, Fig.1).     

Nucleophilic Additions to Unactivated Carbon-Carbon Double Bonds. Base-Catalysed Ether Formation. Preliminary Communication

Several examples (3 → 5, 4 → 7, 6 → 7, 9 → 10) of base-catalysed intramolecular ether formation involving nucleophilic attack on an unactivated carbon-carbon double bond are described.     

吡啶叶立德与查尔酮1,3-偶极环加成反应制备2-苯基-3-乙酰基中氮茚

报道在氧化剂存在下吡啶叶立德与查尔酮进行1,3-偶极环加成反应, 一锅法合成2-苯基-3-乙酰基中氮茚化合物的方法, 收率37%. 用类似的方法由α-溴代异喹啉季铵盐、查尔酮、碱和氧化剂进行反应, 可一锅法得到1-苯甲酰基-2-苯基-3-乙酰基吡咯并[2,1-a]异喹啉, 收率58%.     

1,3-Dipolar Cycloaddition of Azomethine Ylides Generated from Ketimines and Difluorocarbene to Symmetrically Substituted Olefins

Iminiodifluoromethanides generated from difluorocarbene and benzophenone or fluorenone imines enter into reaction of 1,3-cycloaddition with electron-deficient alkenes to furnish pyrrolidone derivatives. The generation of iminiodifluoromethanides from alkyl N-benzhydrylidene glycinates in the presence of dipolarophiles is liable to complication by a concurrent proton shift in the initial imine giving NH-azomethine ylide also capable of 1,3-dipolar cycloaddition resulting in a side product of pyrrolidone series. The use of active lead instead of lead powder as reductant for dibromodifluoromethane in generation of difluorocarbene permits suppressing formation of the side products in these reactions.     

1,3-Dipolar Cycloaddition of Azomethine Ylides Generated from Schiff Bases and Difluorocarbene to Symmetric Olefins

Difluoro(iminio)methanides generated by the action of difluorocarbene on Schiff bases react with derivatives of maleic and fumaric acids, following the 1,3-dipolar cycloaddition pattern to give 2,2-difluoropyrrolidines which were detected by gas chromatography-mass spectrometry. The final products are stereo-isomeric substituted 2-pyrrolidinones formed by hydrolysis of difluoropyrrolidines and their dehydrofluorination products, 2-fluoro-4,5-dihydropyrroles. The observed stereoselectivity of the cycloaddition suggests Z configuration of intermediate ylide and both endo- and exo-approach to the dipolarophile in the transition state corresponding to cycloaddition.     

非经典多重键

在难以形成经典多重键的重原子（第三周期以下）之间可以形成一种非经典多重键。由于构成双键的两部分（即两个分子片）的基态分别是单线态,这种电子结构导致非经典双键由两个配位键构成,非经典三键则是在此基础上再加上一个π键。这种多重键的强度和键级较经典多重键为低。与两个配位键的电子结构相对应,含有非经典多重键的分子具有反式弯曲的几何构型。     

Asymmetric Synthesis of Tetrahydroindolizines by Bimetallic Relay Catalyzed Cycloaddition of Pyridinium Ylides

A highly enantioselective synthesis of tetrahydroindolizines by catalytic multicomponent cycloaddition reactions of diazoacetate, pyridine, and alkenyloxindole was developed. Under the relay catalysis, involving an achiral iron(III) catalyst and chiral N,N′‐dioxide‐scandium(III) complex, a series of tetrahydroindolizines bearing different substituents were obtained in moderate to high yields (up to 99 %) with excellent diastereo‐ and enantioselectivities (up to >19:1 d.r., 99 % ee).