Esters five-membered carbocycles

The following syntheses of five-membered carbocyclic systems involve radical-induced epoxide fragmentation with radical translocation and cyclization. The resulting bicyclic alcohols are formed as a mixture of two epimeric esters with cw-fused rings.[71]... 

An interesting approach to the substituted 6,8-bisdehydro[13]annulenone (238) includes a double Knoevenagel reaction of the mixed acetonedicarboxylic ester (235) with aldehyde (236) in the presence of piperidine to give (237). Oxidative coupling of the acetylene moieties in (237) with Cu(OAc)2 in pyridine affords (238) in 10% yield (Scheme 47).2 a,p-Unsaturated malonodinitriles are suitable intermediates for the synthesis of a variety of carbocyclic systems. Cyclization of the benzylidene malonodinitrile (239) to form a five-membered carbocyclic ring (240) can be achieved upon treatment with acid and subsequent hydrolysis (Scheme 48). A similar cyclization of (241) affords six-mem-bered carbocyclic ring systems. ... 

The Dieckmann condensation is an intramolecular variant of the Claisen condensation where a diester is converted to a 3-ketoester. Typically, an alkoxide is used as the base to form the enolate which attacks the remaining ester to form the carbocycle. Five- and six-membered rings are formed readily with this method. Reviews (a) Davis, B. R. Garrett, P. J. In Comprehensive Organic Synthesis, Trost, B. M. Fleming, 1. Eds. Pergamon Press Oxford, 1991 Vol. 2, Chapter 3.6 Acylation of Esters, Ketones, and Nitriles, pp. 806-829. (b) Schaefer, J. P Bloomfield, J. J. Org. React. 1967,15, 1-203. 

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