Synthèse de composés cyclopentaniques chiraux, di, tri et tétrasubstitués. Application à la synthèse de dérivés Oxa‐13‐prostanoïques

Abstract

The cyclopentenecarbaldehyde 1a, acetals 2a, 2b and the cyclopentenone 2c have been transformed through regio and stereocontrolled reactions into a variety of enantiomerically pure substituted cyclopentanes. Using appropriately selected Wittig reagents, aldehyde 1a furnished the condensation products 3, 4, 5. Michael addition of diethyl malonate on the α,β‐unsaturated aldehyde 1a under phasetransfer conditions led efficiently to 7. Reduction of the cyclopentenone 2c gave 21 in high yield. The cyclopentenes 2a, 2b and 23, submitted to hydroboration‐oxidation furnished the cyclopentanols 10, 13 and 24, respectively, in 30, 70 and 50% yields, reflecting the substitution pattern of the starting alkenes. The salient feature of these reactions is the stereospecificity due to the chiral centre of the molecules 1a, 2a, 2b and 2c, leading to compounds with two, three and four asymmetric centres. The straightforward synthesis of 11α‐hydroxy‐13‐oxaprostanoic acid 20 is described and an approach towards the preparation of 9α, 11α‐dihydroxy‐13‐oxaprostanoic acid 34 is also presented. The structure of these products has been determined by 1H‐ and 13C‐NMR spectroscopy.