Synthesis of exo- and endo-bicyclo[3,2,1]octane-2-carboxylic acids

Abstract

Wittig reaction of bicyclo[3,1,0]hex-2-ene-6-carbaldehyde with (methoxycarbonylmethylene)triphenylphosphorane in the absence of lithium iodide gives, after sigmatropic rearrangement, preferentially methyl bicyclo-[3,2,1]octa-3,6-diene-2-endo-carboxylate (7d) but in the presence of lithium iodide, after rearrangement, the exo-ester (7c) is the major product. From these esters bicyclo[3,2,1]octane-2-exo- and endo-carboxylic acids have been synthesised stereospecifically. The lack of stereospecificity of earlier syntheses of these acids is noted.