Stereoselective total synthesis of racemic (3S,4R/3R,4S)- and a diastereoisomeric mixture of (6E, 10Z)-3,4,7,11-tetramethyl-trideca-6,10-dienal (faranal); the trail pheromone of the Pharaoh's ant

Abstract

Racemic (3S,4R/3R,4S)-faranal [(1a)+(1b)] has been synthesised by a convergent, stereospecific route which employed the addition of alkylcopper complexes to terminal acetylenes, to generate two trisubstituted double bonds, and a Diels–Alder reaction to establish the relative stereochemistry of the C-3, C-4 methyl groups. A diastereoisomeric mixture of faranals, enriched in the (3S,4S/3R,4R)-enantiomeric pair [(1c)+(1d)], has been synthesised by a somewhat shorter route via an intermediate diester, obtained from electrochemical dimerisation of ethyl crotonate.