Reactions of endocyclic linearly conjugated dienolates with Michael acceptors leading to bicyclo[2.2.2]octane derivatives. Application to the synthesis of C13 degradation products of carotenoids

Abstract

The endocyclic linearly conjugated dienolates from substituted cyclohex-2-enones react with but-3-en-2-one, substituted methyl propenoates, but-3-yn-2-one and methyl propiolate to afford bicyclo[2.2.2]-oct-2-en-1-ols 10a–c, 14a–c and bicyclo[2.2.2]octa-2,5-dien-1-ols 15a,b. The AlCl₃-catalysed reaction of 3,5,5-trimethyl-1-(trimethylsiloxy)cyclohexa-1,3-diene 3 with (E)-4-acetoxy- and (E)-4-methoxy-but-3-en-2-one provides trans-8-acetoxy-7-acetyl-3,5,5-trimethyl-1-(trimethylsiloxy)bicyclo[2.2.2]oct-2-enes 22, 23 and trans-7-acetyl-8-methoxy-3,5,5-trimethyl-1-(trimethylsiloxy)bicyclo[2.2.2]oct-2-enes 24, 25. Starting from these bicyclo[2.2.2]octenes, the C₁₃ degradation products of carotenoids including 3-oxo-α-ionone 20, blumenol-C 27 and 1,3,7,7-tetramethyl-2-oxabicyclo[4.4.0]decan-9-one 29 have been synthesized.