A stereoselectivesynthesis of (E)-α-hydroxy-1,3-dienes, by thermal extrusion from adducts of 2,5-dihydrothiopheneS,S-dioxide (1) with aldehydes and ketones, is presented and its extension to the synthesis of the dienone, (E)-tagetone, and of a 1,3,5-triene system, is illustrated.
In the presence of a catalytic amount of trityl salt, α,β-acetylenic ketones react with silylenolethers to afford the corresponding aldol adducts (1,2-addition products) stereoselectively in high yields. Naturally occurring monoterpenes, trans- and cis-tagetones, are synthesized by the use of this reaction.
Useful perfumery compounds have the formula
where there is a double bond in one of the 5,6 or 6,7 or 7,8 positions. The compounds may be made by reaction of 2-methyl-pentan-4-one with isobutyraldehyde followed by dehydration, preferably in the presence of a weak acid.