Light-induced synthesis of 3-alkyltropones

Abstract

Irradiation of 4-acetoxycyclopent-2-en-1 -one (1) and hex-1-yne (8) with Pyrex-filtered light of a Hg lamp, followed by AcOH elimination with alumina, gave 3-n-butyltropone (15), via intermediate 4-acetoxy-7-n-butyl-cis-bicyclo[3.2.0]hept-6-en-1-one (10) and 1 -n-butyltricyclo[4.1.0.0^2,7]hept-4-en-3-one (13) in 21% overall, unoptimized yield whereas when 350 and 363 nm laser light was used, only compound (10) was formed and was isolated as 7-n-butyl-cis-bicyclo[3.2.0] hepta-3,6-dien-l-one (11). 3-(2′-Hydroxyprop-2′-yl)tropone (16), similarly prepared from compound (1) and 2-methylbut-3-yn-2-01 (9), was dehydrated to give 3-isopropenyltropone (17), a synthetic precursor of β-dolabrin (18). 3-Methoxytropone (23) was similarly synthesized.