38 Estradiolの不斉合成

抄録

A new type of asymmetric total synthesis of estradiol (6) has been described. The key step is a thermolysis of optically active 1-tert-butoxy-3-ethenyl-2-[2-(4-methoxybenzocyclobutenyl)-ethyl]-2-methylcylopentane (4) to form stereoselectively 17-O-tert-butyl-3-O-methylestradiol (5), which was converted into estradiol (6) in two steps. The key intermediate 4 was in turn prepared by the condensation of 1-cyano-4-methoxybenzocyclobutene (18) with (+)-(1S,2S,3S)-1-tert-butoxy-3-ethenyl-2-(2-iodoethyl)-2-methylcyclopentane (17) followed by reductive decyanation, the latter of which was derived from the known (1S,3aS,7aS)-1-tert-butoxy-3a,4,7,7a-tetrahydro-7a-methyl-5(6H)-indanone (7) through the following four compounds, namely, (+)-(1S,3aS,7aS)-1-tert-butoxy-3a,4,7,7a-tetrahydro-[6,6-(propane-1,3-dithio)]-7a-methyl-5-indanone (9), (-)-(1S,2S,3S)-1-tert-butoxy-2-[2,2-(propane-1,3-dithio)ethyl]-2-methyl-3-[2-(2-nitrophenylselenyl)ethyl]cyclopentane (12), (-)-(1S,2S,3S)-1-tert-butoxy-2-methyl-3-[2-(2-nitrophenylselenyl)ethyl]-2-(2-hydroxyethyl)-cyclopentane (14), and (+)-(1S,2S,3S)-1-tert-butoxy-3-ethenyl-2-methyl-2-(2-hydroxyethyl)cyclopentane (15).