Abstract
The Diels-Alder reaction of 2-(3-acetoxypropyl)-5-methylcyclohex-2-en-1-one (9) with butadiene in the presence of aluminum chloride was examined. Inspection of the stereostructure of the adduct (8) indicated that addition of butadiene to the dienophile (9) took place stereoselectively from the side opposite to a secondary methyl group at C5 of the dienophile and that this type of Diels-Alder reaction is useful for synthesis of 8-deoxyserratinine type alkaloids. The dienophile (9) was regioselectively prepared from the ketone (10) by two routes. The first route involved the Claisen rearrangement of 12 obtained from 10 via 11. Subsequent conversions of the rearrangement product (13 ; yield, 60% from 11) gave the dienophile (9 ; yield, 26.5% from 14) via 14, 15, 16, 17, 18, and 19. The second route consisted in conversion of the acetal (20) obtained from the ketone (10) and acrolein diethyl acetal into the dienophile (9 ; yield, 70% from 20) via 21 and 22.
