[reaction: see text] 9-Tosyl-3,4-dihydro-beta-carboline (1) reacted with a ketone in the presence of (S)-proline as a catalyst to give the corresponding addition product in good yield and high enantioselectivity. In the process, a small amount of water was found to affect the stereoselectivity of the products. The system was applied to reaction of compound 1 and 3-buten-2-one to give 3,4,6,7,12,12b-hexahydro-1H-indolo[2,3-a]quinolizin-2-one, which is a versatile precursor for the synthesis of some indole alkaloids.

[reaction: see text] 9-Tosyl-3,4-dihydro-beta-carboline reacted with 3-ethyl-3-buten-2-one in the presence of (S)-proline to give (3R,12bR)-3-ethyl-12-tosyl-3,4,6,7,8,9,10,11,12,12b-decahydro-1H-indolo[2,3-a]quinolizin-2-one in complete enantio- and diastereoselectivity. The compound thus obtained was readily transformed to ent-dihydrocorynantheol in three steps.

Enantioselective syntheses Enantioselective syntheses O 0031Proline-Catalyzed Asymmetric Addition Reaction of 9-Tosyl-3,4-dihydro-β-carboline with Ketones. -The first asymmetric organocatalytic addition reactions of carboline (I) are disclosed. In most cases small amounts of water show a beneficial effect with respect to the stereoselectivity. This protocol is expected to become valuable in alkaloid synthesis. -(ITOH, T.; YOKOYA, M.; MIYAUCHI, K.; NAGATA, K.; OHSAWA*, A.; Org. Lett. 5 (2003) 23, 4301-4304; Sch. Pharm. Sci., Showa Univ., Shinagawa, Tokyo 142, Japan; Eng.) -Nuesgen 12-029