A New Indole Alkaloid, 14α-Hydroxyrauniticine : Structure Revision and Partial Synthesis

Oxidation of the enamine (6) with dibenzoyl peroxide followed by reduction with NaBH4 gave the benzoate (8), which was converted to the cis-hydroxyl compound (9), while hydroboration-oxidation of 6 gave the trans-isomer (11). Treatment of a mixture of the enamines (13 and 14) with dibenzoyl peroxide/NaBH4 gave the benzoates (15 and 16), which were converted to 14α-hydroxy-3-isorauniticine (17) and the acetal (18), respectively. Hydroboration-oxidation of 13 gave 14α-hydroxyrauniticine (2), which was found to be identical with the natural alkaloid whose structure had erroneously been proposed as 14β-hydroxy-3-isorauniticine (4).