TOTAL SYNTHESIS OF N-A,O-DI-BOC-5-BETA-CYANO-Z-GEISSOSCHIZINE AND N-A-BOC-21-ALPHA-CYANOTETRAHYDROALSTONINE, THE LATTER A SYNTHETIC EQUIVALENT OF N-A-BOC-CATHENAMINE

Modified Polonovski reaction of the synthetically prepared N-a, O-di-Boc-Z-geissoschizine cis-N-b-oxide (6), followed by cyano trapping of the formed iminium intermediates, led to four compounds (1), (5a), (7), and (8a) [and to two secondary products, (9) and (10)]. The most important of these compounds were N-a, O-di-Boc-5 beta-cyano-Z-geissoschizine (5a) and N-a-Boc-21 alpha-cyanotetrahydroalstonine (8a) [synthetic equivalent of N-a-Boc-cathenamine (8b)]. Change in the reaction temperature caused one (Delta(4(21))) of the intermediate iminium ions to be strongly favoured, leading to the nearly exclusive formation of compound (8a) at the expense of compounds (5a), (7), (9), and (10).