Stereoselective synthesis of some indole alkaloids has been accomplished. 1) Starting from (±)-norcamphor(1), an alternative synthesis of (±)-corynantheidol(26) and the first synthesis of (±)-antirhine(41) have been accomplished via the dithiane intermediates, (18) and (31), respectively. Using the same methodology, a synthesis of (±)-corynantheine(37) has been also attempted. 2) Starting from a symmetric carboxylic acid(51), a new synthetic route to the aspidosperma type alkaloids, e.g., (±)-quebrachamine(48), and the vincamine-eburnamine type alkaloids, e.g., (±)-eburnamine(46), has been developed using halolactonization reaction as a key reaction. Since the chiral halolactone(52) in both enantiomeric forms has been also obtained using (S)-proline as a chiral template, the present synthesis would imply a chiral synthesis. 3) In relating to the synthesis using a halolactonization reaction, the key intermediate(54) has been prepared in a chiral form using the chiral lactone(63), prepared from (S)-proline(62) by Yamada's method. The chiral lactone(54) obtained has been then converted into (+)-quebrachamine(48) in highly enantioselective manner under the same conditions as the racemate. Employing the same methodology, the chiral lactone(63) has been also transformed into the iboga type alkaloids, (-)-velbanamine(74) and (+)-isovelbanamine(75) through the 2-ethylallyllactone(67).
