Selektive Reaktionen an den Tetranortriterpenen Bussein A und B

Selective Reactions of the Tetranortriterpenes Busseins A und B Bussein A ( 1 ) was transformed to the 1′‐ O ‐ and 2‐ O ‐acetyl and the 1′‐ O ‐ and 2‐ O ‐chloroacetyl derivatives 3,5,4 , and 6 , respectively. By hydrolysis with H 2 SO 4 in MeOH bussein J ( 7 ) was obtained from 1 and bussein K (8) from bussein B (2) . Treatment of 1 with H 2 SO 4 in H 2 O and tetrahydrofuran yielded 7 , the acid 9 , and the dilactone 16 . Hydrolysis of 1 with aqueous NH 3 in MeOH gave 10 ; at higher temperature, 12, 13 , and 14 were obtained as additional products. With NaOH in aqueous MeOH 7, 10, 15 , and 17 – the latter being an isomer of 15 of unknown structure – were formed from 1 . Photooxidation of 1 led to 20β,21β:21β,23β‐diepoxybussein A (18) .