A simple and convenient transformation of berberine (1) into trans-, cis-, and unsaturated benzindenoazepines through regioselective C14-N bond cleavage of 8, 14-cycloberbines is described. Acidic treatment of the 8, 14-cycloberbine (2) effected regioselective ring opening to afford the trans-and cis-benzindenoazepines (7a and 7b) as the kinetically and thermodynamically controlled products, respectively. Dehydration of their N-methyl derivatives (11a and 11b) gave the unsaturated benzindenoazepine (20), which was obtained more efficiently from the 8, 14-cycloberbine (2) by treatment with p-toluenesulfonic acid in benzene followed by N-methylation. Similarly, the ring D-inverted 8, 14-cycloberbine (23) was converted to the corresponding trans-, cis-, and unsaturated benzindenoazepines (24a, 24b, and 27, respectively).
Acidic treatment of the 8, 14-cycloberbine (2), derived from berberine (1), in methanol afforded the cis-and trans-benzindanoazepines (7 and 8), whereas the reaction of 2 with p-toluenesulfonic acid in benzene yielded the benzindenoazepine (6) in an excellent yield. This simple conversion method was applied to the synthesis of the benzindenoazepine (21), the key intermediate for the total synthesis of (±)-cis-alpinigenine (22) and (±)-cis-alpinine (23).