Chemical Transformation of Protoberberines. VII. Efficient Conversion of Protoberberines into Benzindenoazepines via 8, 14-Cycloberbines

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).