CARBON-CARBON BOND-CLEAVAGE OF ALPHA-HYDROXYBENZYLHETEROARENES CATALYZED BY CYANIDE ION - RETRO-BENZOIN CONDENSATION AFFORDS KETONES AND HETEROARENES AND BENZYL MIGRATION AFFORDS BENZYLHETEROARENES AND ARENECARBALDEHYDES

4-(alpha-Benzyl-alpha-hydroxybenzyl)quinazoline (4a) underwent retro-b enzoin condensation catalyzed by cyanide ion to give deoxybenzoin (2a) and quinazoline (5a), Similarly, several nitrogen-containing heteroar enes (4, 9, 12, 16-19) having an alpha-hydroxybenzyl group at the alph a-position of the nitrogen underwent retro-benzoin type condensation t o afford ketones (2) and heteroarenes (5), However, similar reaction o f pyrazolopyrimidines (13, 14, 15) having an alpha-benzyl-alpha-hydrox ybenzyl group resulted in benzyl migration, giving benzylpyrazolopyrim idines (8) and arenecarbaldehydes (3), Tetrabutylammonium cyanide (11, Bu4NCN) was a more effective cyanide ion donor than KCN (10). The ret ro-benzoin condensation was applied to the synthesis of 2-substituted quinazolines (38) from 2-chloro-4-aroylquinazolines (34), using the ar oyl group as a protecting and electron-withdrawing group.