4-(α-Benzyl-α-hydroxybenzyl)quinazoline (4a) underwent retro-benzoin condensation catalyzed by cyanide ion to give deoxybenzoin (2a) and quinazoline (5a). Similarly, several nitrogen-containing heteroarenes (4, 9, 12, 16-19) having an α-hydroxybenzyl group at the α-position of the nitrogen underwent retro-benzoin type condensation to afford ketones (2) and heteroarenes (5). However, similar reaction of pyrazolopyrimidines (13, 14, 15) having an α-benzyl-α-hydroxybenzyl group resulted in benzyl migration, giving benzylpyrazolopyrimidines (8) and arenecarbaldehydes (3). Tetrabutylammonium cyanide (11, Bu4NCN) was a more effective cyanide ion donor than KCN (10). The retro-benzoin condensation was applied to the synthesis of 2-substituted quinazolines (38) from 2-chloro-4-aroylquinazolines (34), using the aroyl group as a protecting and electron-withdrawing group.
4-(α-苄基-α-羟基苄基)
喹唑啉(4a)在
氰离子催化下经历逆苯偶姻缩合反应,生成脱氧苯偶姻(2a)和
喹唑啉(5a)。同样,多个含氮杂环
芳烃(4, 9, 12, 16-19)在其氮原子的α位上具有α-羟基苄基的结构,也经历逆苯偶姻型缩合反应,生成了酮(2)和杂环
芳烃(5)。然而,具有α-苄基-α-羟基苄基结构的
吡唑嘧啶(13, 14, 15)在类似的反应中引发了苄基迁移,生成了苄基
吡唑嘧啶(8)和
芳烃羰醛(3)。四丁基
铵氰(11, Bu4NCN)比KCN(10)更有效地作为
氰离子的供体。逆苯偶姻缩合反应被应用于从2-
氯-4-芳酰基
喹唑啉(34)合成2-取代
喹唑啉(38),使用芳酰基作为保护和电子 withdrawing 基团。