Carbon-Carbon Bond Cleavage of .ALPHA.-Substituted Benzoins by Retro-Benzoin Condensation; A New Method of Synthesizing Ketones.
作者:Akira MIYASHITA、Yumiko SUZUKI、Yoko OKUMURA、Ken-ichi IWAMOTO、Takeo HIGASHINO
DOI:10.1248/cpb.46.6
日期:——
When α-benzylbenzoin (3a, α-benzyl-α-hydroxybenzyl phenyl ketone) was treated with potassium cyanide (1) in N, N-dimethylformamide at 80°C for 1 h, the carbon-carbon bond was cleaved, resulting in the formation of deoxybenzoin (4a, benzyl phenyl ketone) and benzaldehyde (2a). This carbon-carbon bond cleavage proceeds through a retro-benzoin condensation mechanism. This mothod of synthesizing ketones was applied to several α-substituted benzoins (3), and the corresponding ketones (4) were formed in good yields. Further, we found that the cyanide ion-donating ability of tetrabutylammonium cyanide (6, Bu4NCN) is more effective than that of potassium cyanide (1, KCN). As expected from the chemical analogy between cyanide ion and azolium ylide, serveral azolium salts (7) can also be employed in the retro-benzoin condensation as catalysts.The benzoin derivatives 3 were synthesized in the following three ways; reaction of alkyl halide (9) with benzoin (5), Michael addition of benzoin (5) with acceptors (10), and Grignard reaction of benzils (8). Alkylation of the benzoins without isolation, followed by carbon-carbon bond cleavage, readily afforded the corresponding ketones (4).
当α-苄基苯偶姻(3a,α-苄基-α-羟基苄基苯甲酮)与氰化钾(1)在80°C下在N,N-二甲基甲酰胺中反应1小时时,碳-碳键发生断裂,形成了脱氧苯偶姻(4a,苄基苯甲酮)和苯甲醛(2a)。这种碳-碳键断裂是通过逆苯偶姻缩合机制进行的。这种合成酮的方法应用于多种α-取代的苯偶姻(3),相应地形成了产率良好的酮(4)。进一步我们发现,四丁基铵氰化物(6,Bu4NCN)的氰化物离子提供能力比氰化钾(1,KCN)更为有效。正如氰化物离子和氮杂环盐之间的化学类比所预期的,几种氮杂环盐(7)也可以作为逆苯偶姻缩合的催化剂。苯偶姻衍生物3通过以下三种方式合成:烷基卤化物(9)与苯偶姻(5)的反应,苯偶姻(5)与受体(10)的迈克尔加成反应,以及苯基(8)的格氏反应。苯偶姻的烷基化不经分离,随后进行碳-碳键断裂,很容易得到相应的酮(4)。