Lewis Acid-Assisted Ene Cyclization of 2-Azetidinone-Tethered Enals: Synthesis of Enantiopure Carbacepham Derivatives
作者:Benito Alcaide、Pedro Almendros、Carmen Pardo、Carolina Rodríguez-Ranera、Alberto Rodríguez-Vicente
DOI:10.1002/asia.200900165
日期:2009.10.5
3‐substituted 4,5‐dihydroxycarbacephams, respectively, by a type I carbonyl‐ene reaction, while the BF3⋅Et2O or SnCl4‐mediated type II carbonyl‐ene cyclization of alkenylaldehydes 2 furnishes 3‐methylene 5‐hydroxycarbacephams along with the corresponding 3‐halo 5‐hydroxycarbacepham. The stereochemical outcome of these carbonyl‐ene cyclizations leading to carbacepham derivatives can be explained in terms of six‐membered
从2-氮杂环丁烷酮系链的烯醛开始,已开发出由非对映体路易斯酸催化的对映体纯的卡巴辛衍生物的制备方法。在BF 3 ⋅Et 2 O形促进alkenylaldehydes的反应1和16有效地作为carbocyclization协议,得到4-取代的5-或hydroxycarbacephams分别3-取代4,5- dihydroxycarbacephams,由I型羰基-烯反应,而在BF 3 ⋅Et 2 O或的SnCl 4 alkenylaldehydes的介导的II型羰基-烯环化2提供3-亚甲基5-羟基咔唑以及相应的3-卤代5-羟基咔p。这些羰基-烯环化的立体化学结果可导致六溴环十二烷衍生物,可以用六元环状椅状过渡态模型来解释。提出通过逐步机理进行卤代咔唑衍生物的形成。