Unprecedented N→C[1,4] Boc migration: synthesis of 3-carboxyl functionalized 7-azaindolo[2,1-c][1,4]benzoxazine ring system
作者:Santosh Kurhade、Parimi Atchuta Ramaiah、Philip Prathipati、Debnath Bhuniya
DOI:10.1016/j.tet.2012.11.073
日期:2013.1
Use of 1 equiv excess n-BuLi in synthesis of azaindolo[2,1-c][1,4]benzoxazine heterocycles furnished the corresponding 3-(tert-butyloxycarbonyl) derivatives presumably via an unprecedented intramolecular N→C[1,4] Boc migration. Thus, treatment of N-Boc-2-aminopicoline 1a with 3 equiv of n-BuLi at −15 °C, to generate the dianion Li2-1a, followed by the reactions with Weinreb amides 2a–h at −40 °C, and
使用1当量过量的n -BuLi合成azaindolo [2,1- c ] [1,4]苯并恶嗪杂环可提供相应的3-(叔丁氧羰基)衍生物,推测是通过空前的分子内N → C [1,4] Boc迁移。因此,治疗的Ñ -Boc-2- aminopicoline 1A与3当量的Ñ在-15℃正丁基锂,以产生二价阴离子锂2 - 1A,随后用的Weinreb反应酰胺类2A - ħ在−40°C下,然后以受控方式(−40至0°C,2小时; 0°C至rt,16小时)使反应混合物升温至室温,导致形成一系列Boc-基团迁移的产品7a – h通常收成良好(约70%的分离收率)。出乎意料的是,从亚环戊烯到亚环己烯(从2d - e到2g - h),发现所需的[1,4] Boc迁移是次要的命运(产率约20%)。在这些情况下,Ñ →邻- c ^ [1,3]的Boc-迁移化合物9克- ħ(以邻-芳基位置)作为主要产物获得。为形成四环杂环3a以及为观察到的N