Straightforward Asymmetric Entry to Highly Functionalized Medium-Sized Rings Fused to β-Lactams via Chemo- and Stereocontrolled Divergent Radical Cyclization of Baylis−Hillman Adducts Derived from 4-Oxoazetidine-2-carbaldehydes
作者:Benito Alcaide、Pedro Almendros、Cristina Aragoncillo
DOI:10.1021/jo005715z
日期:2001.3.1
2-azetidinones fused to medium-sized rings via chemo- and stereocontrolled divergent radical cyclization. The formation of bicyclic beta-lactams 4-6 could be rationalized through a tandem radical Michael addition/endo cyclization or a tandem radical addition/Michael addition, depending on the electronic nature of the radical promoter.
DABCO促进了各种活化的乙烯基系统与光学纯的4-氧杂氮杂环丁烷-2-甲醛1的反应,生成了具有良好顺式立体选择性且没有可消旋外消旋作用的Baylis-Hillman加合物3。产品3用于通过化学和立体控制的发散自由基环化反应不对称地制备不寻常的2-氮杂环丁酮,并将其与中等大小的环稠合。取决于自由基促进剂的电子性质,可以通过串联自由基迈克尔加成/内基环化或串联自由基加成/迈克尔加成来合理化双环β-内酰胺4-6的形成。