Diastereoselective bromine/lithium-exchange applied to the synthesis of a C-1/C-9-segment of the bryostatins
作者:Reinhard W Hoffmann、Hans Christian Stiasny
DOI:10.1016/0040-4039(95)00821-s
日期:1995.6
The α-bromo-alkyllithium compounds 5 are generated by diastereoselective bromine/lithium exchange on the dibromo-compound 4. The minor carbenoid 5b generated cyclizes spontaneously at −110°C to the bicyclo[3.1.0]hexane 6, thus, leaving the major carbenoid 5a in diastereomerically pure form. Application of the boronate extension reaction to this carbenoid 5a ed to 1,3- or 1,6-diol derivatives, viz.
α-溴代烷基锂化合物5是通过在二溴化合物4上进行非对映选择性的溴/锂交换而生成的。生成的次要类胡萝卜素5b在-110°C时自发环化为双环[3.1.0]己烷6,从而留下非对映体纯形式的主要类胡萝卜素5a。将硼酸酯延伸反应应用于该类胡萝卜素5a,得到1,3-或1,6-二醇衍生物,即。9,13,6,具有完整的立体控制。这项技术被应用于外消旋22的合成,对应于bryostatins的C-1 / C-9片段。