A general strategy for catalytic tin radical mediated, radical cascade reactions is proposed in which three rings are constructed in a single step. The initial step in the tricyclisation process has been examined using 2,3-dideoxy-α-D-erythro-hex-2-enopyranosides bearing unsaturated substituents at the 1-O and/or 4-O-positions. Substrates for cyclisation of substituents at the 1-O-position were prepared by a novel zinc chloride catalysed Ferrier rearrangement of tri-O-acetyl-D-glucal with unsaturated alcohols, whereas substrates for cyclisation of substituents at the 4-O-position were prepared by alkylation or acylation of ethyl 6-O-protected 2,3-dideoxy-α-D-erythro-hex-2-enopyranosides. Propargyl substituents cyclise efficiently, but propenyl substituents less so. Propioloyl substituents undergo hydrostannylation without cyclisation.
提出了一种催化
锡自由基介导的自由基级联反应的一般策略,其中在一步中构建了三个环。
三环化过程的初始步骤是使用在1-O和/或4-O位具有不饱和取代基的2,3-脱氧-α-
D-赤藓糖亨糖醛进行研究。用于1-O位取代基环化的底物是通过一种新型的
氯化锌催化的Ferrier重排反应,将三-O-乙酰化的
D-葡糖醛与不饱和醇反应而制备的,而用于4-O位取代基环化的底物则是通过烷基化或酰基化反应,对乙基6-O-保护的2,3-脱氧-α-
D-赤藓糖亨糖醛进行处理。
丙炔基取代基能有效环化,但
丙烯基取代基则较差。
丙炔酰基取代基在没有环化的情况下经历了氢
锡化反应。