Alkoxy Radical Cyclizations onto Silyl Enol Ethers Relative to Alkene Cyclization, Hydrogen Atom Transfer, and Fragmentation Reactions
作者:Montserrat Rueda-Becerril、Joe C. T. Leung、Christine R. Dunbar、Glenn M. Sammis
DOI:10.1021/jo200992m
日期:2011.10.7
chemoselectivity of alkoxy radical cyclizations onto silyl enol ethers compared to competing cyclizations, 1,5-hydrogen atom transfers (1,5-HATs), and β-fragmentations. Cyclization onto silyl enol ethers in a 5-exo mode is greatly preferred over cyclization onto a terminal alkene. The selectivity decreases when any alkyl substitution is present on the competing alkene radical acceptor. Alkoxy radical 5-exo cyclizations
这项研究检查了与竞争性环化,1,5-氢原子转移(1,5-HATs)和β片段化相比,烷氧基自由基环化在甲硅烷基烯醇醚上的化学选择性。以5- exo模式环化到甲硅烷基烯醇醚上比环化到末端烯烃上是更优选的。当竞争的烯烃自由基受体上存在任何烷基取代基时,选择性降低。烷氧基5- exo环化显示出优于竞争性β片段的出色的化学选择性。即使对于活化的苄基氢原子,在甲硅烷基烯醇醚上的烷氧基自由基5- exo环化也胜过1,5-HAT。在四氢吡喃合成中,其中1,5-HAT困扰着烷氧基自由基环化方法,而6- exo环化是反应的主要方式。当在β位上存在芳基时,β-断裂仍然是四氢吡喃合成的挑战。