使用自由基环化已经开发了用于合成[1,2- b ]-稠合的双环吡唑的新颖合成方案。该协议使用了由1- [ω-(苯基硒基)烷基]-吡唑前体生成的吡唑-1-(ω-烷基)自由基的环化作用。使用该方案可以高收率合成吡唑天然产物withasomnine(3-phenyl-5,6-dihydro-4 H -pyrrolo [1,2- b ] pyrazole)和较大的环类似物。用作中间π自由基氧化剂的偶氮或Et 3 B自由基引发剂可促进Bu 3 SnH介导的氧化环化机理。
作者:Steven M. Allin、William R.S. Barton、W. Russell Bowman、Emma Bridge (née Mann)、Mark R.J. Elsegood、Tom McInally、Vickie McKee
DOI:10.1016/j.tet.2008.06.014
日期:2008.8
Alkyl radicals have been cyclised onto pyrroles, imidazoles and pyrazoles, and acyl radicals cyclised onto pyrroles, using Bu3SnH-, (TMS)3SiH- and Bu3GeH-mediated aromatic homolytic substitution for the synthesis of bicyclic N-heterocycles. The reactions yield intermediate π-radicals that lose hydrogen in the rearomatisation step of the aromatic homolytic substitution. Mechanistic studies of these