Gold-Catalyzed Oxidative Cyclizations of {<i>o</i>-(Alkynyl)phenyl propargyl} Silyl Ether Derivatives Involving 1,2-Enynyl Migration: Synthesis of Functionalized 1<i>H</i>-Isochromenes and 2<i>H</i>-Pyrans
作者:Jidong Zhao、Wei Xu、Xin Xie、Ning Sun、Xiangdong Li、Yuanhong Liu
DOI:10.1021/acs.orglett.8b02380
日期:2018.9.7
A new and convenient strategy for the synthesis of functionalized 1H-isochromene and 2H-pyran derivatives based on gold-catalyzed oxidative cyclizations of o-(alkynyl)phenyl propargyl ether derivatives has been developed. The reaction proceeds via gold-catalyzed highly regioselective oxidation, followed by 1,2-migration of an enynyl group and nucleophlic addition. Isocoumarins were also constructed
The regioselectivity of the thermal cyclisations of enyneâallenes 1 can be toggled as a function of the ring size of the cycloalkene. With a cyclopentene as the ene moiety the MyersâSaito (C2âC7) cycloaromatisation product is formed, whereas with six- and seven-membered cycloalkenes the novel C2âC6 cyclisation is observed. DFT calculations are used to rationalise these changes. The implications of these findings for alternative thermal biradical cyclisations of neocarzinostatin are discussed.