Gold-Catalyzed Formal Cycloaddition of 2-Ethynylbenzyl Ethers with Organic Oxides and α-Diazoesters

摘要

Metal-catalyzed intermolecular cycloaddition reactions are powerful tools for the construction of complex carbo-and heterocyclic frameworks. The development of new all-carbon building units is a key focus in this area. Five-and six-membered carbo-and heterocycles are readily accessed by metal-catalyzed [3C+2], [4C+2], and [3C+3] cycloaddition reactions, but less commonly through a [4C+1] or [5C+1] cycloaddition route. The scarcity of four-and five-carbon-atom building units in [nC+1] cycloaddition reactions (n = 4,5) impedes their catalytic development. Reported four-carbon-atom motifs include vinyl allenes, diallenes, and 3-en-l-ynes, whereas five-carbon-atom units comprise only substituted cyclopropane derivatives and 3-acyloxy-1,4-enynes. We sought a new all-carbon motif for an [nC+1] cycloaddition (n = 4,5). We report herein the gold-catalyzed cycloaddition of 2-ethynylbenzyl ethers 1 and 2 with organic oxides and diazocarbonyl species to give formal cycloadducts 3, 4, and 5 [Eqs. (1) and (2); EWG = electron-withdrawing group].