Intramolecular copper- and rhodium-mediated carbenoid reactions of alpha-(propargyloxy)silyl-alpha-diazoacetates

Copper(I) triflate catalyzes the transformation of alpha-[(2-alkynyl) oxy]s ilyl-alpha-diazoacetates la-g into 1,2-bis(2,5-dihydro-1,2-oxasilol-4-yl)et henes 2 and/or 2H-1,2-oxasilines 3. With rhodium(II) perfluorobutyrate as c atalyst, la-e furnish only 3 but no 2. Bicyclic 2-methoxyfurans 6 are forme d when 1a,c,e (containing terminal alkyne functions) are treated with catal ytic amounts of copper(I) chloride. The experimental observations are expla ined in terms of metal-mediated intramolecular cyclopropenation and subsequ ent metal-assisted ring-opening of the strained bicyclic cyclopropene leadi ng to vinylcarbene-metal complexes. An unusual autoxidation of 2H-1,2-oxasi lines 3a,c,e is also described.