Rhodium(I)-catalysed reactions of enynes. Linear coupling vs. cycloaddition

Abstract

The Rh^I-catalysed [2 + 2 + 2]-cycloaddition of dibut-2-ynyl ether (a 2,7-diyne) and acrylonitrile gives the corresponding bicyclic cyclohexadiene. Terminally unsubstituted 1,6-diynes fail to give an analogous reaction. Allyl propargyl ethers undergo a related Rh^I catalysed [2 + 2 + 2]-cyclodimerisation but substitution of the terminal alkene diverts the reaction to linear dimerisation involving the terminal alkyne. 4,9-Dioxadodec-1-ene-6,11-diyne gives a novel bicyclic triene by an unusual intramolecular Rh^I-catalysed [2 + 2 + 2]-reaction. The mechanisms of these various processes are discussed.