Isomerization of Olefins by Means of R3SnH–Et3B and Stereochemical Study on Reduction of Alkenyl Iodides

Abstract

Isomerization of olefins with R₃SnH–Et₃B (R = Ph or n-Bu) system has been studied. Treatment of (Z)-1-triphenylstannyl-1-octene (1) or (E)-1-triphenylstannyl-1-octene (2) with a catalytic amount of Ph₃SnH–Et₃B provided an equilibrium mixture of 1/2 = 2/8. Partial isomerization was observed in the reaction of trivial alkenes such as 6-dodecene and 2,2-dimethyl-3-dodecene with R₃SnH–Et₃B system. Whereas (Z)- or (E)-6-dodecene was recovered unchanged upon treatment with n-Bu₃SnH–Et₃B at −78 °C for 3 h, stirring a benzene solution of (Z)-6-dodecene, Ph₃SnH, and Et₃B at 60 °C for 5 h gave an isomeric mixture of (Z)-6-dodecene and (E)-6-dodecene (Z/E = 64/36). Taking account of these results, the stereochemistry of the reduction of alkenyl iodides at −78 °C with R₃SnH–Et₃B system was studied. 6-Dodecenyl radical proved to isomerize much more rapidly than it abstracts a hydrogen from R₃SnH.