Hydroboration of cyclic allenes with disiamylborane

Abstract

It has been shown that 1,2-cyclononadiene and 1,2-cyclotridecadiene undergo 78 and 100% hydroboration respectively, with disiamylborane. 1,2-Cyclononadiene gave products which represented 83% attack of boron at the central carbon atom and 17% attack at the terminal carbon atom. 1,2-Cyclotridecadiene gave 62% central carbon attack and 38% terminal carbon attack. The reactivity and selectivity may be explained mainly in terms of steric effects on a four-centered transition state.