On the Order of Addition of Sodium Dispersion in Reductive Diborations of Stilbene and 1,2-Diphenylcyclopropane

Abstract

Two extreme methods to add sodium dispersion were investigated in the 1,2-diboration of stilbene and the ring-opening 1,3-diboration of 1,2-diphenylcyclopropane on a 20-mmol scale. Method 1 denotes that a substrate is added to a mixture of sodium dispersion and a boron electrophile. Method 2 denotes that sodium dispersion is slowly added to a mixture of a substrate and a boron electrophile. In these four cases, no significant differences were observed in the yields of the products and their syn/anti ratios, except for the diboration of stilbene by Method 1, wherein aggregation of sodium dispersion in the flask and 5% recovery of stilbene were observed. This information would be helpful in performing sodium-dispersion-mediated transformations on a large scale.