Formation of Pinacol Boronate Esters via Pyridine Iodoborane Hydroboration

Hydroboration of alkenes with pyridine iodoborane followed by treatment with pinacol/NaOH affords monoalkyl pinacol boronates in moderate to good yield. Dialkylborinic acid derivatives are formed competitively, especially in the case of terminal alkenes. This side reaction can be minimized by using excess of pyridine iodoborane. More hindered alkenes give the best results.