The addition of 1-pentene or cyclopentene to a solution of one-half the molar quantity of diborane in tetrahydrofuran solution at 0'results in the formation of 60 to 65% yields of di-n- pentylborane and dicyclopentylborane, readily converted to the corresponding borinic methyl esters by treatment with methanol Equilibration of the initial reaction mixture with a deficiency of diborane (2 olefin/l BHI) leads to the preferred formation of di-n-pentylborane ...