A Highly Diastereoselective Synthesis of (Z)-1-Trimethylgermyl-1-alkenes via the Hydroboration of 1-Trimethylgermyl-1-alkynes Followed by Protonolysis

1-Trimethylgermyl-1-alkynes easily prepared by deprotonation of terminal alkynes with n-butyllithium followed by treatment with trimethylgermanium chloride, readily react with dicyclohexylborane (freshly prepared by reacting cyclohexene with borane-methyl sulfide complex) in tetrahydrofuran. The resulting (Z)-1-trimethylgermyl-1-alkenyl dicyclohexylboranes are readily protonolysed in n-pentane by acetic acid. The monoethanolamine workup, followed by vacuum distillation provides the corresponding (Z)-1-trimethylgermyl-1-alkenes in high stereochemical purities (98%) and in excellent yields (78-92%).