Simple procedures for the preparation of (Z)-2-(1-trimethylsilyl-1-alkenyl)-1,3,2-dioxaborinanes

Two simple procedures for obtaining (Z)-2-(1-trimethylsilyl-1-alkenyl)-1,3,2-dioxaborinanes based on 1-trimethylsilyl-1-alkynes are described. In the first procedure, 1-trimethylsilyl-1-alkynes are hydroborated with diisopinocampheylborane to provide the corresponding (Z)-2-(trimethylsilyl-1-alkenyl)-diisopinocampheylboranes. These are then reacted with excess acetaldehyde to afford the corresponding (Z)-2-(1-trimethylsilyl-1-alkenyl)-diethoxyboranes which are esterified with 1,3-propane diol to give the (Z)-2-(1-trimethylsilyl-1-alkenyl)-1,3,2-dioxaborinanes in good yields and in high stereochemical purities. In the second procedure, 1-trimethylsilyl-1-alkynes are hydroborated with dichloroborane–methyl sulfide complex in the presence of a stoichiometric amount of boron trichloride in hexane, followed by treatment with 1,3-propane diol. These novel stereodefined gem-alkenyldimetallic compounds containing boron and silicon are isolated and characterized by NMR (1H and 13C) spectral data.