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 diisopino campheylborane to provide the corresponding (Z)-2-(trimethylsily1-1-alkenyl )-diisopinocampheylboranes. These are then reacted with excess acetaldehyde to afford the corresponding (2)-2-(1-trimethylsilyl-1-alkenyl)-diethoxybor anes which are esterified with 1,3-propane diol to give the (2)-2-(1-trimet hylsilyl-1-alkenyl)-1,3,2-dioxaborinanes in good yields and in high stereoc hemical purities. In the second procedure, 1-trimethylsilyl-1-alkynes are h ydroborated with dichloroborane-methyl sulfide complex in the presence of a stoichiometric amount of boron trichloride in hexane, followed by treatmen t with 1,3-propane diol. These novel stereodefined gem-alkenyldimetaliic co mpounds containing boron and silicon are isolated and characterized by NMR (H-1 and C-13) spectral data. (C) 2000 Elsevier Science Ltd. All rights res erved.