1- and 2-(Trialkylsilyl)ethanols: New Silyl Reagents from Tin, Lithium, and Boron Chemistry

Article abstract of DOI:10.1021/jo00278a014

Efficient preparations of isomerically pure 1- and 2-(trialkylsilyl)ethanols from vinylsilanes with borane reagents are described.In the former case, the borane reduction of the appropriate acetylsilane (12) gave good yields (82-94percent) of the desired 1-R3Si products (13, R = Me, Et, i-Pr).The reaction of (α-methoxyvinyl)lithium (10) (from Sn/Li exchange) with the appropriate chlorosilanes provided the corresponding (α-methoxyvinyl)silanes (11) (89-94percent).Hydrolysis of 11 afforded acylsilanes (12) in excellent yield (93percent).Hydroboration of the vinylsilanes (1) with9-borabicyclo<3.3.1>nonane (9-BBN) gave (β-borylethyl)silanes (2), which were oxidized to provide isomerically pure 2-silylethanols (3).The formation of Normant's reagent (4, vinylmagnesium bromide in THF) and Seyferth's reagent (7, unsolvated vinyllithium) were examined in some detail, and several new minor processes were identified.Unlike less hindered chlorosilanes, the triisopropylsilyl compound fails to react cleanly with 4, but is smoothly converted to 1c (79percent) with 7.It was demonstrated that 11c (R = i-Pr) afforded 3c (89percent) via a one-pot hydroboration/elimination/hydroboration/oxidation sequence.Complete, assigned 13C NMR data for these silanes are presented and compared to their trimethylsilyl counterparts.