The Hydroboration of 3-Chloro-1-trimethylsilyl-1-propyne with Dialkylboranes and Its Application to the Syntheses of (E)-3-Trimethylsilyl-2-alkenes and 3-Trimethylsilyl-1-alkenes

Article abstract of DOI:10.1246/bcsj.65.685

The reaction of 3-chloro-1-trimethylsilyl-1-propyne with a stoichiometric amount of dialkylborane proceeds to the monohydroboration stage, giving a mixture of regioisomers, (Z)-dialkyl(3-chloro-1-trimethylsilyl-1-propenyl)borane and (Z)-dialkyl<1-chloromethyl-2-(trimethylsilyl)vinyl>borane.The hydroboration mixture is protonolyzed with acetic acid to give (Z)-3-chloro-1-trimethylsilyl-1-propene in quantitative yield.Treatment of the hydroboration mixture with aqueous sodium hydroxide gives a good yield of highly pure (E)-3-trimethylsilyl-2-alkene whose alkyl group migrates from the boron atom.On the other hand, successive treatment of the hydroboration mixture with methyllithium and acetic acid gives a good yield of 3-trimethylsilyl-1-alkene whose alkyl group migrates from the boron atom.The above procedures provide convenient syntheses of (E)-3-trimethylsilyl-2-alkenes and 3-trimethylsilyl-1-alkenes.It is proposed that both products are afforded through the corresponding allylboranes derived from (Z)-dialkyl(3-chloro-1-trimethylsilyl-1-propenyl)borane, respectively.Thus, the former is formed by hydrolysis of alkyl<1-alkyl-1-(trimethylsilyl)allyl>hydroxyborane, while the latter is formed by protonolysis of alkylmethyl<3-alkyl-3-(trimethylsilyl)allyl>borane.