Organofluorosilicates in Organic Synthesis. XVI. Synthesis of Organopentafluorosilicates via the Diels-Alder, Ene, and Friedel-Crafts Reaction. Their Transformations to Organic Halides and Alcohols

Article abstract of DOI:10.1246/bcsj.55.255

Described herein are several representative examples of cleavage reactions of otherwise hardly accessible organopentafluorosilicates which are obtainable via the Diels-Alder reaction, ene reaction, and the Friedel-Crafts reaction of vinyl-, ethynyl-, or allyl-trichlorosilanes.The Diels-Alder reaction between vinyltrichlorosilane and o-xylylene generated in situ by debromination of α,α'-dibromo-o-xylene afforded (1,2,3,4-tetrahydro-2-naphthyl)-trichlorosilane which was converted to the corresponding silicate.The silicate reacted with NBS and MCPBA to give the respective bromide and alcohol.The Diels-Alder reaction between ethynyltrichlorosilane and methyl coumalate gave a mixture of meta and para isomers of methyl (trichlorosilyl)benzoate in the ratio of 55/45, the silicate of which reacted with NBS to give two positional isomers of methyl bromobenzoate.The electronic effect of the methoxycarbonyl group on the Si-C bond cleavage was small.The silicate derived from 4-octenyltrichlorosilane which was obtained by the ene reaction between vinyltrichlorosilane and 1-hexene afforded, upon treatment with NBS, 4-octenyl bromide in the ratio of E/Z=83/17.The sterically crowded neophylsilicate obtainable via the Friedel-Crafts reaction of 2-methyl-1-propenyltrichlorosilane with benzene underwent the cleavage reaction with NBS in methanol.Neophyl bromide was formed with CuBr2 in a low yield, no product being formed arising from rearrangement of the neophyl radical.