Rearrangement and Cleavage of silanes by Organolithium Reagents: Conversion of Phenols into Benzylic Alcohols

Article abstract of DOI:10.1021/jo00147a002

The feasibility of converting phenols into their corresponding benzylic alcohols by means of novel Wittig rearrangement has been investigated.The method consists of (a) treating the phenol with (chloromethyl)trimethylsilane and base to produce the aryl (trimethylsilyl)methyl ether, (b) using sec- or n-BuLi in THF transform this ether into the α-(trimethylsilyl)benzylic alcohol, and (c) removing the silyl group with alcoholic KOH to yield the benzylic alcohol.With phenols, such as phenol itself, 2-naphthol, and 9-phenanthrol, benzylic alcohols were obtained in 50-80percent yields.Ring substituents of a nitro or methoxy type tend to favor α elimination in step b, at the expense of the Wittig rearrangement.The competitive nature of these latter two processes was examined as a function of substituents on the aryloxy groups or on the silicon, as well as a function of the lithium reagent and solvent employed.The independent synthesis and the thermal study of (phenoxymethyl)lithium demonstrated that in THF it undergoes an α elimination almost to the complete exclusion of any Wittig rearrangement.The relative importance of these two processes is discussed in terms of the locoselectivity of lithiation and an electron-transfer view of the Wittig aryl ether rearrangement.