NUCLEOPHILIC SUBSTITUTION AT SILICON: SYNTHESIS OF STERICALLY-HINDERED BIS(2,6-DI-t-BUTYLARYLOXY)SILANES

Article abstract of DOI:10.1016/0022-328X(87)80244-9

The reaction of the monomethylsilane (8a) with two equivalents of the 4-carboalkoxy)-2,6-di-t-butyl-substituted phenol (7b) in toluene using triethylamine as an acid acceptor gave the bis(aryloxy) adduct (9a).The analogous reaction of the dimethylsilane (8b) with sodium 2,6-di-t-butyl-4-(methoxycarboxyl)-phenolate (7a) gave only the monosubstitution product (10a).The raction of the corresponding phenolate (7e) with 8b gave a mixture of 7a, 10a, and bis-adduct (9b), whereas, in the presence of 15-crown-5, the bis adduct 9b was obtained.The bis-adducts 9c-e were prepared in an analogous manner.The reaction of n-hexyl 3,5-di-t-butyl-4-hydroxylbenzoate (7h) with the diphenylsilane (8c) gave only the monosubstitution product 12, while forcing conditions gave, unexpectedly, the methyl ether 13.The reaction of 4-(carboalkoxyethyl)-2,6-di-t-butylphenol (16a) with 8a gave the bis adduct.The reaction af 16a with 8b in THF, without a crown ether, gave a low yield of the monosubstitution product.The bis-adducts 17b-c were obtained by the reaction of 8b with the corresponding phenolates (16a-b) in tetraglyme.Compound 17b was also obtained by the reaction of 8b with 16a in THF with a crown ether.These results are discussed in terms of charge dispersal in the phenolate ion and the corresponding effect upon both ion-pairing and aggregation in solution.