5,6,7,8-Tetrahydroquinolines. Part 6. Silylation vs. Thioamidation in the reaction of silyl isothiocyanates with organometallics: influence of the solvent and of the substituents on silicon.

Abstract

The influence of a number of variables on carbophilic vs. silicophilic attack by 8-lithio-3-methyl-5,6,7,8-tetrahydroquinoline on silyl isothiocyanates is reported. In general carbophilic attack (i.e. thiomidation) is favoured in solvents of low polarity and by bulky and/or electron-donating substituents on silicon. Preliminary blockage of the 8-position with a trimethylsilyl group leads to improved yields as a consequence of the suppression of a yield-limiting proton transfer. A mechanism is proposed for the formation of nitriles in the presence of an excess of reagent.