The mechanisms of dilithiation reactions in organic syntheses: a case study based on the syntheses of ketene dithioacetals

Abstract

An investigation of the lithiation and Cs₂-insertion reactions of R¹R²CH₂ precursors (reactions used in the syntheses of ketene dithioacetals) leads to the crystal structure determination of the monolithiated complexes R¹R²CHCS₂Li·TMEDA, 3(R¹= Ph, R²= pyridyl) and 4 (R¹= H, R²= 2-methylpyrazine); attempted second lithiation of 3 fails to give the R¹R²CCS₂Li₂ species anticipated in the mechanism of reactions of this type, but synthetic and ¹H NMR spectroscopic evidence indicates that 4 can be lithiated further.