Carbon-sulfur bonds thioamides

Addition to thioamides.s Alkyl- or aryllithiums add to the carbon-sulfur bond of aromatic thioamides to give adducts that are hydrolyzed to unsymmetrical ketones. Reduction of the adducts with LiAlHj before hydrolysis provides a-alkylated amines. 

Simple thioaldehydes and thioketones are too unstable to exist and attempts at their preparation lead to appalling smells (Chapter 1). The problem is the poor overlap between the 2sp2 orbital on carbon and the 3sp2 orbital on sulfur as well as the more or less equal electronegativities of the two elements. Stable thiocarbonyl compounds include dithioesters and thioamides where the extra conjugation of the oxygen or nitrogen atom helps to stabilize the weak C-S bond. 

The size difference between carbon and sulfur atoms leads to relatively inefficient overlap of -tr-orbi-tals in the C=S bond. Consequently, thiocarbonyl compounds are in general highly reactive and have a tendency to di-, oligo- or poly-merize. This is particularly true for thioaldehydes, thioketones, and thio-ketenes. In contrast, thioamides (1) are usually perfectly stable and can be handled without problems. This stability can be understood in terms of a pronounced resonance interaction between the C =S TT-bond and the nonbonding electron pair on nitrogen. The analogous electron delocalization prevails in thiolactams. ... 

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