Thiocarbonyl group, formation from carbonyl

Although neither of the two carbonyl groups in 18 is immune to the action of Lawesson s reagent,11 it is possible to bring about the selective conversion of the more Lewis-basic lactam carbonyl to the corresponding thiocarbonyl. Thus, treatment of 18 with Lawesson s reagent results in the formation of thiolactam 19 in 85% overall yield from 13. 

DFT calculations have been used to follow the formation of iminium ions from secondary amines and acrolein.56 Energy barriers in the process can be lowered by incorporation of a heteroatom (N or O) in the a-position of the amine, or an electron-withdrawing group (carbonyl or thiocarbonyl) in the -position. 

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