Thiocaibonyl compounds

A number of thiocaibonyl compounds in the carboxylic acid oxidation state have been utilized in Diels-Alder reactions, but no systematic study in this area has been done. Some of the various structural types of thiocarbonyls which are reactive dienophiles are indicated in equations (90), (91) and (92).16s Reactions of this class show good to moderate regioselectivity, but relatively little is loiown with regard to stereoselectivity. Additional examples can be found in earlier reviews. ... 

Electron-deficient thiocaibonyl compounds such as hexafluorothioacetone, methyl cyanodithiofor-mate and thioglyoxylate esters are particularly reactive enophiles. Since these compounds react primarily or exclusively by pathway (b) to give allylic sulfides (264), rather than by pathway (a) to give homoallylic thiols (263), they are outside the scope of this chapter (Scheme 39). Thiobenzaldehyde, generated in situ, reacts with 3-pinene to give thiol in 38% yield and sulfide in 19% yield. ... 

The last topic in this chapter is the Michael addition of heteroatoms such as nitrogen and sulfur that affords fl-aminocarbonyl and P-thiocaibonyl compounds. 

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