Sulfides Resulting From Michael Additions

Acetylenic sulfides have also been used as Michael acceptors in phase transfer alkylation reactions (see also Chap. 10) [18]. A series of substituted benzyl cyanides have been condensed with w-butylthioacetylene as shown in equation 13.9 to give the products recorded in Table 13.6. 

The phase transfer Wittig-Horner-Emmons reaction has been used to prepare examples of o, i3-unsaturated sulfides, sulfoxides, and sulfones [19]. Although these reactions are discussed in Sect. 14.3, we have summarized in Table 13.7 the results of transformations according to equation 13.10. Note that this reaction yields sulfur compounds on condensation with aldehydes only if the starting phosphonate is sulfur substituted. 

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Table 13.5. Sulfides resulting from Michael addition [17]...

Dealkylation of Ethers. The combination of an aliphatic thiol such as ethanethiol and boron trifluoride etherate has been used to remove benzyl groups. However, although that method works well it does suffer from an incompatibility with certain functional groups. The presence of an a,/3-unsaturated ester in the same molecule can result in Michael addition as well as debenzylation (eq 1). Boron trifluoride in the presence of dimethyl sulfide, being a milder reagent, does not cause this type of complication, as shown in eq 2. ... 

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