Michael Addition Reaction Involving trans-Chalcones

2 Michael Addition Reaction Involving trans-Chalcones 

Rawal and coworkers have developed an enantloselective a-amination reaction of 

3 Chiral Squaramides as Hydrogen-Bond Donor Catalysts 261 

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Optically pure (+)-(i )-3-phenylsulfanyl-l,3-diarylpropan-l-ones are readily available by the enantioselective Michael addition of thiophenols to chalcones. After reduction, acidic dehydration of the racemic alcohol affords a mixture of the racemic cis- and trans- 2,4-disubstituted thiochromans (Scheme 164). A detailed consideration of the stereochemical outcome of the reaction with unsymmetrically substituted diaryl derivatives suggests the involvement of a [1,3] PhS shift via a four-membered sulfonium intermediate and this is backed up by theoretical calculations <2003T3621>. 

Experiment 38 involves the reaction between ethyl acetoacetate and trans-chalcone in the presence of base. Under the conditions of this experiment, a sequence of three reactions takes place a Michael addition followed by an internal aldol reaction and a dehydration. 

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