Pericyclic reactions of a,p-unsaturated sulfoxides

Recent work in this area has concentrated on the use of chiral a,P unsaturated sulfoxides to control facial selectivity in asymmetric cycloaddition processes, and is the main focus of this section. These substrates are an attractive proposition for use in asymmetric Diels-Alder reactions since the sulfoxides can be prepared enantiomerically pure in many cases, and also because the sulfoxide group is close to the dienophilic double bond and can exert a significant effect on the stereochemical outcome of the cyeloaddition. 

There is also considerable current interest in the use of dienyl sulfoxides as 4n components in asymmetric Diels-Alder cycioadditions and as enophiles, and work 

Racemic vinyl sulfoxides have also been used as synthetic equivalents of nitroacetylene [116] and naphthynoquinone [141], their synthetic utility again depending on the ability of the primary cycloadducts to extrude sulfenic acid. 

The stereochemical outcome of the Diels-Alder reaction between racemic vinyl sulfoxides and dienes (usually cyclopentadiene) has been studied since the late 

The endo-exo terminology was explained by considering the orientation of the S=0 bond in the cycloadduct when the S=0 bond was below the norbomenyl skeleton with the S— Ph bond positioned parallel to the bridgehead proton, the cycloadduct was termed syn (172) when the S=0 bond was outside the norbomenyl skeleton, this was termed the anti cycloadduct (173). 

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