Diels-Alder dienophiles Sulfene

Block et al. have discovered that sulfenes 28 can be generated by a desilylation route and that these reactive intermediates act as Diels-Alder dienophiles with cyclopentadiene (Scheme 5-XXI).54a b It is of interest to note that other methods of generating sulfenes did not produce [4 + 2] adducts.54a Moreover, with substituted sulfenes endo stereoisomers predominated. 

Electrophilic sulfenes, R2CMSO2, are recognized for their ability to react with nucleophiles and for their 2ir participation in [2 + 2] and [4 + 2] cycloadditions (Chapter 5). Less well recognized is the demonstrated 4ir participation of vinyl sulfenes in Diels-Alder reactions with a select set of dienophiles. Thermolysis of thiete 1,1-dioxides including the parent thiete 1,1-dioxide (22) in the presence of norbornenes provided the Diels-Alder products derived from 4w participation of the vinyl sulfenes [Eq. (18)].40... 

AAAcylimines, e.g., 4, are the most widely recognized and the most extensively investigated hetero-2-azadiene system capable of participation in Diels-Alder reactions, and comprehensive reviews have been published.7,71 In general, substituents X and Y are strongly electron-withdrawing groups and consequently the AAacylimines participate as electron-deficient partners in cycloaddition reactions with electron-rich dienophiles. Diels-Alder reactions of electron-deficient /V-acylimines with vinyl ethers, enamines, olefins, sulfenes, acetylenes, and the carbon-carbon or carbon-oxygen double bond of ketenes have been detailed.57 71 This 47t participation of electron-deficient AAacylimines does complement the ability of many simple AAacylimines to behave as 2ir dienophile components in Diels-Alder reactions with typical electron-rich dienes.6... 

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