Phenyl-maleimide moiety

Azo compounds like esters or imides of azo dicarboxylic acid act as reactive dienophiles in normal electron demand hetero Diels-Alder reactions due to the strong activation caused by two electron-withdrawing moieties. In the last years, considerable attention has focused on alkyl and phenyl derivatives of 1,2,4-tria-zoline-3,5-diones since their cycloadditions to chiral dienes proceed with often excellent facial selectivities. Thus, when reacting an oxapropellane derived diene with N -methyltriazolinedione, Paquette et al. obtained the cycloadduct as single diastereomer, but both maleic anhydride and N-phenyl maleimide were distinctly less reactive and turned out to undergo cycloadditions with poor selectivities [289]. 

This methodology has been applied successfully by the same group for the addition of phenyl moieties to a variety of unsaturated substrates. For instance, p-arylenals [74], a,p-unsaturated Af-acylamides, and cyclic maleimides [75] and the extension of the methodology to the tandem conjugate addition/aldol cyclization of p-(2-acylaryl)enones to afford optically active l-aryl-lW-indenes [76] represent examples of the work developed by Miyaura s group (Scheme 5.24). 

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