Cleavage 10,2-camphorsultam

The enantiomeric synthesis of rranj-3,4-disubstituted tetrahydrothiophenes using a sulfur ylide cycloaddition has been reported <990L1667>. The sulfur ylide derived from the action of cesium fluoride on sulfide 111 underwent an asymmetric cycloaddition with chiral a,p-unsaturated camphorsultam amide 112 giving tetrahydrothiophene 113 (80% de). The configuration was confirmed by cleavage of the chiral auxiliary followed by reductive desulfurization with Raney-Ni which gave known carboxylic acid 114. 

Introduction. The toluene-2,a-sultams are recently introduced relatives of the well established 10,2-Camphorsultam chiral auxiliary and have been designed to provide similar high levels of face discrimination in reactions of pendent prochiral functionality. Feamres that distinguish them include high crystallinity and facile NMR and HPLC analysis of derivatives, favorable acylation and aldolization characteristics of derived Al-acyl enolates, and improved cleavage characteristics. 

Nondestructive Auxiliary Cleavage. The toluene-2,a-sultam auxiliaries are even more readily cleaved from derivatives than the 10,2-camphorsultam auxiliary. Following iV-acyl bond cleavage, simple extraction and crystallization usually effect almost quantitative recovery of enantiomerically pure auxiliary which may be re-used if desired. 

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