Preparation and evaluation of N-sulfinyl dienophiles for asymmetric hetero-diels-alder reactions

A series of N-sulfinyl dienophiles 1c-i has been screened in asymmetric hetero-Diels-Alder reactions using chiral bis(oxazoline)copper(II) and -zinc(II) triflates. The survey pointed out N-sulfine 1c (R P(O)(OPh)2) as the most promising N-sulfine regarding yield and stereoselectivity (up to 97% ee). The relative configurations, and in one case the absolute configuration, of the HDA adducts were established by X-ray analysis.