Abstract
Chiral ,/9-unsaturated JV-acyloxazolidinones undergo a variety of Lewis acid catalyzed addition reactions to alkenes with modest to excellent asymmetric induction. The nature of the reaction is a ñmction of alkene structure and reaction conditions. JV-Crotonyloxazolidinone lb undergoes MegAlCl-catalyzed ene reactions with methy- lenecyclopentane and allyltrimethylsilane to give 6 (67% de) and 18 (33% de), respectively, as the major products. (Trimethylsilyl)cyclopentane 20 is formed stereospecifically as one of eight possible isomers as a minor product. Isobutylene undergoes an enantiospecific MegAlCl-catalyzed hetero-Diels-Alder reaction with lb to afford, after hydrolysis, lactone 10. 2-Ethyl-l-butene undergoes ene reaction slowly with lb at -30 °C with modest asymmetric induction. The ene adducts 6 and 11 undergo MegAlCl-catalyzed Friedel-Crafts acylation at 0 °C to give cyclohexenones 16 and 13. JV-Acryloyloxazolidinones 21 and 26 undergo MegAlCl-catalyzed ene reactions with 1,1-di- and trisubstituted alkenes to give ene adducts in excellent yield. However, asymmetric induction with ethylidenecyclohexane is poor, since ene reaction can occur by exo or endo transition states and by abstraction of syn or anti hydrogens. Ene reaction of 26 with (£)-3,4,4-trimethyl-2-pentene proceeds selectively through the exo transition state to give 28 with 80% de.