Enantioselective Diels-Alder reactions: room temperature bis(oxazoline)-zinc, -magnesium, and -copper triflate catalysts

A series of chiral bis(oxazoline) ligands, differing in the length of the chain connecting the chiral oxazoline subunits and in the nature of the substituent at the chiral center, were examined in the room temperature Zn(OTf)(2), Mg(OTf)(2) and Cu(OTf)(2) catalyzed reaction of N-crotonyloxazolidinone with cyclopentadiene. A 1,4-bis(oxazoline) ligand proved best for Zn(OTf)(2) and afforded product consistent with reaction via an octahedral model, while 1,3-bis(oxazoline) ligands were best for Mg(OTf)(2) and Cu(OTf)(2). (C) 1997 Elsevier Science Ltd.