Conformational model for asymmetric Diels-Alder reactions with chiral dienes

✍ Scribed by Craig Siegel; Edward R. Thornton

• Publisher: Elsevier Science
• Year: 1988
• Tongue: French
• Weight: 342 KB
• Volume: 29
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(00)80722-4

✦ Synopsis

Abstr&:

1-(0-methylmandeloxy)dienes have significant advantages for asymmetric Diels-Alder reactions, and we now show that high (>90%) diastereofacial selectivities can be obtained with these dienes, permitting considerable choice as to dienophile and the presence of additional functionality. We present experimental support, including X-ray structures showing the conformations of three Diels-Alder adducts, for a transition state model which explains the origin of these selectivities. The distinctive characteristics of this model are that the phenyl group is nearly perpendicular to the ester C=O, i.e., the Ph-C-C=O dihedral angle is near 90°, and that the methoxy group is close to 'the carbonyl oxygen. These features may have wider applications for chiral control by a-chiral ester groups in other types of reactions. Cur results should renew interest in the use of chiral 1-acyloxydienes.