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Bis(oxazoline) and Bis(oxazolinyl)pyridine Copper Complexes as Enantioselective Diels−Alder Catalysts:  Reaction Scope and Synthetic Applications

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journal contribution
posted on 1999-08-06, 00:00 authored by David A. Evans, David M. Barnes, Jeffrey S. Johnson, Thomas Lectka, Peter von Matt, Scott J. Miller, Jerry A. Murry, Roger D. Norcross, Eileen A. Shaughnessy, Kevin R. Campos
The scope of the Diels−Alder reaction catalyzed by bis(oxazoline) copper complexes has been investigated. In particular, [Cu((S,S)-t-Bu-box)](SbF6)2 (1b) has been shown to catalyze the Diels−Alder reaction between 3-propenoyl-2-oxazolidinone (2) and a range of substituted dienes with high enantioselectivity. This cationic complex has also been employed in the catalysis of analogous intramolecular processes with good success. The total syntheses of ent1-tetrahydrocannabinol, ent-shikimic acid, and isopulo’upone, featuring the use of this chiral catalyst in more complex Diels−Alder processes, are described. Similarly, the cationic copper complex 9a, [Cu((S,S)-t-Bu-pybox)](SbF6)2, is effective in the Diels−Alder reactions of monodentate acrolein dienophiles while the closely related complex, 9d [Cu((S,S)-Bn-pybox)](SbF6)2, is the preferred Lewis acid catalyst for acrylate dienophiles in reactions with cyclopentadiene.

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