Complexes containing a Lewis acid and Brønsted acid for the catalytic asymmetric Diels-Alder reaction

Complexes containing a Lewis acid and a Brønsted acid have been prepared by the reaction of an amino alcohol and a trihaloborane. The structures of the complexes were determined by 11B, 1H, and 13C analysis and shown to be the acyclic structures 5 rather than the possible cyclic structures 6 which o...

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Bibliographic Details
Published in:Tetrahedron: asymmetry 1995-06, Vol.6 (6), p.1301-1306
Main Authors: Aggarwal, Varinder K., Anderson, Emma, Giles, Robert, Zaparucha, Anne
Format: Article
Language:English
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Summary:Complexes containing a Lewis acid and a Brønsted acid have been prepared by the reaction of an amino alcohol and a trihaloborane. The structures of the complexes were determined by 11B, 1H, and 13C analysis and shown to be the acyclic structures 5 rather than the possible cyclic structures 6 which only contain the single Lewis acid. A variety of amino alcohols were combined with BBr 3 and BCl 3 and tested in Diels Alder reactions between methacrolein and cyclopentadiene. Whilst very high exo selectivity was observed, enantioselectivity was variable depending on the amino alcohol used. Prolinol 4 gave the highest ee (97%) but quinidine gave the highest ee (64%) for a naturally occurring amino alcohol. The reaction between an amino alcohol and BBr 3 furnishes 5 and not 6; a compound bearing a Lewis acid and Brønsted acid. A range of amino alcohols/BX 3 were tested as catalysts for the Diels Alder reaction between methacrolein and cyclopentadiene and found to give adducts with 0–97 % ee.
ISSN:0957-4166
1362-511X
DOI:10.1016/0957-4166(95)00163-J