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Highly Diastereoselective Aldol Reactions with Camphor-Based Acetate Enolate Equivalents
Claudio Palomo1, Mikel Oiarbide, Jesús M. Aizpurua
1Departamento de Química Orgánica, Facultad de Química, Universidad del País Vasco, Apdo 1072, 20080 San Sebastián, Spain, Departamento de Química Aplicada, Universidad Pública de Navarra, Campus de Arrosadía, E-31006 Pamplona, Spain, and Organisch-chemisches Institut der Universitat Zürich, Winterthurerstrasse 190, CH-8057, Zürich, Switzerland.
Abstract:
New lithium enolates of alpha-hydroxy ketones, derived from camphor, are evaluated for asymmetric aldol reactions in the presence of lithium chloride. The diastereoselectivity of the reactions between the lithium enolate of 3 and a variety of achiral aldehydes is strongly influenced by the lithium chloride salt. In these instances, the achieved levels of asymmetric induction, typically 95:5 dr, are in the range of those attained in aldol reactions involving the lithium enolate of the methyl ketone 4, which is sterically more demanding. The resulting aldol adducts are easily transformed into beta-hydroxy carboxylic acids, ketones, and aldehydes with concomitant recovery of the camphor, the chiral controller of the process, which can be reused.