A Practical Catalytic Asymmetric Addition of Alkyl Groups to Ketones

Many catalysts will promote the asymmetric addition of alkylzinc reagents to aldehydes. In contrast, there are no reports of additions to ketones that are both general and highly enantioselective. We describe herein a practical catalytic asymmetric addition of ethyl groups to ketones. The catalyst i...

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Bibliographic Details
Published in:Journal of the American Chemical Society 2002-09, Vol.124 (37), p.10970-10971
Main Authors: García, Celina, LaRochelle, Lynne K, Walsh, Patrick J
Format: Article
Language:English
Subjects:
Alkylation
Catalysis
Chemistry
Exact sciences and technology
Ketones - chemical synthesis
Ketones - chemistry
Organic chemistry
Stereoisomerism
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Summary:Many catalysts will promote the asymmetric addition of alkylzinc reagents to aldehydes. In contrast, there are no reports of additions to ketones that are both general and highly enantioselective. We describe herein a practical catalytic asymmetric addition of ethyl groups to ketones. The catalyst is derived from reaction of camphor sulfonyl chloride and trans-1,2-diaminocyclohexane. The resulting diketone is reduced with NaBH4 to give the C 2-symmetric exo diastereomer. Use of this ligand with titanium tetraisopropoxide and dialkylzinc at room temperature results in enantioselective addition of the alkyl group to the ketone. The resulting tertiary alcohols are isolated with high enantiomeric excess (all cases give greater than 87% ee, except one). The reaction has been run with 37 mmol (5 g) 3-methylacetophenone and 2 mol % catalyst to afford 73% yield of the resulting tertiary alcohol with 99% ee.
ISSN:0002-7863
1520-5126
DOI:10.1021/ja026568k