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 C2-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.

We describe our full report of the catalytic asymmetric addition of simple and functionalized dialkylzinc reagents to a broad range of saturated ketones and enones. The functionalized organozinc reagents contain esters, silyl ethers, alkyl chlorides, and alkyl bromides. In general, the resulting tertiary alcohol products are isolated with high ee's. With some substrates, yields are low as a result of the formation of aldol byproducts. Most substrates undergo additions with good yields reaching as high as 91%.

Enantioselective syntheses Enantioselective syntheses O 0031A Practical Catalytic Asymmetric Addition of Alkyl Groups to Ketones. -The camphor derivative shown in the scheme is an efficient ligand for asymmetric addition of alkyl groups to ketones. Tertiary alcohols are obtained with excellent enantioselectivity. -(GARCIA, C.; LAROCHELLE, L. K.; WALSH*, P. J.; J.

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Alcohols Q 0230Catalytic Asymmetric Addition of Alkylzinc and Functionalized Alkylzinc Reagents to Ketones. -An effective and highly enantioselective approach to a broad range of tertiary alcohols is reported. -(JEON, S.-J.; LI, H.; GARCIA, C.; LAROCHELLE, L. K.; WALSH*, P. J.; J. Org. Chem. 70 (2005) 2, 448-455; Dep. Chem., Univ. Pa., Philadelphia, PA 19104, USA; Eng.) -Jannicke 24-080