New and Effective Reagents for 1,4 Reduction of α,β-Unsaturated Ketones, LiAlH4-CuI and Its Reactive Species H2AlI
Journal
Journal of Organic Chemistry
Journal Volume
41
Journal Issue
11
Pages
1939-1943
Date Issued
1976
Author(s)
Abstract
Conjugate reduction of six enones by the new reagent LiAlH4-CuI has been studied. The optimum conditions for conjugate reduction depend on the ratio of LiAlH4:CuI:enone, temperature, solvent, and reaction time involving contact of LiAlH4 and CuI before the enone is added. Enone I can be reduced in quantitative yield and 100% regioselectivity in 1 h or less when the ratio of LiAlH4:CuI:enone is 1:4:1, the solvent is THF, and the temperature is 0 °C. The enones II-VI also can be reduced in high yield and 100% regioselectivity. Reduction of enones I and III with LiAlH4-TiCl3 proceeds with 100% regioselectivity; however, the yields are lower (66 and 34%, respectively) compared to the results obtained with the LiAlH4-CuI reagent. The reagent LiAlH4-FeCl3 was found to be ineffective for conjugate reduction. The new reagents (LiAlH4-CuI and LiAlH4-TiCl3) show different stereoselectivity than LiAlH4 toward 4-tert-butylcyclohexanone and 3,3,5-trimethylcyclohexanone. Compared with LiAlH4-CuI, related reagents (LiAlH4-CuCl, LiAlH4-HgI2, and LiAlH4-HgCl2) show less regioselectivity in enone reduction; however, the reagent AlH3-CuI is as effective in conjugate reduction as LiAlH4-CuI. H2AlI has been found to be the reactive species of the reagents LiAlH4-CuI and AlH3-CuI. The compounds H2AlX and HAlX2 where X = I, Br, and Cl were synthesized independently and were evaluated as conjugate reducing agents. © 1976, American Chemical Society. All rights reserved.
SDGs
Type
journal article