Comparative reductive desymmetrization of 2,2-disubstituted-cycloalkane-1,3-diones
作者:Jeremy M. Carr、Timothy S. Snowden
DOI:10.1016/j.tet.2008.01.065
日期:2008.3
Reductive desymmetrization of 2-methyl-2-substituted-cycloalkane-1,3-diones can be effected using either NaBH(4) in DME or lithium tri-tert-butoxyaluminum hydride (LTBA) in THF at -60 degrees C. The former is a new approach that offers slightly greater diastereoselectivity in the reduction of 2,2-disubstituted-cyclopentane- 1,3-diones while LTBA is superior with 2,2-disubstituted-cyclohexane- 1,3-diones. Both conditions minimize subsequent reduction to diols thereby furnishing high yields of 1,3-ketols. Particularly rapid monoreductions are observed with 2-methyl-2-nitroethylcyclopentane-1,3-dione and 2-cyanoethyl-2-methylcyclopentane-1,3-dione when treated with NaBH(4) in DME at -60 degrees C. As expected, diastereoselectivity varies considerably with the substitution at C-2. (C) 2008 Elsevier Ltd. All rights reserved.