Synthesis of cyclohexanols
For highly stereoselective reductions of a large number of five- and six-membered cyclic ketones to the most thermodynamically stable alcohols, ketones are treated with lithium dispersion and either FeCl2·4H2O or CuCl2·2H2O in THF at room temperature. This protocol is more convenient and efficient than those commonly reported for similar reductions.
N. Kennedy, T. Cohen, J. Org. Chem., 2015, 80, 8134-8141..
A tandem 1,4-reduction-aldol cyclization is induced by exposure of monoenone monoketones to catecholborane in THF at ambient temperature. Six-membered cyclic aldol products are formed in excellent yield with high levels of syn diastereoselectivity for aromatic and heteroaromatic enones. Five-membered ring formation proceeds less readily, but the yield is improved through addition of Rh(I) salts.
R. R. Huddleston, D. F. Cauble, M. J. Krische, J. Org. Chem., 2003, 68, 11-14.
Treatment of β,β-disubstituted-α,β-unsaturated ketones bearing a ketone residue with in situ generated, catalytic CuH ligated by a nonracemic ligand leads to cyclic aldol products with three newly created adjacent chiral centers. Excellent diastereoselectivities and enantioselectivities are obtained for several examples studied.
B. H. Lipshutz, B. Amorelli, J. B. Unger, J. Am. Chem. Soc., 2008, 130, 14378-14379.
A highly enantioselective catalytic protocol for the intramolecular reductive coupling of ketones and hydrazones furnishes cyclic syn 1,2-amino alcohol derivatives with excellent levels of diastereo- and enantioselectivity. The reaction proceeds through neutral ketyl radical intermediates generated via a concerted proton-coupled electron transfer event jointly mediated by a chiral phosphoric acid catalyst and a photoredox catalyst.
L. J. Rono, H. G. Yayla, D. Y. Wang, M. F. Armstrong, R. R. Knowles, J. Am. Chem. Soc., 2013, 135, 17735-17738.
An efficient lithium amide-induced intramolecular cyclopropanation of bishomoallylic and trishomoallylic epoxides is described. The methodology is used in an asymmetric synthesis of sabina ketone.
D. M. Hodgson, Y. K. Chung, J.-M. Paris, J. Am. Chem. Soc., 2004, 126, 8654-8655.