catalysts based on Al2O3, supercritical carbon dioxide not only acts as a good solvent for the reaction of aromatic and aliphaticaldehydes with 1-nitroalkanes but, most importantly, it also allows the selectivity to be tuned between the competitive formation of beta-nitroalcohols and nitroalkenes (from the Henry reaction and the nitroaldol condensation, respectively). In particular, when the pressure
A method of controlling the diastereoselectivity of the nitroaldol reaction by the use of titanium, zirconium and aluminum based Lewis acids is disclosed. In a preferred embodiment, the reaction of lithium nitronate anion with aldehydes in THF/CH.sub.2 Cl.sub.2 at reduced temperature in the presence of isopropoxy titanium trichloride (TiCl.sub.3 (OPr.sup.i)) yields nitro alcohols enriched in the erythro diastereomer. Erythro-threo ratios of 11.2:1-3.4:1 for aromatic aldehydes and 3.8:1-1:1 for aliphatic aldehydes are typically obtained.
Cetyltrimethylammonium hydroxide (CTAOH) as a general, ecofriendly catalyst for the formation of carbon–carbon bond through nitroalkanes
作者:Roberto Ballini、Dennis Fiorini、Maria Victoria Gil、Alessandro Palmieri
DOI:10.1016/j.tet.2004.01.067
日期:2004.3
Nitroalkanes have been found to give good yields in Michael and nitroaldol (Henry) reactions by the use of a catalytic amount (10 mol%) of CTAOH. at room temperature and under solvent free conditions and in very short reaction times. The methods do not need a large excess of the nitroalkanes and show good chemoselectivity toward further functionalities. (C) 2004 Elsevier Ltd. All rights reserved.