Catalysis by cobalt compounds of aldol and retroaldol reactions

Article abstract of DOI:10.1016/0022-328X(91)86055-U

Aldol condensation of acetone, butanone, and 2-pentanone, and retroaldol reaction of neat diacetone alcohol and 3-methyl-3-hydroxyheptan-5-one are catalyzed by (Ph3P)3CoCH3 and (Ph3P)3CoSi(CH3)3.The condensations are reversible and the retroaldol reaction is favoured.Several hindered or cyclic ketones, such as higher homologues, 3-pentanone, methyl isopropyl ketone or cyclohexanone do not condense.By comparison, aliphatic aldehydes react fast and irreversibly to yield products comprised of three aldehyde units. (Ph3P)3CoCH3 also catalyzes protium/deuterium scramblingbetween ketones and acetone-d₆.This exchange takes place preferably at the C3 carbon whereas condensation takes place at the C1 carbon.The reactions take place at 20 deg C or below, and of the several organometallic compounds tested only the two mentioned above were found to be active.