RHODIUM-CATALYZED ALDOL-TYPE CHEMISTRY UNDER SYNGAS - SELECTIVE REDUCTIVE DIMERIZATIONS OF ALDEHYDES TO MONOALDEHYDES AND FURTHER OXIDATIONTO NOR-KETONES

Under a pressure of syngas in pyridine, RhCl(PPh3)3 selectively cataly zes the dimerization of enolizable C(n) aldehydes, possessing one meth ylene group in the alpha-position to the aldehyde function, into satur ated dimers, C2n monoaldehydes. The yields are good to moderate. The p ressure and relative composition of syngas, together with the use of a triphenylphosphine-ligated metal complex are crucial for obtaining go od selectivities. Monosubstitution of the alpha-carbon severely limits the dimerization. Alcohols and aromatic aldehydes do not react. A ten tative reaction mechanism is proposed in which water is involved. The dimer aldehydes can subsequently be oxidized in situ by air or various oxidants such as m-chloroperbenzoic acid or t-butylhydroperoxide into the corresponding nor-ketones. This process constitutes a novel acces s to such ketones. (C) 1994 Academic Press, Inc.