Platinum/tin catalyzed hydroformylation of naturally occurring monoterpenes

(-)-beta-Pinene, R-(+)-limonene, and (-)-camphene have been hydroformylated regiospecifically to give exclusively the linear isomers Of corresponding aldehydes. The following systems were used as catalysts: PtCl2(PPh3)(2)/SnCl2/PPh3, and PtCl2(diphosphine)/SnCl2/PPh3 whose diphosphines were 1,2-bis(diphenylphosphino)ethane, 1,3-bis(diphenylphosphino)propane and 1,4-bis(diphenylphosphino) butane. The hydroformylation of beta-pinene yields trans-10-formylpinane with a 98% diastereoisomeric excess (d.e.), while limonene and camphene give the diastereoisomers of the corresponding aldehydes in approximately equal amounts (d.e. of ca. 10 and 15%, respectively). Differently from most of the rhodium and cobalt catalysts, the undesirable isomerization of beta- to alpha-pinene is rather slow (1-5% based on reacted beta-pinene). The primarily formed aldehyde of limonene undergoes the highly diasteroselective intramolecular cyclization (d.e. of virtually 100%) catalyzed by the platinum/tin active species yielding 4,8-dimethyl-bicyclo[3.3.1]non-7-en-2-ol. The effects of the catalyst composition and ligand nature on the product distribution have been studied. The use of PPh3 as the only phosphorous-containing ligand, as well as the excess of SnCl2 (Sn/Pt > 1) promote the isomerizations of monoterpenes. The system with 1,3-bis(diphenylphosphino)propane causes excessive hydrogenation of the olefinic double bonds. Under optimized conditions, chemoselectivities for aldehyde formation of near 90% have been attained for all monoterpenes studied. (C) 2000 Elsevier Science B.V. All rights reserved.