Factors affecting the regioselectivity in the rhodium-catalysed hydroformylation of vinyl ethers

Abstract

The rhodium catalysed hydroformylation of vinyl ethers ROCHCH 2, where R is an alkyl, a benzyl or a phenyl group, has been investigated over the 20–100°C temperature range in the presence of Rh 4(CO) 12 or [Rh(CO) 2Cl] 2/PPh 3 ( 1 6 ) as catalytic precursors. A mixture of 2-alkoxy-(or phenoxy)propanal (the α-isomer) and 3-alkoxy-(or phenoxy)propanal (the β-isomer) is obtained in good yield. The isomeric composition of the aldehydes depends on the structure of the substrate, on the catalytic precursor employed, and on the reaction temperature. The α-isomer predominates in all the cases, its predominance being greater (i) at low temperatures, (ii) in the presence of Rh 4(CO) 12 as catalyst precursor, and (iii) when a phenyl group is present in the β or γ position with respect to the double bond in the substrate. Electronic factors arising from the presence in the substrate of the oxygen atom and a phenyl group are more important than the steric hindrance of the R group in determining the regioselectivity of the reaction.