Highly Efficient Rhodium Catalysts for the Asymmetric Hydroformylation of Vinyl and Allyl Ethers using C1-Symmetrical Diphosphite Ligands

Abstract

Here, we describe the successful application of novel glucofuranose-derived 1,3-diphosphites in the rhodium-catalysed asymmetric hydroformylation of vinyl acetate, 2,5-dihydrofuran and 2,3-dihydrofuran. In the hydroformylation of vinyl acetate, total regioselectivity and high ee (up to 73%) were obtained. When 2,3- and 2,5-dihydrofuran were the substrates, total chemo- and regioselectivities were achieved together with ees up to 88%. These results correspond to the highest ee values reported to date in the asymmetric hydroformylation of these substrates. The HP-NMR studies of the [RhH(CO)₂(L)] species (L=15 and 17) demonstrated that both ligands coordinate to the Rh centre in an eq-eq fashion. The complex [RhH(CO)₂(15)] was detected as a single isomer with characteristic features of eq-eq coordination. However, the broadening of the corresponding signals indicated that this species is rapidly interchanging in solution. In contrast, complex [RhH(CO)₂(17)] was detected as a mixture of two conformational isomers at low temperature due to the greater flexibility of the monocyclic backbone of this ligand.