Substrate control asymmetric hydroformylation

Although significant progress in the field of asymmetric hydroformylation has been made, it is limited to a rather narrow substrate scope. An alternative approach to a stereoselective hydroformylation might employ substrate control of a chiral alkenic starting material. Of particular use... 

Effects of GO and H2 partial pressures on the reaction rate and selectivity of asymmetric hydroformylation of 1-hexene and styrene are examined using (7 ,A)-BINAPHOS-Rh catalyst system. For both substrates, high GO partial pressure tends to retard the reaction the partial pressure of H2 hardly affects the reaction rate (Phz -5 MPa). In most cases, the regio- and enantioselectivities are independent of H2 and GO pressure. Deuterioformylation experiments clearly demonstrate the irreversibility of the olefin-insertion step at total pressures of 2-10MPa (D2/G0=I/I). This fact proves that the regio- and enantioselectivity of the present hydroformylation should be controlled by the olefin-insertion step. Herrmann reported the theoretical calculation of the olefin coordination step, explaining selectivity obtained with (i ,A)-BINAPHOS/Rh system for the hydroformylation of styrene. 

This section deals with substrate-controUed stereoselective hydroformylation, since asymmetric hydroformylation is covered in chapter 5. The stereoselectivity of the hydroformylation reaction is the result of the cis addition of the proton and the formyl group to the less hindered face of the double bond [41]. The presence of heteroatoms in the substrate causes chelation, so the stereoselectivity can be controlled, (see section 6.5). 

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