Regioselective rhodium-catalyzed hydroformylation of 1,3-dienes to highly enantioenriched ß,γ-unsaturated aldehyes with diazaphospholane ligands.

Regioselective and enantioselective rhodium-catalyzed hydroformylation of 1,3-dienes with chiral bisdiazaphospholane ligands yields ß,γ-unsaturated aldehydes that retain a C═C functionality for further conversion. The reaction conditions are mild, featuring low catalyst loadings (0.5 mol %), pressures readily obtained in glass bottles, and convenient reaction times (1.5-12 h). Optimized reaction conditions produce high enantioselectivity (>90% ee), regioselectivity (88-99%), and conversion to ß,γ-unsaturated aldehydes (99%) for ten 1,3-dienes encompassing a variety of substitution patterns.

Origin of pressure effects on regioselectivity and enantioselectivity in the rhodium-catalyzed hydroformylation of styrene with (S,S,S)-BisDiazaphos.

Gas pressure influences the regioselectivity and enantioselectivity of aryl alkene hydroformylation as catalyzed by rhodium complexes of the BisDiazaphos ligand. Deuterioformylation of styrene at 80 degrees C results in extensive deuterium incorporation into the terminal position of the recovered styrene. This result establishes that rhodium hydride addition to form a branched alkyl rhodium occurs reversibly. The independent effect of carbon monoxide and hydrogen partial pressures on regioselectivity and enantioselectivity were measured. From 40 to 120 psi, both regioisomer (b:l) and enantiomer (R:S) ratios are proportional to the carbon monoxide partial pressure but approximately independent of the hydrogen pressure. The absolute rate for linear aldehyde formation was found to be inhibited by carbon monoxide pressure, whereas the rate for branched aldehyde formation is independent of CO pressure up to 80 psi; above 80 psi one observes the onset of inhibition. The carbon monoxide dependence of the rate and enantioselectivity for branched aldehyde indicates that the rate of production of (S)-2-phenyl propanal is inhibited by CO pressure, while the formation rate of the major enantiomer, (R)-2-phenyl propanal, is approximately independent of CO pressure. Hydroformylation of alpha-deuteriostyrene at 80 degrees C followed by conversion to (S)-2-benzyl-4-nitrobutanal reveals that 83% of the 2-phenylpropanal resulted from rhodium hydride addition to the re face of styrene, and 83% of the 3-phenylpropanal resulted from rhodium hydride addition to the si face of styrene. On the basis of these results, kinetic and steric/electronic models for the determination of regioselectivity and enantioselectivity are proposed.

Highly enantioselective hydroformylation of aryl alkenes with diazaphospholane ligands.

Asymmetric, rhodium-catalyzed hydroformylation of terminal and internal aryl alkenes with diazaphospholane ligands is reported. Under partially optimized reaction conditions, high enantioselectivity (>90% ee) and regioselectivities (up to 65:1 alpha:beta) are obtained for most substrates. For terminal alkenes, both enantioselectivity and regioselectivity are proportional to the carbon monoxide partial pressure, but independent of hydrogen pressure. Hydroformylation of para-substituted styrene derivatives gives the highest regioselectivity for substrates bearing electron-withdrawing substituents. A Hammett analysis produces a positive linear correlation for regioselectivity.