Hydroformylation of vinyl acetate

Using the combination of ESPHOS with rhodium a catalytic hydroformylation of vinyl acetate may be achieved in high regio- and enantioselectivity using as little as 

5 Mol% of catalyst. This ligand benefits from a selectivity similar to that exhibited by the very best ligands for this application.111 

Tzamarioudaki and D. Bonafoux, Organic Reactions 56, pp 1-354, ed. L. Overman et al., John Wiley and Sons, 2000. 

Thomaier and H. Gruetzmacher, Synthetic Methods of Organometallic and Inorganic Chemistry, 1996, 3, 73-75. 

Acknowledgement We thank, D. J. Cole-Hamilton, D. F. Foster and G. J. Schwarz of the St Andrews catalyst evaluation service (CATS) for the hydroformylation 

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Hydroformylation of vinyl acetate to give mainly the branched product in >90% ee has been achieved using a rhodium catalyst containing binaphthol and phosphine ligands anchored to polystyrene. 

Related systems are the bis-diazaphospholane ligands of which ESPHOS has proved optimal. Best results were obtained upon hydroformylation of vinyl acetate with ee values up to 89% for the branched lactalde-hyde acetate (Scheme 23) [72], Even more efficient variations are bis-3,4-diazaphospholane ligands, which furnished up to 96% ee upon hydroformylation of vinyl acetate [73]. 

Rh(acac)(CO)2] in combination with ESPHOS (76a) was applied in the asymmetric hydroformylation of vinyl acetate with excellent results. ESPHOS was effective in styrene hydroformylation, but the product is essentially racemic.270... 

The first reports on asymmetric hydroformylation using diphosphite ligands revealed no asymmetric induction. In 1992, Takaya et al. published the results of the asymmetric hydroformylation of vinyl acetate (ee = 50%) with chiral diphosphites.358... 

Rhodium-Catalyzed Asymmetric Hydroformylation of Vinyl Acetate. .. 52... 

The asymmetric hydroformylation of functionalized aliphatic alkenes is generally more difficult than the hydroformylation of vinyl arenes. The rhodium-catalyzed hydroformylation of vinyl acetate (36) yields 2- and 3-acetoxypropanals, 37 and 38, with high chemoselectivity. Ethyl acetate and acetic acid can also be found as by-products. One of the potential applications of vinyl acetate hydroformylation is the production of enantiopure propane 1,2-diol (Scheme 6). 

The influences of the ligand-to-metal ratio, reaction temperature and syngas pressure on the enantioselectivity and regioselectivity were also studied. A multi-substrate screening approach has recently been used by Dow Chemical Company to identify the best catalyst for the hydroformylation of vinyl acetate. Here, the chiral phosphite Kelliphite, 5 (Fig. 1) gave enantioselectivity up 88% ee and excellent regioselectivity for the branched isomer [24,25]. 

The first reports on asymmetric hydroformylation using diphosphite ligands revealed no asymmetric induction [71], In 1992, Takaya et al. published the results of the asymmetric hydroformylation of vinyl acetate (e.e.=50%) with chiral diphosphites [72], In 1992, an important breakthrough appeared in the patent literature when Babin and Whiteker at Union Carbide reported the asymmetric hydroformylation of various alkenes with e.e. s up to 90%, using bulky diphosphites derived from homochiral (2R,4R)-pentane-2, 4-diol (see Figure 8.20). Van Leeuwen et al. studied the influence of the bridge length, bulky substituents and cooperativity of chiral centres on the performance of the catalyst [73,74],... 

Rh2Cl2(CO)4] together with DIOP, benzyl(methyl)phenylphosphine or neomenthyl-diphenylphosphine has been investigated in the hydroformylation of vinyl acetate (equation 66). 

A number of chiral bisphosphines related to DiPAMP(l) were prepared and evaluated in asymmetric catalysis. Many variants were closely equivalent but none were superior to the parent compound. In addition, some monophosphines containing sulfone substituents were quite effective. These had the particular advantage of being usable in water solution. Several new DIOP derivatives were tried in the hydroformylation of vinyl acetate but only modest enantiomeric excesses were achieved. A 72% enantiomeric excess was achieved on dehydrovaline under relatively forcing conditions using DiCAMP(3). This result was remarkable since these phosphine ligands generally work very poorly, if at all, on tetrasubstituted olefins. 

Over the past decade we have explored a number of phosphine ligands for incremental improvements of present systems and for studies in new types of reductions and hydroformylations. Even though bisphosphines continue to dominate the field, we have found fairly efficient monophosphines. This chapter deals with these and other systems that we have explored for a-phenylacrylic acid, dehydrovaline, and hydroformylation of vinyl acetate. Even though we have not solved efficiently any of these cases, we ve learned a lot about the behavior of a variety of ligands and hope that this knowledge will contribute to these and other unsolved problems in this field. 

Hydroformylations. The hydroformylation of vinyl acetate was run at 6 to 7 atm with a 44 56 CO/H2 mixture at 80°-100°C using benzene as a solvent and an 8 x 10"4M concentration of rhodium and a 3.45M concentration of vinyl acetate. The ratio of ligand to metal was varied from 1 to 6 and the best results were obtained only at high ratios. 

Rhodium catalysts with Kelliphite (177) have been tested in the asymmetric hydroformylation of vinyl acetate. Enantioselectivities of 90% ee and regioselectivities of >99.5/0.5 (b/1) have been achieved in initial screening experiments.230... 

Much more recently, enantiocontrol issues have been addressed in hydroformylation reactions. The first study on stereoselective biphasic hydroformylation in IL appeared in 2007, using the chiral sulfonated ligand 56 in [bmim][BF4] for the enantioselective hydroformylation of vinyl acetate and styrene (Scheme 1.26). The hydroformylation of vinyl acetate resulted in the predominant formation of 2-acetoxypropanal with ee > 50%. In the hydrophilic IL [bmim][BF4], the 56 derived catalyst showed 79% conversion with high selectivity for the branched product, while the ee was moderate at around 22%. ... 

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