PennPhos enol acetates

DuPhos. The exception for rhodium-catalyzed reductions are CnrPhos and BPE-4 [168, 264—268]. MalPhos has proven useful for the reductions of yS-acylamino-acrylates [260]. The ferrocene hybrid (FerroTANE) was referred to earlier (see Section 23.4.1) [167, 222]. The PennPhos ligand is useful for the reductions of cyclic enamides and enol acetates both classes of compounds are difficult for DuPhos itself to reduce with high selectivity [269, 270]. 

Highly enantioselective hydrogenation of cyclic enol acetates was achieved using the complex Rh-PennPhos (XIII), offering a good synthetic method for optically pure alcohols [23a],... 

The very new highly enantioselective hydrogenation of enol acetates by a rhodium PennPhos chelate should be mentioned here [55], Cyclic... 

The asymmetric hydrogenation of cyclic enol acetate has also proven to be a challenging problem. In this respect, Me-PennPhos 125 was shown to be an effective ligand in the rhodium-catalyzed asymmetric hydrogenation of five- or six-membered cyclic enol acetates such as 172. " In addition, Tang et al. found that the TangPhos-Rh catalyst system provided good-to-excellent (92%-99%) enantioselectivities for a diverse set of aryl enol acetates. ... 

To a solution of [Rh(cod)2]Bp4 (5.0 mg, 0.012 mmol) in MeOH (10 mL) in a glove box was added (, 5, 7 ,5)-Me-PennPhos (125) (0.15 mL of a 0.1-M solution in MeOH, 0.015 mmol). After the mixture was stirred for 30 min, the enol acetate 172 (1.2 mmol) was added. The hydrogenation was performed at room temperature under 1.7 atm of hydrogen for 24 h. After the hydrogen was released, the reaction mixture was passed through a short silica gel column to remove the catalyst. The enantiomeric excess of 173 was measured by capillary GC without any further purification. The absolute configurations of the product was determined by comparing the observed optical rotation with that of chiral acetate made from a readily available secondary alcohol. ... 

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