3-Methoxyphenyl phenylphosphine

Preparation of bis(4-methoxyphenyl)phenylphosphine oxide — Reaction of a Grignard reagent with a phosphorus halide... 

Three types of experiments have proved informative in the mechanistic study of asymmetric hydrogenation. These are, respectively, rate measurements and product analysis, X-ray crystallography and NMR-derived identification of stable and transient species involved in the catalytic cycle. The first two of these have been reviewed elsewhere (2, 3, 4) our own work has been concerned with NMR and has provided a surprising wealth of structural and mechanistic detail. A variety of chiral phosphine procatalysts have been used but the current discussion will be concerned largely with two. Thus (R,R)-1,2-ethanediylbis-[(2-methoxyphenyl)phenylphosphine] (1) (DiPAMP)... 

Toste and coworkers have developed effective gold(I)-catalyzed protocols for the intramolecular enantioselective hydroalkoxylation of y- and 8-hydroxy allenes employing chiral, enantiomerically pure silver salts [107]. For example, treatment of y-hydroxy allene 66 with a catalytic 1 2 mixture of the achiral bis(gold) complex (dppm)Au2Cl2 [dppm = bis(diphenylphosphino)methane] and chiral silver phos-phonate Ag-(J )-67 in benzene at room temperature led to isolation of 2-alkenyl tetrahydrofuran 68 in 90% yield with 97% ee (Eq. (12.36)). A combination of chiral bis(gold) complex with a chiral silver salt proved effective for terminally unsubstituted allenyl alcohols. For example, reaction of 5,6-heptadienol catalyzed by a mixture of [(S,S)-DIPAMP]Au2Cl2 [DIPAMP = l,2-ethanediylbis[(2-methoxyphenyl) phenylphosphine] and Ag-(J )-67 gave 2-vinyltetrahydropyran 69 in 96% yield with 92% ee (Eq. (12.37)). 

Aryl 2,3-unsaturated 0-glycosides also result from the reaction of unsubstituted glycals with phenols in the presence of diethyl azodicarboxylate and tri-phenylphosphine, some reactions affording the products in high yields and with stereospecific introduction of the aglycone. In this way, the p-methoxyphenyl 2,3-unsaturated a-glycoside is obtained in 80% yield from L-rhamnal using dichloromethane as solvent [55]. 

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