Me-Duphos

An iron complex-catalyzed asymmetric hydrosilylation of ketones was achieved by using chiral phosphoms ligands [68]. Among various ligands, the best enantios-electivities (up to 99% ee) were obtained using a combination of Fe(OAc)2/(5,5)-Me-Duphos in THF. This hydrosilylation works smoothly in other solvents (diethylether, n-hexane, dichloromethane, and toluene), but other iron sources are not effective. Surprisingly, this Fe catalyst (45% ee) was more efficient in the asymmetric hydrosilylation of cyclohexylmethylketone, a substrate that proved to be problematic in hydrosilylations using Ru [69] or Ti [70] catalysts (43 and 23% ee, respectively). 

Recently, the chiral Pt(0) precatalyst Pt[(R, R)-Me-Duphos](trows-stilbene) (11) has been used to prepare enantiomerically enriched chiral phosphines via hydrophosphination of acrylonitrile, t-butyl acrylate and related substrates. This chemistry is summarized in Scheme 5-13. 

Scheme 5-13 Platinum(Me-Duphos)-catalyzed asymmetric hydrophosphination...

Scheme 5-14 Stoichiometric reactions of Pt(Me-Duphos) complexes relevant to the proposed catalytic cycle for asymmetric hydrophosphination...

The reaction rate appears to be limited by the P-H oxidative addition because of tight binding of the olefin in the complexes Pt(Me-Duphos)(olefin). Increasing the reaction temperature to speed up this step, however, reduced the enantiomeric excess [13]. 

Scheme 8.9 Hydrogenations of olefins with UlluPHOS and Me-DuPHOS.

More recently, these authors have reported the synthesis of a new thiophene-based analogue of (I ,i )-Me-DuPHOS called UlluPHOS. The facial recognition and enantioselection associated with ruthenium complexes of UlluPHOS and Me-DuPHOS were shown to be similarly high in various hydrogenations of p-keto esters (Scheme 8.32). The most important difference between these two ligands was found by comparing the reaction rates. Indeed, the authors have observed that the use of UlluPHOS considerably increased the activity of the complexes. 

Morken et al. developed a reductive Claisen rearrangement of substituted allyl acrylates. The reaction of ( )-hex-2-enyl acrylate 175 was catalyzed by [Rh(COD)Cl]2 (0.25 mol %) and Me-DuPhos (0.5 mol %) with C MeSiH in benzene at 22 °C to give y,8-unsaturated ester 176 with high diastereoselect-ivity, 11 1 (Scheme 46) [80]. The reaction was carried out on a 10 g scale to provide a 70% yield of 176. This reaction was applied to allylic ester 177 to provide 178, which is a key intermediate in the total synthesis of inos-tamycin [24],... 

The carbon supported AHC catalysts, (Rh(COD)(Me-Duphos)/PTA/C (AHC-1) and Rh(COD)(BoPhoz)/PTA/C, (AHC-2) were prepared using the general procedure described previously (1-3). The catalysts contained about 0.9% Rh which corresponds to about an 8.5% load of the anchored complex. The hydrogenations were run using the low pressure apparatus previously described (11) under the conditions listed in the discussion. 

Using this technique, Brandts et al. (24-26) have successfully anchored two homogeneous catalysts, that is [(AyR)-(Me-DuPHOS)Rh(COD)]BF4 and the non-chiral [Rh(DiPFc)(COD)BF4],... 

Asymmetric hydrophosphination has been utilized as a route for preparing chiral phosphines. The Pt° complex [(Me-DUPHOS)Pt(t/ tf/ ,s-PhCII ClIPh)] (73) brings about the catalytic P-H addition of bulky secondary phosphines to activated alkenes with modest enantioselectivity. The most promising substrate combinations for further development appear to be bulky alkenes and less bulky phosphines (Scheme 46).195... 

Recently, a series of chiral diphosphines (S. -Me-Duphos, (S. -chiraphos, (R,R)-diop and (+)-Norphos were grafted after an ionic exchange onto Al-MCM-41 134 complexes of the form [Rh(cod)(diphosphine)]+ were tested for the hydrogenation of dimethylitaconate. The supported complex with (S,S)-methyl-Duphos reached an activity for the formation of dimethyl ( -methyl-succinate as high as TON = 4000 with an ee close to 92%. Both (R,R)-diop and (,S S )-chiraphos give lower enantioselectivities (ee = 34% and 47% respectively). With (+)-Norphos, dimethyl-([Pg.457]

Allyl acrylates have been reacted with the combination of ClMe2SiH/ [(cod)RhCl]2/Me-DuPHOS (l,2-bis(2,5-dimethylphospholano)benzene) to bring about reduction of the ,/l-unsaturated ester followed by a Claisen rearrangement to the y,8-unsaturated carboxylic acid (Eq. 293)474 Other silanes did not perform as well in this sequence. 

The industrially important cis-(+)-methyl jasmonate 119 is conveniently prepared by the hydrogenation of enone 120 with Me-DuPHOS and [Ru(l,2 5,6- ]-cod)( ]3 -methallyl)2.65°... 

The Rh(I)/136 or Rh(I)/137 combination can be used in the asymmetric hydrogenation of 1-arylenamides in 90-99% ee, with Rh(I)/137 being the better of the two.676 Me-DuPHOS and related ligands with rhodium reduce 1-aryl-2-alkylenamides in >90% ee677 whereas the Rh(I)/DIOP combination carries this out in 97.3-99% ee selectivity.678 Finally, the Rh(I)/138 system reduces /3-substituted-a-arylenamides in 95-99% ee, and a-substituted acetamidoethylenes in 75.7-90% ee.674... 

Kovacik, I., Wicht, D.K., Grewal, N.S., Glueck, D.S., Incarvito, C.D., Guzei, I.A., and Rheingold, A.L., Pt(Me-Duphos)-catalyzed asymmetric hydrophosphination of activated olefins enantioselective synthesis of chiral phosphines,... 

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