Hydrophosphinations, asymmetric

Chen K (2011) Application of palladacycles in asymmetric hydrophosphinations, asymmetric hydroamination and tandem allylic aminations/aza-Cope rearrangements. PhD Dissertation, Nanayang Technological University... 

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

Similar catalytic reactions allowed stereocontrol at either of the olefin carbons (Scheme 5-13, Eqs. 2 and 3). As in related catalysis with achiral diphosphine ligands (Scheme 5-7), these reactions proceeded more quickly for smaller phosphine substrates. These processes are not yet synthetically useful, since the enantiomeric excesses (ee s) were low (0-27%) and selectivity for the illustrated phosphine products ranged from 60 to 100%. However, this work demonstrated that asymmetric hydrophosphination can produce non-racemic chiral phosphines [13]. 

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

Metal-catalyzed hydrophosphination has been explored with only a few metals and with a limited array of substrates. Although these reactions usually proceed more quickly and with improved selectivity than their uncatalyzed counterparts, their potential for organic synthesis has not yet been exploited fully because of some drawbacks to the known reactions. The selectivity of Pt-catalyzed reactions is not sufficiently high in many cases, and only activated substrates can be used. Lanthanide-catalyzed reactions have been reported only for intramolecular cases and also sulfer from the formation of by-products. Recent studies of the mechanisms of these reactions may lead to improved selectivity and rate profiles. Further work on asymmetric hydrophosphination can be expected, since it is unlikely that good stereocontrol can be obtained in radical or acid/base-catalyzed processes. 

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... 

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,... 

Abstract In the first part of this mini review a variety of efficient asymmetric catalysis using heterobime-tallic complexes is discussed. Since these complexes function at the same time as both a Lewis acid and a Bronsted base, similar to enzymes, they make possible many catalytic asymmetric reactions such as nitroal-dol, aldol, Michael, Michael-aldol, hydrophosphonyla-tion, hydrophosphination, protonation, epoxide opening, Diels-Alder and epoxi-dation reaction of a, 3-unsaturated ketones. In the second part catalytic asymmetric reactions such as cya-nosilylations of aldehydes... 

The mechanistic study on the hydrophosphination of activated olefins, in conjunction with rapid inversion of the configuration at the phosphorus center, was elaborated to develop asymmetric hydrophosphination catalyzed by a chiral phosphine platinum complex although the % ee is not excitingly high yet (Scheme 9) [15]. 

Simultaneous publication of the iminium ion catalysed hydrophosphination of a,p-unsaturated aldehydes by Melchiorre and Cordova showed diarylprolinol silyl ether 55 was effective in the conjugate addition of diphenylphosphine 74 [117, 118], Direct transformation of the products allowed for one-pot methods for the preparation of P-phosphine alcohols 75 (72-85% yield 90-98% ee), P-phosphine oxide acids 76 (65% yield 92% ee) and 3-amino phosphines 77 (71% yield 87% ee) (Scheme 34). These reports represent the first examples of the addition of P-centred nucleophiles and the resulting highly functionalised products may well have further use in asymmetric catalysis. 

For example, an effective procedure for the synthesis of LLB (where LL = lanthanum and lithium) is treatment of LaCls 7H2O with 2.7 mol equiv. BINOL dilithium salt, and NaO-t-Bu (0.3 mol equiv.) in THF at 50 °C for 50 h. Another efficient procedure for the preparation of LLB starts from La(0-/-Pr)3 [54], the exposure of which to 3 mol equiv. BINOL in THF is followed by addition of butyllithium (3 mol equiv.) at 0 C. It is worthy of note that heterobimetallic asymmetric complexes which include LLB are stable in organic solvents such as THF, CH2CI2 and toluene which contain small amounts of water, and are also insensitive to oxygen. These heterobimetallic complexes can, by choice of suitable rare earth and alkali metals, be used to promote a variety of efficient asymmetric reactions, for example nitroaldol, aldol, Michael, nitro-Mannich-type, hydrophosphonylation, hydrophosphination, protonation and Diels-Alder reactions. A catalytic asymmetric nitroaldol reaction, a direct catalytic asymmetric aldol reaction, and a catalytic asymmetric nitro-Mannich-type reaction are discussed in detail below. 

The Duphos ligand (157) has been used to prepare organometallic complexes of palladium.385 Rhodium complexes of ligands (156), (157), or (159) are efficient catalysts for enantioselective hydrogenations337-341,343,345,386-388 and furthermore, in the case of platinum complexes with (157), as catalysts for the asymmetric hydrophosphination of activated olefins.71... 

Although no mechanism was proposed, the Pd(Me-DuPhos)-catalyzed asymmetric hydrophosphination of an alkyne with a phosphine-borane under kinetic resolution conditions (Scheme 6) presumably involves similar insertion and reductive elimination steps [14]. 

Scheme 33 Proposed mechanism for nickel-catalyzed asymmetric hydrophosphination via attack on a methacrylonitrile complex...

Yuan M, Zhang NA, Pullarkat S, Li Y, Liu F, Pham P-T, Leung P-H (2010) Asymmetric synthesis of functionalized 1,3-diphosphines via chiral palladium complex promoted hydrophosphination of activated olefins. Inorg Chem 49 989-996... 

Chen K, Pullarkat SA, Li Y, Leung PH (2012) Chiral cyclopalladated complex promoted asymmetric synthesis of diest -substituted P, N-ligands via stepwise hydrophosphination and hydroamination reactions. J Chem Soc Dalton Trans 41 5391-5400... 

In 2007, Glueck s group reported a catalytic DKR process in which secondary phosphines were converted into the corresponding enantio-enriched tertiary phosphines through palladium-catalysed asymmetric hydrophosphination of aryliodides using secondary phosphines. The key intermediates were diaster-eomeric phosphide complexes with chiral ancillary ligands (L Pd PRR ). Their relative rates of P-inversion and phosphorus-carbon bond formation controlled the enantioselectivity of the prodnct formation. As shown in Scheme 2.63, the reaction allowed moderate enantioselectivities of up to 70% ee to be achieved. 

Hydroxo-bridged dinuclear complexes, [Pt(P-P)(/u-OH)]2 (where P-P = DIOP, BINAP, NORPHOS, MeDUPHOS, and BPPM) as precursors have been used for the enantioselective Baeyer-Villiger oxidation of ketones (290). The platinum(O) catalyst precursor, Pt(MeDUPHOSXfrans-stylbene), catalyzes the asymmetric hydrophosphination of activated olefins (291). 

Organolanthanide complexes are known to be highly active catalysts for a variety of organic transformations, which can be either intramolecular or intermolecular in character. Successful intramolecular transformations include hydroelementation processes, which is the addition of a H-E (E = N, O, P, Si, S, H) bond across unsaturated C-C bonds, such as hydroamination, hydroalkoxylation, and hydrophosphination. Intermolecular transformations include a series of asymmetric syntheses, the amidation of aldehydes with amines, Tishchenko reaction, addition of amines to nitriles, aUcyne dimerization, and guanylation of terminal aUcynes, amines, and phosphines with carbodiimides. 

SCHEME 4.27 Use of a P-stereogenic PCP pincer ligand in asymmetric hydrophosphination reactions [20]. 

Busacca and co-workers have prepared menthol-derived phosphinite boranes 101 and 102, by direct addition of anionic secondary phosphine borane 100 to carbodiimides, yielding the chiral phosphinite boranes under ambient temperature conditions (Scheme 25). These and other derivatives, prepared by hydrophosphination of carbodiimides, were used in the synthesis of enantiomerically enriched phosphaguanidines with potential use as ligands in asymmetric catalysis. 

BartoU G, Bosco M, Carlone A, LocateUi M, Mazzanti A, Sambri L, Melchiorre P. Organocatalytic asymmetric hydrophosphination of lutroalkenes. Chem. Commun. 2007 722-724. 

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