Trisubstituted phosphine

Triethylammonium formate is another reducing agent for q, /3-unsaturated carbonyl compounds. Pd on carbon is better catalyst than Pd-phosphine complex, and citral (49) is reduced to citronellal (50) smoothly[55]. However, the trisubstituted butenolide 60 is reduced to the saturated lactone with potassium formate using Pd(OAc)2. Triethylammonium formate is not effective. Enones are also reduced with potassium formate[56]. Sodium hypophosphite (61) is used for the reduction of double bonds catalyzed by Pd on charcoal[57]. 

Addition-elimination reactions occur on treatment of 2,3-diphenylthiirene 1,1-dioxide with benzenesulfonate ion or with trisubstituted phosphines (Scheme 86) (75JQC3189). 

Whereas the barrier for pyramidal inversion is low for second-row elements, the heavier elements have much higher barriers to inversion. The preferred bonding angle at trivalent phosphorus and sulfur is about 100°, and thus a greater distortion is required to reach a planar transition state. Typical barriers for trisubstituted phosphines are BOSS kcal/mol, whereas for sulfoxides the barriers are about 35-45 kcal/mol. Many phosphines and sulfoxides have been isolated in enantiomerically enriched form, and they undergo racemization by pyramidal inversion only at high temperature. ... 

The initial step of olefin formation is a nucleophilic addition of the negatively polarized ylide carbon center (see the resonance structure 1 above) to the carbonyl carbon center of an aldehyde or ketone. A betain 8 is thus formed, which can cyclize to give the oxaphosphetane 9 as an intermediate. The latter decomposes to yield a trisubstituted phosphine oxide 4—e.g. triphenylphosphine oxide (with R = Ph) and an alkene 3. The driving force for that reaction is the formation of the strong double bond between phosphorus and oxygen ... 

Simple ylides are sensitive towards water as well as oxygen. By reaction with water, the ylide is hydrolyzed to give the trisubstituted phosphine oxide 4 and the hydrocarbon 10 ... 

Between all the classes of substituted phosphinous amides summarized in Table 1, those with the P atom totally substituted are more stable than others with H-P bonds, as in many other classes of organophosphorus compounds. Between those, the trisubstituted or fully substituted (typed in boldface) are by far the most stable and the main actors of the chemistry described in the following pages. 

The stability of phosphinous amides depends, to a large extent, on the substituents at phosphorus and nitrogen. Normally, tetrasubstituted and N,P,P-trisubstituted phosphinous amides are stable and well-known compounds. The parent compound H2PNH2 is a volatile compound that is formed on hydrolysis of a solid state solution mixture of magnesium phosphide and magnesium... 

Among the routes for preparing phosphinous amides, the most frequently used method is the aminolysis of halophosphanes, most usually chlorophosphanes [32-34], because a number of such halophosphanes are easily accessible from commercial sources. These reactions usually provide the target species, i.e., trisubstituted compounds 1 in Scheme 1, in high yield. The HCl liberated from the reaction forms a salt with an organic base (either excess of the starting amine or externally added as, for example TEA or DBU, sometimes in the presence of DM AP) which is insoluble in the reaction solvent, typically diethyl ether... 

A tandem palladium catalyzed multi-component approach has been devised providing direct access to for instance trisubstituted thiophenes from the simple starting material 3-iodothiophene 41. In a representative experiment, the substrate 41 was converted to the product 42 by treatment with ethyl acrylate and iodobutane in the presence of a catalytic system consisting of Pd(OAc)2, tri(2-furyl)phosphine (TFP), norbomene, and a base. A mechanistic rationale accounting for this outcome was also proposed <06OL3939>. 

Relies, H.M. and Schulenz, R.W., Chemical transformations with regenerable polymer-supported trisubstituted phosphine dichlorides. The efficacious incorporation of phosphine reagents on polymer supports, /. Am. Chem. Soc., 96, 6469, 1974. 

Type III (no homodimerization) Acrylonitrile," protected 3° allylamines" Vinyl trialkoxysilanes, vinyl siloxanes 1,1-Disubstituted olefins, " non-bulky trisubstituted olefms, vinyl phosphonates, " vinyl phosphine oxides,phenyl vinyl sulfone, acrylonitrile, 4° allylic carbons (all alkyl substituents), protected 3° allylic alcohols, 7,Aolefm of 2-subst. 1.3- butadienes, 7,Aolefin of electronically deactivated 1.3- butadienes ... 

Trisubstituted X -phosphorins or X -phosphorins can be isolated unchanged even after long periods of irradiation when oxygen is excluded. Stade discovered that cyclic phosphinic acid esters 208 a-c which contain a cyclic butadiene (1.3)-moiety, photochemically rearrange smoothly to the tricyclic compounds 214 a-c. 

Trisubstituted alkenes.9 A stereoselective synthesis of trisubstituted alkenes uses (E)-alkenyl sulfoxides (1)>U as the starting material. These are reduced to the corresponding sulfides (2)," which undergo coupling with Grignard reagents in the presence of complexes of nickel chloride and phosphines as catalyst.12 The products (3) are obtained in steroisomeric purity of > 99%. 

Only limited successful examples of asymmetric hydrogenation of acrylic acids derivatives have included the use of chiral Rh complexes (Scheme 1.17). The diamino phosphine (28) utilizes selective ligation of the amino unit to a Rh center and also exerts electrostatic interaction with a substrate. Its Rh complex catalyzes enantioselective hydrogenation of 2-methylcinnamic acid in 92% optical yield [116], Certain cationic Rh complexes can attain highly enantioselective hydrogenation of trisubstituted acrylic acids [ 1171. 2-(6 -Methoxynaphth-2 -yl)acrylic acid is hydrogenated by an (.S ..S )-BIPNOR- Rh complex in methanol at 4 atm to give (.S)-naproxen with 98% ee but only in 30% yield [26]. 

Later, the chiral bicyclic phosphine catalyst 5a was also used for kinetic resolution of allylic alcohols with isobutyric anhydride [8, 9]. The best results were obtained for trisubstituted allylic alcohols - selectivity factors ranged from 32 to 82 at -40 °C. 

The first examples of catalytic asymmetric conjugate addition of alkylzinc reagents to trisubstituted nitroalkenes, such as PhC(Me)=CHN02, leading to the formation of nitroalkanes bearing a quaternary carbon stereogenic centre, have been reported. Reactions are promoted by the readily available amino acid-based phosphine (211)... 

Reaction of FeCo2(CO)9S with a series of phosphines (31, 133) and isocyanides (126) yielded mono-, di-, and trisubstituted derivatives, Eqs. (77) and (78). 57Fe-Mossbauer spectra of the phosphine-substituted derivatives indicated that substitution at cobalt occurs prior to substitution at iron (31). Unfortunately, no crystallographic evidence has been obtained for any of these derivatives, and the precise stereochemistry has not been resolved, even with the aid of l3C-NMR spectra (9). The problem is compounded with the isocyanide ligands since several isomers of the trisubstituted derivatives are formed. 

At this juncture, Danishefsky decided to investigate the possibility of setting the C(ll) and C(17) methyl stereocentres of 23 by hydroxyl-directed hydrogenation.13 Some years earlier, Evans had shown that cationic rhodium- and iridium-phosphine complexes can mediate highly diastereoselective reductions of trisubstituted homoallylic alcohols. However, for excellent stereoselectivities to generally be observed, it... 

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