Phosphine oxides rearrangement

If aromatic aldehydes or ketones are used, the tertiary phosphine product sometimes rearranges to a mixed phosphine oxide. 

The [l,2]-a rearrangement of phosphinothioates into (alkylsulfanyl-methyl)phosphine oxides using a chiral phosphinoyl group has also been reported (see Sect. 5.1.1.). 

In the asymmetric version of the [1,2] -aWittig rearrangement (see Sect. 3.2), the deprotonation of S-methyl (ferf-butyl)arylphosphinothioate 103 followed by alkylation affords the corresponding (alkylthiomethyl)phosphine oxides 104 together with over-reacted products 105 (no diastereomeric excess is observed for this compound) and 106 [67] (Scheme 30). 

Well known carbanionic sigmatropic rearrangements, applied to mixed P and S compounds, regio- and/or stereoselectively lead to new (a-sulfanylalkyl) or P-sulfanylaryl) phosphonates, phosphine oxides, or phosphorodiamidates. In these difunctional compounds, chirality can be either introduced on the phosphorus, on the a-carbon, or on the sulfur atom. 

In contrast to the situation on flash pyrolysis, methyleneoxophosphoranes generated by thermolysis or photolysis in the presence of protic nucleophiles can be directly trapped to form corresponding derivatives of phosphinic acid (17- 19) however, the possibility of competing insertion of carbenes into the H/X bond of the additives is always present, giving phosphine oxides with X in the a-position (16- 18). Reaction branching at the carbene 16 was first observed on photolysis of 7 in water 13) and prompted detailed investigations on the phosphorylcarbene/ methyleneoxophosphorane rearrangement. 

Detailed investigations of the chemical reactivity of the diketiminato-stabilized phosphenium cations like 28 (Scheme 17) are to date rare and include only two reports dealing with the substitution and reduction of P-halogen-derivatives. Thus, reaction of 28 (X=Br) with sodium hydroxide in toluene was reported to proceed with displacement of the halide substituent at phosphorus and conservation of the heterocyclic ring to give a mixture of bromide and triflate salts containing a P-hydroxy-substituted cation, both of which were isolated in small yields [89], The products are remarkable as they represent one of very few examples of a stable phosphinous acid which does not rearrange to the tautomeric secondary phosphine oxide. Potassium reduction of the P-chloro-substituted derivative 34 produced the... 

The benzotriazolyl derivative of acrolein acetal, compound 882, is lithiated, treated with chlorodiphenylphosphine, and the obtained intermediate is oxidized with hydrogen peroxide to phosphine oxide 883 (Scheme 145). The relatively acidic proton in derivative 883 is easily removed by a base, and the obtained anion adds to a carbonyl group of aldehyde or ketone. Subsequent rearrangement and elimination of the phosphorane group generates diene 884. For the derivatives of aldehydes (884, R2 = H), (E)-(E) stereoselectivity of the elimination is observed. Acidic alcoholysis of dienes 884 affords esters of P,y-unsaturated carboxylic acids 885 < 1997JOC4131>. 

The intermediate product 162, formed from the nudeophilic addition of 1,2-alle-nic phosphonate or 1,2-allenic phosphine oxide with allylic alcohol, would also undergo a Claisen rearrangement to form 2-oxo-5-alkenyl phosphonate or phosphine oxide 163 [85], The rearrangement is accelerated by the carbanionic nature of the intermediate 162. For the conjugate addition step, the reaction temperature is crucial since the reaction at 0 °C afforded mainly /i,y-unsaturated product whereas a,/8-unsaturated products were formed at 20 °C. 

Several reports have appeared on the effect of additives on the Pauson-Khand reaction employing an alkyne-Co2(CO)6 complex. For example, addition of phosphine oxide improves the yields of cyclopentenones 119], while addition of dimethyl sulfoxide accelerates the reaction considerably [20]. Furthermore, it has been reported that the Pauson-Khand reaction proceeds even at room temperature when a tertiary amine M-oxide, such as trimethylamine M-oxide or N-methylmorpholine M-oxide, is added to the alkyne-Co2(CO)6 complex in the presence of alkenes [21]. These results suggest that in the Pauson-Khand reaction generation of coordinatively unsaturated cobalt species by the attack of oxides on the carbonyl ligand of the alkyne-Co2(CO)6 complex [22] is the key step. With this knowledge in mind, we examined further the effect of various other additives on the reaction to obtain information on the mechanism of this rearrangement. 

R S(Q)CH, R2 — R AC(0)R2The conversion of sulfoxides (2) into thiol esters (5) is possible via the sulfoxide phosphines (3), which rearrange slowly at 0-20° or, more efficiently, in the presence of iodine, to phosphine oxides 4. These can be oxygenated via the a-lithio derivative to thiol esters 5. 

Singlet oxygen reacts with binaphthylphosphine derivatives such as 1, l -binaphthyldi-/-butylphosphine to form the corresponding binaphthyl-2-oxide phosphine oxides. This intramolecular arene epoxidation reaction proceeds with complete retention of stereochemistry. The binaphthyl-2-oxide di-/-butylphosphine oxide undergoes a slow NIH rearrangement to form the corresponding hydroxylated product. A transient phospha-dioxirane intermediate has been directly observed by low-temperature NMR.241... 

Similar mass-spectral rearrangements have been observed in sulphon-amides (66, 67), sulphonimides (68), and phosphine oxides (69, 70). 

Intramolecular rearrangement of 2-alkynyl phosphites or phosphinites gives allenyl phospho-nates or phosphine oxides, respectively, and in most cases proceeds with high stereoselectivity (cf. Houben-Weyl, Vol. E2, p 19). 

Thus, l-alkynyl-2-methylcyclopentanols react with chlorodiphcnylphosphine in the presence of base to give transient phosphinites, which rearrange stereoselectively to allenyl phosphine oxides I24... 

Apart from their properties as ligands, other aspects of the reactivity of phosphinite esters have been of interest. It has been shown that phosphinite esters (77) undergo the Michaelis-Arbuzov rearrangement to give the phosphine oxides (78) between room temperature and 80°C in the presence of trimethylsilyl halides, the reaction not needing the presence of any alkyl halide. The rearrangement proceeds even more efficiently at room temperature in the... 

Ph), or phosphonic amides (97 R = NMe2 or MC HgO) with sodium in dioxane, or with magnesium activated by anthracene in THF, affords the bis(2-hydroxyaryl)phosphinic acid derivative (or phosphine oxide) (98) following a carbanionic rearrangement. 

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