Phosphinates rearrangement

The schematic (Figure 9) for a drum indicates how it is related to two cluster molecules. Formally, two bridging phosphinates rearrange, two oxygen atoms are added, four Sn-0 bonds are cleaved, the six Sn-O-Sn linkages become Sn(OH)Sn units, and two phosphinates are added to hydrogen bond to the hydroxyls. 

There has been the very interesting report that dialkyl(hydroxymethyl)phosphines rearrange to dialkylmethylphosphine oxides on irradiation with u.v. light.4 No mechanistic details are available. 

On the basis of the isolation of the intermediate compound 4 a reaction pathway was proposed (Scheme 1). Initially there is coordination of one phosphine with the formation of adduct III. This phosphine rearranges from axial to equatorial coordination with partial displacement of one acetate group. Proton transfer in this species IV yields the monometalated compound V, which further reacts with one additional phosphine to form the bimetalated compound. 

Although the 1 2 conversion occurs for Cp[P(OMe)3](CO)WsC(c-C3H5) (3) upon photooxidation in CHCl3/PMe3, in the absence of the phosphine, rearrangement and carbonylation of the carbyne ligand ultimately lead to cyclopentenone (Eq. 2) [4]. 

Diallylsulfonium salts undergo intramolecular allylic rearrangement with strong bases to yield 1,5-dienes after reductive desulfurization. The straight-chain 1,5-dienes may be obtained by double sulfur extrusion with concomitant allylic rearrangements from diallyl disulfides. The first step is achieved with phosphines or phosphites, the second with benzyne. This procedure is especially suitable for the synthesis of acid sensitive olefins and has been used in oligoisoprene synthesis (G.M. Blackburn, 1969). 

Allylic ester rearrangement is catalyzed by both Pd(II) and Pd(0) compounds, but their catalyses are different mechanistically. Allylic rearrangement of allylic acetates takes place by the use of Pd(OAc>2-Ph3P [Pd(0)-phosphine] as a catalyst[492,493]. An equilibrium mixture of 796 and 797 in a ratio of 1.9 1.0 was obtained[494]. The Pd(0)-Ph3P-catalyzed rearrangement is explained by rr-allylpalladium complex formation[495]. 

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

A number of ruthenium(II) complexes have been prepared. Cole-Hamilton and Stephenson isolated cts-[Ru(Me2dtc)2L2] (L = PPhj, PMe2, Ph, PPhMe2, or P(OPh)3) from Ru(II) and Ru(III) tertiary phosphine and phosphite complexes with NaMe2dtc, and found that they undergo rearrangements (288). 

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. 

Finally, the N-propargyl-P,P-dialkyl or diaryl phosphinous amides rearrange at room temperature to the P-(4-azabutadienyl)phosphanes 28 [127] (Scheme 29). Interestingly, this rearrangement did not occur in other structurally similar P-N functionalities (R=OEt, OTr, NEt2). 

Numerous other reactions can be used to access phosphaalkenes. For example, treating the primary phosphine Mes PH2 with CH2CI2 in the presence of KOH gives Mes P=CH2 [54]. In addition, interesting reactions of tantalum-or zirconium-phosphinidenes with aldehydes have afforded phosphaalkenes [55, 56]. The 1,3-hydrogen rearrangement of secondary vinylphosphines to phosphaalkenes has also been used to prepare phosphaalkenes [57,58]. 

Bromo-j3-nitrostyrene and triphenylphosphine in dry benzene gave the phosphonium bromide (47). Using methanol as the solvent, the rearranged product (48) was formed, possibly via an azirine intermediate. Substituted -bromo-/3-nitrostyrenes yield the phosphoranes (49) and a phosphonium salt. When the aryl group is electron-donating, the reaction follows a different course to form the styrene (50) by initial attack of the phosphine on halogen. 

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. 

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