Phosphoranes formation

Timosheva NV, Chandrasekaran A, Holmes RR (2005) Atrane and phosphorane formation with aminotriphenols [1]. J Am Chem Soc 127 12474-12475... 

The reactions of bis(phosphoryl) disulphides with a variety of tervalent phosphorus acid derivatives or triphenylphosphine have been studied by means of low-temperature n.m.r. Intermediates were detected which indicated initial attack on one sulphur atom followed by substitution reactions at one of the phosphorus atoms, Arbuzov dealkylations, or phosphorane formation. An example is shown for the reaction of tributyl phosphite with bis(diethoxyphosphoryl) disulphide (25). In order to obtain solely thiophosphate products it is necessary to use bis(thiophosphoryl) disulphides, and one such compound (26) has been proposed as a highly effective reagent for the oxidation of oligonucleoside phosphites to phosphorothioates. A comparison of the efficiency of (26) with that of four other sulphurizing agents for use in... 

The formation of 27a-27e, 28, and 29 makes use of a chemistry developed by Akiba and coworkers in the 1990s for the synthesis and applications of cyclic lO-P-5 phosphoranes made of two Martin ligands. Methyl, benzyl and phenylth-... 

Finally, the lower symmetry of compounds 27 and 28, of type P(ab)2(cd), and 29, of type P(ab)2(cc), could have lead to the formation of many (racemic) di-astereomers. Interestingly, this is not the case as the configuration of the 10-P-5 phosphorane precursors is translated integrally to the P(VI) derivatives, as shown by Akiba and Kawashima [45-48]. Further manifestation of this phenomenon will be described in Sect. 3.1. A particularly striking example is the exclusive formation of 29 over 29 and 29" (Fig. 18) [48]. 

The basic hydrolysis of A - and A -phospholenium bromides gives mixtures of (96) and (97), the ratio depending upon the conditions used. Ylide (98) formation can compete with phosphorane generation, particularly in media where anions are stabilized by solvation. Under these... 

The formation of the phosphoranes (23) in the preparation of the phosphonites (24) has been shownto be due to two processes firstly, the acid-catalysed disproportionation of the phosphonites to give (23) and cyclopolyphosphines and secondly, the remarkable base-catalysed reaction of the phosphonites with catechol to give (23) and hydrogen. 

A. Preparation.—Halogen displacement reactions have been used to prepare a number of new aminofluorophosphines. Aminodifluorophos-phine (1) has been prepared for the first time, from either bromodifluoro-phosphine or chlorodifluorophosphine, and ammonia. Studies of its n.m.r. spectrum have been made (see Chapter 11). The related NN-difluoroaminodifluorophosphine (2) has been prepared, from difluoroiodo-phosphine, and found to be explosive. Two syntheses of A-alkyl-amino-difluorophosphines have been reported, one of which was complicated by the subsequent formation of the phosphorane (3) and the bis-(A-alkylamino)fluorophosphine (4). 

Reaction of perthiophosphonic anhydrides (64) with amines leads first to (105) and then, by further attack, to (106). With ammonia itself the second addition proceeds at the same phosphorus atom as the initial attack, giving (107) and (108). The anhydride (64) is also reported to react with 1,3-dioIs to give cyclic phosphonyl disulphides (109). Thermal decomposition of phenylphosphinic anhydride (110) may lead to the formation of PhP since in the presence of benzil the formation of the phosphorane (111) was observed. ... 

Wittig product (57). The methylenecyclobutanes (60) were formed from the same phosphoranes and the methylenecyclopropene (59). The formation of the pyran-2-ones may involve the intermediate cyclobutenones (56) as shown. 

A mechanism for this reaction involving nucleophilic attack of the ylide on the cyanide group and formation of the P=N linkage via a four-centred intermediate was formulated. The structure of this phosphazene was confirmed by its synthesis from the vinyl azide, Ph(N3)C=CHPh, and triphenylphosphine. Phosphoranes stabilized by electron-withdrawing... 

The stereoselectivity of the Wittig reaction is believed to be the result of steric effects that develop as the ylide and carbonyl compound approach one another. The three phenyl substituents on phosphorus impose large steric demands that govern the formation of the diastereomeric adducts.240 Reactions of unstabilized phosphoranes are believed to proceed through an early TS, and steric factors usually make these reactions selective for the d.v-alkcnc.241 Ultimately, however, the precise stereoselectivity is dependent on a number of variables, including reactant structure, the base used for ylide formation, the presence of other ions, solvent, and temperature.242... 

Monocyclic Phosphoranes. - Further studies on the mechanism and stereochemistry of the Wittig reaction have been conducted by a combination of 1H, 13C and 3 P n.m.r.2k 25. The results show that at -18°C both ois and trans diastereomeric oxaphosphetans (e.g. 17 and 18) may be observed and their decomposition to alkenes monitored by n.m.r. Evidence was presented to suggest that during this process oxaphosphetan equilibration involving the siphoning of (17) into (18) occurred in competition with alkene formation. 

Viewed systematically, formation of the olefins 24 on reaction of methyleneoxo-phosphorane 9 with a,P-unsaturated carbonyl compounds is to be classified as an olefination reaction. The similarity to the Wittig reaction is obvious, the differences being just a matter of degree. 

Attempts to initiate formation of a nitrene, and its rearrangement to the iminooxo-phosphorane 80, by subjecting l-chloroamino-2,2,3,4,4-pentamethylphosphetane 1-oxide to a-elimination with sodium methoxide proved unsuccessful48). In contrast, however, the phosphorylhydroxylamides 88 rearrange in the presence of tert-butyl-amine to the heterocumulene 89 and then add base to give the phosphonic diamides 90 (>90%)49). The reaction is reminiscent of the well-known Lossen degradation. 

Macomber et al. achieved formation of cyclic phosphoranes 82 [86], The latter on treatment with water or with alcohols gave the corresponding oxaphosphole derivatives (Scheme 34). 

Finally, a reaction should be mentioned in which a nucleophile gives support to another reacting species without appearing in the final product. Diphenyl cyclopropenone interacts with 2,6-dimethyl phenyl isocyanide only in the presence of tri-phenylphosphine with expansion of the three-ring to the imine 344 of cyclobutene-dione-1,2229,230 Addition of the isocyanide is preceded by formation of the ketene phosphorane 343, which can be isolated in pure formss 231 it is decomposed by methanol to triphenyl phosphine and the ester 52. 

However, other reaction directions via the formation of the phosphorane structure with migration of the methyl anion from one phosphorus atom... 

The formation of the stable betaine system P+—C—O—B is the driving force for this reaction. With 4,6-disubstituted ammonium 1,3,2,5-dioxaborataphosphorinanes (108), there is the possibility of making a choice between two reaction directions. The reaction product formed by the phosphorane transition state, as 1,3,2,5-dioxaborataphosphoniarinane... 

The disulfide fragment separating phosphorus and boron atoms was not replaced in 181 by chloral even after refluxing in benzene, evidence for high betaine stability. In methylene chloride, 175 reacts with 1,2-naphthoquinone, yielding phosphorane 182 [Eq. (135)]. This result is surprising, as one could have expected the formation of a betaine structure. 

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