Monocyclic Phosphoranes

1 Monocyclic Phosphoranes - A study of the spectral composition of luminescence and of the kinetics of attenuation of chemiluminescence during the thermal decomposition of triphenylphosphite ozonide, has shown that the emitter of chemiluminescence in the i.r. region is singlet oxygen whereas the emitter in the visible region is triphenyl phosphate. 

Four-membered oxaphosphetan rings are, of course, an integral feature of the mechanism of the Wittig reaction whidi has again received an exhaustive treatment during the year. The first two papers by Vedejs et argue that kinetic (not equilibrium) factors are dominant in Wittig 

In a continuation of an investigation of the chemistry of P-halogeno ylids, P-fluoro ylids (29) have been shown to react with aldehydes and ketones to form 2-fluoro-l,2X -oxaphosphetans (30) which rearrange to alkylphosphonates (31). The pentaco-ordinated phosphorus compounds ( 8 P= -41.6/-56.0) were also characterised by and n.m.r. 

Triphenylphosphine (benzoyl)methylene (38) reacts with the phosphetan disulphide (39) to give a mixture of the phosphorane (42) and either (43) or (44) via intermediates (40) and (41).26 The available spectroscopic data was apparently unable to distinguish between (43) and (44) due to lack of solubility but 

The reactivity and S mthetic utility of l,3,2X -dioxaphospholanes are discussed in a paper presented at Tallinn by Evans et al. The abstract includes a summary of the kinetics of Lewis add-mediated decomposition and a report on the use of dioxaphospholanes to prepare a-D-pyranosides mentioned in Section 3 (reference 17). 

1 Monocyclic Phosphoranes. - Further studies of the reaction of P-fluoro-ylids (53) with carbonyl compounds (54) reveals formation of P-fluoro-oxaphosphetans (55) as the initial addition products. These may decompose in a conventional Wittig reaction to form alkenes (56)21 ajgo lose HF to form alkyl phosphonates (57).22 

A further mechanistic study of the Wittig reaction between lithium-free isopropylidenetriphenylphosphorane (58) and benzophenone (59) in THF was shown by 51p n.m.r. to proceed via the oxaphosphetan intermediate (60) with ki= 1.3 x 10 3 lmol l s l, k2 = 4.0 x lO s l and k3 = 7.0 x 10 4 s l. In addition carbonyl kinetic isotope effects and a value of p = +1.4 based on variations of substituents in the aryl group of the ketone, were consistent with rate-determining formation of the oxaphosphetan (60).23 

The oxidative addition of alcohols and primary amines to 2-alkyl (or aryl) - 

Phosphoroisocyanatidites (e.g. 83) react with 3-alkylidene-2,4-pentanediones (e.g. 84a) or 2-alkylideneacetoacetic esters (e.g. 84b) to form phosphoranes (85,a,b) which decompose on heating to the cyclic phosphonates (86a, b)27. in an analogous study, dialkylalkynylphosphonates (87) have been shown to react with alkyl pyruvates (88) below 0°C to form mixtures of alkynyl phosphonates (90) and monocyclic tetraoxaphosphoranes (91) via (89)28. At 80°C, however, (89) reacts with excess (88) via (92) to form the bicyclic phosphorane (93). 

Multinuclear dynamic n.m.r. has been used to study the influence of temperature, solvent polarity and the electronic and steric properties of the C- and N-substituents on the chlorotropic tautomerism between tetrachlorophosphoranes (94) and the 6-co-ordinate amidiniotetrachlorophosphates (95)29. The high negative entropies of activation ( AS = - 67 to -142 Jmol K ) found for the tautomerism indicate the formation of a contact ion-pair in the T.S. and with R = Pr, restricted rotation about the N-R bond in (95) was observed. 

1 Monocyclic Phosphoranes. - Pentaco-ordinate phosphorus compounds containing four-membered rings are scarce this year but one example is provided by an extension of the reaction of N-substituted ureas with PQ5 in which, for instance, the reaction of (20) with excess PCI5 

Insertion of aldehydes into the P-halogen bond of phosphoranes referred to in Section 3 (ref.8) is also exemplified by the reaction of the pyrocatecholtribromophosphorane (22) with fluoral (23) to give (24) with 5 P,-55ppm. Further studies in this area by Pudovik et al. have shown that the reaction of the phosphite (25) with one mole of pyruvic ester (26) results in the formation of (29) via (27) and (28) but with two moles of (26) the phosphorane (30) is formed. The reaction of (25) with tetrachloro-benzoquinone to form a cyclic phosphorane (5 P,-53) is also reponed in this paper. 

In further studies relevant to the mechanism of the Mitsunobu reaction, the reaction of diphenylphosphine (40) with di-isopropyl azodicarboxylate (41) was found to give a mixture of products one of which was assigned structure (44) formed via (42) and (43). The reaction of trico-ordinate phosphorus compounds with ortho-quinones,p-ketoalkenes and p-ketoimines is also a well-established source of pentaco-ordinate phosphorus compounds but in some cases the dipolar ion structure is more stable. Thus the reaction of (4Sab) with (46) produced the dipolar ion structures (47ab) but on the other hand, reaction of (45b) with the quinone imine (48) produced what appeared to be an equilibrium mixture of (49) and the pentaco-ordinate structure (50). The 1,3,2-X o -diazaphospholenes (Slab) have proved to be useful synthetic reagents in that on hydrolysis they yield the bis-hydroxylamine (52) which reacts with benzaldehyde to form the imidazoline (53).  

2 Bicvclic and Tricyclic Phosphoranes - The work of Schmutzler et al. reported in references 25 and 26, also includes the preparation and characterisation of a number of spirophosphoranes. For example the reaction of (60) with (66a-e) produced a range of spirocyclic phosphoranes (67a-e). Likewise the reaction of (66a-e) with two moles of (63) produced a series of 

Bicyclic phosphoranes (87a-d) prepared by the reaction of (85a-d) with (86) were isolated and then characterised by m.s., elemental analysis, i.r. and multinuclear n.m.r. spectroscopy no pseudorotation was observed at ambient temperature. In a related study, tricyclic phosphoranes (89a-d) were obtained from the reaction of (88a-d) with (86). An analogous reaction between (90a-i) and (86) furnished another series of tricyclic phosphoranes (91a-i). The single crystal X-ray structure of (91a) revealed a tbp configuration about phosphorus with a 26% distortion along the Berry coordinate using P-01 as the pivot. 

Mono- and bis-phosphonopyrimidinediones (14) have been synthesised in moderate to excellent yields from monocyclic phosphoranes (12) and isocyanates 

In a study designed to produce monoclonal antibodies which would catalyse the hydrolysis of phosphorus nerve agents, Moriarty et al. used a synthetic strategy involving a monocyclic phosphorane as hapten for the production of a monoclonal catalytic antibody based on the T.S. for phosphonate hydrolysis. These haptens (18 and 19), which are effective catalysts for the hydrolysis of Soman [Bu MeCHOPMe(0)F], were generated from the reaction of (15) with the protected 3(S) aminoalcohols (16 and 17).  

Methods for synthesising phosphoranes and spirophosphoranes containing a l,3,2X -oxazaphosphetidine ring from N-methyl-N-trifluoroacetyl-phosphorami-dites have been developed. For example the reaction of (20) with chlorine gave (22) via the intermediate (21) and the spirophosphorane decomposed to (23) and 

Reaction of tetrachloro-o-benzoquinone (29) with the monocyclic trihalophos-phoranes (30ab) in CH2Q2 gave the thermodynamically stable spirophosphor-anes (Slab) by substitution of the halogen at pentacoordinate phosphorus.  

Heating a mixture of pentachlorophosphole (26) and phenylacetylene (27) gave the phosphorane (28) which, on the basis of variable temperature NMR, appeared to be in equilibrium with the phosphonium salt (29) The most 

During a study of the reaction of a CT -l,2,3-diazaphosphole (30) with the trichlorophosphorane (31) Mironov et al. obtained a mixture of products (32-35) which included a phosphorane (35) whose structure was assigned on the basis of and NMR.  

The reaction of (36) with trimethyl phosphite in aprotic medium (hexane or benzene) leads to the formation of (38) as the sole product via a regiospecific [4 + 2] cycloaddition presumably involving (37) as an intermediate. Hydrolysis of (38) gave the ketophosphonate (40) apparently via an enol intermediate (39).  

Three diazaphosphetidines (41a-c) have been studied by variable-tempera-ture solid-state and NMR. The NMR data depended upon the 

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Structure, Bonding and Ligand Reorganisation. - An X-ray analysis of the monocyclic phosphorane (2) reveals a tbp structure with the hydrogen in an axial position and an H-P bond length of... 

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. 

Pseudorotation.—A number of spirocyclic phosphoranes possess square-pyramidal structures rather than the trigonal-bipyramidal structures previously assumed, and this could have important consequences on the interpretation of their variable-temperature spectra. There is, as yet, no evidence that acyclic or monocyclic phosphoranes favour the square-pyramidal geometry, and the variable-temperature XH... 

Monocyclic phosphoranes and fused bicyclic phosphoranes with a... 

To our knowledge, the first examples of asymmetrically substituted monocyclic phosphoranes are 60 and 61, described by Moriarty et al.135 and involving the reaction of a substituted o-benzoquinone136,137 (Scheme 6) on an aminophosphine (59), itself obtained by alcoholysis of 58 with l-( — )-menthol. In contrast to the amino phosphine 53 (Scheme 5), 59 is a mixture of the diastereoisomers 59a and b, and its reaction with 3,5-di-tert-butyl-l,2-benzoquinone yields two diastereoisomeric phosphoranes, 60a and b. Finally, alcoholysis of the P(V)—NR2 bond138 in 60a and b leads to 61a and b or 62. 

It was shown by potentiometric titration163 that the acidity of the proton of the PH bond is stronger in spiranic than in the homologous monocyclic phosphoranes. 

Kawashima et al. have devised a new method for the synthesis of monocyclic phosphoranes by the reaction of the thiophosphinate (33) with triethyloxonium tetrafluoroborate to form the phosphonium salt (34) which, on exchange of the CH2CI2 solvent for Et20, was converted quantitatively to (35) by fluoride abstraction from the counterion. 

In a study of ylides containing bis(trifluromethyl) groups Roschenthaler et al. also reported an unusual method for the formation of monocyclic phosphoranes (37ab) by the reaction of ylide (36ab) with hexafluoroacetone. The products were characterized by H, NMR, mass spectrometry and... 

A study of the reaction of N-arylhydrazides (74ab) with phosphorus pentachloride depends upon the molar ratio of the reactants and may lead to either the monocyclic phosphoranes (75ab) or spirophosphoranes (76ab) in which the P-Cl bonds may undergo a number of nucleophilic displacement reactions (e.g. by alcohols). ... 

We have explored other factors in a preliminary way to ascertain their influence on pV geometry and ring conformation and have isolated the monocyclic phosphorane (O) for study. X-ray analysis (40) shows the usual (a-e) ring orientation but the presence of a chair conformation. This represents the first example of the appearance of the chair conformation stabilized in the absence of hydrogen bonding interactions. Comparison with the related dithiaphosphorinane P analog (P) shows the same (a-e) ring orientation but in the normally observed boat conformation (40). 

A further investigation of these oxidative addition reactions revealed a complete redistribution of ligands between (69) and (70) involving a series of observable phosphoranes (71), (73), (75) and (76) containing P-H bonds (Scheme 1) 25. Monocyclic phosphoranes with P-H bonds have also been shown to add to activated carbon-carbon and carbon-nitrogen double bonds to form new phosphoranes containing P-C bonds. For example (78) reacts with acrylonitrile (79) or the imine (80) to give (81) and (82) respectively. 

The bis(trimethylsilyl) ether (36) with fluorophosphoranes gave the monocyclic phosphoranes (37), except with tetrafluorophosphoranes and... 

PFs when the major products were the bicyclic compounds (38). However, using the bis-t-butyl-substituted ether (39) the monocyclic phosphoranes (40 n = 0 or 1) were obtained as stable distillable liquids. At — 88 °C the n.m.r. of (40 n = 1, R = Me) showed two distinct fluorines, i.e. the pseudorotation which places the two fluorines equatorial is slow on the n.m.r. timescale at this temperature. 

Phosphoranes (91) have been prepared in 21—90% yield by the reaction of (89) with various three-co-ordinated phosphorus compounds (90). A detailed study of the reaction between methyl diphenylphosphinite and 1-nitropropene shows that at ca. — 5 °C a quantitative yield of the monocyclic phosphorane (94)... 

Perphosphoranides with phosphorus spiro to three rings one of which is different from the other two (e.g. 101 X = Y = Cat, Z = Dpe) may be prepared by the reaction of a monocyclic phosphorane bearing three exocyclic dimethylamino leaving groups and a chelating ligand such as catechol... 

G.-V. Rdschenthaler Introduction Acyclic phosphoranes Monocyclic phosphoranes Bicyclic and polycyclic phosphoranes Phosphatranes... 

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