Preparation of Cyclic Phosphine Oxides

The dihydrophosphete oxide (18), although it has not been characterised, is suggested to be the major product of air oxidation of 1,2-dihydro-phosphete (17).9 

A new route to 2-aryl and 2-heteroaryl 2,5-dihydrophosphole oxides (20) and sulphides (21) is available from arylation of the phosphole metal 

The phosphine oxide exo-exo cages (30) and (31) and exo-endo cages (32) and (33) have been prepared from tris(4-hydroxyphenyl)phosphine oxide (29) and in two cases, (30) and (33), X-ray structural analyses were carried out.l i Compounds (30 to 33) all form 1 2 complexes with p-nitrophenol. 

3-PhosphoIene sulphides (IS) and oxides have been prepared by [1+4] cycloaddition reactions of (14) with various dienes. Phosphorus analogues (17) and (19) of erythrofuranose have been prepared by stereospecific ci.y-hydroxylation of the 2-phospholene-l-oxides (16) and (18), respectively.Compounds (17) and (19) readily epimerise at C-2 on treatment with base. 

The previously reportedly ring-expansion of phosphole-dichlorocarbene adducts to dihydrophosphorins has now been studied in detail.14.15 Heating the adducts (21) at 135°C for 3 minutes leads to optimum yields of a mixture of isomeric 1,2-dihydrophosphorin 1-oxides (22) and (23). 14 Mercuric-catalysed ring-opening in acetic acid leads to the isomers (24) and (25).1 Both chlorine atoms in (21) may be replaced by phenyl groups in a Friedel-Crafts reaction. 

The novel heterocycle (27) has been obtained in low yield from multiple Aldol reaction of the tetraketone (26).16 The structure assigned to (27) is based on detailed iH, l C and 31p n.m.r. studies. 

Quin s group have reported the synthesis of a number of tricyclic phospholene oxides, e.g., (9), by the McCormack reaction. The isomeric bicyclic phosphine 

DMSO vi, KHSO4, xylene vii, HSiCls, py viii, Bu Li ix, HjOg 

Bodalski, T. Janecki, Z. Galdecki, and M. Glowka, Phosphorus Sulfur, 1983, 14, 15. 

4-t-Butyl-2-methyl-6-alkyl-l,4-oxaphosphorin 4-oxides (27) have been obtained by hydrolysis of the salts (26). The oxides (27) undergo acid-catalysed ringopening and aldol condensation to give 3(2 f)-phosphorinone 1-oxides (28) 

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Aromatic isocyanates, particularly those containing electron-attracting substituents, react noticeably more easily than aliphatic isocyanates. In the former case it often suffices to leave the components for some hours at room temperature in a water-pump vacuum, whereas for aliphatic compounds boiling under reflux is usually necessary and sometimes use of a higher-boiling solvent such as decalin. The best catalysts are cyclic phosphine oxides of type (1) (phospholene oxides)862 and cyclic phosphonic diamides of type (2) (1,3,2-diazaphospholidine oxides).863 The best results were obtained with compound (1, R = C2H5) (for its preparation see Campbell et a/.862) the phenyl compound, although more readily prepared,864 is somewhat less reactive. The amounts of catalyst needed are 0.1% for (1) or 0.5% for (2). 

Arylphosphonic acid esters are produced in the reaction of diaryl iodonium salts with trialkyl phosphites in the presence of copper salts, but despite the simplicity of the procedure yields are low owing to side reactions. The cyclic bisarylphosphinic acid (66) is conveniently prepared by fusion of the phosphine oxide (67) with sodium hydroxide. A successful... 

Most of the work in enantioselective deprotonation of cyclic phosphine derivatives has been carried out in phospholane derivatives. Simpkins and co-workers studied the stereoselective deprotonation of a readily available triphenylphospholane oxide and prepared several P-stereogenic compounds (Scheme 5.47). 

Another ligand including a thiophene moiety but lacking the C2-symmetry and thus bearing electronically different phosphorus atoms was prepared by these authors, in 2001. The electrochemical oxidative potential was obtained by cyclic voltammetry. The oxidation potential of the phosphine group located on the phenyl ring was found to be 0.74 V (vs. Ag/Ag" ) and the authors attributed a value of 0.91 V to the phosphine attached to the thiophene moiety. This second functionality is a rather electron-poor phosphine. As shown... 

These compounds have been prepared via oxidative addition reactions between the appropriate phosphate or phosphine and either a quinone or via displacement reactions with a suitable diol. Compounds 81 and 83 were prepared by such a displacement reaction between monocyclic pentaoxyphosphorane 317 and 3-fluorocatechol or catechol in toluene, respectively. This reaction takes advantage of the chelation effect of forming a bicyclic system from a monocyclic one <1997IC5730>. Compound 82 and compound 84 were synthesized via oxidation addition between tetrachloroquinone and the respective sulfur-containing cyclic phosphate or phosphine <1997IC5730>. Compound 93 was prepared from the phosphine 318 and the diol 319 in the presence of iV-chlorodiisopropylamine in an ether solution <1998IC93>. 

A number of macrocycles containing only one phosphorus atom have been prepared, and they are usually referred to as phosphorus-containing crown ethers rather than as P macrocycles. The 18-crown, or [18]anePOs, was prepared by van Zon (equation 28).82 This cyclic phosphine is stable in air, even in solution (cf. Ph3P). However, when the non-macrocyclic substituent is Bul the phosphorus is oxidized in solution by air in the presence of alumina. This unwelcome discovery was made by van Zon when purifying the material by chromatography on an alumina column. 

Currently accepted mechanism of the Wittig reaction of aldehydes with non-stabilized ylides involves the formation of oxaphosphetanes through a [2-I-2]-cycloaddition-like reaction . The oxaphosphetanes are thermally unstable and collapse to alkene and phosphine oxide below room temperature. Under salt-free conditions there is no formation of betaine intermediates. The salt-free ylides can be prepared by the reaction of phosphines with carbenes generated in situ. Vedejs etal proposed a puckered 4-centre cyclic transition state I for sy -oxaphosphetane and planar structure J for anff-oxaphosphetane. In general, the flnfi-oxaphosphetane J is more stable than the syn-oxaphosphetane I, and under equilibrium conditions (when stabilized ylides are used) the E-alkene product is favoured (Scheme 4.24). However, kinetic control conditions, which appear to dominate when non-stabilized ylides are used, would lead to Z-alkene. 

Derivatives of phosphonic acids, RP==O(0H)2, can be prepared by several different oxidative methods. Primary phosphines RPH2 are oxidized to phosphonic acids by hydrogen peroxide or by sulfur dioxide thus, phenylphosphine gave benzenephosphonic acid (96%) on reaction with sulfur dioxide at room temperature in a sealed tube. Phosphinic acids, RI sO(OH)H, can also be oxidized to the corresponding phosphonic acids with hydrogen peroxide. Ozone oxidized the dioxaphosphorane (54) to the phosphonic ester in 73% yield. Ozone is also capable of stereospecific oxidation of phosphite esters to phosphates. For example, the cyclic phosphite (SS) was oxidized to the phosphate (56) with retention of configuration. Peroxy acids and selenium dioxide are other common oxidants for phosphite esters. 

Carbonates and carbamates. In the presence of phosphine-CBr4 and base, alcohols combine with CO2 to afford carbonates. Mixed carbonates are obtained under different conditions, and with a Mg—A1 mixed oxide as catalyst, epoxides formed cyclic carbonates. The preparation of dimethyl carbonate from acetone dimethyl acetal and supercritical carbon dioxide in the presence of a metal catalyst (e.g., dibutyltin methoxide) is successfully carried out. ... 

Methyleneaminophosphines (10), on treatment with methyl iodide, give the expected phosphonium salts (11), which on thermolysis undergo a reaction analogous to the Arbusov reaction to give imidophosphoranes. Various phosphonates and phosphine oxides have been prepared by the reaction of the anions (RO)aP—0 Na+ and R2P—0 Na+ with alkyl halides. The analogous reactions of the chlorohydrin (12) with sodium diethyl phosphonate give the cyclic phosphonate (13) as a mixture of geometrical isomers of approximately equal stability. ... 

In order to examine the stereochemical implications in the synthesis of (largely) phosphinic acids (but also tertiary phosphine oxides), Inch and coworkers " employed carbohydrate frameworks as chiral templates. As primary substrates, the cyclic phospho-rochloridate 161 and the corresponding phosphorofluoridate 162 were prepared from methyl 1,2,3-di-O-methyl-a-D-glucopyranoside, each phosphoryl halide being obtained as a mixture of diastereoisomers, anomeric at phosphorus, and from which, in each case, the major component (thought to have an equatorial P=0 bond) was isolated. Configurations in both substrates and reaction products were assigned with the aid of proton and NMR... 

A further type of degradation occurs during the photolysis or thermolysis of derivatives of the 2,3-oxaphosphabicyclo[2.2.2]octene system, formally derivatives of cyclic phos-phonic or phosphinic acids. The compounds 42 are obtained by Baeyer-Villiger oxidations, with 3-chloroperoxybenzoic acid, of the 1 1 adducts from monomeric l//-phospho-les and iV-phenylmaleimide, and 43 by the identical oxidation of the products of dimerization of monomeric but unstable li/-phospholes. The simpler substrates 44, similarly obtained by the oxidation of the Diels-Alder adducts prepared from acetylene dicarboxylic ester, have also been examined. The thermolysis (at 80-110 °C in toluene) or... 

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