1.3.2- Dioxaphospholane derivatives

A more serious complication for the betaine mechanism arose when it was found that oxaphosphetanes are more stable than betaines. The earliest evidence was encountered by Ramirez et al. (17), who found that certain phosphines react with two equivalents of hexafluoroacetone to give 1,3,2-dioxaphospholane derivatives 23 (Scheme 6). These compounds rearrange into unusually stable oxaphosphetanes 26 via fragmentation to 24, followed by a proton shift to generate an intermediate ylide 25 (17). Shortly thereafter, Vedejs and Snoble (18) used P nuclear magnetic resonance (NMR) methods to show that more typical Wittig reactions of nonstabilized ylides PhjP CHR also produce oxaphosphetanes and that these intermediates can be easily observed at temperatures below 0°. Since betaines did not accumulate in any of the experiments, their conversion to oxaphosphetanes could not be rate... 

Phosphorus(y) Compounds. The chemistry of phosphate species containing a peroxy linkage and the stereochemical implications of reaction mechanisms at phosphorus(v) have been reviewed. The cyclic 1,3,2-dioxaphospholans derived from meso- and ( )-hydrobenzoin show different n.m.r. spectra, and the crystal structures of the 2-phenoxy- and 2-/>-bromophenoxy-5-chloromethyl-5-methyI-2-oxo-l,3,2-dioxaphosphorinans have been determined. Factors influencing the stereochemistry in substituted 1,3,2-dioxa-phosphorinans as shown mainly by n.m.r. data are considered in a number of papers. Changes in the O—H stretching frequency of phenol in the... 

Other work in this area includes (i) study of pseudorotation and P—N bond rotation in 1,3,2-dioxaphospholans derived from diphenylphosphoramidites (MiO)2P-NR2 (R = Me or Pr NRa = pyrrolidino or NMePh) and hexafluoro-... 

Derivatives of this type can usnally be isolated without difficulty, but a further reaction can occur to give a 1,3,2 dioxaphospholane derivative (6.344). This is believed to proceed through an ionised tetrahedral form of the molecule as indicated. Similar type derivatives can be obtained by reacting phosphites with a keto carboxylic acids at low temperatures in polar solvents (6.345). 

Table 6. IP-NMR Chemical Shift Differences (AS, ppm) for Diastereomeric38 Dioxaphospholane Derivatives ...

It is well-documented that substituted 1,3,2X5-dioxaphospholanes are viable precursors to the substituted epoxides (15-16), However, while mono- and disubstituted 1,3,2X5. dioxaphospholanes derived from the corresponding diols readily collapse to epoxides (35-50°C), highly substituted l,3,2x5-dioxaphospholanes from tri- and tetrasubstituted... 

In one study (Dayrit et al., 2008), phosphorus-31 nuclear magnetic resonance spectroscopy ( P NMR) was used to differentiate virgin coconut oil from refined, bleached, deodorized coconut oil. MGs, DGs, sterols and FFAs in virgin coconut oil and refined coconut oil were converted into dioxaphospholane derivatives and analyzed by NMR. 

A 0.15 M soln. of 2,2,2-trimethoxy-4,5-dimelhyl-l,3,2-dioxaphospholene in dry acetone stirred by a Na-stream irradiated 12 hrs. with a broad spectrum UV-source and a Vycor filter -> dioxaphospholane derivative. Y 54%. W. G. Bentrude and K. R. Darnall, Tetrah. Let. 1967, 2511. 

In a related paper, reaction of(60a) with (56) gave the hydrospirophosphorane (61) which upon u.v. irradiation in the presence of dimethyl disulphide gave the methylthio derivative (62) which was also prepared by the reaction of(60b) with hexafluoroacetone1 2. In contrast, the reaction of (63) with hexafluoro-acetone furnished a 1 1 mixture of the 1,3,2-A3- and 1,3,4-A5-dioxaphospholanes (64) and (65). 

The halogenation of the allenesubstituted 2-oxo-l,3,2-dioxaphospholanes also leads to 2,5-dihydro-l,2-oxaphosphole-2-oxide derivatives 182 (Scheme 72) [99]. 

The disulfide derived from a thioglycerol was converted into the corresponding sulfenyl chloride (step a) and allowed to react with 2-triethylsily-loxy-l,3,2-dioxaphospholane to give a cyclic thiophosphate (step b). Reactions a and b were performed as a one-flask procedure and the crude thiophosphate was transformed into the desired thiophosphocholine by opening the phospholane ring with trimethylamine (step c). 

The reactivity and use in organic synthesis of l,3,2,>l5-dioxaphospholanes has been presented230. Further details on various topics can be found in the following reviews Gloede (1988)344 Markovskii et a/.342, work prior to 1987 on linear equilibria between phosphoranes and phosphonium salts and Polezhaeva and Cherkasov340, results obtained prior to 1982 with cyclic derivatives. 

For the sensitive and selective detection of trace amounts of low-molecular-weight alcohols and other hydroxyl-containing compounds by means of the alkali FID, Vilceanu and Schulz [43] prepared phosphorus-containing derivatives. Derivatives 5.1 and 5.2 were prepared by the reaction with 2-chloro-l, 3,2-dioxaphosphorinane (5.3) and 2-chloro-1,3,2-dioxaphospholane (5.4), respectively, in the presence of triethylamine in benzene, which proceeds very quickly, and were particularly suitable for the determination of trace amounts of alcohols in non-alcoholic and anhydrous media. Retention indices of these derivatives of alcohols up to C5 are listed in Table 5.4. 

A second type of five-membered cyclic oxyphosphorane is represented by derivatives of the 1,4,2-dioxaphospholane ring.111 These are made from the reaction of trivalent phosphorus compounds with certain aldehydes, for example 111... 

The reaction of the aminophosphanes t-Bu2PNH2 and F2PNH2 results in the formation of hexafluoroacetoneimine and phosphoric acid derivatives with and without addition of HFA. With aminodifluorophosphane, the expected formation of a 1,3,2-dioxaphospholane (see Section III,A,4) has been observed (263). 

In addition to the compounds 57, 60, and 61 listed in Tables II-IV, further l,3,2-2 -dioxaphospholanes are accessible via halogen exchange reactions 106,115, 229, 230, 232, 263, 263a, 277) (vide infra), oxidative addition of a,/S-diketones to 2 -dioxaphospholanes (32), hydrolysis of silylamino compounds with HCl to yield unsubstituted amines (121), and thermal elimination of McsSiF from the silylaminofluoro derivatives 57ah and 57ai (115,118). 

Enthalpies of activation of both reactions, proceeding with rate constants kiand k2 are nearly the same for 2-methoxy substituted monomer. Ratio ki/k2 = 3 was calculated in 40° and 100°. 2-Neopenthoxy substituted monomer does not participate in Arbuzov type transfer and the rate constant ki is approximately 40 times lower than for 2-methoxy derivative. When substituent was changed to t-buthoxy group decomposition of intermediate salt into isobutylene, 2-hydro-2-oxo-l,3,2-dioxaphospholane and 2-methyl-2-oxo-l,3,2-dioxaphospholane was observed. 

Other Studies. - The P NMR chemical shifts of alcohols, carboxylic acids and phenols phosphitylated with 2-chloro-4,4,5,5-tetramethyl-dioxaphospholane have been correlated with substituent effects of phenols. P NMR spectroscopy has also been used to study activation pathways of aryl H-phosphonate ester condensation reactions, the conversion of allenyl and divinyl phosphines to 1- and 2-phosphadienes, the reaction of tetraphosphorus decasulfide with dialkyl disulfides, the reaction of phosphine with cyclic olefins, the chemical shift tensors of powder samples of phosphole derivatives, the reactions of alcohols and mercaptans with tetraphosphorus trichalcogen diiodides, the structure of aminomethanebisphosphonic acids, and reactions of 00-di-(2-ethylhexyl)dithiophosphoric acids. ... 

Phosphorus Compounds.—Treatment of the dioxaphospholen (635) with sulphur yields a mixture of the oxathiole (636) and fran -dibenzoylstilbene, PhCOCPh=CPhCOPh." 2-Phenyl-l,3,2-dioxaphospholan (637 R = Ph) dimerizes in solution to a ten-membered-ring compound, which was isolated as (638) by sulphurization." The cyclic thiophosphorous acid (639) exists in equilibrium with the betaine (640) in aqueous ethanol/ The spiro-compound (641), which contains a phosphorus-hydrogen bond, is formed by the action of (637 R = Cl) on diethyl tartrate. The phosphazene (642) spontaneously cyclizes to the spiro-compound (643). " Stable derivatives (645) and (646 R = Br) of five-co-ordinate phosphorus have been obtained by the action of bromine on the o-phenylene phosphite (644)/ The chlorine analogue (646 R Cl) reacts with 3,5-dimethylpyrazole to give the corresponding pyrazole derivative (646 R = 3,5-dimethylpyrazol-l-yl), which reversibly dimerizes to the zwitterion (647). ... 

The oxide radical (648) exchanges the unpaired electron, as evidenced by e.s.r. spectroscopy.Treatment of the catechol with phosphorus pentachloride yields, inter alia, the spiro-dioxaphospholan (649), which equilibrates with the six-co-ordinate phosphorus acid (650)." A hexa-t-butyl-derivative is obtained by the joint action of white phosphorus and triethylamine on 3,5-di-t-butyl-l,2-benzo-... 

A full paper has appeared on the stereoselective phosphonylation of aldehydes with the 1,3,2-oxazaphospholans (16) derived from (lR,2S)-ephedrine. From NOE and other n.m.r. data on one of the products the main isomer formed was assigned the structure (17). Similar highly stereoselective Abramov reactions have been studied using (18), and the X-ray structure of the main product determined in one case. New chiral 1,3,2-dioxaphospholans (19) and a cyclic phosphite derived from l,l -binaphth-2-ol prepared by the same group were much less reactive towards aldehydes than (16) or (18). 

A soln. of the startg. 1,3,2-dioxaphospholane in 2,3-dimethylbut-2-ene irradiated at 40° in a quartz test tube with low-pressure Hg-lamps -> cyclopropane derivative. Y 60-70%. F. e. s. P. Petrellis and G. W. Griffin, Chem. Commun. 1968, 1099. 

General procedure for the preparation of2-hydroxy-2-oxo-l,3,2-dioxaphospholanes or 2-hydroxy-2-oxo-l,3,2-dioxaphosphorinanes and their derivatives (ref Can. J. Chem., 1959, 37, 1498). 

Cyclic allq lene phosphonates, namely 2-oxo-l,3,2-dioxaphospholanes and 2-oxo-l,3,2-dioxaphosphorinanes, can be obtained through either the controlled hydrolysis of the corresponding phosphorus(III) derivative (Scheme 6.9, route A) or by a transesterification reaction between a diol and a diall l phosphonate (Scheme 6.9, route B). An alternative method has been described, based on the reaction of cyclic ethers with phosphonic acid in the presence of acetic anhydride. ... 

Phosphobetaine monomers may also be prepared via a number of routes (239,274). Probably the most common phosphobetaine monomer is 2-(methacryloyloxy)ethyl phosphorylcholine (MPC), although other derivatives are also known (275-278). MPC is prepared from the reaction of 2-hydroxyethyl methacrylate with 2-chloro-2-oxo-l,3,2-dioxaphospholane, followed by ring... 

Cationic chelate (8) was prepared and reported to exhibit excellent catalytic properties in asymmetric hydrogenation reactions, The phosphitylation of methyl a-D-mannopyranoside with P(NEt2)3 has afforded the cyclic phosphite (9), and a similar reaction applied to D-xylose gave (16), whereas both the pyranose (11) and furanose (12) derivatives were obtained from 2-O-substituted D-glucoses. The synthesis of a carbohydrate derivative of a dibenzo-substituted phosphorus heterocycle is mentioned in Chapter 7, and the conversion of methyl a-D-glucopyranoside into epoxides via dioxaphospholanes is covered in Chapter S. 

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