Dioxaphospholans

2-Dioxaphospholans.—1,2-Diols with TDAP and carbon tetrachloride gave either epoxides (46) or, more commonly, spirophosphoranes (47).37 cw-Cyclohexane- 

2-diol gives initially one symmetrical isomer, either (48) or (49), which rapidly equilibrates (AG 24 kcal mol-1) with the other two possible isomers. Another account of the condensation of cyclic phosphites with benzoyl cyanide has appeared.88 

Details have appeared39 of the addition of PH-tetraoxyspirophosphoranes to aldehydes and activated ketones. These phosphoranes also add to activated acetylenes,40 e.g. diethyl acetylenedicarboxylate with (50) gives a mixture of cis- and trans-(51). Further addition of (50) to (51) at higher temperatures gives the bisphos-phorane (52). Metallation of the spirophosphorane (53) followed by reaction with 

Pseudorotation in the phosphoranes (57) and (58) has been studied using variable-temperature 13C n.m.r. spectroscopy.42 The results on (57 R = Me) agree with those previously obtained using proton resonance. 

2-DioxaphosphoIens.—The condensation of a-diketones with tervalent phosphorus compounds has been extended to monothiobenzil.43 Hydrolysis of the resulting adducts (59) gave both P-O and P-S bond fission. Exchange reactions on the benzil- 

2-Dioxaphospholans.— The spirophosphoranes (56) have been prepared, using a-keto-esters or benzoyl cyanide. Cyclic phosphoramidites (55 R =NEt2) gave the 

PH-phosphoranes (56 =Hj. a-Keto-acids and the cyclic phosphite or phosphonite 

Details have appeared of the reactions of a wide range of PH-spirophosphoranes (61) with aldehydes, imines, and aminals, from which the products are spirophos- 

Enamines, e.g. (67), rve as oxidizing agents in the coupling of PH-spirophos-phoranes with alcohols to give alkoxyspirophosphoranes, e.g. (68), and in the oxidation of the phosphonites (69) to spirophosphoranes.  

2-Dioxaphospholans.— Triphenylphosphine and the 1,2-dioxetan (26) give a high yield of the phosphorane (27), which decomposes at 55 °C to give phosphine oxide and epoxide. The dihalogenophosphoranes (28) and (29) were obtained as shown. 

The variable-temperature n.m.r. of the diaryl phosphoramidite-hexafluoroacetone adducts (30) have been interpreted in terms of a substantial difference in apicophilicity between aryloxy- and amino-groups, changing substituents on nitrogen having little effect. The variable-temperature C, F, and n.m.r. spectra of the caged polycyclic phosphorane (31) have now been studied down to —165 °C. Permutational isomerization is still rapid at this temperature. 

3 -Dioxaphospholans.—The cyclic phosphonites (25 R = Me or Et) reacted with butadiene and with isoprene less rapidly than did (25 R = Ph), but more rapidly than did (25 R = Cl or NCS). The phosphite (25  

R = PhO) reacted with dienes to give the phosphinate esters (26), doubtless via the phosphoranes.  

For the preparation of 1,3,2-dioxaphospholans by exchange reactions between diethoxyphosphoranes and 1,2-diols, see Section 3 above. 

The 2 1 adducts (28) have been prepared from pyruvate esters and the cyclic esters (27).  

Base-catalysed additions of the phosphoranes (33 X = O or NH) to acrylic esters and acrylonitrile have been reported, as well as radical addition of the phosphorane (33 X = O) to vinyl ethers.  

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Several other types of monomers have been successfully used for the spontaneous copolymerization266). For MN, 2-oxazine, N-benzyliminotetrahydrofuran, N-ben-zylidene aniline, dioxaphospholanes and 1,3,3-trimethylazetidine were used and as Mg, succinic anhydride, propane sultone, acrylic acid and acrylamide were used268"273). 

Conformation problems in five- and six-membered rings containing phosphorus continue to attract attention and, using n.m.r., i.r., and dipole-moment measurements, studies have been reported on 1,3,2-dioxaphospholan systems (118), > 1,3,2-dioxaphosphorinane systems... 

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 reactions of 1,3,2-dioxaphospholans (23)-(26) with five acceptor alkenes (27)—(31), and of trimethyl phosphite, tris(dime-... 

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 mechanism of the reaction involves oxaphosphole ring closure followed by 1,3,2-dioxaphospholane rind opening. 

The reaction of l,3-dienephosphonic-l,3,2-dioxaphospholanes with arenesul-phenyl chlorides followed the mechanism discussed earlier to give 202 (Scheme 81) [158],... 

Hydrophosphorylation has recently been extended to rhodium catalysts as a route to anti-Markovnikoff products.198 Thus, 3mol.% Rh(PPh3)3Cl affords the ( )-alkenylphosphonates (R = H, Ph, -Cr,I I ]3, CH2CH2CN, SiMe3, or cyclohexenyl) in high yields (>80%) at room temperature when 4,4,5,5-tetramethyl-l,3,2-dioxaphospholane-2-oxide (74) is used as the PH source (Equation (19)).199 The rate of reaction is highly solvent dependent... 

Ramirez, F., Gulati, A.S., and Smith, C.P, Reactions of five-membered cyclic triaminophosphines with hexafluoroacetone, trifluoroacetophenone, and fluor-enone. Attack by phosphorus on carbonyl oxygen and isolation of crystalline 2,2,2-triamino-l,3,2-dioxaphospholanes, /. Am. Chem. Soc., 89, 6283, 1967. 

Mathieu-Pelta, I. and Evans, S.A., Highly regioselective and stereospecific functionalization of 1,2-propanediol with trimethyl(X)silanes employing the l,3,2 5-dioxaphospholane methodology, Phosph., Sulf. Silic., 75, 23, 1993. 

Kelly, J.W., Robinson, P.L., Murray, W.T., Anderson-Eskew, N., Pautard-Cooper, A., Mathieu-Pelta, I., and Evans, S.A., Substituted l,3,2X5-dioxaphospholanes. New synthetic methodologies, in ACS Symposium Series 486 Phosphorus —Developments in American Science, Walsh, E.N., Griffith, E.J., Parry, R.W., and Quin, L., Eds., American Chemical Society, 1992, Chapter 15, p. 186. 

Reactions.—Nucleophilic Attack at Carbon. (/) Carbonyls. Methyl arylglyoxylates react with trisdimethylaminophosphine (TDAP) to form m-a/S-dimethoxycarbonyl-stilbene oxides.63 The initially formed zwitterion (61) reacts with a second molecule of the ester to form a fra/ -diphenyl-1,4,2-dioxaphospholan intermediate, which undergoes a concerted symmetry-allowed retrograde n2s + 4 cycloaddition to give a carbonyl ylide, conrotatory cyclization of which leads to the cw-oxirans (62) (Scheme 3). 

Cyclic Esters of Phosphorous Acid.—A large number of 2-substituted-4-methyl-l,3,2-dioxaphospholans (88) have been prepared and their stereochemistry and conformations investigated by 1H and 31P n.m.r.69 Unlike the corresponding 1,3-dioxans, the tra/w-isomer (88a) is favoured in all cases, and each isomer is best described in terms of two rapidly equilibrating half-chair conformers with the 4-alkyl group pseudo-axial or pseudo-equatorial. 

A synthesis of alkenes from 1,2-diols depends upon the initial formation of the 1,3,2-dioxaphospholans (128), followed by rupture of the heterocyclic ring and removal of phosphorus with Li-NH3 or Na-Ci 0H 8. The reaction is reasonably stereo-... 

Alkenes are much less reactive in the H-P bond addition reactions than alkynes. However, 1,3,2-dioxaphospholane 2-oxide (4a), a five-membered hydrogen phosphonate of pinacol, is exceptionally reactive with alkenes although dialkyl and diaryl phosphonates such as 4b-d are totally unreactive (Scheme 25) [26]. Very interestingly, six-membered hydrogen phosphonates 4e,f are also unreactive under identical conditions. 

Example 66 the phosphoroamidite route has been used to prepare phospholipid analogues holding biocompatible properties. Brown et al. [106] have prepared the 2-(methacryloyloxy)ethylphosphorylcholine monomer using the 2-iV,iSr-diisopropyl-l,3,2-dioxaphospholane which was coupled with 2-hydroxyethyl methacrylate (step a) in the presence of 4,5-dichloroimida-zole. 

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). 

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