1,3,2-Dioxaphospholanes

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). 

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

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). 

---