With 1,3,4-dioxaphospholanes

Ether, a solvent with a low dielectric constant, favours cyclization over chain extension. Heating the phosphorane to 120 °C yields the alternating copolymer. Terpolymers are formed when either acrylates or acrylonitrile are copolymerized with dioxaphospholane in a carbon dioxide atmosphere. 

Finally, we previously reported that 1,3,2X -dioxaphospholane 14, prepared in situ from the reaction of diol 1 with diisopropyl azodicarboxylatc (DIAD), reacts with benzoic acid at -78 C to afford the two regioisomeric C-1 and C-2 oxyphosphonium ions in tetrahydrofuran (THF) solvent. Based on the low temperature ip NMR data, we concluded that these regioisomeric oxyphosphonium ions, U and V, undergo rapid equilibration with dioxaphospholane 14 in benzoic acid. However, the results of our most recent experiments (Mathieu-Pelta, I., The University of North Carolina at Chapel... 

Hill, unpublished data) involving dioxaphospholane 14 [prepared from the bis(transoxyphosphoranylation) of diol 1 with DTPP] do not corroborate this slow equilibration between oxyphosphonium ions U and V and dioxaphospholane 14 in benzoic acid in THF solvent. In fact, at -78°C the addition of benzoic acid to dioxaphospholane 14 in THF solvent gives the regioisomeric benzoates directly and the isomeric oxyphosphonium ions U and V are not observed by ip NMR spectroscopy. However, in dichloromethane solvent ions U and V are actually observable and do undergo a temperature dependent, dynamic exchange with dioxaphospholane 14 and benzoic acid (Mathieu-Pelta, I., The University of North Carolina at Chapel Hill, unpublished data). 

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

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. 

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). 

In general, it was found that low temperatures and the presence of a five-membered iminophosphane ring (e.g. an R2R3P=dioxaphospholane ring, or an R2R3P= oxazaphospholane ring, for A ) tend to favour the formation of an aminophosphorane, in accordance with the stability sequence acyclic < monocyclic < spirocyclic. Similarly, one can deduce, from Scheme 28, that if the XZ bond cannot be broken, Z cannot migrate to the N atom and the only possibility will be the equilibrium b. 

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. 

Much work has been done on configuration and conformation, e.g. of 2-methoxy-2-oxo-4,5-diphenyl-l,3,2-dioxaphospholanes with 170 and lsO labelled reagents (81CC245). A large number of 2-dimethylamino-l,3,2-dioxaphospholanes or 3-methoxy-2-methyl-l,3,2,-oxazaphospholanes are mentioned in a recent publication, in which spiro compounds of the general structure (108) were prepared by addition to diethyl azodicarboxylate (equation (69)) (80PS(8)147>. 

Included in this class of olefins is ( )-stilbene (entry 20), which throughout studies of AD has usually been the olefin dihydroxylated with the highest degree of enantioselectivity. Availability of (R,R) or (.5,5)-1,2-diphenyl-1,2-ethanediol (also referred to as stilbenediol or dihydrobenzoin) with high enantiomeric purities has led to reports of a number of applications, including incorporation into chiral dioxaphospholanes [50], chiral boronates [51], chiral ketene acetals [52], chiral crown ethers [53], and conversion into 1,2-diphenylethane-1,2-diamines [54]. Dihydroxylation of the substituted rran.r-stilbene 46 with Os04/NMO and DHQD-CLB gives the i ,/ -diol 47 with 82% ee in 88% yield [55]. 

Published data on the reaction of isatin with di- and trialkyl phosphites are somewhat contradictory. In particular, the authors in [78] showed that isatin with trialkyl phosphite forms 2 1 adduct, which has the structure of 1,3,2-dioxaphospholane containing a pentacoordinated phosphorus atom. More recently analogous results were obtained in the reaction of isatin with amidophosphites [79], At the same time it was shown [80] that 5-methylisatin reacts with trialkyl phosphites with the formation of 3-dialkoxyphosphoryl-3-hydroxy-2-indolinones, identical with the compounds obtained in the reaction of isatin with dialkyl phosphites [78]. In the monograph [4] with reference to the patent [61] the reaction of diethyl phosphite with isatin under the conditions of the Abramov reaction was indicated to lead to 3-dialkoxyphosphoryl-2-indolinone. In all probability this needs verification. 

These published data prompted the authors [82] to undertake a more detailed study of the phosphorylation of isatin by the esters of P(III) acids and hydrophosphoryl compounds. At room temperature in the absence of traces of moisture isatin 49a, 1-acetylisatin 49b, and 5-bromoisatin 49c react with trialkyl phosphites and phosphonites with the formation of the unstable 1,3,2-dioxaphospholanes 87 with a pentacoordinated phosphorus atom, which isomerize in alcohol solution to the stable phosphoryl compounds 88 ... 

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 n.m.r. spectra of (71) and (72) show no changes in the temperature range +30° to +100°, at which point irreversible decomposition of the molecules become apparent. The n.m.r. data of these and of related phosphoranes are summarized in Table 15. The syntheses of (47) and of (64) were described above.111,114 Their variable temperature proton n.m.r. will be discussed in the appropriate sections corresponding to the symmetry properties of the molecule. Note, for further reference, the Permutational Description- " of the energetically preferred isomer (47-(l 5)) of the 1,4,2-dioxaphospholane with the cis-H/H configuration, made from the reaction of trimethyl phosphite with pentafluoro-benzaldehyde. 

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). 

The reaction of HFA with tris(dimethylamino)phosphane leads mainly to the formation of tris(dimethylamino)difluorophosphorane and a smaller amount of hexamethylphosphoric acid triamide, although indirect evidence for the formation of 1,3,2-dioxaphospholanes (Section III,A,4) has been found (277). 

The reaction of monoammonium perfluoropinacolate with 2-amino-1,3,2-dioxaphospholane (52) provides a spirocyclic phosphorane 53 with hydrogen attached to phosphorus, with evolution of ammonia occurring 263). 

The primary intermediates (dipolar 1 1 adducts 54) can add another molecule of HFA to form five-membered rings. l,3,4-A -Dioxaphospholanes 56 are the kinetically favored products from reactions of trivalent phosphorus compounds with HFA, but normally rearrange below ambient temperatures to yield the thermodynamically stable l,3,2-2 -dioxaphospholanes 57. 

The majority of the publications in the field of oxidative addition of HFA to tertiary phosphanes deal with the formation and properties of l,3,2-A -dioxaphospholanes 57 (60,61). These compounds are generally stable when the a carbon atoms do not bear hydrogen atoms. Heterocycles with a hydrogen atoms are stable up to about 70°C at this temperature the isomeric phosphetanes are formed. The syntheses of some sterically hindered phosphoranes require drastic conditions. 

The reaction of HFA with 2,2,3,4,4-pentamethyl-A -phosphetane has been investigated (204). A crystalline 2 1 adduct has been obtained. NMR studies indicate two isomers of the dioxaphospholane 60e relative to the position of the 3-methyl group. Compound 60e slowly decomposes to yield diastereo-meric phosphites 62 with the same isomeric composition. Further action of HFA affords 6O0 (204). 

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). 

A -Dioxaphospholanes show no inversion at the phosphorus atom, which can be seen in the nonequivalence of the CFj groups (273). A -Dioxaphospholanes 73 can be oxidized with halogens to form A -dioxaphospholanes 74 (228). Exchange of the halogens in 73a-c with suitable reaction partners (e.g., LiNHj) yields substituted A -phospholanes [e.g., 73g (265)] (see also Section III,A,2). 

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