1.3.2- Dioxaphospholanes reactions

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 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. 

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). 

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. 

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). 

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. 

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 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). 

Most reactions of halophosphorus compounds do not involve direct attack of HFA. However, the reduced species dilithio perfluoropinacolate, accessible from HFA and lithium metal, is used as a precursor for and A -dioxaphospholanes [Eq. (60)] (Table VI). 

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). 

Five-membered heterocycles with two vicinal chalcogen atoms in the ring system can be used as stable precursors for sulfur as well as for selenium-containing hetero-1,3-dienes in cycloaddition reactions. Consequently, 3//-1,2,4-thiaselenazoles have been used for the in situ formation of 4,4-bis(trifluoromethyl)-l-thia-3-azabuta-1,3-dienes, which exist at room temperature only as 4,4-bis(trifluoromethyl)-2//-l,3-thiazetes. This strategy was applied to the synthesis of the first stable selenophosphorane from bis(trifluoromethyl)-substituted 3//-diselenazol and 2-methoxy-1,3,2-dioxaphospholan [78AG(E)774] (Scheme 83). 

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. 

Studies of the oxaphosphorylation properties of diethoxytriphenyl-phosphorane (23) have been extended to include methyl a-D-glucopyranoside (24) which affords two isomeric dioxaphospholanes (25 and 26). Thermolysis of these phosphoranes in DMF at 40°C in the presence of LiBr, afibrds the allop3n anoside (27) in a regiospecific reaction whereas thermolysis in the absence of LiBr... 

Mechanistic Studies.- A number of substitution reactions of alcohols, phenols, or amines with 1,3,2-dioxaphospholans, e.g. (73), oxazaphospholans, and diazaphos-pholans have been followed by n.m.r. and shown to involve H-phosphoranes, e.g. (74). The reactions are run in toluene or without solvent, and without addition of an acidic catalyst in some systems, with 4-chlorophenol as the nucleophile, an equilibrium was established between an H-phosphorane (75) and a phosphonium salt (76), but the authors still favour (75) as the true intermediate. The equilibrium constants for a series of exchange reactions between (thio)phosphites (77) and (thio)phosphoro-dichloridites (78), and some analogous bromidites and a fluoridite, have been measured.The constants increase with increased electron donor ability of R. 

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