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Stable 1,4,2-dioxaphosmolanium salts
PergamonPress. Printed in &eat Britain.
TetrahedronLetters No. 52, pp 5191 - 5194, 1973.
S!MBL,E 1,4.2-DIOXAITiO%PHOLANIDM SALTS
Dy N. J. DetAth, J. A. Milleti, and M. J. Nunn (Departmentof Chemistry,Universityof Dundee, Dundee DDI @IN) (Receivedin IJK22 October1973; acceptedfor publication15 November1973)
ALNOXYPHOSPHONIUM salts have long been postulatedas reactiveintermediatesin organophosphorus 1 reactions, but only relativelyrecentlyhave examplesof their isolationend studiesof their reactivityconfirmed*this view. We wish to report that the reactionof benzaldehydewith monochlorophosphines leads to the 1,4,24ioxaphospholeniuchlorides(1). These salts are unique, in that they have an alkoxy ligend incorporatedinto a strainedheterocyclicring, and their stabilityis of considerableinterest. Moreover,their propertiesallow a rationalisation of the thermalreactionbetween aldehydesend chlorophosphines. In a typicalpreparation,benzaldehyde(2 moles) and a monochlorophosphine (2), (1 mole) are reacted,eitherneat or in solvent,to give a high yield of a crystellineproduct,to which we assign structure(1) on the basis of chemicaland physicalevidence. The stoichiometry of the reactionsuggeststhat (1) is a 2:l adduct, and this was confirmedby the hydrolysisof (la) to en equimolermixture of benzaldehydeand n-hydroxybenzyldiphenylphosphine oxide (3). Provided that they are kept in a moisture-freeatmosphere,these salts remain stable end crystallineduring storage. The main evidencefor structure(1) comes from n.m.r. studiesin deutemchloroform. Of particularrelevanceare the 31P n.m.r. shifts*,which are always downfieldfrom 8% phosphoric acid [at -28.5 p.p.m. for (la) and at -56.5
p.p.m. for (lb)],end thereforeindicate3a
phosphoniumstructure. This evidencerules out' a phosphorsnestructuresuch as (4),
which
4
might have been expectedon grounds of precedent. Moreover,the salts (1) show no tendency to convert to phosphoranesin favourablecircumstances, even when a spirophosphorane would result, as with (lb). The 'H n.m.r. spectraof (1) show two non-aromaticabsorptions,each
5191
No. 52
5192
integratingfor one hydrogen,which we assign to the hydrogen6at C-5 and C-3 respectively. In the adduot (la) these bards occur at t3.4 (J
(J ClHz), and t 4.3 (J
end ? 3.9 (J 8.5 Hz), while in (lb) These absorptionscould, however,be
compatiblewith en equimolarmixture of the -cis- end
isomersof the related l,j,2-
dioxaphospholsnium salts (5), the phosphorsnesneloguesof which have severalprecedents4 in the literature. 'phiapossibilitycan be discountedon the basis of the 13C n .m .r . spectra* of (1). For exsmple,in the adduct (lb), the five-memberedring carbonsabsorb at 93.7 p.p.m. (c-5S ‘J31p_ljc me
10.4 Hz) and 76.4 (C-3, 2J 31,13,
36.9 Hz).
The "P-13C couplingconstants
typical of couplingover one end two bonds respectively,end are in general agreement
with publishedwolk5 on couplingin strainedphosphorusheterocyclicrings. The oorresponding couplingconstantsof (la) (12Hz and 87.4 Hz) show this trend even more clearly. Heating of the salts (1) convertsthem into a-ohlorodkylphosphine oxides (6) and benzaldehyde,via the a-ohloroethers(7), as outlinedin the scheme. The formationof the intermediate ethers (7) is the result of an [email protected] The subsequent tranarmation into the oxides (6) appears to resemblethe known fregmentationof P-chloroether ( 9)7. 1,Fdioxolenes (8)6, or of bis-a-chlorobenzyl Cd
This reactionsequenceprovidesa rationalisationof the hithertounexpldned8general reactionof aldehydeswith monoohlorophosphines.The pathway to the phosphorylcompounds (6) is very differentfrom that observedwith phosphorustrihslides,which react aa eleotro7 philes towards aldehydes. A related dependenceof reactionproductupon reacted structure
No. 52
5194
REFERENCES
1.
Significantexamplesare the Perkow and Arbusov reactions. See A. J. Kirby end S. G. Warren, 'The Organic Chemistryof Phosphorus',Elsevier,Amsterdam,1967, pp. 37-44.
2.
Teichmann,M. Jatkowski,and G. Hilgetag,Angew.Chem.Internat.Edn., 1967, 6, 372; V. Nesterov and R. I. Mutalapova,TetrahedronLetters, 1968, 51; J. H. Finley, 2. Denney, and D. B. Denney,J.Amer.Chem.Soc., 1969, yl, 5826; A. I. Razumov, G. Liorber,T. V. Zhykova and I. Ya Bsmbushek,Zhur. obshcheiKhim., 1970, 40, 2009 ; H. R. Hudson,R. G. Rees and J. E. Weekes, Chem.Comm.,1971, 1297; G. K. M&wan and J. G. Verkade,Chem.Comm.,1971, 668
3.
M. M. Crutchfield,C. H. Dungan,J. M. Letcher,V. Mark, and J. R. Van Wazer, "Topics in PhosphorusChemistry",Interscience,New York, 1967, Vol. 5, p.46
4.
For reviews of phosphoraneformationfrom ddehydes see F. Ramirez,Acc.Chem.Res., 1968, 1, 168; Pure ADDI.Chem.,1964, 2, 337
5.
G. A. Grqf and S. E. Cremer,J.Org.Chem.,1972, 11, 3458; 1972, 11, 3470
6.
M. S. Newman and C. H. Chen, J.Ora.Chem.,1973, 36, 1173
7.
J. A. Miller and M. J. Nunn, TetrahedronLetters,1972, 3953
‘3.
Chemistry,Penguin,London, 1972, p.67; K. Sasse in B. J. Walker, Organophosphorus "OrganischePhosphorverbonbing, Methoden der OrgsnischenChemie (Houben-Weyl)" G. Thieme Verlsg, Stuttgart,1963, Vo1.12, part 1, pp. 155-156,362-365,403-404.
9.
S. Kh. Nurtdinov,V. S. Tsivunin,R. S. Khairullin,V. G. Kashtanova,and G. Kh. Kemai, zhur. obshoheiKbim, 1970, j.0,36.
IO.
H. L. D. B.
S. Kh. Nurtdinov,R. S. Khairullin,T. V. Zykova,V. S. Tsivunin,end g. Kh. Kamai, Zhur. obshcheiKhim., 1971, fi, 2158
TetrahedronLetters No. 52, pp 5191 - 5194, 1973.
S!MBL,E 1,4.2-DIOXAITiO%PHOLANIDM SALTS
Dy N. J. DetAth, J. A. Milleti, and M. J. Nunn (Departmentof Chemistry,Universityof Dundee, Dundee DDI @IN) (Receivedin IJK22 October1973; acceptedfor publication15 November1973)
ALNOXYPHOSPHONIUM salts have long been postulatedas reactiveintermediatesin organophosphorus 1 reactions, but only relativelyrecentlyhave examplesof their isolationend studiesof their reactivityconfirmed*this view. We wish to report that the reactionof benzaldehydewith monochlorophosphines leads to the 1,4,24ioxaphospholeniuchlorides(1). These salts are unique, in that they have an alkoxy ligend incorporatedinto a strainedheterocyclicring, and their stabilityis of considerableinterest. Moreover,their propertiesallow a rationalisation of the thermalreactionbetween aldehydesend chlorophosphines. In a typicalpreparation,benzaldehyde(2 moles) and a monochlorophosphine (2), (1 mole) are reacted,eitherneat or in solvent,to give a high yield of a crystellineproduct,to which we assign structure(1) on the basis of chemicaland physicalevidence. The stoichiometry of the reactionsuggeststhat (1) is a 2:l adduct, and this was confirmedby the hydrolysisof (la) to en equimolermixture of benzaldehydeand n-hydroxybenzyldiphenylphosphine oxide (3). Provided that they are kept in a moisture-freeatmosphere,these salts remain stable end crystallineduring storage. The main evidencefor structure(1) comes from n.m.r. studiesin deutemchloroform. Of particularrelevanceare the 31P n.m.r. shifts*,which are always downfieldfrom 8% phosphoric acid [at -28.5 p.p.m. for (la) and at -56.5
p.p.m. for (lb)],end thereforeindicate3a
phosphoniumstructure. This evidencerules out' a phosphorsnestructuresuch as (4),
which
4
might have been expectedon grounds of precedent. Moreover,the salts (1) show no tendency to convert to phosphoranesin favourablecircumstances, even when a spirophosphorane would result, as with (lb). The 'H n.m.r. spectraof (1) show two non-aromaticabsorptions,each
5191
No. 52
5192
integratingfor one hydrogen,which we assign to the hydrogen6at C-5 and C-3 respectively. In the adduot (la) these bards occur at t3.4 (J
(J ClHz), and t 4.3 (J
end ? 3.9 (J 8.5 Hz), while in (lb) These absorptionscould, however,be
compatiblewith en equimolarmixture of the -cis- end
isomersof the related l,j,2-
dioxaphospholsnium salts (5), the phosphorsnesneloguesof which have severalprecedents4 in the literature. 'phiapossibilitycan be discountedon the basis of the 13C n .m .r . spectra* of (1). For exsmple,in the adduct (lb), the five-memberedring carbonsabsorb at 93.7 p.p.m. (c-5S ‘J31p_ljc me
10.4 Hz) and 76.4 (C-3, 2J 31,13,
36.9 Hz).
The "P-13C couplingconstants
typical of couplingover one end two bonds respectively,end are in general agreement
with publishedwolk5 on couplingin strainedphosphorusheterocyclicrings. The oorresponding couplingconstantsof (la) (12Hz and 87.4 Hz) show this trend even more clearly. Heating of the salts (1) convertsthem into a-ohlorodkylphosphine oxides (6) and benzaldehyde,via the a-ohloroethers(7), as outlinedin the scheme. The formationof the intermediate ethers (7) is the result of an [email protected] The subsequent tranarmation into the oxides (6) appears to resemblethe known fregmentationof P-chloroether ( 9)7. 1,Fdioxolenes (8)6, or of bis-a-chlorobenzyl Cd
This reactionsequenceprovidesa rationalisationof the hithertounexpldned8general reactionof aldehydeswith monoohlorophosphines.The pathway to the phosphorylcompounds (6) is very differentfrom that observedwith phosphorustrihslides,which react aa eleotro7 philes towards aldehydes. A related dependenceof reactionproductupon reacted structure
No. 52
5194
REFERENCES
1.
Significantexamplesare the Perkow and Arbusov reactions. See A. J. Kirby end S. G. Warren, 'The Organic Chemistryof Phosphorus',Elsevier,Amsterdam,1967, pp. 37-44.
2.
Teichmann,M. Jatkowski,and G. Hilgetag,Angew.Chem.Internat.Edn., 1967, 6, 372; V. Nesterov and R. I. Mutalapova,TetrahedronLetters, 1968, 51; J. H. Finley, 2. Denney, and D. B. Denney,J.Amer.Chem.Soc., 1969, yl, 5826; A. I. Razumov, G. Liorber,T. V. Zhykova and I. Ya Bsmbushek,Zhur. obshcheiKhim., 1970, 40, 2009 ; H. R. Hudson,R. G. Rees and J. E. Weekes, Chem.Comm.,1971, 1297; G. K. M&wan and J. G. Verkade,Chem.Comm.,1971, 668
3.
M. M. Crutchfield,C. H. Dungan,J. M. Letcher,V. Mark, and J. R. Van Wazer, "Topics in PhosphorusChemistry",Interscience,New York, 1967, Vol. 5, p.46
4.
For reviews of phosphoraneformationfrom ddehydes see F. Ramirez,Acc.Chem.Res., 1968, 1, 168; Pure ADDI.Chem.,1964, 2, 337
5.
G. A. Grqf and S. E. Cremer,J.Org.Chem.,1972, 11, 3458; 1972, 11, 3470
6.
M. S. Newman and C. H. Chen, J.Ora.Chem.,1973, 36, 1173
7.
J. A. Miller and M. J. Nunn, TetrahedronLetters,1972, 3953
‘3.
Chemistry,Penguin,London, 1972, p.67; K. Sasse in B. J. Walker, Organophosphorus "OrganischePhosphorverbonbing, Methoden der OrgsnischenChemie (Houben-Weyl)" G. Thieme Verlsg, Stuttgart,1963, Vo1.12, part 1, pp. 155-156,362-365,403-404.
9.
S. Kh. Nurtdinov,V. S. Tsivunin,R. S. Khairullin,V. G. Kashtanova,and G. Kh. Kemai, zhur. obshoheiKbim, 1970, j.0,36.
IO.
H. L. D. B.
S. Kh. Nurtdinov,R. S. Khairullin,T. V. Zykova,V. S. Tsivunin,end g. Kh. Kamai, Zhur. obshcheiKhim., 1971, fi, 2158