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The reaction of phosphorus ylids with singlet oxygen
TetrahedronLettersKo. 51, pp 4531- 4534,1977. PergamonPress. Printedin Great Britain.
THE REACTION OF PHOSPHORUS YLIDS WITH SINGLET OXYGEN
CharZes Department
W. Jefford
of Organic 1211 Geneva
and Giacomino
Chemistry,
Barchietto,
University
of Geneva,
4, Switzerland
(Receivedin UK 21 October1977;acceptedfor Publication 27 October1977)
Phosphorusylids find great utilityin synthesiswhere the best known reactionssuch as the Wittigand variantsthereofare used for the construction of carbon-carbon bonds.' We now reporta new, sinplereactionof ~tho~carbonylalkylidenephosphoranes with singletoxygento give a-ketocarboxylicesters.2The generalprocedureconsistsin placingthe ylid in a solvent, such as chloroform,benzeneor methanol,addingas sensitizermeso-tetraphenylporphin or rose bengaland then irradiating with light frcana 500 W tungstenfilamentlampwhile oxygen is passed throughthe solution3 After a few minutes,the solutionis filteredfrcxntriphenylphospbine oxide and the cc-keto carboxylicester is recoveredin yieldsof 94-100%. We presentthree typicaland one atypicalexanples. The nrxt clean-cutreactionis with ~~~carbony~lid~~i~ylphosp
(1) (Tablel).4 Photo-oxygenation is rapid,1
has a half-lifeof only a few minutesat loo, and.a quantitative yield of rne'chyl phenylglyoxylate 2is obtained. Insethanol,the rate of reaction is twice as slawas that in chloroformand traces (1.4%)of uncharacterized substancesare also forned. The behaviourof the isobutylidenephosphorane(3, is strictlyanalogous(Table1). High yieldsof xuathyl a-keto-isobutyrate (4, are obtained(95-98%)in the halofonnsand benzene,but an insignificantly lm
yieldWW ~CCQR-
paniedby unspecifiedside productsis found in z&hanol. Sinrllarly, the ethylidenephosphorane 5 reactsrapidlygivingessentially methyl pyruvate 2 (94-98%yields)adulteratedby sxnall amDuntsof methyl acrylateepoxide (1) and tiny amountsof impurities(Table1). In all cases,singletoxygenappearsto be the reagentresponsibleinaach
as replacing
oxygenby nitrogenor addingdiazobicyclo[2.2.2]octane (DAECO)(2.5x 10B4 M)' stops and retards
4531
No. 51
4532
Table
1.
Photo-oxygenation of Some Phosphoranes '0
@sP=C(R)COOMe
Reactanta
Half-lifeb
2
>
Conditions'
& R=@
RCOC02Me + Side productse
Yield in %
d
1 4'20"
CDCl,/TPP
100
4'30"
CHCl,/TPP
100
6'15"
C~HG/TPP
100
8'43"
CHsOH/RB
98.6
1.4
-4
1 R=iPr 3'08"
CDCIJ/TPP
95
5
3'30"
CHCls/TPP
94
6
5'46"
C6Hs/TPP
98
2
7'18"
CH30H/RB
89
11
2 R=Me
a 2'24"
CDC13/TPP
94
gf
2'36"
CHC13/TPP
95.4
4.6'
5'05"
C~HG/TPP
98.6
1.4
6'37"
CHaOH/RB
98
2.0f
aConcentration of phosphorane was 0.2 M in 2.5 ml of solvent. b
Half-lives of reactant were estimated from the rate of absorption of oxygen assuming an equimolar reaction with substrate.
'The concentration of sensitizer , meso-tetraphenylphorphin (TPP) or rose bengal (RB) was 10-3 M. The temperature of the solution was 12' for 2, and 10' for -1 and -5. d Absolute yields were obtained by glc (5% OV-225 on Chromosorb WAW at 19Ot carrier gas nitrogen). Internal standards were hexadecane (Fluka) for I, pentadecane (Fluka) for 3_, tridecane (Fluka) for -5. eExcept where specified, these were unidentified. fThe only side product was the epoxide of methyl acrylate (1). '1.2% of 1 was also present.
No.51
4533
Table
2.
Photo-oxygenation of MethoxycarbonylmethylidenetriphenylphosphoraneQ
@3P=CHC02Me
HCC02Me II MeOCOCH
d
-12
+
HCCO,Me II HCCO,Me -15
-14 Conditions
Yield in %
1'24"
CDCl,/TPP
89.9
10.1
1'32"
CHC13/TPP
89.3
10.7
2'47"
CBHG/TPP
98.9
1.1
3'18"
CH30H/RB
67.8
32.2
Half-life
aThe general remarks mentioned in Table 1 are valid
-
12
12 lo* HCOC02Me aMeOCOCH=CHC02Me
13
RCOCOZMe
11
E
2
(d3P+-CHC02Me-
qJ3P=0
14 and 15
No. 51
4534
respectivelythereaction.Auto-oxidation is also negligiblesincethe adjunctionof di-t-butylcresol (2.27x 10s4 M) to the reactionmixturescarcelyaffectsthe courseor the rate of photooxygenation.6 We can safelyassumathat the mchanism is electrophilic attack'by a singletoxygenmolecule on the carbanioniccentre (g) to createthe zwitterionic peroxide-9.' Closurethen cccurs to the phx#&ane
-10 followedby cleavageto the product-11. Once the a-ketoester fom
it
reactsno furtherwith singletoxygen,althoughas we have reportedelsewhere,gthe free acids themselvesundergooxidativedecarbxylation. In principle,furtherreactionbetweenthe ylid and the newly fonmada-ketoester could occur,howeverin the three exsn@es quoted,therewas no evidencefor this under the experimental conditions.'oNevertheless, in the case of the parent ylid, the methoxycarbonyln&hylidenephosphorme (g), photo-oxygenation occursreadily,but w diatelygives insteadamixture of dimethyl
fmarate
(14)audmleate (2) (Table2). Evidently,
the glyoxylicester13 as soon as it forms reactsrapidlywith the ylid to give the observed products. Acknowledgment. We are indebted to the Fends National Suisse de la Recherche Scientifique
(grant No 2.430.0.75)for supportingthis work. REFERENCES AND NOTES (1)
Reviews:H.J. Bestmann,Anger.Chem. Internat.Edit 4, 645 (1965);Bull. Sot. Chim. France 1619 (1971);M. Schlosser,A. Pi&ala, C. Taxchini& Huynh Ba Tuong,Chimia2, 341 (1975).
(2)
For preparativen&hods see: L.R. Waters,Chem. Rev. 41, 586 (1947);F. Weygand,W. Steglich & H. Tamer, LiebigsAnn. 658, 128 (1962);G. Billek,Org. Synth.43, 49 (1963);M.G. Johnson,J.P. Turhbull& H.A. Crisp,Ger. Offen. 2, 528, 786, Chen. Abs. 84, 150492k (1976).
(3) Our procedure(C.W.Jefford& A.F. Boschung,Helv. Chim. Acta 57, 2242 (1974))makes use of a SylvaniaFFx 500 Wlamp, cooledwithair and surroundedbyapyrexglasswater-cooled jacket. Light below 400 nm was stoppedby an interposedSchott-JenaKV 418 filter. (4) Thephosphoraneswerepreparedby standardmethods:cmpomds~and2accordingtoH.J. Bestmann& H. Schultz,LiebigsAnn. 674, 11 (1964);cxxtpounds 5 and 12 following0. Isler, H. Gum, M. Montavon,R. Riiegg, G. Ryser & P. Zeller,Helv. Chim.xcta 40, 1242 (1957). quenchessingletoxygen (C. Cuann& & T. Wilson,J. Am. Chem. Sot. 90, 6527 (1968). (5) DAEiCO (6) K.U. Ingold,Chem. Rev. 61, 563 (1961). (7) R.H. Young,Chem. Conm. 704 (1970);H.H. Wasserman& J.E. Van Werth,J. Am. Chem. Sot. 3, 585 (1974);D.P. Higley & R.W. Murray,ibid.96, 3330 (1974). (8) I. Saito,M. Irmta,Y. Takahashi,S. Matsugo& T. Matsuura,J. Am. Chem. Sot. 99, 2005 (1977);C.W. Jefford& C.G. Rinbault,TetrahedronLetters,2375 (1977). (9) C.W. Jefford,A.F. Boschung,T.A.B.M.Bolsman,R. Moriarty& B. Melnick,J. Am. Chem. Sot. 98, 1017 (1976). was stoppedat 50% absorptionand.then the solutionwas heatedunder (10) If photc-oxygenation reflux,the three expxted productsof Wittig reactionware obtained.
THE REACTION OF PHOSPHORUS YLIDS WITH SINGLET OXYGEN
CharZes Department
W. Jefford
of Organic 1211 Geneva
and Giacomino
Chemistry,
Barchietto,
University
of Geneva,
4, Switzerland
(Receivedin UK 21 October1977;acceptedfor Publication 27 October1977)
Phosphorusylids find great utilityin synthesiswhere the best known reactionssuch as the Wittigand variantsthereofare used for the construction of carbon-carbon bonds.' We now reporta new, sinplereactionof ~tho~carbonylalkylidenephosphoranes with singletoxygento give a-ketocarboxylicesters.2The generalprocedureconsistsin placingthe ylid in a solvent, such as chloroform,benzeneor methanol,addingas sensitizermeso-tetraphenylporphin or rose bengaland then irradiating with light frcana 500 W tungstenfilamentlampwhile oxygen is passed throughthe solution3 After a few minutes,the solutionis filteredfrcxntriphenylphospbine oxide and the cc-keto carboxylicester is recoveredin yieldsof 94-100%. We presentthree typicaland one atypicalexanples. The nrxt clean-cutreactionis with ~~~carbony~lid~~i~ylphosp
(1) (Tablel).4 Photo-oxygenation is rapid,1
has a half-lifeof only a few minutesat loo, and.a quantitative yield of rne'chyl phenylglyoxylate 2is obtained. Insethanol,the rate of reaction is twice as slawas that in chloroformand traces (1.4%)of uncharacterized substancesare also forned. The behaviourof the isobutylidenephosphorane(3, is strictlyanalogous(Table1). High yieldsof xuathyl a-keto-isobutyrate (4, are obtained(95-98%)in the halofonnsand benzene,but an insignificantly lm
yieldWW ~CCQR-
paniedby unspecifiedside productsis found in z&hanol. Sinrllarly, the ethylidenephosphorane 5 reactsrapidlygivingessentially methyl pyruvate 2 (94-98%yields)adulteratedby sxnall amDuntsof methyl acrylateepoxide (1) and tiny amountsof impurities(Table1). In all cases,singletoxygenappearsto be the reagentresponsibleinaach
as replacing
oxygenby nitrogenor addingdiazobicyclo[2.2.2]octane (DAECO)(2.5x 10B4 M)' stops and retards
4531
No. 51
4532
Table
1.
Photo-oxygenation of Some Phosphoranes '0
@sP=C(R)COOMe
Reactanta
Half-lifeb
2
>
Conditions'
& R=@
RCOC02Me + Side productse
Yield in %
d
1 4'20"
CDCl,/TPP
100
4'30"
CHCl,/TPP
100
6'15"
C~HG/TPP
100
8'43"
CHsOH/RB
98.6
1.4
-4
1 R=iPr 3'08"
CDCIJ/TPP
95
5
3'30"
CHCls/TPP
94
6
5'46"
C6Hs/TPP
98
2
7'18"
CH30H/RB
89
11
2 R=Me
a 2'24"
CDC13/TPP
94
gf
2'36"
CHC13/TPP
95.4
4.6'
5'05"
C~HG/TPP
98.6
1.4
6'37"
CHaOH/RB
98
2.0f
aConcentration of phosphorane was 0.2 M in 2.5 ml of solvent. b
Half-lives of reactant were estimated from the rate of absorption of oxygen assuming an equimolar reaction with substrate.
'The concentration of sensitizer , meso-tetraphenylphorphin (TPP) or rose bengal (RB) was 10-3 M. The temperature of the solution was 12' for 2, and 10' for -1 and -5. d Absolute yields were obtained by glc (5% OV-225 on Chromosorb WAW at 19Ot carrier gas nitrogen). Internal standards were hexadecane (Fluka) for I, pentadecane (Fluka) for 3_, tridecane (Fluka) for -5. eExcept where specified, these were unidentified. fThe only side product was the epoxide of methyl acrylate (1). '1.2% of 1 was also present.
No.51
4533
Table
2.
Photo-oxygenation of MethoxycarbonylmethylidenetriphenylphosphoraneQ
@3P=CHC02Me
HCC02Me II MeOCOCH
d
-12
+
HCCO,Me II HCCO,Me -15
-14 Conditions
Yield in %
1'24"
CDCl,/TPP
89.9
10.1
1'32"
CHC13/TPP
89.3
10.7
2'47"
CBHG/TPP
98.9
1.1
3'18"
CH30H/RB
67.8
32.2
Half-life
aThe general remarks mentioned in Table 1 are valid
-
12
12 lo* HCOC02Me aMeOCOCH=CHC02Me
13
RCOCOZMe
11
E
2
(d3P+-CHC02Me-
qJ3P=0
14 and 15
No. 51
4534
respectivelythereaction.Auto-oxidation is also negligiblesincethe adjunctionof di-t-butylcresol (2.27x 10s4 M) to the reactionmixturescarcelyaffectsthe courseor the rate of photooxygenation.6 We can safelyassumathat the mchanism is electrophilic attack'by a singletoxygenmolecule on the carbanioniccentre (g) to createthe zwitterionic peroxide-9.' Closurethen cccurs to the phx#&ane
-10 followedby cleavageto the product-11. Once the a-ketoester fom
it
reactsno furtherwith singletoxygen,althoughas we have reportedelsewhere,gthe free acids themselvesundergooxidativedecarbxylation. In principle,furtherreactionbetweenthe ylid and the newly fonmada-ketoester could occur,howeverin the three exsn@es quoted,therewas no evidencefor this under the experimental conditions.'oNevertheless, in the case of the parent ylid, the methoxycarbonyln&hylidenephosphorme (g), photo-oxygenation occursreadily,but w diatelygives insteadamixture of dimethyl
fmarate
(14)audmleate (2) (Table2). Evidently,
the glyoxylicester13 as soon as it forms reactsrapidlywith the ylid to give the observed products. Acknowledgment. We are indebted to the Fends National Suisse de la Recherche Scientifique
(grant No 2.430.0.75)for supportingthis work. REFERENCES AND NOTES (1)
Reviews:H.J. Bestmann,Anger.Chem. Internat.Edit 4, 645 (1965);Bull. Sot. Chim. France 1619 (1971);M. Schlosser,A. Pi&ala, C. Taxchini& Huynh Ba Tuong,Chimia2, 341 (1975).
(2)
For preparativen&hods see: L.R. Waters,Chem. Rev. 41, 586 (1947);F. Weygand,W. Steglich & H. Tamer, LiebigsAnn. 658, 128 (1962);G. Billek,Org. Synth.43, 49 (1963);M.G. Johnson,J.P. Turhbull& H.A. Crisp,Ger. Offen. 2, 528, 786, Chen. Abs. 84, 150492k (1976).
(3) Our procedure(C.W.Jefford& A.F. Boschung,Helv. Chim. Acta 57, 2242 (1974))makes use of a SylvaniaFFx 500 Wlamp, cooledwithair and surroundedbyapyrexglasswater-cooled jacket. Light below 400 nm was stoppedby an interposedSchott-JenaKV 418 filter. (4) Thephosphoraneswerepreparedby standardmethods:cmpomds~and2accordingtoH.J. Bestmann& H. Schultz,LiebigsAnn. 674, 11 (1964);cxxtpounds 5 and 12 following0. Isler, H. Gum, M. Montavon,R. Riiegg, G. Ryser & P. Zeller,Helv. Chim.xcta 40, 1242 (1957). quenchessingletoxygen (C. Cuann& & T. Wilson,J. Am. Chem. Sot. 90, 6527 (1968). (5) DAEiCO (6) K.U. Ingold,Chem. Rev. 61, 563 (1961). (7) R.H. Young,Chem. Conm. 704 (1970);H.H. Wasserman& J.E. Van Werth,J. Am. Chem. Sot. 3, 585 (1974);D.P. Higley & R.W. Murray,ibid.96, 3330 (1974). (8) I. Saito,M. Irmta,Y. Takahashi,S. Matsugo& T. Matsuura,J. Am. Chem. Sot. 99, 2005 (1977);C.W. Jefford& C.G. Rinbault,TetrahedronLetters,2375 (1977). (9) C.W. Jefford,A.F. Boschung,T.A.B.M.Bolsman,R. Moriarty& B. Melnick,J. Am. Chem. Sot. 98, 1017 (1976). was stoppedat 50% absorptionand.then the solutionwas heatedunder (10) If photc-oxygenation reflux,the three expxted productsof Wittig reactionware obtained.