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Stereochemistry of a thermal rearrangement in the (CH)12 series. Establishment of the suprafacial nature of a [1,5] carbon migration
TetrahedronLettersNo.47, pp. 4159-4162,1969.
PergamonPress. Printed in Great Britain.
STERECCREMISlRYOFA 'MERMALREMRAEGEMENT IB TRE (Cl&s SERIES. ESTABLISHMENT OF DIE SUPRAFACIALNATURE OF A [1,51 CARBON MIGRATION Leo A. Paquetteend J&n C. Stowell* Departmentof Chemistry,The Qio State University,Columb_m,chio 45210 (Receivedin USA 7 August 1969; receivedin UICfor publication9 September1969) Heating of cis,syn,cis-tiicyclo~8.2.0.02~s (9 at 120' for ]dodeca-5,5,7,ll-tetraene 24 hr has been reported to result in the formationof equal smouuts of benzene end hydrocarbcm 2.i
form&y
lhe stereochemistry of cwas not determined. l?xethermlrearraugemsnt of&to
involvesthe [lj5]
migrationof C-l frau C-2 to
C-6,
a
sigmatropic
change
2
which,
if concerted,would be restrictedfor reasons of orbital synmetryconservationto the use of 2
a suprafacialorbital at the migrationlxrmi.nus. However, while the preferredconformation of I cs~ be consideredto resemble closelythe tub structurei, this arrangementdoes not lend itself geometricallyto such a concertedbond migration. Also, althoughalternative tub conformation&wouldnot
suffer fkpran such a stereochemicaldisadvantsge,the non-boded
interactionspresent in & suggest,a priori, that this structuralarrangementmight be ener-
\9I
k_
2
getically inaccessible. Consequently,the bond reorgsnizatiouin 1 could be occurringin non-concertedfashionv&
diradicalLwhich would cyclizeto give either 6 or &
*The Ohio State UniversityPostdoctoralFellow, 1969.
4159
The ease
4160
with
No.47
which severalbonds in kare rupturedhas alreadybeen note&,"' in addition,the con-
&)-(&_& ._I
6
2..
diticmerequired for the &-gresxrsngement than that tided
I
can be construedto be smtmore
by a concertedintrsmolecuJ.ar Cl,51shift,aJ_though very few excmples 4
of
sucha
vigorous
carlxmmigraticm
are
knmn.
Cm
the
other
hand,
Schrijderls observationthat2_is
a single iscrmer is difficultto rationalizeti the basis of intermediateb
since energy con-
siderationsdisclosethat formationof 6 and lfrcan this diradicslshouldbe equally facile. In the preeentpaper,we wishtoreport thatthermolyais of &leads
uniquely to hsndto
describebriefly the phutoisomerizatian & this (C?I& polyolefin. When powdered ceric anmvmiumnitrate is slowly added to a solutionof cyclobutadieneircm tricarbm1
(8_)and a cis,izansmixture of ~,8-dichlorobicyclo[4.2.O]octadiene (s5 in ace-
tone at rocentemperature,the Diels-Alderadducts &O_and &&Fe 52$. Colunmchrcmrrtcgraphy
formed in a combinedyield of
of the product cm neutrsl aluminaresults in reedy separationof
cnck 2.5-3.0 (m, 6H, methine motca~), 4.14.25 (m, 2H, mp 131-132' CS,
c+s-dichloride3'
>CX_CI),5.87 (8, 2~, cyclotiteneprutons),end 6.05-6.25 (broadenedtriplet, ZH, vinyl protons)] from the txiscrmer
l&6 mp 94-95' [SC2
2.5-3.1 (m, 6H, methine protrms),4.1-
4.70 (m, 2H,>aJZl), 5.87 (8, 2H, cyclobuteneprotons),and 5.96.4 (m, 2H, vinyl potons)]. 'IheAereochemicelLconfQuraticms of send
sare
in accardsncewith establishedprecedence,7
symn&ry-c~trolJ.edsecondaryabital interacticmsoperativein the transitianstates for 8
cycloedditionto a
and spectroscopicevidence. Far example, it follows that because the
dichlorocycloh.&ane moiety in 2 stericallyinhibitsthe amoach top surface, thishalcgenatedring necessarily
becomes
etothe
of cyclokddiene fran the developingethylelle Widge.
Additionally,the exo orientaticmof the cyclobutenering was confirrszd by dechlorinationof god mp
zwith
sodiumwene
in 'IHFsolution (6% yield). the resulting
hydrocarbon
(I&,
25.526.5',e dlspleysa highly symmetricalnmr spectrum (CDt&) casisting inter alia of a --
single sharp si.n&iet at b 5.84 due to the four equivalentcycloktene protons. The exo,exo stereochemistry of &2_is further substantiatedbyccanparisanwith the spectrwnof lJ(see below).
4161
No.47
Cl
d
+
Cl Ce+4 l
\
Fe(CO),
acetone
4_
/d!27 / 4
pyrolysis
of Eat
A
6
hv A ether
500' and 15 mu readily affords the iscmsric (CH),shydrocarbon&
e which proved to be identicalin all respectswith the thermal rearrangementproduct of &. Ultravioletirradiation(Hanovia45Ow light source) of a l$ solutionof e in ether far ap10,ll
proximately3 hr at room temperaturegives l2_and 13 in equal smounts. of lJdisplsys, inter alia, two cyclobutenesingletsat B 6.27
Ihe nmr spectrum
end 5.62. This photoreerrange-
ment affords additionalconfirmati~ of structure6 since &2_wouldnot be expectedfromthe irradiationof 1. Psrtiel decompositionof such an equimolarmixture of gend undergoesthenml rearrangementslightlymore rapidly than lJ
lJat 500' revealedthat 12 Ihermalrearrsngementof pure
lJgave only 6_,indicatingthat the endo oyclobutenering in &is
cleavedexclusivelyunder
these conditions. 'Iheidentificaticnof pyrolysisproduct gas stereoisomergrequires that the thermal rearrangementof &be necessarilysuprafacial. It w
well be that the transitionstate for
this sigmatropicchange is not severelyconstrainedas in 3 sion interactionspresent in &&
rather, the unfavorablerepul-
be balancedagainstthe internalangle strain that develops
as the cyclooctatriene ring attains planarityas in &.
In this conformation,the pentadienyl
systemrequired for the 1,5-suprafacialbonding is capable of maintainingthe approximateco-
4162
No.47
? l -________ ___,
2
planaritynecessary
rules.
for application
chemicaloutcome of the reexrengement
of 1 denotes
In
4
any case,
the
stereo-
once again the considerableimportanceof
orbitsl symetry control in a polyene where a mltitude of alternativebond rearrsngemznts are possible. A-
Wewishtothank
BadischeAnilinundSodaFabrikfar
agenerous gift of
the cyclooctatetraene reqdred in the weparation of 8_md s References 1.
G. Schr&lerand W. Martin, Annew. Chem., & h 130 (1966).
117 (1966);Anuew. Chem. Intern.Ed. En&,
2. R. B. woodward end R. Hoffmnn, J. Am. Chem. Sot., 5 3.
25ll (1965).
G. S&r&r, w. Martin and H. Rtittele, Angew. Chem., 8~ 33 (1969);Angew. Chem. Idem. Ea. ~ngl., s 6g (19693.
4. J. A. Berson,Accts. of.Chem. Res., S 5. R. Huisgen, G. Boche, W. He&t1 w 3 585 (d.
152 (1968).
and H. Huber, Ang&
$,
595 (1966);Angew. Chem.
6. Satisfactoryelementelanalyses ('-0.3) were obtainedfor all new chemistry,see G. Schr&r, 7. For a review of cyclooctatetraene Verlsg Chemie,Weinheim/Bergstr., Germany, 1965.
mupounds.
"Cyclooctatetraen,'l
8. R. Hoffmann and R. B. woodward,J. Am. Chem. sot., 8~ 4388 (1%5). 9. Spectraldata for 6_may be f-a
in reference1.
10.
G. s&+&r snd'w. Martin have also observedthis photorearrangement [unpublishedresults mentioned in G. S&r&r and J. F. M. Oth, Angew. Chem Intern.Ed. I&@., 6_, 414 (1967)];however, stereochemicalassignmentswere not made by these authors since the stereochemistryof 6_was mlmown to them.
ll.
In contrast,irradiationof 6_unaer triplet conditions(acetonesolution)&fords & /I QIP L
'
PergamonPress. Printed in Great Britain.
STERECCREMISlRYOFA 'MERMALREMRAEGEMENT IB TRE (Cl&s SERIES. ESTABLISHMENT OF DIE SUPRAFACIALNATURE OF A [1,51 CARBON MIGRATION Leo A. Paquetteend J&n C. Stowell* Departmentof Chemistry,The Qio State University,Columb_m,chio 45210 (Receivedin USA 7 August 1969; receivedin UICfor publication9 September1969) Heating of cis,syn,cis-tiicyclo~8.2.0.02~s (9 at 120' for ]dodeca-5,5,7,ll-tetraene 24 hr has been reported to result in the formationof equal smouuts of benzene end hydrocarbcm 2.i
form&y
lhe stereochemistry of cwas not determined. l?xethermlrearraugemsnt of&to
involvesthe [lj5]
migrationof C-l frau C-2 to
C-6,
a
sigmatropic
change
2
which,
if concerted,would be restrictedfor reasons of orbital synmetryconservationto the use of 2
a suprafacialorbital at the migrationlxrmi.nus. However, while the preferredconformation of I cs~ be consideredto resemble closelythe tub structurei, this arrangementdoes not lend itself geometricallyto such a concertedbond migration. Also, althoughalternative tub conformation&wouldnot
suffer fkpran such a stereochemicaldisadvantsge,the non-boded
interactionspresent in & suggest,a priori, that this structuralarrangementmight be ener-
\9I
k_
2
getically inaccessible. Consequently,the bond reorgsnizatiouin 1 could be occurringin non-concertedfashionv&
diradicalLwhich would cyclizeto give either 6 or &
*The Ohio State UniversityPostdoctoralFellow, 1969.
4159
The ease
4160
with
No.47
which severalbonds in kare rupturedhas alreadybeen note&,"' in addition,the con-
&)-(&_& ._I
6
2..
diticmerequired for the &-gresxrsngement than that tided
I
can be construedto be smtmore
by a concertedintrsmolecuJ.ar Cl,51shift,aJ_though very few excmples 4
of
sucha
vigorous
carlxmmigraticm
are
knmn.
Cm
the
other
hand,
Schrijderls observationthat2_is
a single iscrmer is difficultto rationalizeti the basis of intermediateb
since energy con-
siderationsdisclosethat formationof 6 and lfrcan this diradicslshouldbe equally facile. In the preeentpaper,we wishtoreport thatthermolyais of &leads
uniquely to hsndto
describebriefly the phutoisomerizatian & this (C?I& polyolefin. When powdered ceric anmvmiumnitrate is slowly added to a solutionof cyclobutadieneircm tricarbm1
(8_)and a cis,izansmixture of ~,8-dichlorobicyclo[4.2.O]octadiene (s5 in ace-
tone at rocentemperature,the Diels-Alderadducts &O_and &&Fe 52$. Colunmchrcmrrtcgraphy
formed in a combinedyield of
of the product cm neutrsl aluminaresults in reedy separationof
cnck 2.5-3.0 (m, 6H, methine motca~), 4.14.25 (m, 2H, mp 131-132' CS,
c+s-dichloride3'
>CX_CI),5.87 (8, 2~, cyclotiteneprutons),end 6.05-6.25 (broadenedtriplet, ZH, vinyl protons)] from the txiscrmer
l&6 mp 94-95' [SC2
2.5-3.1 (m, 6H, methine protrms),4.1-
4.70 (m, 2H,>aJZl), 5.87 (8, 2H, cyclobuteneprotons),and 5.96.4 (m, 2H, vinyl potons)]. 'IheAereochemicelLconfQuraticms of send
sare
in accardsncewith establishedprecedence,7
symn&ry-c~trolJ.edsecondaryabital interacticmsoperativein the transitianstates for 8
cycloedditionto a
and spectroscopicevidence. Far example, it follows that because the
dichlorocycloh.&ane moiety in 2 stericallyinhibitsthe amoach top surface, thishalcgenatedring necessarily
becomes
etothe
of cyclokddiene fran the developingethylelle Widge.
Additionally,the exo orientaticmof the cyclobutenering was confirrszd by dechlorinationof god mp
zwith
sodiumwene
in 'IHFsolution (6% yield). the resulting
hydrocarbon
(I&,
25.526.5',e dlspleysa highly symmetricalnmr spectrum (CDt&) casisting inter alia of a --
single sharp si.n&iet at b 5.84 due to the four equivalentcycloktene protons. The exo,exo stereochemistry of &2_is further substantiatedbyccanparisanwith the spectrwnof lJ(see below).
4161
No.47
Cl
d
+
Cl Ce+4 l
\
Fe(CO),
acetone
4_
/d!27 / 4
pyrolysis
of Eat
A
6
hv A ether
500' and 15 mu readily affords the iscmsric (CH),shydrocarbon&
e which proved to be identicalin all respectswith the thermal rearrangementproduct of &. Ultravioletirradiation(Hanovia45Ow light source) of a l$ solutionof e in ether far ap10,ll
proximately3 hr at room temperaturegives l2_and 13 in equal smounts. of lJdisplsys, inter alia, two cyclobutenesingletsat B 6.27
Ihe nmr spectrum
end 5.62. This photoreerrange-
ment affords additionalconfirmati~ of structure6 since &2_wouldnot be expectedfromthe irradiationof 1. Psrtiel decompositionof such an equimolarmixture of gend undergoesthenml rearrangementslightlymore rapidly than lJ
lJat 500' revealedthat 12 Ihermalrearrsngementof pure
lJgave only 6_,indicatingthat the endo oyclobutenering in &is
cleavedexclusivelyunder
these conditions. 'Iheidentificaticnof pyrolysisproduct gas stereoisomergrequires that the thermal rearrangementof &be necessarilysuprafacial. It w
well be that the transitionstate for
this sigmatropicchange is not severelyconstrainedas in 3 sion interactionspresent in &&
rather, the unfavorablerepul-
be balancedagainstthe internalangle strain that develops
as the cyclooctatriene ring attains planarityas in &.
In this conformation,the pentadienyl
systemrequired for the 1,5-suprafacialbonding is capable of maintainingthe approximateco-
4162
No.47
? l -________ ___,
2
planaritynecessary
rules.
for application
chemicaloutcome of the reexrengement
of 1 denotes
In
4
any case,
the
stereo-
once again the considerableimportanceof
orbitsl symetry control in a polyene where a mltitude of alternativebond rearrsngemznts are possible. A-
Wewishtothank
BadischeAnilinundSodaFabrikfar
agenerous gift of
the cyclooctatetraene reqdred in the weparation of 8_md s References 1.
G. Schr&lerand W. Martin, Annew. Chem., & h 130 (1966).
117 (1966);Anuew. Chem. Intern.Ed. En&,
2. R. B. woodward end R. Hoffmnn, J. Am. Chem. Sot., 5 3.
25ll (1965).
G. S&r&r, w. Martin and H. Rtittele, Angew. Chem., 8~ 33 (1969);Angew. Chem. Idem. Ea. ~ngl., s 6g (19693.
4. J. A. Berson,Accts. of.Chem. Res., S 5. R. Huisgen, G. Boche, W. He&t1 w 3 585 (d.
152 (1968).
and H. Huber, Ang&
$,
595 (1966);Angew. Chem.
6. Satisfactoryelementelanalyses ('-0.3) were obtainedfor all new chemistry,see G. Schr&r, 7. For a review of cyclooctatetraene Verlsg Chemie,Weinheim/Bergstr., Germany, 1965.
mupounds.
"Cyclooctatetraen,'l
8. R. Hoffmann and R. B. woodward,J. Am. Chem. sot., 8~ 4388 (1%5). 9. Spectraldata for 6_may be f-a
in reference1.
10.
G. s&+&r snd'w. Martin have also observedthis photorearrangement [unpublishedresults mentioned in G. S&r&r and J. F. M. Oth, Angew. Chem Intern.Ed. I&@., 6_, 414 (1967)];however, stereochemicalassignmentswere not made by these authors since the stereochemistryof 6_was mlmown to them.
ll.
In contrast,irradiationof 6_unaer triplet conditions(acetonesolution)&fords & /I QIP L
'