- Email: [email protected]
Dimeric photoreduction in 2-methylbenzophenones
Tetrahedron
Letters
l-30.32,
DMWIC
pp.
3579-3582,
1968.
Pergamon
Press.
Printed in heat
Britain.
PHOTOREDUCTION IN 2-MBTHYWZOPHENONEs(l) Ned D. Heindel and E. W. Sarver Chandler Laboratory of Chemistry Lehigh University Bethlehem, Penna.
18015
Miobsl A. Pfau Laboratoire de Cbimie Ecola Normals Superieure Paris (Ve), Franae 19 February 1968; received in UK for publication 14 May1968) The concept of internal pbotoaotivated bTdrogen transfer (pbotoenoliza-
(Received in USA
tion) was originally postulated to explain tbe apparent lack of bimoleoular pboto(2). Yang and other reduction of 2-alkyl, 2-amino- and 2-bydroxybenzopbenonea
workershave provided obemioal and physical ovidenoa to support the internal enoliration prooess(3'4) and an en01 of 2-metbglbenzopbenone baa been "trapped" uitb dimetbgl aoetylenedicarboxglate(3).
It tbsrsrors appeared,
rr0m erriorts 0r pre-
vioua workers, that the normal H atom abstraotioo from solvent which is a necessary prerequisite ror pbotopinaoolization(5) was oiroumvented by internal abstraction of the triplet state oarbonyl in a-alkylketonea(6). We have already demonstrated the synthetic generality of this pbotoenolization in a variety of o.-metbglbenzo-
3579
No.32
3580 We now wish to report
tbat
is open to 2-zmtbylbenzopbenoner demonstrated.
While tea ting
dime thy1 maleate, tial
dienopbllea
were obtained
ethyl for
The dimer uaa Identified the oorresponding
pinaool
reduction(8)
*/y2
benzene normally
panol.
aoetglenlo
and olefinio
oinnamate , dipbenylaoetglene
low yields
(S-10%)
by infrared,
and was subsequently
of pinaool
The ketones
as 0.09
equipped
experiments
analysis
synthesized m.p.
by the
medium aa the
encouraged
us to iain 2-pro-
in the alcohol
with 3500 A” lamps.
as
179-18OOC.
or 2-metbylbeazopbenones aolutiona
adduots
were isolated.
and mass speotral
in 31% yield,
aa poten-
no trapped
aubatanoe
independently
trapping
oi’ a series
were irradiated
a Rayonet reactor
and pbenyleoetylene)
in such a poor H atom-donating
employed in pbotoenol
previously
oompouoda (oyolobexene,
of a dimerlc
oombustion,
pathway
prooess
of 2,4-dimetbylbenzopbenone,
the photopinaoolization
hour period+ln reported
otber
pbotoreduatlon
to the pbotoenolic
of the parent benzophenone
The production
vestlgate
a bimoleoular
in addition
the pbotoeaol
hut instead
indeed
for
The results
a 10 are
in the Table. TABIS
Ketone
Plnacola Yield
Trapned Enola m
E-metbylbenzopbenone
33
144-145"
82b
2,4-dlmetbylbenzophenone
28
179-1800
81b
2,5-dimetbylbenzopbenone
50
142-143o
86h
2,3 f,4’-trimetbylbenzopbenone
33
139-1410
62’
3-methyl-4-benzoylpgridine
40
170-1710
_- d
a. b.
Satisfactory
c. d.
lot reported in (71, m.p. 126-127OC. Bo trapped adduct could be obtained beoauae the pyridine moiety of the ketone underwent a vigorous “dark reaction” with dlmetbyl ap?fyleae-dioarboxylate presumably a8 desoribed for pyridines in general in
By utilization reduotion
combustion analyses were obtained for all produots. analytically pure 1-aryl-2,3-dioarbometboxy-1,4-dibydro-l-
of a benzopbenone
aotinometer
of 2,4-dimetbylbenzopbenone
the quantum yield
was calculated
to be 0.03.
for the pbotoTbe quantum
3581
No.32
yield for the pbotoenol trapping process on 2-metbylbennropbenonewas reported to be 0.5(3). To investigate the oompetitive pbotoenolisation-pbotoreduotionprocesses under conditions in which both pathways would be stoiobio~trically possible, equimolar (0.05 Molar) quantities OS 2,4-dlmetbylbeneopbenone, dlmetbyl aoetylenedioarboxylate, and E-propanol were Irradiated in benzene solution for 10 hours. A 78% yield of the "trapped" enol, 1-pbenyl-6-methyl-2,3-dicarbometboxy-1,4-dibydro-1-napbthol, waa isolated.
Speatral examination of the mother liquors showed
no evidence for the presence of pinaool. However, when similar equimolar quantities of the 2,b-dimetbylbenzopheaone and dimethyl aoetylenedioarboxylate were irradiated in 2-propanol medium, the only pbotoproduct was a 30$ yield of tbe dlol. We are currently exploring the variation of reactant oonoentrations to establish condition8 under which competitive quantum gielda Sor the two processes can be measured. Aolcnowledgement: E.W.S. gratefully h~knowledges iellouship support i'romthe National Aeronautics and Spaoe Administration and the Lehigh University Institute of Research.
A
grant from the Frederick Cardner Cottrell Research Corporation to
N.D.H. assisted with the purchase of the photochemical equipment. REJ?ERENCES 1.
Presented at the Third Annual Middle Atlantic Regional A.C.S. Meeting, February 1, 1968, Pbiledelphia, Pennsylvania.
2.
J. N. Pitta, Jr., H. W. Johnson, Jr., and
T. Kuuana, J. Phys. Chem., 66,
2456 (1962). 2213
(1961).
3.
N. C. Yang and C. Rivas, J. Am. Chem. Soo., a,
4.
W.
5.
An excellent review of the literature on the pbotopinacolization reaction of
A. Henderson, Jr., and E. F. Ullman, J. Am. Chem. SOC., a,
$424 (1965).
benzophenones is found in N. J. Turro, Eolecular Pbotocbemistry, W. A. Benjamin, New York, 1965, Chapter 6.
No.32
3582 6.
E. F. Zwicker, L. I. Oromiweiner, and N. C. Pang, J. Am. Cbem. Sm.,
&,
2671
(1963). 7.
M. A. Pfau, N. D. Reindel and T. F. Lemke, Coopt. Rend. 261, 1017 (1965).
8.
H. Oomberg and W. E. Bacbmann, J. Am. Cbem. SQC., &,
9.
R. M. Acbeson, in Advanoea in Heteroogclic Cbemiatry, Volume 1, A.
236 (1927).
Katritzky, editor, Academia Press, New York, 1963, p. 125.
R.
Letters
l-30.32,
DMWIC
pp.
3579-3582,
1968.
Pergamon
Press.
Printed in heat
Britain.
PHOTOREDUCTION IN 2-MBTHYWZOPHENONEs(l) Ned D. Heindel and E. W. Sarver Chandler Laboratory of Chemistry Lehigh University Bethlehem, Penna.
18015
Miobsl A. Pfau Laboratoire de Cbimie Ecola Normals Superieure Paris (Ve), Franae 19 February 1968; received in UK for publication 14 May1968) The concept of internal pbotoaotivated bTdrogen transfer (pbotoenoliza-
(Received in USA
tion) was originally postulated to explain tbe apparent lack of bimoleoular pboto(2). Yang and other reduction of 2-alkyl, 2-amino- and 2-bydroxybenzopbenonea
workershave provided obemioal and physical ovidenoa to support the internal enoliration prooess(3'4) and an en01 of 2-metbglbenzopbenone baa been "trapped" uitb dimetbgl aoetylenedicarboxglate(3).
It tbsrsrors appeared,
rr0m erriorts 0r pre-
vioua workers, that the normal H atom abstraotioo from solvent which is a necessary prerequisite ror pbotopinaoolization(5) was oiroumvented by internal abstraction of the triplet state oarbonyl in a-alkylketonea(6). We have already demonstrated the synthetic generality of this pbotoenolization in a variety of o.-metbglbenzo-
3579
No.32
3580 We now wish to report
tbat
is open to 2-zmtbylbenzopbenoner demonstrated.
While tea ting
dime thy1 maleate, tial
dienopbllea
were obtained
ethyl for
The dimer uaa Identified the oorresponding
pinaool
reduction(8)
*/y2
benzene normally
panol.
aoetglenlo
and olefinio
oinnamate , dipbenylaoetglene
low yields
(S-10%)
by infrared,
and was subsequently
of pinaool
The ketones
as 0.09
equipped
experiments
analysis
synthesized m.p.
by the
medium aa the
encouraged
us to iain 2-pro-
in the alcohol
with 3500 A” lamps.
as
179-18OOC.
or 2-metbylbeazopbenones aolutiona
adduots
were isolated.
and mass speotral
in 31% yield,
aa poten-
no trapped
aubatanoe
independently
trapping
oi’ a series
were irradiated
a Rayonet reactor
and pbenyleoetylene)
in such a poor H atom-donating
employed in pbotoenol
previously
oompouoda (oyolobexene,
of a dimerlc
oombustion,
pathway
prooess
of 2,4-dimetbylbenzopbenone,
the photopinaoolization
hour period+ln reported
otber
pbotoreduatlon
to the pbotoenolic
of the parent benzophenone
The production
vestlgate
a bimoleoular
in addition
the pbotoeaol
hut instead
indeed
for
The results
a 10 are
in the Table. TABIS
Ketone
Plnacola Yield
Trapned Enola m
E-metbylbenzopbenone
33
144-145"
82b
2,4-dlmetbylbenzophenone
28
179-1800
81b
2,5-dimetbylbenzopbenone
50
142-143o
86h
2,3 f,4’-trimetbylbenzopbenone
33
139-1410
62’
3-methyl-4-benzoylpgridine
40
170-1710
_- d
a. b.
Satisfactory
c. d.
lot reported in (71, m.p. 126-127OC. Bo trapped adduct could be obtained beoauae the pyridine moiety of the ketone underwent a vigorous “dark reaction” with dlmetbyl ap?fyleae-dioarboxylate presumably a8 desoribed for pyridines in general in
By utilization reduotion
combustion analyses were obtained for all produots. analytically pure 1-aryl-2,3-dioarbometboxy-1,4-dibydro-l-
of a benzopbenone
aotinometer
of 2,4-dimetbylbenzopbenone
the quantum yield
was calculated
to be 0.03.
for the pbotoTbe quantum
3581
No.32
yield for the pbotoenol trapping process on 2-metbylbennropbenonewas reported to be 0.5(3). To investigate the oompetitive pbotoenolisation-pbotoreduotionprocesses under conditions in which both pathways would be stoiobio~trically possible, equimolar (0.05 Molar) quantities OS 2,4-dlmetbylbeneopbenone, dlmetbyl aoetylenedioarboxylate, and E-propanol were Irradiated in benzene solution for 10 hours. A 78% yield of the "trapped" enol, 1-pbenyl-6-methyl-2,3-dicarbometboxy-1,4-dibydro-1-napbthol, waa isolated.
Speatral examination of the mother liquors showed
no evidence for the presence of pinaool. However, when similar equimolar quantities of the 2,b-dimetbylbenzopheaone and dimethyl aoetylenedioarboxylate were irradiated in 2-propanol medium, the only pbotoproduct was a 30$ yield of tbe dlol. We are currently exploring the variation of reactant oonoentrations to establish condition8 under which competitive quantum gielda Sor the two processes can be measured. Aolcnowledgement: E.W.S. gratefully h~knowledges iellouship support i'romthe National Aeronautics and Spaoe Administration and the Lehigh University Institute of Research.
A
grant from the Frederick Cardner Cottrell Research Corporation to
N.D.H. assisted with the purchase of the photochemical equipment. REJ?ERENCES 1.
Presented at the Third Annual Middle Atlantic Regional A.C.S. Meeting, February 1, 1968, Pbiledelphia, Pennsylvania.
2.
J. N. Pitta, Jr., H. W. Johnson, Jr., and
T. Kuuana, J. Phys. Chem., 66,
2456 (1962). 2213
(1961).
3.
N. C. Yang and C. Rivas, J. Am. Chem. Soo., a,
4.
W.
5.
An excellent review of the literature on the pbotopinacolization reaction of
A. Henderson, Jr., and E. F. Ullman, J. Am. Chem. SOC., a,
$424 (1965).
benzophenones is found in N. J. Turro, Eolecular Pbotocbemistry, W. A. Benjamin, New York, 1965, Chapter 6.
No.32
3582 6.
E. F. Zwicker, L. I. Oromiweiner, and N. C. Pang, J. Am. Cbem. Sm.,
&,
2671
(1963). 7.
M. A. Pfau, N. D. Reindel and T. F. Lemke, Coopt. Rend. 261, 1017 (1965).
8.
H. Oomberg and W. E. Bacbmann, J. Am. Cbem. SQC., &,
9.
R. M. Acbeson, in Advanoea in Heteroogclic Cbemiatry, Volume 1, A.
236 (1927).
Katritzky, editor, Academia Press, New York, 1963, p. 125.
R.