Unexpected oxadi-π-methane rearrangement of β,γ-unsaturated aldehydes

Article abstract of DOI:10.1021/jo951032l

The oxadi-π-methane rearrangement (ODPM) is considered to represent the normal photochemical behavior of β,γ-unsaturated ketones in the triplet excited π,π* state. However, the usual photoreactivity reported for the majority of β,γ-unsaturated aldehydes i

Full text of DOI:10.1021/jo951032l

J . Org. Chem. 1996, 61, 1459-1466
1459
Un exp ected Oxa d i-π-m eth a n e Rea r r a n gem en t of â,γ-Un sa tu r a ted
Ald eh yd es
Diego Armesto,* Maria J . Ortiz, Santiago Romano, Antonia R. Agarrabeitia,
Mar G. Gallego, and Ana Ramos
Departamento de Quimica Organica I, Facultad de Ciencias Quimicas, Universidad Complutense,
28040-Madrid, Spain
Received J une 7, 1995X
The oxadi-π-methane rearrangement (ODPM) is considered to represent the normal photochemical
behavior of â,γ-unsaturated ketones in the triplet excited π,π* state. However, the usual
photoreactivity reported for the majority of â,γ-unsaturated aldehydes is decarbonylation. There
are only two published reports of â,γ-unsaturated aldehydes that undergo the ODPM rearrangement.
We now report efficient ODPM rearrangement in the triplet-sensitized irradiation of twelve cyclic
and acyclic â,γ-unsaturated aldehydes, namely, 2,2-dimethyl-4,4-diphenyl-3-butenal (6), 1-methyl-
3-phenyl-2-cyclohexene-1-carbaldehyde (7), 1-methyl-3-phenyl-2-cyclopentene-1-carbaldehyde (14a ),
1-methyl-3-phenyl-2-cycloheptene-1-carbaldehyde (14b), 2,2-dimethyl-4-phenyl-3-butenal (18), 2-(3,4-
dihydro-2-naphthyl)-2-methylpropanal (23), 3-(9-fluorenylidene)-2,2-dimethylpropanal (24), 5-cy-
clopentylidene-2,2-dimethyl-3-pentenal (27), 2,2,6-trimethyl-3,5-heptadienal (28), 2,2,4,4-tetraphenyl-
3-butenal (35), 2-methyl-4,4-diphenyl-2-vinyl-3-butenal (36), and 4-methyl-2,2-diphenyl-3-pentenal
(47). All of them afford the corresponding cyclopropyl aldehydes in 8-96% yield. Our results show
that the ODPM rearrangement of aldehydes should be considered a normal photoreactivity of this
type of compound. In one case (7), the formation of the corresponding 1,3-formyl migrated product
was also observed. Aldehydes 35 and 47 undergo, in addition to the ODPM rearrangement,
decarbonylation to the alkenes 37 and 51, respectively. The ODPM reaction takes place when the
triplet energy from the sensitizer is efficiently transferred to the alkene moiety generating a T1
(3π,π*) excited state and, furthermore, when the biradical intermediates are stabilized by phenyl
or vinyl substitution. Thus, 2,2,4-trimethyl-3-pentenal (46), in which these two requirements are
not met, undergoes decarbonylation exclusively. Some structural factors that influence the efficiency
of other di-π-methane processes, such as the di-π-methane (DPM) and azadi-π-methane (ADPM)
rearrangements, are also operative in the ODPM rearrangement of aldehydes. Thus, diphenyl
substitution on the central carbon of the â,γ-unsaturated aldehyde, as in 47, also promotes the
ODPM rearrangement. In cases in which the competition between the ODPM and the DPM
processes can occur, the selectivity observed depends on the relative stabilities of the 1,4-bridged
biradical intermediates. Thus, aldehyde 36 yields the ODPM product exclusively, while 2-(2,2-
diphenylvinyl)-2-methyl-4,4-diphenyl-3-butenal (43) affords the DPM product 44 only.
In tr od u ction
pounds do not undergo the ODPM rearrangement.2 â,γ-
Unsaturated aldehydes are the most typical example of
carbonyl compounds that do not undergo either 1,3-
formyl migration or the ODPM reaction. According to
the literature, the normal photochemical reactivity of
such compounds, both on direct or sensitized irradiations,
is decarbonylation to the corresponding alkene.2 There
are only two examples of aldehydes that do not follow
this general rule. The first example of an ODPM
rearrangement in a â,γ-unsaturated aldehyde was re-
ported by Schaffner et al.3 in the direct irradiation of the
steroidal aldehyde 1 that gives the ODPM product 2 in
30% yield in addition to two other compounds derived
from 1,3-formyl migration and decarbonylation. Many
years later, Zimmerman and Cassel4 reported the ODPM
reactivity of the sterically hindered aldehyde 3 that yields
the cyclopropyl aldehyde 4 on acetophenone-sensitized
irradiation. However, apart from these two cases, all the
studies carried out on the photochemical reactivity of â,γ-
unsaturated aldehydes failed to detect the ODPM rear-
rangement, and decarbonylation to the corresponding
alkenes was the only reaction observed.2 Thus, Schaffner,
The photochemistry of carbonyl compounds has held
the interest of organic photochemists for many years.1
The number of studies of this class of compounds exceeds
that of any of the other functional groups. Among all
the different types of carbonyl compounds, â,γ-unsatur-
ated ketones have been the subject of extensive studies.2
The results obtained show that, in simple terms, direct
irradiation of â,γ-unsaturated ketones usually yields the
corresponding 1,3-acyl migration product,2a,b while the
triplet photochemical reactivity of these compounds
brings about the formation of the corresponding cyclo-
propyl ketones by an oxadi-π-methane (ODPM) re-
arrangement.2b,c However, there are exceptions to this
general rule, and many â,γ-unsaturated carbonyl com-
X Abstract published in Advance ACS Abstracts, J anuary 15, 1996.
(1) For example, see: (a) Calvert, G. J .; Pitts, J . N. Photochemistry;
J ohn Wiley: New York, 1966. (b) Turro, N. J . Modern Molecular
Photochemistry; Benjamin Cummings Publishing Co.: Menlo Park, CA,
1978. (c) Horspool, W. M.; Armesto, D. Organic Photochemistry; Ellis
Horwood and PTR Prentice Hall: Chichester, England, 1992. (d) CRC
Handbook of Organic Photochemistry and Photobiology; Horspool, W.
M., Song, P., Ed.; CRC Press: Boca Raton, FL, 1995.
(2) (a) Houk, K. N. Chem. Rev. 1976, 76, 1. (b) Schuster, D. I. In
Rearrangements in Ground and Excited States; de Mayo, P., Ed.;
Academic Press: New York, 1980; Vol. 3, pp 167-279. (c) Demuth, M.
In Organic Photochemistry; Padwa, A., Ed.; Marcel Dekker: New York,
1991; Vol. 11, pp 37-109.
(3) Pfenninger, E.; Poel, D. E.; Berse, C.; Wehrli, H.; Schaffner, K.;
J eger, O. Helv. Chim. Acta 1968, 51, 772.
(4) Zimmerman, H. E.; Cassel, J . M. J . Org. Chem. 1989, 54, 3800.
0022-3263/96/1961-1459$12.00/0 © 1996 American Chemical Society

1460 J . Org. Chem., Vol. 61, No. 4, 1996
Armesto et al.
Sch em e 1
J eger, and co-workers published, about 20 years ago, a
series of papers on the photoreactivity of differently
substituted steroidal and cyclic â,γ-unsaturated alde-
hydes.3,5 The main photochemical reaction observed for
the aldehydes studied was decarbonylation to the corre-
sponding alkenes. Apart from compound 1, none of them
underwent the ODPM rearrangement. Du¨rr et al.6 have
studied the photochemistry of some aryl-substituted
2-cyclopentene-1-carbaldehydes 5. In this instance, cis-
stilbene-type electrocyclic cyclization and decarbonylation
were the only reactions observed. Surprisingly, the
triplet photoreactivity of acyclic â,γ-unsaturated alde-
hydes has merited very little attention. The only two
cases reported on the reactivity of this type of compound
in the triplet excited state were aldehydes 3 and 6. As
mentioned before, aldehyde 3 undergoes the ODPM
rearrangement on sensitized excitation.4 However, the
reactivity reported for 6 on direct irradiation was decar-
bonylation and what the author described as “ambiguous
results” on acetophenone sensitization.7
63
known aldehyde 7,10 which could be transformed into
different imine derivatives, was selected as the target
molecule. Since the photochemistry of the aldehyde 7
was not described, it was of importance to establish the
photochemical behavior of this compound to compare its
reactivity with that of the corresponding nitrogen deriva-
tives. Brief (10 min) direct irradiation of 7 afforded, after
workup, a mixture of starting material (20%) and the
known alkene 811 (63%) resulting from decarbonylation
of aldehyde 7 (Scheme 1). This result was not a surprise
since, as mentioned above, it has been established that
decarbonylation is the main photochemical reactivity of
â,γ-unsaturated aldehydes. However, acetophenone-
sensitized irradiation of 7 for 20 min brought about
different reactions and afforded the 1,3-migration product
(9, 25%), the ODPM product (10, 25%), and starting
material (11%) (Scheme 1).8 The identity of aldehyde 9
was established by IR and MS evidence, showing that
this compound was isomeric with starting material. The
1H and 13C NMR resonances also agree with the structure
proposed for 9. The structure of the bicyclic aldehyde
10 was unequivocally established by reduction, using
LiAlH4, to the known alcohol 11.10 By this method it was
also possible to assign the stereochemistry of the photo-
product 10 as the endo-isomer exclusively. The stereo-
selectivity observed in this reaction is similar to that
reported by Mariano and Ko10 in the sensitized irradia-
tion of the 1,4-diene 12 that yields the endo-isomer of
the corresponding di-π-methane product 13 exclusively.
The formation of the 1,3-migration product 9 under
sensitized conditions involving the T2 excited state has
been reported for several â,γ-unsaturated ketones.12
However, it is extremely rare to observe such a reaction
with analogous aldehydes, and even more surprising is
the formation of the ODPM product 10. At this point it
was difficult to explain the photoreactivity observed in
the irradiation of 7, although it was thought to be due to
the influence of some unknown structural factors present
in 7.
From all these precedents a general conclusion that is
reflected in all the reviews and monographs is that
decarbonylation is the normal photochemical fate of â,γ-
unsaturated aldehydes. The ODPM reaction is consid-
ered to be an exception with only two precedents. We
wish to report here a serendipitous discovery that
changes the accepted ideas about the photoreactivity of
â,γ-unsaturated aldehydes. Some of the results described
here have been the subject of a preliminary communica-
tion.8
Resu lts a n d Discu ssion
Th e ODP M Rea r r a n gem en t of 1-Meth yl-3-p h en yl-
2-cycloa lk en e-1-ca r ba ld eh yd es. Our interest in the
azadi-π-methane rearrangement (ADPM) has led us to
a study of its application to the synthesis of bicyclo[n.1.0]-
alkanes.9 An extension of such a study was aimed at
identifying ring contraction processes. To this end the
Compounds 14a and 14b were synthesized to deter-
mine whether this unexpected reactivity could be ex-
tended to other related aldehydes. The synthesis of 14a
was achieved by the one-pot conversion of 3-phenyl-2-
cyclopentenone,13 according to the method described by
Martin et al.14 for similar compounds. Aldehyde 14b was
(5) (a) Hill, J .; Iriarte, J .; Schaffner, K.; J eger, O. Helv. Chim. Acta
1966, 49, 292. (b) Baggiolini, E.; Hamlow, H. P.; Schaffner, K. J . Am.
Chem. Soc. 1970, 92, 4906. (c) Bozzato, G.; Schaffner, K.; J eger, O.
Chimia 1966, 20, 114. (d) Baggiolini, E.; Berscheid, H. G.; Bozzato,
G.; Cavalieri, E.; Schaffner, K.; J eger, O. Helv. Chim. Acta 1971, 54,
429. (e) Saboz, J . A.; Lizuka, T.; Wehrli, H.; Schaffner, K.; J eger, O.
Helv. Chim. Acta 1968, 51, 1362.
(6) (a) Du¨rr, H.; Heitka¨mper, P.; Herbst, P. Tetrahedron Lett. 1970,
1599. (b) Du¨rr, H.; Herbst, P.; Heitka¨mper, P.; Leismann, H. Chem.
Ber. 1974, 107, 1835.
(10) Mariano P. S.; Ko, J . J . Am. Chem. Soc. 1973, 95, 8670.
(11) Suen, Y. S.; Kagan, H. B. Bull. Soc. Chim. Fr. 1970, 10, 3552.
(12) (a) Dalton, J . C.; Shen, M.; Snyder, J . J . J . Am. Chem. Soc.
1976, 98, 5023. (b) Schaffner, K. Tetrahedron 1976, 32, 641. (c)
Schuster, D. I.; Calcaterra, L. T. J . Am. Chem. Soc. 1982, 104, 6397.
(13) Farnum, D. G.; Mostashari, A.; Hagedorn, A. A. J . Org. Chem.
1971, 36, 698.
(7) Pratt, A. C. J . Chem. Soc., Perkin Trans. 1 1973, 2496.
(8) Armesto, D.; Ortiz, M. J .; Romano, S. Tetrahedron Lett. 1995,
36, 965.
(14) Martin, S. F.; Phillips, G. W.; Puckette, T. A.; Colapret, J . A.
J . Am. Chem. Soc. 1980, 102, 5866.
(9) Armesto, D.; Ramos, A. Tetrahedron 1993, 49, 7159.

Rearrangement of â,γ-Unsaturated Aldehydes
J . Org. Chem., Vol. 61, No. 4, 1996 1461
obtained from 2-phenylcycloheptanone15 according to the
method described by Mariano and Ko for the synthesis
of aldehyde 7.10 Acetophenone-sensitized irradiation (5
min) of 14a afforded, after conventional workup, the
ODPM product 15a in 90% isolated yield. In this
1
instance, a careful study of the H and 13C NMR spectra
of the crude photolysate demonstrated that the 1,3-formyl
migration product is not formed. The identity of 15a was
established by comparison of the 1H NMR resonances
from 15a with those reported by Schaffner et al.16 for the
1
analogous ketone 16. Thus, the H NMR spectrum of 16
shows a singlet at δ 1.3 and a multiplet at δ 1.7-2.5
corresponding to the angular methyl group and the
1
cycloalkane hydrogens, respectively. The H NMR spec-
trum of aldehyde 15a is very similar, showing a singlet
at δ 1.3 and a multiplet at δ 1.4-2.6. The assignment
of structure was also confirmed by the analogy between
1
the H and 13C NMR spectra recorded for this compound
whether the partial suppression of the free rotor effect
was essential for the success of the rearrangement the
study was extended to the aldehyde 18.18 When 18 was
irradiated (15 min) under similar conditions to those used
for 7 and 14, the cyclopropyl aldehyde 19, resulting from
an ODPM rearrangement, was obtained in 90% isolated
yield. The identity of 19 was easily determined by
with those obtained for the bicyclic aldehyde 10. The
endo-configuration was also established on the basis of
this comparison. Thus, the aldehyde proton in 15a
appears as a doublet at δ 9.9, with a coupling constant
of 6.0 Hz and, similarly, compound 10 shows a doublet
at δ 9.7, with a coupling constant of 6.3 Hz for the
aldehyde proton. The result obtained in the irradiation
of 14a demonstrates that the ODPM reactivity observed
for 7 can be extended to other cyclic â,γ-unsaturated
aldehydes. However, it is still unclear why 14a does not
undergo the 1,3-formyl migration and only yields the
ODPM product. This might be due to an inefficient
energy transfer from the triplet sensitizer to the formyl
group. Similarly, acetophenone-sensitized irradiation (10
min) of 14b afforded, after workup, the ODPM product
15b in 25% isolated yield and recovered starting material
(60%). No product resulting from a 1,3-formyl migration
was observed. The identity of 15b was established by
1
comparison of its H and 13C NMR resonances with those
previously reported by us for the corresponding oxime
acetate 20.19 In this case, the reaction is stereoselective,
yielding the trans-isomer exclusively. Further proof of
the structure proposed for 19 was obtained by its conver-
sion, using standard procedures, into the oxime acetate
20. This result demonstrated clearly that the ODPM
reactivity of â,γ-unsaturated aldehydes is not restricted
to cyclic compounds, such as 7 and 14, but can also be
extended to acyclic analogs. Therefore, the suppression
of the free rotor effect is not essential for the success of
the ODPM rearrangement.
comparison of its H and 13C NMR resonances with those
1
The efficient ODPM reactivity of 18 was extremely
surprising considering that Pratt7 had reported in an
early study the absence of such a rearrangement in the
direct and sensitized irradiations of the closely related
diphenyl-substituted aldehyde 6. The reactivity observed
for 6 was decarbonylation on direct irradiation, and what
the author described as “ambiguous results”, on ac-
etophenone sensitization. No evidence for the formation
of the corresponding ODPM product was obtained. There-
fore, a logical extension of our study was to reinvestigate
the photoreactivity of the aldehyde 6. Surprisingly,
m-methoxyacetophenone-sensitized irradiation of 6 (2 h)
brought about the formation of the previously described
cyclopropyl aldehyde 21,20 resulting from an ODPM
rearrangement, in 57% isolated yield and recovered
starting material (30%). It is worth noting that the
corresponding methyl ketone 22 was also investigated
by Pratt.7 In that early study the acetophenone-
sensitized irradiation of 22 for 97 h did not lead to
formation of the corresponding ODPM product.7 We have
reinvestigated the photoreactivity of ketone 22 using
m-methoxyacetophenone as sensitizer. Under these con-
ditions, only starting material (80%) and a mixture of
highly polar compounds were obtained after 11 h of
irradiation, confirming Pratt's observation. Thus, this
recorded for 10 and 15a . In qualitative terms, the
efficiency of the rearrangement of 14a is greater than
that observed for 7 and 14b. This could be due to the
suppression in 14a of other alternative routes of deacti-
vation of the excited state, such as E,Z-isomerization
around the C-C double bond, that can be operative in
the six- and seven-membered rings present in 7 and
14b.17
Th e ODP M Rea r r a n gem en t of Acyclic â,γ-Un sa t-
u r a ted Ald eh yd es. The ODPM reactivity of the cyclic
derivatives 7, 14a , and 14b was very surprising consider-
ing the precedents on the photochemistry of â,γ-unsatur-
ated aldehydes. At this point, it was clear that there
must be structural features in compounds 7, 14a , and
14b that are critical for the success of the ODPM process.
This is evident, not only from the fact that compounds 7
and 14 undergo rearrangements that have seldom been
seen in related compounds, but also because of the very
high efficiency of the rearrangement. The most likely
controlling features are (a) the excitation of the molecule
to the T1 (3π,π*) excited state, (b) the stabilizing influence
of the phenyl group on the bridging 1,4-biradical reaction
intermediates 17, and (c) the difficulty of deactivation of
the excited state by the free rotor effect of the vinyl
component in cyclic alkenes. In order to determine
(18) van der Weerdt, A. J . A.; Cerfontain, H. Tetrahedron 1981, 37,
2121.
(19) Armesto, D.; Horspool, W. M.; Gallego, M. G.; Agarrabeitia, A.
R. J . Chem. Soc., Perkin Trans. 1 1992, 163.
(20) Zimmerman, H. E.; Mariano, P. S. J . Am. Chem. Soc. 1969,
91, 1718.
(15) Gutsche, C. D.; J ason, E. F. J . Am. Chem. Soc. 1956, 78, 1184.
(16) Gonzenbach, H. V.; Tegmo-Larsson, I. M.; Grosclaude, J . P.;
Schaffner, K. Helv. Chim. Acta 1977, 60, 1091.
(17) Kropp, P. J . In Organic Photochemistry; Padwa, A., Ed.; Marcel
Dekker: New York, 1979; Vol. 4, p 1.

1462 J . Org. Chem., Vol. 61, No. 4, 1996
Armesto et al.
is the first example of a situation in which a â,γ-
unsaturated aldehyde undergoes efficient ODPM reactiv-
ity while the corresponding methyl ketone is inert toward
the rearrangement.21
The next question to be answered was whether or not
substituents other than phenyl at that position could also
promote the reaction. In order to answer this question,
the known aldehydes 27 and 28, with differently substi-
tuted vinyl units at the γ position, were synthesized.22
Previously, we have observed efficient ADPM rearrange-
ment of the corresponding oxime acetates 29 and 30
showing that the substitution pattern present in 27 and
28 was suitable for promoting DPM reactivity.22 Brief
(20 min) m-methoxyacetophenone-sensitized irradiation
of 27 afforded, after workup, starting material (30%), as
a 3:2 mixture of E:Z isomers, and the cyclopropyl deriva-
tive 31 (47%) as a 1:8 mixture of cis:trans isomers.
Similarly, irradiation of 28, for 15 min, under the same
conditions used for 27, yielded 32 (52%) as the trans
isomer exclusively and starting material (42%). The
identity of compounds 31 and 32 was established by
comparison with authentic samples, previously obtained
by us.22 The rearrangements of aldehydes 27 and 28
demonstrated that the ODPM reactivity of â,γ-unsatur-
ated aldehydes is not restricted to phenyl-substituted
compounds but can also be extended to systems in which
the intermediate biradicals are stabilized by conjugation
with a vinyl group. Furthermore, the efficient synthesis
of compounds 31 and 32 is of importance since it opens
a novel photochemical route to chrysanthemic acid and
other cyclopropyl components present in pyrethrins and
pyrethroids.24
In flu en ce of P h en yl a n d Vin yl Su bstitu tion a t C-2
on th e ODP M Rea ctivity of â,γ-Un sa tu r a ted Ald e-
h yd es. Com p et it ion b et w een t h e ODP M a n d t h e
DP M P r ocesses. The next step in this study was to
determine whether other substitution patterns that have
been demonstrated to increase the efficiency of DPM
processes could also promote ODPM reactivity in â,γ-
unsaturated aldehydes, namely phenyl or vinyl substitu-
tion at position 2 of the â,γ-unsaturated system. Zim-
merman et al.25 have demonstrated that diphenyl
substitution at that position increases the quantum yield
of the rearrangement and also allows DPM reactivity of
acyclic 1,4-dienes in the triplet excited state. Our studies
have shown that oximes 33a 23 and 34a 23 and oxime
acetates 33b26 and 34b23b undergo efficient ADPM rear-
rangement. Therefore, the known aldehydes 3525a and
3623 were selected for this study. The photoreactivity of
aldehyde 35 on direct irradiation has been reported by
Adam et al.27 Under these conditions the only observed
product was the alkene 37, resulting from decarbonyla-
tion of the starting aldehyde. However, in our study,
acetophenone-sensitized irradiation of 35 for 10 min
afforded, after workup, the ODPM product 3825a (82%)
and the alkene 37 (8%).
Th e ODP M Rea r r a n gem en t of â,γ-Un sa tu r a ted
Ald eh yd es P r om oted by Ar yl a n d Vin yl Su bstitu -
tion a t C-4. The results obtained in the sensitized
irradiation of compounds 6, 7, 14a , 14b, and 18 show
that, contrary to general opinion, â,γ-unsaturated alde-
hydes can undergo the ODPM rearrangement very ef-
ficiently. Particularly, the reactivity observed in simple
compounds such as 6 and 18 demonstrates that the
ODPM reactivity of aldehydes is not restricted to mol-
ecules with special structural features as in the two cases
previously reported. The question that remains to be
answered is: which factors control the ODPM reactivity
of aldehydes? On the basis of precedent it seems logical
to assume that the stabilization of the corresponding 1,4-
cyclopropyl biradical intermediate by conjugation with
a phenyl ring might be essential for the success of the
rearrangement. In order to test this hypothesis, the
study was extended to aldehydes 239 and 24.22 Thus,
m-methoxyacetophenone-sensitized irradiation of 23 for
10 min brought about the formation of cyclopropane 25
in 83% yield. The identity of 25 was demonstrated by
its conversion into the corresponding oxime, previously
described by us.23 A similar result was obtained in the
m-methoxyacetophenone-sensitized irradiation of 24. In
this instance, the spirocyclopropyl aldehyde 26, previ-
ously described by us,22 was obtained in 96% yield, after
2 h of irradiation. It is clear from these results that aryl
substitution at the γ-position of the â,γ-unsaturated
aldehyde skeleton promotes highly efficient ODPM re-
activity in the triplet excited state.
In the case of aldehyde 36 two alternative rearrange-
ments, the DPM and the ODPM, are open to the excited
state. Irradiation of 36 using m-methoxyacetophenone
as sensitizer, for 10 min, afforded recovered starting
material (55%) and the cyclopropyl aldehyde 39 (19%),
as a 3:2 mixture of RS,SR:RR,SS isomers, resulting from
(21) It is difficult at this point to explain why aldehyde 6 undergoes
the ODPM rearrangement while the analogous methyl ketone 22 does
not. It will be necessary to carry out additional studies in order to
establish the possible analogies and differences between the reactivity
of â,γ-unsaturated aldehydes and ketones before giving a reasonable
explanation for this observation.
(22) Armesto, D.; Gallego, M. G.; Horspool, W. M.; Agarrabeitia, A.
R. Tetrahedron 1995, 33, 9223.
(23) (a) Armesto, D.; Ramos, A.; Mayoral, E. P. Tetrahedron Lett.
1994, 35, 3785. (b) Armesto, D.; Ortiz, M. J .; Ramos, A.; Horspool, W.
M.; Mayoral, E. P. J . Org. Chem. 1994, 59, 8115.
(24) Naumann, K. Synthetic Pyrethroid Insecticides; Springer-Ver-
lag: Berlin, 1990; Vols. 4 and 5.
(25) (a) Zimmerman, H. E.; Boettcher, R. J .; Braig, M. J . Am. Chem.
Soc. 1973, 95, 2155. (b) Zimmerman, H. E.; Armesto, D.; Amezua, M.
G.; Gannett, T. P.; J ohnson, R. J . Am. Chem. Soc. 1979, 101, 6367. (c)
Zimmerman, H. E.; Factor, R. E. Tetrahedron, 1971, 37, Suppl. 1, 125.
(26) Armesto, D.; Horspool, W. M.; Langa, F.; Ramos, A. J . Chem.
Soc., Perkin Trans. 1 1991, 223.
(27) Adam, W.; Berkessel, A.; Hildenbrand, K.; Peters, E. M.; Peters,
K.; Schnering, H. G. J . Org. Chem. 1985, 50, 4899.

Rearrangement of â,γ-Unsaturated Aldehydes
J . Org. Chem., Vol. 61, No. 4, 1996 1463
an ODPM rearrangement exclusively.28 The assignment
somers (RR,SS:RS,SR).23b It was of interest, therefore,
to study the reactivity of aldehyde 43 in order to
determine whether the DPM or the ODPM rearrange-
ments will be predominant. The known aldehyde 4323b
was irradiated using m-methoxyacetophenone as sensi-
tizer, for 15 min, yielding starting material (46%) and
the cyclopropane 44 (48%), resulting from a DPM rear-
rangement, as a 1:1 mixture of RR,SS:RS,SR isomers.
The identity of 44 was demonstrated by its conversion
into the corresponding oxime.23b This result indicates
that the same factors that control the competition
between the ADPM and the DPM rearrangements are
also operative in controlling the competition between the
DPM and ODPM rearrangement of aldehydes.
From all of the foregoing it is evident that â,γ-
unsaturated aldehydes in the T1 (3π,π*) excited state,
which can give rise to sufficiently stable 1,4-cyclopropyl
biradical intermediates (schematically represented by
structure 45) by conjugation with phenyl or vinyl sub-
stituents, undergo efficient ODPM rearrangement. This
is in clear contrast with the general opinion that decar-
bonylation is the normal photochemical reaction of this
type of compound.
of the structure and the stereochemistry of 39 was
1
achieved by NMR spectroscopy. The H NMR spectrum
of 39 shows resonances at δ 1.2 and δ 1.6 for two methyl
groups of the RS,SR and RR,SS isomers, respectively,
and two doublets at the correct resonance position for
hydrogens in a three-membered ring (δ 2.53 and δ 2.57).
The 13C NMR spectrum of 39 shows two methyl groups
at δ 15.4 and δ 20.2 and six cyclopropyl carbon atoms (δ
37.5, 38.0, 44.9, 47.0, 52.1 and 52.7), as well as two
aldehyde carbons (δ 200.8 and 201.0), corresponding to
the RS,SR and RR,SS isomers. These resonances are
only compatible with the proposed structure 39. Fur-
thermore, final proof of structure and the assignment of
the stereochemistry were obtained by comparison of the
1H and 13C NMR spectra of 39 with those reported for
both stereoisomers of the corresponding nitrile.23b The
other possible isomer 40, resulting from the alternative
DPM reaction path, was not observed, showing that in
this instance the ODPM rearrangement dominates over
the DPM process. A similar regioselectivity has been
observed by us in the irradiation of the oxime 34a 23 and
the oxime acetate 34b.23b In these two cases the ADPM
rearrangement took precedence over the alternative DPM
process. The regioselectivity observed was interpreted
as being dependent on the relative stabilities of the 1,4-
bridged biradicals for the two possible rearrangement
paths.23b
In flu en ce of Dim eth yl Su bstitu tion a t C-4 on th e
ODP M Rea ctivity of â,γ-Un sa tu r a ted Ald eh yd es.
The next question to be answered is: would it be possible
to observe ODPM rearrangement in â,γ-unsaturated
aldehydes with a smaller degree of stabilization of the
intermediate 1,4-cyclopropyl biradicals? Compounds 4629
and 4730 were synthesized in an attempt to answer this
question. Both aldehydes would give 1,4-cyclopropyl
biradicals 48a and 48b that will be stabilized by dimethyl
substitution. The photoreactivity of aldehyde 46 has
been studied previously by us.26 However, because of the
unexpected results obtained in this study, the irradiation
of 46 was repeated in an attempt to detect ODPM
reactivity. In agreement with our previous report,
sensitized irradiation of 46 using acetone as sensitizer
yielded the diene 49 resulting from the dimerization of
the radical 50, formed by decarbonylation of 46. How-
ever, irradiation of 47 for 30 min, under the same
conditions used for 46, afforded the corresponding cyclo-
propyl aldehyde 21 (8%), the decarbonylation product
In our previous study on the competition between the
ADPM and DPM rearrangements, we observed that
sensitized irradiation of the oxime acetate 41 affords the
DPM product 42 exclusively as a 3:2 mixture of stereoi-
(28) The stereochemical results observed by us for the ODPM
rearrangements of aldehydes 7, 14, 18, 27, 28, and 36 are similar to
those reported in the photochemistry of related 1,4-dienes,10 â,γ-
unsaturated ketones,16 and â,γ-unsaturated oxime acetates.19,22,23
Apparently, the same factors that control the stereochemistry of these
compounds in the triplet excited state also operate for â,γ-unsaturated
aldehydes.
(29) Rasek, R. H.; Clark, R. D.; Chaudet, J . H. J . Org. Chem. 1961,
26, 3130.
(30) Zimmerman, H. E.; Oaks, F. L.; Campos, P. J . Am. Chem. Soc.
1989, 111, 1007.

1464 J . Org. Chem., Vol. 61, No. 4, 1996
Armesto et al.
5118 (14%), and starting material (70%). This result
demonstrated that the ODPM rearrangement of alde-
hydes can occur even when there is a relatively low
degree of stabilization of the 1,4-cyclopropyl biradical
intermediates. The reactivity observed for 47 could be
due to the facile ring opening of the 1,4-cyclopropyl
biradical 48b, formed by vinyl-vinyl bridging, yielding
the intermediate 52. This interpretation is in agreement
with similar increases in efficiency and triplet reactivity
promoted by phenyl substitution at the methane carbon,
observed by Zimmerman et al. in the DPM process.4,25
1-Meth yl-3-ph en yl-2-cyclopen ten e-1-car baldeh yde (14a).
To a solution of diethyl [(N-benzylideneamino)methyl]phos-
phonate31 (1.5 g, 6 mmol) in dry THF (5 mL) under argon and
at -78 °C was added n-BuLi (4 mL, 1.6 M in hexane) in dry
THF (10 mL) slowly dropwise. The resulting red solution was
stirred at -78 °C for 1 h, and then 3-phenyl-2-cyclopentenone13
(0.7 g, 4.4 mmol) in THF (4 mL) was added. The reaction
mixture was stirred at -40 °C for 20 min, and then n-BuLi (4
mL, 1.6 M in hexane) was added at -78 °C. After the mixture
was stirred at -78 °C for 1 h, MeI (1 mL, 17.6 mmol) was
added dropwise. The reaction was quenched with 1 M aqueous
HCl (22.7 mL), and the resulting heterogeneous mixture was
stirred vigorously at 0 °C for 20 min. A saturated aqueous
solution of NaCl (11.4 mL) was added, and the aqueous layer
was extracted with Et2O. The organic layer was washed with
saturated aqueous NaHCO3, dried (MgSO4), filtered, and
concentrated to dryness. Flash chromatography of the residue
using hexane/Et2O (95:5) yielded aldehyde 14a (141 mg, 18%)
as an oil: 1H NMR (300 MHz) δ 1.2 (s, 3 H), 1.7 (m, 1 H), 2.4
(m, 1 H), 2.8 (m, 2 H), 5.8 (s, 1 H), 7.2-7.4 (m, 5 H), 9.5 (s, 1
H); 13C NMR (75 MHz) δ 20.0, 31.7, 32.6, 60.9, 125.7, 126.0,
127.8, 128.2, 135.1, 146.3, 201.9; IR (neat) 1725 cm-1; UV λmax
259 (ꢀ 13 900).
1-Me t h yl-3-p h e n yl-2-cycloh e p t e n e -1-ca r b a ld e h yd e
(14b). This compound was synthesized in four steps from
2-phenylcycloheptanone15 according to the method previously
described for the synthesis of the corresponding cyclohexyl
derivative,10 under the following reaction conditions:
Sodium (2,75 g, 0.12 mol), 2-phenylcycloheptanone15 (5 g,
0.026 mol) and ethyl formate (7.96 g, 0.1 mol) yielded 2-oxo-
3-phenylcycloheptane-1-carbaldehyde (3.5 g, 63%) as a slightly
yellow oil: 1H NMR (300 MHz) δ 1.3-2.5 (m, 8 H), 3.9 (m, 1
Con clu sion s
H), 7.0-7.4 (m, 6 H); IR (neat) 1730, 1690 cm-1
.
It is our belief that the results described herein will
change the ideas that most photochemists have on the
photoreactivity of â,γ-unsaturated aldehydes. From the
work carried out mainly by Schaffner, Du¨rr, and Pratt
on the study of a series of compounds of this type a
general consensus surrounding their lack of ODPM
reactivity was originated. Most of the compounds studied
previously underwent decarbonylation, with only two
exceptions. The decarbonylation takes place via either
the S1 (1n,π*) or T2 (3n,π*) excited states.12 However, on
the basis of studies with analogous ketones the ODPM
rearrangement of â,γ-unsaturated aldehydes almost surely
occurs via the T1 (3π,π*) excited state.2 The lack of ODPM
reactivity of the aldehydes previously studied is probably
due to the absence of the adequate substitution pattern
that would allow both efficient transfer of the triplet
energy from the sensitizer to the alkene moiety and
stabilization of the biradical intermediates. However, our
study shows that suitably substituted â,γ-unsaturated
aldehydes undergo the ODPM rearrangement with high
chemical efficiency. The results obtained herein indicate
that the ODPM rearrangement of â,γ-unsaturated alde-
hydes occurs when the triplet energy from the sensitizer
is efficiently transferred to the alkene moiety generating
a T1 (3π,π*) excited state and, furthermore, when the
biradical intermediates are stabilized by phenyl or vinyl
substitution. Further studies are planned to determine
the scope of this novel rearrangement.
2-Oxo-3-phenylcycloheptane-1-carbaldehyde (3.5 g, 0.016
mol), i-PrOH (40 mL), benzene (30 mL), and p-toluensulfonic
acid (1 mg) yielded 2-(isopropoxymethylidene)-7-phenylcyclo-
heptanone (3.35 g, 81%) as an oil: 1H NMR (300 MHz) δ 1.2
(d, J ) 6.5 Hz, 6 H), 1.5-2.5 (m, 8 H), 3.9 (m, 1 H), 4.0 (m, 1
H), 7.1-7.5 (m, 6 H).
2-(Isopropoxymethylene)-7-phenylcycloheptanone (3.3 g, 13
mmol) and LiAlH4 (0.5 g, 13 mmol) yielded 3-phenyl-1-
cycloheptene-1-carbaldehyde (1.97 g, 77%) as a brown oil: 1H
NMR (300 MHz) δ 1.3-2.3 (m, 6 H), 2.6 (m, 1 H), 2.9 (m, 1 H),
3.8 (m, 1 H), 6.8 (m, 1 H), 7.2-7.4 (m, 5 H), 9.3 (s, 1 H); IR
(neat) 1730 cm-1
.
3-Phenyl-1-cycloheptene-1-carbaldehyde (1.9 g, 9.5 mmol),
MeI (1.2 mL, 0.019 mmol), and t-BuOK (106 g, 0.014 mol) in
t-BuOH (10 mL) at 50 °C yielded 1-methyl-3-phenyl-2-cyclo-
heptene-1-carbaldehyde (14b) (0.6 g, 30%) as a colorless oil:
1H NMR (300 MHz) δ 1.2 (s, 3 H), 1.6-2.0 (m, 6 H), 2.3 (m, 1
H), 2.6 (m, 1 H), 5.7 (s, 1 H), 7.2-7.3 (m, 5 H), 9.5 (s, 1 H); 13
C
NMR (75 MHz) δ 21.9, 23.3, 25.0, 26.4, 31.8, 51.4, 125.6-129.7,
145.0, 146.0, 203.3; IR (neat) 1690 cm-1; UV (CH2Cl2) λmax 248
(ꢀ 5500).
Gen er a l P r oced u r e for P r ep a r a tive P h otolyses. The
photolyses were carried out in a quartz immersion well
apparatus with a Pyrex filter and a 400-W medium-pressure
Hg arc lamp. Solutions of the compounds and the sensitizer
(in the sensitized irradiations) in dry CH2Cl2 (420 mL) were
purged for 1 h with argon and irradiated under a positive
pressure of argon. After completion of the irradiation, the
solvent (and the acetophenone or m-methoxyacetophenone in
sensitized irradiations) was removed under reduced pressure,
and the products were separated by flash chromatography on
silica gel.
Dir ect Ir r a d ia tion of 7. Compound 7 (300 mg, 1.5 mmol)
was irradiated for 10 min. Flash chromatography using
hexane/Et2O (9:1) gave 162 mg (63%) of 3-methyl-1-phenylcy-
clohexene11 (8): 1H NMR (300 MHz) δ 1.1 (d, J ) 6.8 Hz, 3
H), 1.2-2.4 (m, 7 H), 5.9 (br s, 1 H), 7.2-7.4 (m, 5 H); IR (KBr)
1620 cm-1. Further elution gave recovered starting material
(60 mg, 20%).
Exp er im en ta l Section
Melting points were determined in open capillaries and are
uncorrected. UV/vis spectra were recorded in CH2Cl2 solution.
Column chromatography was performed using silica gel 60
(40-63 µm) from Merck. Commercially available starting
materials and reagents were purchased from Aldrich.
Ald eh yd es 6,7 7,10 18,18 23,9 24,22 27,22 28,22 35,25a 36,23
43,23b 46,29 and 4730 were synthesized by the methods previ-
ously described.
(31) Ratcliffe, R. W.; Christensen, B. G. Tetrahedron Lett. 1973, 46,
4645.

Rearrangement of â,γ-Unsaturated Aldehydes
J . Org. Chem., Vol. 61, No. 4, 1996 1465
Acetop h en on e-Sen sitized Ir r a d ia tion of 7. Compound
7 (308 mg, 1.54 mmol) and acetophenone (21.7 g, 0.18 mol)
were irradiated for 20 min. Flash chromatography using
hexane/Et2O (9:1) as eluent gave 34 mg (11%) of 7, 77 mg (25%)
of 9, and 78 mg of 10 (25%) as oils.
Compound 6 (500 mg, 2 mmol) and m-methoxyacetophenone
(5 g, 33.3 mmol) were irradiated for 2 h. Flash chromatogra-
phy using hexane/Et2O (9:1) as eluent gave 150 mg (30%) of
recovered 6 and 285 mg (57%) of cyclopropyl aldehyde 21.20
m -Meth oxya cetop h en on e-Sen sitized Ir r a d ia tion of 22.
Compound 22 (60 mg, 0.2 mmol) and m-methoxyacetophenone
(2 g, 13.3 mmol) were irradiated for 11 h. Flash chromatog-
raphy using hexane/Et2O (9:1) as eluent gave 48 mg (80%) of
recovered starting material.
Com p ou n d 9: 1H NMR (300 MHz) δ 1.8 (s, 3 H), 1.4-2.4
(m, 6 H), 5.5 (s, 1 H), 7.1-7.4 (m, 5 H), 9.4 (s, 1 H); 13C NMR
(75 MHz) δ 18.9, 24.3, 29.8, 30.5, 37.3, 117.9, 124.8-130.1,
135.7, 141.3, 199.3; IR (KBr) 1695 cm-1
.
Com p ou n d 10: 1H NMR (300 MHz) δ 0.9 (s, 3 H), 1.8 (d,
J ) 6.3 Hz, 1 H), 1.5-2.4 (m, 6 H), 7.1-7.5 (m, 5 H), 9.7 (d, J
) 6.3 Hz, 1 H); 13C NMR (75 MHz) δ 20.3, 22.8, 34.7, 37.3,
43.3, 45.3, 50.5, 126.6-128.9, 132.9, 140.9, 201.5; IR (KBr)
m -Meth oxya cetop h en on e-Sen sitized Ir r a d ia tion of 23.
Compound 23 (291 mg, 1.5 mmol) and m-methoxyacetophe-
none (2.2 g, 14.7 mmol) were irradiated for 10 min. Flash
chromatography using hexane/Et2O (99:1) as eluent gave 242
mg (83%) of cyclopropyl aldehyde 25 as a colorless oil: 1H NMR
(300 MHz) δ 0.8 (s, 3 H), 1.5 (s, 3 H), 1.6 (m, 1 H), 2.5 (m, 2
1690 cm-1
. This compound was further characterized by
reduction to the corresponding alcohol 11.10 A solution of 10
(107 mg, 0.53 mmol) in dry Et2O (20 mL) was added dropwise
at 0 °C to a suspension of LiAlH4 (43 mg, 1.1 mmol) in dry
Et2O (20 mL). The resulting mixture was stirred overnight
at rt. The residual LiAlH4 was decomposed by addition of a
saturated aqueous solution of sodium sulfate, followed by
water. The ethereal layer was separated, and the aqueous
layer was extracted with CHCl3. The combined organic
extracts were dried (MgSO4), filtered, and evaporated to
dryness, giving 98 mg (91%) of an oil which was characterized
as 6-endo-(hydroxymethyl)-5-methyl-1-phenylbicyclo[3.1.0] hex-
ane (11). Spectral data were identical in all respects to those
previously described.10
H), 2.6 (s, 1 H), 2.9 (m, 1 H), 7.0-7.1 (m, 4 H), 9.4 (s, 1 H); 13
C
NMR (75 MHz) δ 18.7, 19.2, 22.3, 28.4, 34.5, 34.9, 41.0, 126.1-
137.8, 202.1; IR (neat) 1700, 1610 cm-1. This compound was
further characterized by its conversion into the corresponding
oxime using standard procedures.23b
m -Meth oxya cetop h en on e-Sen sitized Ir r a d ia tion of 24.
Compound 24 (400 mg, 1.6 mmol) and m-methoxyacetophe-
none (10 g, 66 mmol) were irradiated for 2 h. Flash chroma-
tography using hexane/Et2O (9:1) as eluent gave 385 mg (96%)
of cyclopropyl aldehyde 26 as a colorless oil: 1H NMR (300
MHz) δ 1.4 (s, 3 H), 1.7 (s, 3 H), 2.7 (d J ) 5.4 Hz, 1 H), 7.1-
7.8 (m, 8 H), 9.9 (d, J ) 5.4 Hz, 1 H); IR (neat) 1690 cm-1. The
spectral data of this compound were identical in all respects
with those described previously.22
m -Meth oxya cetop h en on e-Sen sitized Ir r a d ia tion of 27.
Compound 27 (300 mg, 1.7 mmol) and m-methoxyacetophe-
none (1.7 g, 11 mmol) were irradiated for 20 min. Flash
chromatography using hexane/Et2O (9:1) as eluent gave 90 mg
(30%) of aldehyde 27 as a 3:2 mixture of E:Z isomers and 140
mg (47%) of cyclopropyl aldehyde 31 as an oil and as a 1:8
mixture of cis:trans isomers.
Acetop h en on e-Sen sitized Ir r a d ia tion of 14a . Com-
pound 14a (65 mg, 0.35 mmol) and acetophenone (15.8 g, 0.13
mol) were irradiated for 5 min. Flash chromatography using
hexane as eluent gave 58.5 mg (90%) of the endo isomer of
the bicyclic aldehyde 15a as an oil: 1H NMR (300 MHz) δ 1.3
(s, 3 H), 1.9 (d, J ) 6.0 Hz, 1 H), 1.4-2.6 (m, 4 H), 7.1-7.3 (m,
5 H), 9.9 (d, J ) 6.0 Hz, 1 H); 13C NMR (63 MHz) δ 17.3, 23.4,
24.6, 29.6, 41.8, 44.4, 126.4-128.3, 201.9; IR (neat) 1700 cm-1
.
Acetop h en on e-Sen sitized Ir r a d ia tion of 14b. Com-
pound 14b (201 mg, 0.93 mmol) and acetophenone (4.5 g, 37.5
mol) were irradiated for 10 min. Flash chromatography using
hexane/Et2O (9:1) as eluent gave 121 mg (60%) of 14b and 51
mg (25%) of the endo isomer of the bicyclic aldehyde 15b as
an oil: 1H NMR (300 MHz) δ 1.3 (s, 3 H), 1.8 (d, J ) 6.7 Hz,
1 H), 1.5-2.3 (m, 8 H), 6.8-7.5 (m, 5 H), 9.8 (d, J ) 6.7 Hz, 1
H); 13C NMR (75 MHz) δ 14.0, 22.6, 29.3, 29.5, 29.6, 32.0, 42.0,
46.0, 128.2, 128.5, 130.0, 133.1, 138.5, 202.0; IR (neat) 1705
E:Z isom er s 27: 1H NMR (250 MHz) δ 1.13 (s, 3.6 H,
E-isomer), 1.16 (s, 2.4 H, Z-isomer), 1.6 (m, 4 H), 2.3 (m, 4 H),
5.1 (d, J ) 11.2 Hz, 0.4 H, Z-isomer), 5.3 (d, J ) 15.4 Hz, 0.6
H, E-isomer), 5.9 (m, 1 H), 6.1 (m, 1 H), 9.3 (s, 0.6 H, E-isomer),
9.4 (s, 0.4 H, Z-isomer); 13C NMR (63 MHz) δ 21.6, 23.5, 26.1,
26.2, 26.3, 26.4, 29.2, 29.5, 34.1, 34.5, 48.0 (Z-isomer), 48.8
(E-isomer), 115.5, 120.0, 128.7, 129.3, 129.6, 130.9, 148.8 (E-
isomer), 151.8 (Z-isomer), 202.3 (E-isomer), 203.7 (Z-isomer);
IR (neat) 2810, 2710, 1730, 1640 cm-1
.
cm-1
.
Com p ou n d 31: 1H NMR (250 MHz) δ 1.12 (s, 2.64 H, trans-
isomer), 1.14 (s, 0.36 H, cis-isomer), 1.26 (s, 2.64 H, trans-
isomer), 1.32 (m, 0.36 H, cis-isomer), 1.6 (m, 5.88 H), 2.0 (m,
0.12 H, cis-isomer), 2.2 (m, 4 H), 5.0 (dt, J ) 8.5, 2.3 Hz, 0.88
H, trans-isomer), 5.4 (dt, J ) 8.5, 2.3 Hz, 0.12 H, cis-isomer),
9.37 (d, J ) 6.5 Hz, 0.88 H, trans-isomer), 9.38 (s, J ) 5.6,
0.12 H, cis-isomer); IR (neat) 1700 cm-1. The spectral data of
this compound were identical in all respects with those
described previously.22
Acetop h en on e-Sen sitized Ir r a d ia tion of 18. Compound
18 (213 mg, 1.22 mmol) and acetophenone (20 g, 0.16 mol) were
irradiated for 15 min. Flash chromatography using hexane/
Et2O (9:1) as eluent gave 192 mg (90%) of cyclopropyl aldehyde
19 as a colorless oil: 1H NMR (300 MHz) δ 0.9 (s, 3 H), 1.4 (s,
3 H), 2.2 (dd, J ) 5.5, 5.0 Hz, 1 H), 2.9 (d, J ) 5.5 Hz, 1 H),
7.1-7.4 (m, 5 H), 9.6 (d, J ) 5.0 Hz, 1 H); 13C NMR (75 MHz)
δ 21.6, 21.9, 32.1, 38.7, 41.1, 126.5-128.5, 132.9, 136.3, 200.7;
IR 1705 cm-1. This compound was further characterized by
conversion into the corresponding oxime acetate 20.19 Thus,
the aldehyde 19 (192 mg, 1.1 mmol), hydroxylamine hydro-
chloride (85 mg, 1.23 mmol), and pyridine (97 mg, 1.23 mmol)
were refluxed in EtOH (20 mL) for 2 h. The solvent was
evaporated, and the crude was dissolved in Et2O and washed
with aqueous HCl (10%), water, and brine. The extract was
dried (MgSO4), filtered, and evaporated to dryness. Flash
chromatography using hexane/Et2O (8:2) as eluent gave 166
mg (80%) of the corresponding oxime: 1H NMR (300 MHz) δ
0.9 (s, 3 H), 1.3 (s, 3 H), 2.2 (d, J ) 5.6 Hz, 1 H), 2.5 (dd, J )
5.6, 8.4 Hz, 1 H), 6.5 (d, J ) 8.4 Hz, 1 H), 7.2-7.4 (m, 5 H);
13C NMR (75 MHz) δ 21.6, 22.8, 24.8, 26.6, 38.2, 126.2-128.8,
152.4; IR (neat) 3100, 1610 cm-1. To a solution of this oxime
(100 mg, 0.5 mmol) in pyridine (1 mL) at 0 °C was added acetyl
chloride (0.05 mL, 0.8 mmol). The mixture was stirred for 1
h at 0 °C. The crude was dissolved in Et2O (100 mL) and
washed successively with 10% aqueous NaHCO3 and brine.
The organic layer was dried (MgSO4), filtered and evaporated
to dryness. Flash chromatography using hexane/Et2O (9:1) as
eluent gave 75 mg (62%) of oxime acetate 2019 as a colorless
oil. Spectral data were identical to those previously described.
m -Meth oxya cetop h en on e-Sen sitized Ir r a d ia tion of 6.
m -Meth oxya cetop h en on e-Sen sitized Ir r a d ia tion of 28.
Compound 28 (300 mg, 2 mmol) and m-methoxyacetophenone
(1.3 g, 8.6 mmol) were irradiated for 15 min. Flash chroma-
tography using hexane/Et2O (98:2) as eluent gave 127 mg
(42%) of aldehyde 28 as a 1:1 mixture of E:Z isomers and 155
mg (52%) of trans-cyclopropyl aldehyde 32 as a colorless oil:
1H NMR (300 MHz) δ 1.2 (s, 3 H), 1.3 (s, 3 H), 1.61 (m, 1 H),
1.70 (s, 3 H), 1.72 (s, 3 H), 2.1 (m, 1 H), 4.91 (d, J ) 7.8 Hz, 1
H), 9.4 (d, J ) 5.4 Hz, 1 H); 13C NMR (63 MHz) δ 18.6, 21.8,
22.3, 25.7, 29.8, 31.6, 34.7, 45.2, 120.1, 135.9, 200.6; IR (neat)
2720, 1700 cm-1
. The spectral data of this compound were
identical in all respects with those described previously.22
Acetop h en on e-Sen sitized Ir r a d ia tion of 35. Compound
35 (350 mg, 94 mmol) and acetophenone (5.7 mL, 46.6 mmol)
were irradiated for 10 min. Flash chromatography of the crude
using hexane/Et2O (98:2) as eluent gave 28 mg (8%) of 1,1,3,3-
tetraphenylpropene (37)27 and 287 mg (82%) of cyclopropyl
aldehyde 38 as a white solid: mp 200-202 °C (lit.25a mp 205-
207 °C); 13C NMR (75 MHz) δ 42.4, 51.6, 126.4-142.3, 202.5.
m -Meth oxya cetop h en on e-Sen sitized Ir r a d ia tion of 36.
Compound 36 (300 mg, 1.15 mmol) and m-methoxyacetophe-
none (1.25 mg, 8.3 mmol) were irradiated for 10 min. Flash

1466 J . Org. Chem., Vol. 61, No. 4, 1996
Armesto et al.
chromatography using hexane/Et2O (98:2) as eluent gave 164
mg (55%) of 36 and 56 mg (19%) of cyclopropyl aldehyde 39
as an oil and as a 3:2 mixture of RS,SR:RR,SS isomers: 1H
NMR (300 MHz) δ 1.2 (s, 1.8 H, RS,SR isomer), 1.6 (s, 1.2 H,
RR,SS isomer), 2.53 (d, J ) 7.3 Hz, 0.6 H, RS,SR isomer), 2.57
(d, J ) 7.3 Hz, 0.4 H, RR,SS isomer), 5.0-5.25 (m, 1.8 H),
5.34 (dd, J ) 1.2, 17.1 Hz, 0.6 H, RS,SR isomer), 6.1 (dd, J )
10.4, 17.1 Hz, 0.6 H, RS,SR isomer), 7.1-7.4 (m, 10 H), 9.25
(d, J ) 7.3 Hz, 0.6 H, RS,SR isomer), 9.26 (d, J ) 7.3 Hz, 0.4
H, RR,SS isomer); 13C NMR (75 MHz) δ 15.4, 20.2, 37.5, 38.0,
44.9, 47.0, 52.1, 52.7, 113.1, 114.6, 126.2-130.5, 137.3, 138.6,
139.0, 141.8, 142.6, 200.8, 201.0.
Aceton e-Sen sitized Ir r a d ia tion of 46. Compound 46
(660 mg, 5.2 mmol) and acetone (450 mL) were irradiated for
3.5 h. Flash chromatography of the crude using hexane/Et2O
(95:5) as eluent gave 100 mg (19%) of 2,4,4,5,5,7-hexamethyl-
2,6-octadiene (49)32 and 520 mg (79%) of 46.
Aceton e-Sen sitized Ir r a d ia tion of 47. Compound 47
(130 mg, 0.52 mmol) and acetone (450 mL) were irradiated
for 30 min. Flash chromatography of the crude using hexane/
Et2O (95:5) as eluent gave 16 mg (14%) of 3-methyl-1,1-
diphenyl-2-butene (51),18 10 mg (8%) of cyclopropane 21,20 and
97 mg (75%) of 47.
m -Meth oxya cetop h en on e-Sen sitized Ir r a d ia tion of 43.
Compound 43 (280 mg, 0.67 mmol) and m-methoxyacetophe-
none (4.3 g, 28.6 mmol) were irradiated for 15 min. Flash
chromatography using hexane/Et2O (9:1) as eluent gave 130
mg (46%) of 43 and 134 mg (48%) of cyclopropyl aldehyde 44
as a 1:1 mixture of RR,SS:RS,SR isomers and as a white
solid: 1H NMR (300 MHz) δ 0.9 (s, 1.5 H, RR,SS isomer), 1.3
(s, 1.5 H, RS,SR isomer), 2.6 (d, J ) 9 Hz, 0.5 H, RR,SS
isomer), 3.1 (d, J ) 9 Hz, 0.5 H, RS,SR isomer), 5.6 (d, J ) 9
Hz, 0.5 H, RS,SR isomer), 6.2 (d, J ) 9 Hz, 0.5 H, RR,SS
isomer), 6.8-7.8 (m, 20 H), 8.4 (s, 0.5 H, RS,SR isomer), 9.3
(s, 0.5 H, RR,SS isomer); 13C NMR (75 MHz) δ 11.4, 15.3, 34.7,
39.4, 43.5, 43.8, 49.2, 52.4, 122.5, 123.1, 126-130.8, 138.0,
138.9, 139.2, 139.5, 141.8, 142.4, 142.8, 144.6, 145.3, 201.8,
Ack n ow led gm en t. We thank the Direccion General
de Investigacion Cientifica y Tecnica (Grant No. PB 91/
0396) and the European Union (Contract No. CHRX-
CT93-0151) for financial support.
Su p p or tin g In for m a tion Ava ila ble: 1H NMR spectra of
9, 14b, 15b, and 44 as well as 13C NMR spectra of 10, 14a ,
15a , 19, 25, and 39 (10 pages). This material is contained in
libraries on microfiche, immediately follows this article in the
microfilm version of the journal, and can be ordered from the
ACS; see any current masthead page for ordering information.
J O951032L
201.9; IR (neat) 1695 cm-1
. This compound was further
characterized by conversion into the corresponding oxime using
(32) van der Weerdt, A. J . A.; Cerfontain, H. J . Chem. Soc., Perkin
Trans. 2 1977, 1358.
standard procedures.23b