Novel photoreactions of 2-Aza-1,4-dienes in the triplet excited state and via radical-cation intermediates. 2-Aza-di-π-methane rearrangements yielding cyclopropylimines and N-vinylaziridines

Article abstract of DOI:10.1021/jo034452g

Triplet-sensitized irradiation of 2-aza-1,4-dienes affords N-cyclopropylimines via 2-aza-di-π-methane (2-ADPM) rearrangement pathways. In the case of the pentaphenyl-substituted azadiene 1, irradiation leads to formation of cyclopropylimine 2 as well as N-vinylaziridine 3. The transformations represent the first examples of di-π-methane rearrangement reactions that yield three-membered heterocyclic products. SET-sensitized irradiation of 2-aza-1,4-dienes, by using 9,10-dicyanoanthracene (DCA) as an electron-acceptor sensitizer and biphenyl as cosensitizer, brings about regioselective formation of N-vinylaziridines. Under these conditions, azadiene 1 also affords cyclopropylimine 37, resulting from an aryl-di-π-methane rearrangement. This result demonstrates that di-π-methane reactions can also take place via radical-cation intermediates. In some instances, imine and olefin centered cation-radical intermediates, generated by SET-sensitized irradiation, undergo alternative reactions to produce isoquinoline and benzoazepine products.

Full text of DOI:10.1021/jo034452g

Novel P h otor ea ction s of 2-Aza -1,4-d ien es in th e Tr ip let Excited
Sta te a n d via Ra d ica l-Ca tion In ter m ed ia tes. 2-Aza -d i-π-m eth a n e
Rea r r a n gem en ts Yield in g Cyclop r op ylim in es a n d
N-Vin yla zir id in es
Diego Armesto,* Olga Caballero, Maria J . Ortiz, Antonia R. Agarrabeitia,
Mar Martin-Fontecha, and M. Rosario Torres†
Departamento de Quimica Organica I, Facultad de Ciencias Quimicas, Universidad Complutense,
28040-Madrid, Spain
darmesto@quim.ucm.es
Received April 10, 2003
Triplet-sensitized irradiation of 2-aza-1,4-dienes affords N-cyclopropylimines via 2-aza-di-π-methane
(2-ADPM) rearrangement pathways. In the case of the pentaphenyl-substituted azadiene 1,
irradiation leads to formation of cyclopropylimine 2 as well as N-vinylaziridine 3. The transforma-
tions represent the first examples of di-π-methane rearrangement reactions that yield three-
membered heterocyclic products. SET-sensitized irradiation of 2-aza-1,4-dienes, by using 9,10-
dicyanoanthracene (DCA) as an electron-acceptor sensitizer and biphenyl as cosensitizer, brings
about regioselective formation of N-vinylaziridines. Under these conditions, azadiene 1 also affords
cyclopropylimine 37, resulting from an aryl-di-π-methane rearrangement. This result demonstrates
that di-π-methane reactions can also take place via radical-cation intermediates. In some instances,
imine and olefin centered cation-radical intermediates, generated by SET-sensitized irradiation,
undergo alternative reactions to produce isoquinoline and benzoazepine products.
In tr od u ction
yet to be described although Mariano and co-workers5
have previously documented the interesting SET-pro-
moted photocyclization reactions of iminium salts derived
from 2-aza-1,4-dienes.
Studies of excited state reactions of 1,4-unsaturated
systems comprise one of the most fruitful areas of organic
photochemistry. Substances in this family typically un-
dergo unique and synthetically useful photoreactions.
Examples of this are found in di-π-methane (DPM)
rearrangements of 1,4-dienes,1,2 oxa-di-π-methane (ODPM)
photoreactions of â,γ-unsaturated ketones1,3 and alde-
hydes,1 1,3-acyl migration processes of â,γ-unsaturated
ketones,3a-c and 1-aza-di-π-methane (1-ADPM) rear-
rangements of 1-aza-1,4-dienes containing imine, oxime,
and oxime ester groups.1,4 Surprisingly, the photoreac-
tivity of closely related 2-aza-1,4-diene derivatives has
Our earlier efforts exploring the excited-state chemis-
try of 1-aza-1,4-dienes1,4 have been extended recently to
include investigations with the potentially more interest-
ing 2-aza-1,4-dienes. Our interest in these substrates was
stimulated by the fact that di-π-methane-type rearrange-
ments of 2-aza-1,4-dienes would lead to the production
of vinylaziridines and/or cyclopropylimines, substances
which have the capability of undergoing thermal trans-
formation to five-membered N-heterocyclic products.6
Results arising from this investigation have demon-
strated that 2-aza-1,4-diene systems participate in un-
precedented photorearrangement reactions to produce
* To whom correspondence should be addressed. Phone: (34)
913944316. Fax: (34) 913944103.
† To whom inquires regarding the X-ray data should be addressed.
Permanent address: Laboratorio de Difraccion de Rayos X, Facultad
de Ciencias Quimicas, Universidad Complutense, 28040-Madrid, Spain.
(1) Zimmerman, H. E.; Armesto, D. Chem. Rev. 1996, 96, 3065-
3112.
(4) (a) Armesto, D. In CRC Handbook of Organic Photochemistry
and Photobiology; Horspool, W. M., Soon, P.-S., Eds.; CRC Press: New
York, 1995; pp 915-930. (b) Armesto, D. EPA Newslett. 1995, 53, 6-21.
(c) Armesto, D.; Ortiz, M. J .; Agarrabeitia, A. R. In Advanced
Functional Molecules and Polymers; Nalwa, H. S., Ed.; Gordon and
Breach: Amsterdam, The Netherlands, 2001; Vol. 1, pp 351-379. (d)
Armesto, D.; Ortiz, M. J .; Agarrabeitia, A. R. In Photochemistry of
Organic Molecules in Isotropic and Anisotropic Media, Molecular and
Supramolecular Photochemistry; Ramamurthy, V., Schanze, K. S., Eds.;
Marcel Dekker: New York, 2003; Vol. 9, pp 1-41.
(5) Mariano, P. S. In CRC Handbook of Organic Photochemistry and
Photobiology; Horspool, W. M., Soon, P.-S., Ed.; CRC Press: New York,
1995; pp 867-878.
(6) (a) Whitlock, H. W.; Smith, G. L. Tetrahedron Lett. 1965, 1389-
1393. (b) Smith, G. L.; Whitlock, H. W. Tetrahedron Lett. 1966, 2711-
2716. (c) Whitlock, H. W.; Smith, G. L. J . Am. Chem. Soc. 1967, 89,
3600-3606. (d) Lindstrom, V. M.; Somfai, P. J . Am. Chem. Soc. 1997,
119, 8385-8386.
(2) (a) Zimmerman, H. E. In Rearrangements in Ground and Excited
States; DeMayo, P., Ed.; Academic Press: New York, 1980; Vol. 3, pp
131-166. (b) Zimmerman, H. E. In Organic Photochemistry; Padwa,
A., Ed.; Marcel Dekker: New York, 1991; Vol. 11, pp 1-36. (c) De
Lucchi, O.; Adam, W. In Comprehensive Organic Synthesis; Trost, B.
M., Fleming, I., Paquette, L. A., Eds.; Pergamon Press: Oxford, UK,
1991; Vol. 5, pp 193-214.
(3) (a) Dauben, G. W.; Lodder, G.; Ipaktschi, J . Top. Curr. Chem.
1975, 54, 73-114. (b) Houk, K. N. Chem. Rev. 1976, 76, 1-74. (c)
Schuster, D. I. In Rearrangements in Ground and Excited States;
DeMayo, P., Ed.; Academic Press: New York, 1980; Vol. 3, pp 167-
279. (d) Demuth, M. In Organic Photochemistry; Padwa, A., Ed.; Marcel
Dekker: New York, 1991; Vol. 11, pp 37-109. (e) Demuth, M. In
Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Paquette,
L. A., Eds.; Pergamon Press: Oxford, UK, 1991; Vol. 5, pp 215-237.
10.1021/jo034452g CCC: $25.00 © 2003 American Chemical Society
Published on Web 07/29/2003
J . Org. Chem. 2003, 68, 6661-6671
6661

Armesto et al.
SCHEME 1
SCHEME 2
N-vinylaziridine and N-cyclopropylimine products, re-
spectively, under SET- and triplet-sensitized irradiation
conditions. These processes are the first examples of
2-aza-di-π-methane (2-ADPM) rearrangements. Perhaps
of greater interest are observations which show that
2-ADPM rearrangements take place via radical-cation
intermediates.7,8 A portion of the results described here
has been the subject of a preliminary communication.9
which affords 1,3-biradical 7 that cyclizes to generate
cyclopropylimine 2 (path a). Competitive C-C bond
fragmentation in 6 provides the intermediate 8, the
precursor of vinylaziridine 3 (path b). This photoreaction
represents the first example of a 2-aza-di-π-methane
rearrangement that occurs via a three-membered-ring
heterocyclic biradical and brings about the formation of
a heterocyclic product.13 It is worth noting that interme-
diate 8 could be either a triplet 1,3-biradical or a singlet
azomethine ylide, depending on whether ISC occurs prior
to C-C bond cleavage in 6. Only the singlet azomethine
ylide is capable of undergoing cyclization to form 3.
Resu lts a n d Discu ssion
Tr ip let-Sen sitized Ir r a d ia tion of 2-Aza -1,4-d ien es.
Previous studies have shown that diphenyl substitution
at the central methane carbon promotes highly efficient
DPM, ODPM, and 1-ADPM reactions in acyclic 1,4-
dienes,10 â,γ-unsaturated aldehydes,11 and 1-aza-1,4-
dienes,12 respectively. On the basis of these observations,
pentaphenyl-2-aza-1,4-diene 19 was selected for our
initial studies. Acetophenone, triplet-sensitized irradia-
tion of (E)-1 in CH2Cl2 for 25 min, followed by column
chromatography on silica gel, affords propenylamine 4
(82%), resulting from hydrolysis of the starting material.
In addition, two new products, identified as cyclopropy-
lamine 5 (11%) and vinylaziridine 3 (3%), are formed in
this process (Scheme 1). The former substance arises by
hydrolysis of cyclopropylimine 2 during chromatography.
The identity of 5 was established by use of spectroscopic
methods while unambiguous structure assignment of 3
was made by using X-ray diffraction analysis.9
Direct irradiation of (E)-1 in CH2Cl2 for 10 h by use of
Pyrex filtered light (λ >290 nm), followed by column
chromatography on silica gel, affords propenylamine 4
(82%) and 5 (4%). The direct irradiation reaction is
qualitatively less efficient than the triplet-sensitized
process. In addition, the direct irradiation photoreaction
of 1 is quenched by 1,3-cyclooctadiene, suggesting that
it also occurs via the triplet excited-state manifold.
To determine the scope of this novel rearrangement
reaction, studies were extended to the 2-azadienes 9a and
9b. Compound 9a was prepared by condensation of amine
10a with benzaldehyde. Compound 10a was synthesized
starting with methyl 4,4-diphenyl-3-butenoate14 by using
standard procedures. The synthesis of 9b has been
described previously.9 m-Methoxyacetophenone-sensi-
tized irradiation of (E)-9a in t-BuOH for 6 h, followed by
column chromatography on silica gel, affords amine 10a
(81%), resulting from hydrolysis of the starting material,
and cyclopropylimine (E)-11a (5%) (Scheme 3). Irradia-
tion of (1E,4Z)-9b for 9.5 h, using m-methoxyacetophe-
none as sensitizer, followed by column chromatography
on silica gel, affords amine 10b (78%), as a 3:2 mixture
of Z:E diastereoisomers, and cyclopropylimine 11b (4%),
The production of 2 and 3 in this photoreaction is in
accord with the operation of a mechanistic pathway,
involving generation and competitive cleavage of aziri-
dinyl-dicarbinyl biradical 6 (Scheme 2). Thus, the major
photoproduct 2 is formed by C-N bond cleavage in 6,
(7) (a) Recent studies carried out by us show that 1-aza-1,4-dienes
also undergo SET-sensitized 1-ADPM rearrangements (refs 7b and 7c).
(b) Ortiz, M. J .; Agarrabeitia, A. R.; Aparicio-Lara, S.; Armesto, D.
Tetrahedron Lett. 1999, 40, 1759-1762. (c) Armesto, D.; Ortiz, M. J .;
Agarrabeitia, A. R.; Aparicio-Lara, S.; Martin-Fontecha, M.; Liras, M.;
Martinez-Alcazar, M. P. J . Org. Chem. 2002, 67, 9397-9405.
(8) (a) Within this area of SET-promoted di-π-methane rearrange-
ments, we have described recently the first examples of 1-ADPM and
DPM rearrangements that take place via radical-anion intermediates
(ref 8b). (b) Armesto, D.; Ortiz, M. J .; Agarrabeitia, A. R.; Martin-
Fontecha, M. J . Am. Chem. Soc. 2001, 123, 9920-9921.
(9) Armesto, D.; Caballero, O.; Amador, U. J . Am. Chem. Soc. 1997,
119, 12659-12660.
(10) Zimmerman, H. E.; Boetcher, R. J .; Braig, W. J . Am. Chem.
Soc. 1973, 95, 5, 2155-2163.
(11) Armesto, D.; Ortiz, M. J .; Romano, S.; Agarrabeitia, A. R.;
Gallego, M. G.; Ramos, A. J . Org. Chem. 1996, 61, 1459-1466.
(12) Armesto, D.; Horspool, W. M.; Langa, F.; Ramos, A. J . Chem.
Soc., Perkin Trans. 1 1991, 223-228.
(13) (a) Previous attempts by Adam et al. (ref 13b) to promote the
formation of oxiranes by the DPM rearrangement were unsuccessful.
(b) Adam, W.; Berkessel, A.; Krimm, S. J . Am. Chem. Soc. 1986, 108,
4556-4561.
(14) J ohnson, W. S.; Petersen, J . W.; Scheneider, W. P. J . Am. Chem.
Soc. 1947, 69, 74-79.
6662 J . Org. Chem., Vol. 68, No. 17, 2003

Novel Photoreactions of 2-Aza-1,4-dienes
SCHEME 3
SCHEME 5
SCHEME 4
hyde. m-Methoxyacetophenone sensitized irradiation of
(E)-17 in t-BuOH, for 3.5 h, after column chromatography
on silica gel, affords amine 18 (71%), cyclopropylamine
20 (12%), and a new, as of yet unidentified, compound
(10%).18 Amines 18 and 20 result from hydrolysis of the
starting material 17 and the 2-ADPM product 19, re-
spectively, during chromatography (Scheme 5). The
identity of 20 was established by comparison of its
spectral data with those reported for related com-
pounds.11,17 Again, the corresponding N-vinylaziridine
was not formed in this photoreaction.
The results obtained from our studies of triplet-
sensitized irradiations of 1, 9a , 9b, and 17 indicate that
the 2-ADPM rearrangement process occurs in low yields
on a number of differently substituted 2-azadienes.
Attempts to increase the chemical efficiencies of these
reactions have not been successful. Prolonged irradiation
results in destruction of the starting materials and
photoproducts. The corresponding regioisomeric product,
N-vinylaziridine 3, is formed only in the photoreaction
of 1. The reasons for the high regioselectivities of these
processes are still unclear, but it is obvious that dimethyl
substitution at the methane carbon in the 2-aza-1,4-diene
system suppresses the formation of the corresponding
N-vinylaziridines. This observation supports the idea that
nonstabilized zwitterions that could be formed in these
instances probably decompose to a complex mixture of
products, instead of undergoing cyclization to the corre-
sponding aziridines.
as a 3:2 mixture of (Zcyclo,EC-N):(Ecyclo,EC-N) diastereoiso-
mers (Scheme 3).15
The corresponding N-vinylaziridines are not produced
in the two photoreactions. These results, particularly in
the case of 9b, are surprising because it is anticipated
that competitive ring opening of a triplet aziridinyl-
dicarbinyl biradical intermediate 12 would afford com-
parably stable triplet 1,3-birradicals 13 and 14, the
respective precursors of 11b and aziridine 16 (Scheme
4). Intersystem crossing in 13 would afford a singlet
biradical that cyclizes to form cyclopropylimine 11b (path
a) while intersystem crossing within biradical 14 would
yield the zwitterionic intermediate 15 (path b). The latter
intermediate is not stabilized by phenyl substitution, as
in the case of 8 (Scheme 2). Literature precedents16 show
that nonstabilized 1,3-dipolar intermediates similar to
15 do not cyclize to three-membered heterocycles but
rather undergo different reactions including 1,4-hydrogen
migration to yield enamines, which could undergo hy-
drolysis during isolation to produce a complex mixture
of products. This interpretation is speculative and ad-
ditional studies are required to establish its accuracy.
In our preliminary communication we reported the lack
of 2-ADPM reactivity in the triplet-sensitized irradiation
of compound 21a .9 Thus, m-methoxyacetophenone-sen-
sitized irradiation of (E)-21a , after column chromatog-
raphy on silica gel, affords amine 22 (66%), resulting from
hydrolysis of the starting imine, along with a complex
mixture of products. However, a more careful examina-
tion of the fractions obtained from the chromatography
allowed us to isolate a new product in 6% yield, whose
spectral and analytical properties are consistent with
structure 23a (Scheme 6). To confirm this structural
assignment, compound (E)-21b was irradiated under the
same conditions used for 21a , for one third of the time,
affording, after column chromatography on silica gel,
amine 22 (43%), compound 23b (16%), and recovered
starting material (E)-21b in 16% yield (Scheme 6).
The study was extended to the azadiene 17, which has
a substitution pattern that is observed to promote ef-
ficient 1-ADPM rearrangement of an 1-aza-1,4-diene
analog17 and ODPM of a â,γ-unsaturated aldehyde ana-
logue.11 The synthesis of 17 was achieved by condensation
of amine 18, obtained from â-tetralone, with benzalde-
(15) This compound was reported as unreactive in the 2-ADPM mode
in a preliminary communication (ref 9). In this experiment CH2Cl2 was
used as solvent. However, when the reaction was repeated in t-BuOH
the cyclopropylimine 11b was isolated in low yield.
(16) (a) Grigg, R.; Thornton-Pett, M.; Yoganathan, G. Tetrahedron
1999, 55, 1763-1780. (b) Pearson, W. H.; Clark, R. B. Tetrahedron
Lett. 1999, 40, 4467-4471.
(17) Armesto, D.; Ortiz, M. J .; Ramos, A.; Horspool, W. M.; Mayoral,
E. P. J . Org. Chem. 1994, 59, 8115-8124.
(18) At this point it is not possible to establish the structure of the
minor product based on spectroscopic evidence. Our aim is to obtain a
crystalline sample that would permit us to determine its structure by
X-ray diffraction analysis.
J . Org. Chem, Vol. 68, No. 17, 2003 6663

Armesto et al.
SCHEME 6
tion efficiencies. However, the situation is opposite for
the 2-ADPM process. Thus, while the dimethyl-substi-
tuted 2-azadienes 9a and 9b undergo the 2-ADPM
rearrangement to afford the corresponding cyclopropy-
limines 11a and 11b (Scheme 3), the diisopropyl-
substituted azadiene 25 does not react by this mode.
Compound 23b was crystallized from hexane and its
structure was determined by X-ray diffraction analysis.19
It is difficult to envisage how 23 are formed as primary
products from photoreaction of azadienes 21. An alterna-
tive possibility is that 23 is produced by secondary ring
expansion reactions (e.g., vinylcyclopropane rearrange-
ment)20 of the initially formed cyclopropylimines 24,
the initial 2-ADPM rearrangement products, in the
photolysis medium or upon chromatographic separation
(Scheme 6).
Several features of the 2-ADPM rearrangement make
it different from the DPM, ODPM, and 1-ADPM versions
studied previously. This is clearly demonstrated by the
results obtained in studies with the 2-azadiene 25,
bearing diisopropyl substitution at the central carbon,
and the ketoimines 26a and 26b. Azadiene 25 was
prepared by condensation of the corresponding amine
with benzaldehyde while 26a and 26b were derived by
using two-step sequences starting with the respective
azadienes 9a and 9b. Triplet-sensitized irradiation of 25
and 26a -b, followed by column chromatography on silica
gel, gave the amines resulting from hydrolysis of the
starting materials and a complex mixture of products,
in which the cyclopropylimines or N-vinylaziridines were
not present. The lack of 2-ADPM reactivity of 25 is
surprising since previous studies on the DPM21 and
ODPM22 rearrangement processes have shown that re-
placement of two methyl groups at the methane carbon
by two isopropyl groups significantly increases the reac-
The lack of reactivity of ketoimines 26a -b is also
surprising, considering the fact that the aziridinyl di-
carbinyl biradical intermediates 27 should either have
comparable or greater stability than the corresponding
intermediates derived from aldimines 9. The absence of
2-ADPM products in the photoreaction of ketoimines 26
could be due to the presence of two phenyl rings at C-1
of the azadiene system that favor preferential ring
opening of the aziridinyl intermediates 27 by breaking
bond b to afford 1,3-biradicals 28. Intersystem crossing
in 28 would give azomethine ylide intermediates 29 that
could decompose to a mixture of products, instead of
undergoing cyclization to the corresponding vinylaziri-
dines.
In summary, the results obtained from investigations
of the triplet-sensitized photochemistry of a series of
2-aza-1,4-dienes have uncovered the first examples of
2-ADPM rearrangements yielding cyclopropylimines. In
the case of azadiene 1, N-vinylaziridine 3 was also
obtained in the first example of a di-π-methane rear-
rangement that yields a heterocyclic product. Azadienes
21 afford spirodihydropyrrols 23 that probably result
from a spontaneous vinylcyclopropane rearrangement of
the initially formed cyclopropylimines 24. The studies
have demonstrated that features of the 2-ADPM rear-
rangement make it different from the other versions of
the rearrangement previously described. Further studies
are needed to understand the mechanistic aspects of
the 2-ADPM rearrangement and the factors that control
how substituents affect the nature of the reaction.
Finally, although the isolated yields of products in these
reactions are low, better estimates of the chemical
efficiencies of these reactions are obtained when product
yields are calculated based on converted starting materi-
als (Table 1).
(19) X-ray data of 23b: crystallized from hexane; C25H20N2 (Mr
)
348.43); monoclinic; space group P2(1)/c; a ) 11.692(2) Å, b ) 20.932-
(3) Å, c ) 8.007(1) Å, â ) 102.600(3)°; V ) 1912.4(4) Å3; Z ) 4; dc )
1.210 mg‚m-3; µ ) 0.071 mm-1; F(000) ) 736. A transparent crystal
of 0.3 × 0.3 × 0.3 mm3 was used; 9902 reflections were measured on
a Bruker Smart CCD diffractometer, 3357 independent reflections
[R(int)) 0.06]. The structure was solved by direct methods and Fourier
synthesis. The refinement was done by full-matrix least-squares
procedures on F2 (SHELXTL version 5.1). The non-hydrogen atoms
were refined anisotropically. The hydrogen atoms were included in
calculated positions, R1 ) 0.047 for 1429 observed reflections and wR2
) 0.134 (all data). Further crystallographic details for the structure
reported in this paper may be obtained from the Cambridge Crystal-
lographic Data Center, 12 Union Road, Cambridge CB2 1EZ, U.K.;
depository no. CCDC-198688.
(20) For reviews see: (a) Hudlicky, T.; Reed, J . W. In Comprehensive
Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon: Oxford,
UK, 1991; Vol. 5, pp 899-970. (b) Wong, H. N. C.; Hon, M.-Y.; Tse,
C.-W.; Yip, Y.-C.; Tanko, J .; Hudlicky, T. Chem. Rev. 1989, 89, 165-
198. (c) Goldschmidt, Z.; Crammer, B. Chem. Soc. Rev. 1988, 17, 229-
267. (d) Hudlicky, T.; Kutchan, T. M.; Naqvi, S. M. Org. React. 1985,
33, 247-335.
(21) Zimmerman, H. E.; Schissel, D. N. J . Org. Chem. 1986, 51, 196-
207.
(22) Zimmerman, H. E.; Cassel, J . M. J . Org. Chem. 1989, 54, 3800-
3816.
SET-Sen sitized Ir r a d ia tion of 2-Aza -1,4-d ien es. To
gain a more complete understanding of the photoreac-
tivity of 2-aza-1,4-dienes, we have subjected substances
in this family to 9,10-dicyanoanthracene (DCA) electron-
6664 J . Org. Chem., Vol. 68, No. 17, 2003

Novel Photoreactions of 2-Aza-1,4-dienes
TABLE 1. Rea ction Con d ition s a n d Yield s of P r od u cts Ba sed on Con ver ted Sta r tin g Ma ter ia l (SM) in th e Tr ip let- a n d
DCA-Sen sitized Ir r a d ia tion of 2-Aza -1,4-d ien es
2-ADPM
cyclopropanes
(yield, %)
2-ADPM
aziridines
(yield, %)
other
products
(yield, %)
converted
SM (%)
compd
irra. time
sens.
1
9a
9b
17
21a
21b
1
9b
21a
25
25 min
6 h
9.5 h
3.5 h
10 h
3 h
30 min
2 h
triplet
triplet
triplet
triplet
triplet
triplet
DCA
DCA
DCA
DCA
DCA
2 (61)a
11a (26)
11b (18)
19a(41)
3 (16)
(18)a
(19)a
(22)a
(29)a
(34)a
(41)b
(59)a
(44)a
(57)a
(45)a
(67)b
(89)a
(33)a
23a (18)
23b (39)
37a (32)
3 (19)
39a (11)
41 (42)
39b (31)
1 h
42 (28)
15 min
10 min
40 min
12 min
26a
26b
40
45a (82)
45b (80)
DCA
DCA
39c (40)
a
Isolated as the corresponding amine. b Isolated as a mixture of starting azadiene and the corresponding amine resulting from hydrolysis.
SCHEME 7
electron transfer and biradical cyclization yields 3. The
alternative ring opening of 33, by path b, which would
have produced the corresponding cyclopropylimine, does
not occur, perhaps because the intermediate radical-
cation 36 is less stable than 34. A competitive route
involving phenyl migration in 32 generates cation-
radical 35, the precursor of 37 (Scheme 7). The 1,2-phenyl
shift in 32 is probably promoted by the greater degree of
stabilization of the radical-cation intermediate 35.
To our knowledge, these reactions represent the first
examples of SET-promoted rearrangements in 1,4-
unsaturated systems (a 2-ADPM reaction generating 3
and an aryl-di-π-methane rearrangement yielding 37)
that afford three-membered-ring products.7-9 Of equal
interest is the fact that the same vinylaziridine 3 is
obtained in both the triplet- and SET-sensitized photo-
reactions of 1. The formation of 37 in this reaction
suggests that DPM rearrangements of other allylbenzene
derivatives and 1,4-dienes could also occur via radical-
cation intermediates.
This study was extended to azadienes 9a , 9b, 17, and
25. DCA-sensitized irradiation of azadiene (E)-9a under
the conditions used for compound 1 for 15 min, followed
by chromatography, gave amine 10a (79%), resulting
from hydrolysis of the starting material, and a complex
mixture of products in which the corresponding viny-
acceptor sensitized photoreactions. Previous studies by
Zimmerman and Hoffacker23 have shown that aryl-
substituted 1,4-pentadienes 30 do not undergo DCA-
sensitized DPM rearrangement reactions but, rather they
are transformed to the corresponding dihydronaphtha-
lenes 31 under these conditions.
Irradiation of azadiene (E)-1 in acetonitrile for 30 min,
using DCA as a sensitizer and biphenyl as a cosensitizer,
followed by column chromatography on silica gel, yields
propenylamine 4 (41%), vinylaziridine 3 (11%), and a new
cyclopropylamine 38 (19%) resulting from the hydrolysis
of imine 37 (Scheme 7). The identity of 38 was estab-
lished by using spectroscopic methods.
1
laziridine was not present (by H NMR analysis). The
use of longer irradiation times results in the complete
consumption of the starting material. Irradiation of
(1E,4Z)-9b for 2 h, following column chromatography on
silica gel, affords N-vinylaziridine 39a (5%), as a 2:1
mixture of Z:E isomers, and amine 10b (56%), as a 7:3
mixture of Z:E diastereoisomers. Irradiation of (E)-25 for
15 min under the above conditions yields the correspond-
ing N-vinylaziridine 39b (14%) and amine 10c (55%)
(Scheme 8). However, DCA-sensitized irradiation of (E)-
17 for 90 min gave, after column chromatography on
silica gel, 1-methyl-1-naphthalen-2-yl-ethylamine (78%),
resulting from aromatization of the dihydronaphthalene
unit. This observation shows that oxidation of the dihy-
dronaphthalene moiety takes preference over the 2-ADPM
reaction.
The products generated in this photoreaction appear
to arise by a pathway in which an initially formed olefin-
localized cation-radical intermediate 32 bridges by C-N
bond formation to give aziridinyl cation-radical 33. Ring
opening in 33, by path a, generates 34, which by back
The results summarized above demonstrate that the
novel 2-ADPM rearrangement of 2-aza-1,4-dienes to form
N-vinylaziridines, occurring via radical-cation interme-
(23) Zimmerman, H. E.; Hoffacker, K. D. J . Org. Chem. 1996, 61,
6526-6534.
J . Org. Chem, Vol. 68, No. 17, 2003 6665

Armesto et al.
SCHEME 8
SCHEME 9
diates, is not restricted to 1 but can be extended to
azadienes 9b and 25. However, there are clear differences
between the 2-ADPM rearrangement in the triplet ex-
cited state and the corresponding reaction via radical-
cation intermediates. Probably the most significant of
these is the regiochemistry. Thus, while the triplet
reaction yields cyclopropylimines, SET-promoted rear-
rangement affords the corresponding N-vinylaziridines.
Although the reasons for the triplet regioselectivity are
still unclear, formation of the vinylaziridines can be easily
explained based on the differences in stability between
the two possible radical-cation intermediates resulting
from ring opening of the intermediate aziridinyl radical-
cation (Scheme 7). Another important difference has been
observed in the reactions of 9a and 25. Thus, while 9a
undergoes triplet 2-ADPM rearrangement in low yield,
the corresponding aziridine is not formed in its SET-
sensitized reaction. On the other hand, azadiene 25
reacts to produce aziridine 39b via radical-cation inter-
mediates but does not rearrange under triplet-sensitiza-
tion conditions. These results are difficult to interpret
at this point, but they clearly show that the structural
factors that control these two reactions are very different.
Attempts to uncover additional examples of the SET-
promoted 2-ADPM rearrangement led to studies with
azadienes 40, 21a , 21b, 26a , and 26b. Compound 40 was
obtained by condensation of amine 10d with benzalde-
hyde by standard procedures. DCA-sensitized irradiation
of (E)-40 for 12 min, followed by column chromatography
on silica gel, yields N-vinylaziridine 39c (13%), prope-
nylamine 10d (67%), arising by hydrolysis of the starting
material, and an unidentified24 minor product (ca. 4%)
that is isomeric with the starting material (Scheme 8).
Irradiation of (E)-21a for 1 h, under the above condi-
tions, followed by column chromatography on silica gel,
leads to N-vinylaziridine 41 (24%), amine 22 (43%), and
a new compound (16%), identified as dihydroisoquinoline
42 (Scheme 9). The latter product is formed by electro-
philic addition of the olefin-localized radical-cation 43
on the phenyl ring at C-1 yielding intermediate 44, the
precursor of 42 (Scheme 9). This cyclization process is
similar to the one observed by Zimmerman and Hoffacker
in their study of the DCA-sensitized irradiation of aryl-
substituted 1,4-pentadienes 30.23 However, irradiation of
(E)-21b for 35 min, under the same conditions used for
21a , after column chromatography, affords amine 22
SCHEME 10
(70%) and recovered starting material (E)-21b in 10%
yield, along with a complex mixture of products in which
the corresponding N-vinylaziridine and the dihydroiso-
quinoline are not present. Although not completely
understood, the lack of 2-ADPM reactivity of 21b could
be due to the fact that the p-cyano substituent reduces
the nucleophilicity of the imine moiety. As a result, an
initially formed cation-radical related to 43 (Scheme 9)
would not be able to participate in C-N or C-C bonding
by nucleophilic addition of either the nitrogen or aryl
centers.
Finally, irradiation of compounds 26a and 26b under
the SET-sensitized conditions for short time periods
affords the respective amines 10a and 10b and the
corresponding dihydrobenzoazepines 45a and 45b, re-
spectively, in good isolated yields (Scheme 10). The fact
that the corresponding N-vinylaziridines are not gener-
ated in these processes shows that diphenyl substitution
at C-1 in ketoimines 26 allows an alternative dihy-
drobenzoazepine forming cyclization to occur in prefer-
ence to 2-ADPM rearrangement.
The formation of 45 is consistent with a mechanism
involving the generation of an imine-localized radical-
cation 46 that reacts to yield 47, the precursor of 45, by
electrophilic attack on the phenyl ring at C-5 (Scheme
10). The high product yields obtained in the DCA-
sensitized irradiation of 26 suggest that this process
might be applicable to the synthesis of dihydroben-
zoazepines from â,γ-unsaturated ketoimines.
The yields of vinylaziridine photoproducts obtained in
the SET-sensitized irradiation of 2-azadienes are usually
low. Attempts to increase the yield of products by
prolonged irradiation resulted in destruction of the
(24) This minor photoproduct proved to be isomeric with the starting
material. However, at this point it is not possible to establish its
structure based on spectroscopic evidence. Our aim is to obtain a
crystalline sample that would permit us to determine its structure by
X-ray diffraction analysis. The triplet-sensitized photoreactivity of 40
was also explored. 1H NMR analysis of the photomixture indicates the
presence of two cyclopropane derivatives. However, all the attempts
to isolate them resulted in decomposition of the photoproducts. No
N-vinylaziridine was detected in this instance.
6666 J . Org. Chem., Vol. 68, No. 17, 2003

Novel Photoreactions of 2-Aza-1,4-dienes
starting materials and photoproducts. However, a better
estimation of the chemical efficiency of these reactions
is obtained when the yield of products is calculated based
on converted starting material (Table 1). Attempts have
been made to increase them by using longer irradiation
times but without success.
Exp er im en ta l Section
Azadienes 1,9 9b,9 and 21a 9 were synthesized by the
methods previously described.
Gen er a l P r oced u r e for th e Syn th esis of Aza d ien es 9a ,
17, 21b, 25, a n d 40. These azadienes were synthesized from
the corresponding â,γ-unsaturated esters by a procedure
consisting of hydrolysis, transformation into the acid chloride,
Curtius reaction, and condensation of the corresponding
amines with benzaldehyde or p-cyanobenzaldehyde, according
to the following general procedures. When describing the
experimental procedure below for individual products, a
further reference to the general procedure is not always given.
Hyd r olysis of â,γ-u n sa tu r a ted ester s: A solution of KOH
and the ester in dry EtOH was refluxed for different times
(for specific cases, see below). The ester/KOH ratio was 1:3
for all experiments. The solvent was evaporated to dryness,
and the residue was dissolved in water. The aq solution was
extracted with Et2O to remove unreacted starting material and
the aq layer was acidified with a 20% aq HCl solution and
extracted with Et2O. The organic phases were dried (MgSO4),
filtered, and evaporated to dryness. The â,γ-unsaturated acids
were purified by flash chromatography on silica gel, using
hexane/Et2O (7:3) as eluent.
The results obtained from studies of the SET-sensitized
irradiation of azadienes 21a and 26 demonstrate that in
addition to the 2-ADPM rearrangement to N-vinylaziri-
dines, alternative cyclization paths are open to the
radical-cation intermediates, yielding dihydroisoquino-
lines and dihydrobenzoazepines, respectively. Further
studies are needed to determine if it is possible to control
the outcome of the photoreactions by modifying the
substituents present on the 2-azadiene’s skeleton. Some-
thing worth noting in regard to the formation of com-
pounds 42 and 45 is that, while dihydroisoquinoline 42
results from a radical-cation centered in the alkene unit,
compounds 45 are formed from radical-cations centered
in the imine moiety. This is somewhat surprising and
demonstrates that two different radical-cation interme-
diates can be generated from the alkene and imine
functional groups, which have different ionization po-
tentials. A similar situation has been observed in our
studies of the SET-sensitized photochemistry of 1-aza-
1,4-dienes.7c
Tr a n sfor m a tion of â,γ-u n sa tu r a ted a cid s in to th e a cid
ch lor id es: The corresponding â,γ-unsaturated acid and SOCl2
were heated at reflux for different times (for specific cases,
see below). The acid/SOCl2 ratio was 1:1.5 for all experiments.
The residual SOCl2 was removed under reduced pressure
yielding the corresponding acid chloride, which was used
without further purification.
Cu r tiu s r ea ction : A solution of the corresponding acid
chloride in CH2Cl2 containing tetrabutylammonium bromide
was cooled in an ice bath. Sodium azide dissolved in water
was added and the reaction mixture was stirred vigorously at
0 °C for 2 h. The acid chloride/sodium azide ratio was 1:1.2
for all experiments. The organic layer was separated, washed
with H2O, dried (MgSO4), filtered, and evaporated to dryness.
A solution of acylazide in toluene under argon was refluxed
for different times (for specific cases, see below). The solvent
was evaporated to dryness yielding the corresponding isocy-
anate, which was used without further purification. A solution
of 8 M HCl and the isocyanate was refluxed for different times
(for specific cases, see below). The mixture was extracted with
Et2O and the aq layer was neutralized with a 10% aq NaOH
solution and extracted with Et2O. The organics layers were
separated, washed with H2O, dried (MgSO4), filtered, and
evaporated to dryness. The amine was purified by distillation.
Con d en sa tion of a m in es w ith ben za ld eh yd e or p-
cya n oben za ld eh yd e: A solution of the corresponding amine
and aldehyde in anhyd Et2O was refluxed for different times
(for specific cases, see below). The amine/aldehyde ratio was
1:1 for all experiments. The solvent was evaporated and the
imine was purified by recrystallization or by distillation.
3,3-Dim eth yl-1,5,5-tr ip h en yl-2-a za -1,4-p en ta d ien e (9a ).
Compound 9a was synthesized from methyl 2,2-dimethyl-4,4-
diphenyl-3-butenoate. This ester was converted into the cor-
responding acid chloride by the method previously described.7c
2,2-Dimethyl-4,4-diphenyl-3-butenoyl chloride (4.81 g, 17 mmol),
tetrabutylammonium bromide (0.02 g, 0.05 mmol) in CH2Cl2
(100 mL), and sodium azide (1.34 g, 20.6 mmol) in water (19
mL) yielded 2,2-d im et h yl-4,4-d ip h en yl-3-b u t en oyla zid e
Con clu sion s
In summary, the results outlined above clearly dem-
onstrate that 2-aza-1,4-dienes undergo novel photochemi-
cal reactions. Our studies of the triplet-sensitized pho-
toreactions of these compounds have led us to uncover
the first examples of 2-ADPM rearrangements that yield
cyclopropylimines. In the case of azadiene 1, the reaction
also affords N-vinylaziridine 3, representing the first
example of a di-π-methane rearrangement that yields a
three-membered heterocyclic photoproduct. However,
azadienes containing a substitution pattern that has been
demonstrated to promote efficient DPM, ODPM, and
1-ADPM reactions do not undergo the 2-ADPM rear-
rangement. This result shows that the structural factors
that control the former reactions do not govern the latter
process. A possible reason for this difference might reside
in the unique involvement of azomethine ylides in the
2-ADPM rearrangement.
A more significant conclusion of this study is that
2-ADPM rearrangements can also take place under SET-
sensitized irradiation conditions to generate N-vinylaziri-
dines regioselectively. In the case of azadiene 1, cyclo-
propylimine 37, resulting from an aryl-di-π-methane
reaction via a radical-cation intermediate, is observed.
An alternative cyclization mode has been detected with
azadiene 21a yielding the corresponding dihydroiso-
quinoline 42. Ketoimines 26 do not undergo the 2-ADPM
rearrangement. Rather, these substances react to pro-
duce the corresponding dihydrobenzoazepines 45 in good
yield. It is our belief that the results coming from these
studies have led to new views of an old but still important
photochemical rearrangement process. Further work is
in progress to determine the scope, synthetic applications,
and mechanistic aspects of these reactions.
(4.9 g) as a yellow oil; IR (neat) ν 2135, 1714 cm-1
.
2,2-Dimethyl-4,4-diphenyl-3-butenoylazide (4.9 g, 17 mmol)
in toluene (30 mL) was refluxed for 4 h yielding 1,1-d im eth yl-
3,3-d ip h en yl-2-p r op en yl isocya n a te (4.9 g) as a yellow oil;
IR (neat) ν 2260 cm-1
.
1,1-Dimethyl-3,3-diphenyl-2-propenyl isocyanate (4.9 g, 17
mmol) and 8 M HCl (60 mL) were refluxed for 4 h yielding
1,1-d im eth yl-3,3-d ip h en yl-2-p r op en yla m in e (10a ) (2.77 g,
1
69%) as an oil: bp 110 °C (0.2 mbar); H NMR (300 MHz) δ
7.40-7.18 (m, 10H), 6.24 (s, 1H), 2.44 (br s, 2H), 1.23 (s, 6H);
13C NMR (63 MHz) δ 143.5-127.0, 51.8, 32.6; IR (neat) ν 3440
J . Org. Chem, Vol. 68, No. 17, 2003 6667

Armesto et al.
cm-1; MS m/e (%) 237 (M+, 6), 222 (100), 205 (15), 178 (8), 165
(8), 77 (11), 58 (32).
31.0, 19.4, 18.7; IR (KBr) ν 3058, 1687 cm-1; MS m/e (%) 322
(M+, 4), 279 (100), 251 (23), 233 (88), 219 (28), 191 (35), 178
(10), 165 (10), 91 (24). Anal. Calcd for C22H26O2: C, 81.99; H,
8.07. Found: C, 82.19; H, 8.33.
Compound 10a (1.13 g, 4.8 mmol) and benzaldehyde (0.5 g,
4.8 mmol) in anhyd Et2O (35 mL) were refluxed for 10 h
yielding (E)-3,3-d im eth yl-1,5,5-tr ip h en yl-2-a za -1,4-p en ta -
d ien e (9a ) (1.24 g, 80%) as a white solid: mp 78-79 °C
(hexane); 1H NMR (300 MHz) δ 8.21 (s, 1H), 7.62-7.13 (m,
15H), 6.26 (s, 1H), 1.31 (s, 6H); 13C NMR (63 MHz) δ 156.9,
143.7-126.9, 62.0, 30.0; IR (neat) ν 1635 cm-1; UV (CH2Cl2)
2,2-Diisopropyl-4,4-diphenyl-3-butenoic acid (0.88 g, 2.7
mmol) and SOCl2 (0.49 g, 4.1 mmol) were refluxed for 1 h
yielding 0.93 g of a 1:1 mixture of 2,2-d iisop r op yl-4,4-
d ip h en yl-3-bu ten oyl ch lor id e and 2,2-diisopropyl-4-phenyl-
1
2H-naphthalen-1-one, as a yellow oil; H NMR (300 MHz) δ
λ
max 247 (ꢀ 25 185); MS m/e (%) 325 (M+, 9), 310 (7), 269 (100),
8.12-7.13 (m, 10H), 6.23 (s, 0.5H), 6.00 (s, 0.5H), 2.40-2.15
221 (41), 191 (44), 143 (56), 91 (70), 77 (30), 51 (24). Anal. Calcd
for C24H23N: C, 88.57; H, 7.13; N, 4.31. Found: C, 88.82; H,
7.23; N, 4.14.
(m, 2H), 0.96-0.87 (m, 12H).
The mixture of 2,2-diisopropyl-4,4-diphenyl-3-butenoyl chlo-
ride and 2,2-diisopropyl-4-phenyl-2H-naphthalen-1-one (0.93
g), tetrabutylammonium bromide (3 mg, 0.01 mmol) in CH2-
Cl2 (13 mL), and sodium azide (0.22 g, 3.3 mmol) in water (2
mL) yielded 0.93 g of a 1:1 mixture of 2,2-d iisop r op yl-4,4-
d ip h en yl-3-bu ten oyla zid e and 2,2-diisopropyl-4-phenyl-2H-
naphthalen-1-one, as a yellow oil; IR (neat) ν 2131, 1695, 1662
3-(3,4-Dih yd r o-2-n a p h t h a len yl)-3-m et h yl-1-p h en yl-2-
a za -1-bu ten e (17). Compound 17 was synthesized from ethyl
2-(3,4-dihydro-2-naphthalenyl)-2-methylpropanoate.25 This es-
ter was converted into the corresponding acid chloride by the
method previously described.17 2-(3,4-Dihydro-2-naphthalenyl)-
2-methylpropanoyl chloride (2.1 g, 8.9 mmol), tetrabutylam-
monium bromide (9 mg, 0.03 mmol) in CH2Cl2 (30 mL), and
sodium azide (0.7 g, 10.8 mmol) in water (6 mL) yielded 2-(3,4-
d ih yd r o-2-n a p h th a len yl)-2-m eth ylp r op a n oyla zid e (2.12
cm-1
.
2,2-Diisopropyl-4,4-diphenyl-3-butenoylazide and 2,2-diiso-
propyl-4-phenyl-2H-naphthalen-1-one (0.93 g) in toluene (20
mL) were refluxed for 4 h yielding 0.85 g of a 1:1 mixture of
1,1-d iisop r op yl-3,3-d ip h en yl-2-p r op en yl isocya n a te and
2,2-diisopropyl-4-phenyl-2H-naphthalen-1-one, as a yellow oil;
g) as a yellow oil; IR (neat) ν 2133, 1709 cm-1
.
2-(3,4-Dihydro-2-naphthalenyl)-2-methylpropanoylazide (2.12
g, 8.8 mmol) in toluene (15 mL) was refluxed for 4 h yielding
2-(3,4-d ih yd r o-2-n a p h th a len yl)-2-m eth yleth yl isocya n a te
IR (neat) ν 2275, 1662 cm-1
.
1,1-Diisopropyl-3,3-diphenyl-2-propenyl isocyanate and 2,2-
diisopropyl-4-phenyl-2H-naphthalen-1-one (0.85 g) in 8 M HCl
(25 mL) were refluxed for 30 min. The mixture was extracted
with Et2O and the organic layer was washed with H2O, dried
(MgSO4), filtered, and evaporated to dryness yielding 2,2-
diisopropyl-4-phenyl-2H-naphthalen-1-one (0.4 g, 49%) as an
oil. The aq layer was neutralized with a 10% aq NaOH solution
and extracted with Et2O. The organics layers were separated,
washed with H2O, dried (MgSO4), filtered, and evaporated to
dryness yielding 1,1-d iisop r op yl-3,3-d ip h en yl-2-p r op en y-
la m in e (10c) (0.35 g, 44%) as an oil. 2,2-Diisop r op yl-4-
p h en yl-2H-n a p h th a len -1-on e: 1H NMR (200 MHz) δ 8.12-
7.90 (m, 1H), 7.52-7.13 (m, 8H), 6.00 (s, 1H), 2.34 (sept, J )
7.0 Hz, 2H), 0.94 (d, J ) 7.0 Hz, 6H), 0.89 (d, J ) 7.0 Hz, 6H);
13C NMR (50 MHz) δ 203.3, 140.0-126.4, 58.5, 34.1, 17.3, 17.2;
IR (neat) ν 1662 cm-1; MS m/e (%) 304 (M+, 3), 276 (3), 262
(100), 247 (61), 215 (13), 202 (23), 178 (6), 165 (7), 91 (7). 10c:
1H NMR (200 MHz) δ 7.40-7.15 (m, 10H), 5.95 (s, 1H), 1.87
(sept, J ) 6.8 Hz, 2H), 0.99 (d, J ) 6.9 Hz, 6H), 0.91 (d, J )
6.7 Hz, 6H); 13C NMR (50 MHz) δ 144.1-126.7, 63.1, 34.8, 18.0,
16.8; IR (neat) ν 3400, 3350 cm-1; MS m/e (ESI) 294 (M + 1),
207, 178, 129.
Compound 10c (0.35 g, 1.2 mmol) and benzaldehyde (0.13
g, 1.19 mmol) in anhyd Et2O (25 mL) were refluxed for 10 h
yielding (E)-3,3-d iisop r op yl-1,5,5-tr ip h en yl-2-a za -1,4-p en -
ta d ien e (25) (0.41 g, 90%) as an oil: bp 163 °C (0.05 mbar);
1H NMR (200 MHz) δ 8.01 (s, 1H), 7.27-7.11 (m, 15H), 6.10
(s, 1H), 2.32 (sept, J ) 6.7 Hz, 2H), 1.03 (d, J ) 6.6 Hz, 6H),
0.81 (d, J ) 6.6 Hz, 6H); 13C NMR (50 MHz) δ 154.7, 145.5-
125.5, 72.5, 31.9, 18.7, 17.1; IR (neat) ν 1645 cm-1; UV (CH2-
Cl2) λmax 248 (ꢀ 23 938); MS m/e (%) 381 (M+, <1), 338 (100),
294 (5), 233 (7), 218 (9), 203 (5), 191 (10), 165 (6), 115 (5), 91
(19).
(1.87 g) as a yellow oil; IR (neat) ν 2257 cm-1
.
2-(3,4-Dihydro-2-naphthalenyl)-2-methylethyl isocyanate (1.87
g, 8.8 mmol) and 8 M HCl (30 mL) were refluxed for 1.5 h
yielding 1-(3,4-d ih yd r o-2-n a p h t h a len yl)-1-m et h ylet h y-
la m in e (18) (1.28 g, 78%) as an oil; 1H NMR (300 MHz) δ
7.25-7.03 (m, 4H), 6.45 (s, 1H), 2.79 (t, J ) 8.0 Hz, 2H), 2.33
(t, J ) 8.0 Hz, 2H), 1.54 (br s, 2H), 1.31 (s, 6H); 13C NMR (75
MHz) δ 149.3-119.0, 53.0, 29.5, 28.7; IR (neat) ν 3360, 3290
cm-1
.
Compound 18 (0.3 g, 1.6 mmol) and benzaldehyde (0.17 g,
1.6 mmol) in anhyd Et2O (25 mL) were refluxed for 9 h yielding
(E)-3-(3,4-d ih yd r o-2-n a p h th a len yl)-3-m eth yl-1-p h en yl-2-
a za -1-bu ten e (17) (0.39 g, 89%) as an oil: bp 175 °C (0.4
mbar); 1H NMR (300 MHz) δ 8.33 (s, 1H), 7.78-7.75 (m, 2H),
7.42-7.40 (m, 3H), 7.20-7.08 (m, 4H), 6.52 (s, 1H), 2.77 (t, J
) 8.0 Hz, 2H), 2.26 (t, J ) 8.0 Hz, 2H), 1.50 (s, 6H); 13C NMR
(75 MHz) δ 158.1, 146.2-122.5, 63.8, 28.4, 27.3, 24.2; IR (neat)
ν 1640 cm-1; UV (CH2Cl2) λmax 247 (ꢀ 20 886); MS m/e (%) 275
(M+, 15), 260 (48), 219 (12), 171 (100), 155 (47), 141 (25), 129
(50), 115 (28), 106 (60), 91 (31), 77 (14).
1-(4-Cya n op h en yl)-4-(flu or en -9-ylid en )-3,3-d im eth yl-2-
a za -1-bu ten e (21b). 2-(Fluoren-9-yliden)-1,1-dimethylethy-
lamine9 (22) (0.33 g, 1.4 mmol) and p-cyanobenzaldehyde (0.18
g, 1.4 mmol) in anhyd Et2O (25 mL) were refluxed for 7 h
yielding (E)-1-(4-cya n op h en yl)-4-(flu or en -9-ylid en )-3,3-
d im eth yl-2-a za -1-bu ten e (21b) (0.29 g, 59%) as a white
solid: mp 134.5-135.5 °C (hexane); 1H NMR (300 MHz) δ 8.38
(s, 1H), 7.86-7.61 (m, 8H), 7.35-7.11 (m, 4H), 6.95 (s, 1H),
1.75 (s, 6H); 13C NMR (75 MHz) δ 157.8, 141.7-113.7, 61.8,
30.9; IR (KBr) ν 2240, 1640 cm-1; UV (CH2Cl2) λmax 258 (ꢀ 64
963); MS m/e (%) 348 (M+, 28), 292 (100), 219 (27), 165 (16),
129 (4), 115 (8). Anal. Calcd for C25H20N2: C, 86.17; H, 5.79;
N, 8.04. Found: C, 86.10; H, 5.73; N, 7.86.
3-Meth yl-1,3,5,5-tetr a p h en yl-2-a za -1,4-p en ta d ien e (40).
Compound 40 was synthesized from ethyl 2-methyl-2,4,4-
triphenyl-3-butenoate. This ester was obtained in three steps
from diethyl phenylmalonate according to the following pro-
cedure: to a solution of sodium ethoxide (3.6 g, 52.9 mmol) in
dry EtOH (30 mL) under argon was added diethyl phenylma-
lonate (6 g, 25.4 mmol) and MeI (4.33 g, 30.5 mmol). After
refluxing for 3 h, the solvent was evaporated to dryness and
the mixture was extracted with Et2O. The organic layer was
washed with H2O, dried (MgSO4), filtered, and evaporated to
dryness. The crude product was distilled under reduced
pressure yielding d ieth yl 2-m eth yl-2-p h en ylm a lon a te (5.14
3,3-Diisop r op yl-1,5,5-t r ip h en yl-2-a za -1,4-p en t a d ien e
(25). Compound 25 was synthesized from methyl 2,2-diiso-
propyl-4,4-diphenyl-3-butenoate, obtained by the method pre-
viously described for the corresponding ethyl ester.22 Methyl
2,2-diisopropyl-4,4-diphenyl-3-butenoate (1 g, 3 mmol) and 1
M t-BuOK in anhyd DMSO (45 mL) were heated for 30 min
at 100 °C yielding 2,2-d iisop r op yl-4,4-d ip h en yl-3-bu ten oic
a cid (0.72 g, 75%) as a white solid: mp 143-143.5 °C (hexane);
1H NMR (200 MHz) δ 7.34-7.16 (m, 10H), 6.15 (s, 1H), 2.21
(sept, J ) 6.8 Hz, 2H), 0.97 (d, J ) 6.8 Hz, 6H), 0.92 (d, J )
6.8 Hz, 6H); 13C NMR (50 MHz) δ 180.7, 145.4-126.8, 60.4,
1
g, 81%) as a yellow oil: bp 76 °C (0.05 mbar); H NMR (200
(25) Armesto, D.; Ramos, A. Tetrahedron 1993, 49, 7159-7168.
6668 J . Org. Chem., Vol. 68, No. 17, 2003
MHz) δ 7.41-7.23 (m, 5H), 4.22 (q, J ) 7.1 Hz, 4H), 1.86 (s,

Novel Photoreactions of 2-Aza-1,4-dienes
3H), 1.24 (t, J ) 7.1 Hz, 6H); 13C NMR (50 MHz) δ 171.5, 138.4,
128.1-127.4, 61.6, 58.8, 22.3, 13.9; IR (neat) ν 1732 cm-1; MS
m/e (%) 250 (M+, 29), 235 (3), 206 (4), 177 (100), 160 (8), 149
(43), 131 (45), 105 (25), 103 (39), 91 (24), 77 (23).
(%) 300 (M + 1, 17), 299 (M+, 67), 284 (100), 267 (19), 256
(22), 222 (74), 205 (14), 165 (16), 120 (40), 77 (18).
Compound 10d (0.12 g, 0.4 mmol) and benzaldehyde (0.04
g, 0.4 mmol) in anhyd Et2O (25 mL) were refluxed for 20 h
yielding (E)-3-m eth yl-1,3,5,5-tetr a p h en yl-2-a za -1,4-p en ta -
d ien e (40) (0.14 g, 90%) as an oil; 1H NMR (300 MHz) δ 8.29
(s, 1H), 7.70-7.68 (m, 2H), 7.45-7.09 (m, 16H), 6.95-6.92 (m,
2H), 6.56 (s, 1H), 1.51 (s, 3H); 13C NMR (75 MHz) δ 158.4,
148.1-126.3, 67.7, 30.3; IR (neat) ν 1643 cm-1; UV (CH2Cl2)
λmax 248 (ꢀ 28 639); MS m/e (%) 387 (M+, 15), 372 (3), 310 (5),
299 (3), 283 (19), 269 (100), 205 (57), 191 (49), 178 (11), 165
(20), 152 (9), 131 (64), 105 (18), 91 (30), 77 (17).
Gen er a l P r oced u r e for th e Syn th esis of Aza d ien es 26a
a n d 26b. Azadienes 26a and 26b were synthesized in two
steps from azadienes 9a and 9b, respectively, by a procedure
consisting of reaction of these imines with PhLi27 and oxidation
with the radical di-tert-butyliminoxyl,28 according to the fol-
lowing general procedures.
To a solution of 2-aza-1,4-diene in anhyd Et2O under argon
was added dropwise PhLi. The 2-aza-1,4-diene/PhLi ratio was
1:1.1 for all experiments. The resulting mixture was refluxed
for 6 h before quenching with H2O. The organic layer was
separated, washed with H2O, dried (MgSO4), filtered, and
evaporated under reduced pressure to give, after purification
by flash chromatography on silica gel with hexane/Et2O (99:
1), the corresponding amines.
To a solution of radical di-tert-butyliminoxyl in pentane
under argon was added the corresponding amine. The radical
di-tert-butyliminoxyl/amine ratio was 3:1 for all experiments.
The solution was stirred for 4 days at room temperature. The
solvent was evaporated to dryness and the crude product was
purified by recrystallization or by distillation.
3,3-Dim e t h yl-1,1,5,5-t e t r a p h e n yl-2-a za -1,4-p e n t a d i-
en e (26a ). (E)-3,3-Dimethyl-1,5,5-triphenyl-2-aza-1,4-penta-
diene (9a ) (0.92 g, 2.8 mmol) in anhyd Et2O (40 mL) and PhLi
(1.73 mL, 1.8 M in hexane) yielded N-ben zh yd r yl-1,1-
d im eth yl-3,3-d ip h en yl-2-p r op en yla m in e (0.58 g, 51%) as
an oil; 1H NMR (200 MHz) δ 7.41-6.93 (m, 20H), 6.10 (s, 1H),
5.04 (s, 1H), 1.58 (s, 1H), 1.00 (s, 6H); 13C NMR (50 MHz) δ
146.6-126.5, 62.5, 56.7, 30.0; IR (neat) ν 3350, 1596 cm-1; MS
m/e (%) 403 (M+, 1), 388 (42), 236 (30), 220 (55), 205 (100),
183 (21), 167 (70), 106 (87), 77 (28).
N-Benzhydryl-1,1-dimethyl-3,3-diphenyl-2-propenylamine
(0.55 g, 1.4 mmol) and radical di-tert-butyliminoxyl in pentane
(18 mL, 0.18 M) yielded 3,3-d im eth yl-1,1,5,5-tetr a p h en yl-
2-a za -1,4-p en ta d ien e (26a ) (0.4 g, 73%) as a white solid: mp
146-147 °C (Et2O); 1H NMR (200 MHz) δ 7.52-6.93 (m, 20H),
5.97 (s, 1H), 1.19 (s, 6H); 13C NMR (50 MHz) δ 165.0, 143.4-
126.5, 60.5, 31.5; IR (KBr) ν 1710 cm-1; UV (CH2Cl2) λmax 250
(ꢀ 32 232); MS m/e (%) 401 (M+, 6), 386 (2), 220 (49), 205 (97),
180 (100), 104 (37), 77 (39). Anal. Calcd for C30H27N: C, 89.73;
H, 6.78; N, 3.49. Found: C, 89.91; H, 6.99; N, 3.61.
3,3-Dim eth yl-1,1,5-tr iph en yl-2-aza-1,4-pen tadien e (26b).
(1E,4Z)-3,3-dimethyl-1,5-diphenyl-2-aza-1,4-pentadiene (9b)
(0.65 g, 2.61 mmol) in anhyd Et2O (30 mL) and PhLi (1.6 mL,
1.8 M in hexane) yielded (E)-N-ben zh yd r yl-1,1-d im eth yl-
3-p h en yl-2-p r op en yla m in e (0.48 g, 56%) as an oil; 1H NMR
(200 MHz) δ 7.40-7.12 (m, 15H), 6.38 (d, J ) 16.0 Hz, 1H),
6.11 (d, J ) 16.0 Hz, 1H), 4.92 (s, 1H), 1.58 (s, 1H), 1.21 (s,
6H); 13C NMR (50 MHz) δ 146.4-126.2, 61.9, 55.7, 28.2; IR
(neat) ν 3336, 1660 cm-1; MS m/e (%) 327 (M+, 1), 321 (60),
167 (100), 145 (26), 91 (13), 77 (8).
To a solution of diethyl 2-methyl-2-phenylmalonate (12.11
g, 48.4 mmol) in anhyd CH2Cl2 (100 mL) under argon and at
-78 °C was added DIBALH (97 mL, 1 M in toluene). The
mixture was stirred for 3 h at -78 °C before quenching with
a saturated aq NH4Cl solution (16.7 mL) and 4% aq HCl (16.7
mL). The white solid obtained was filtered and the organic
layer was washed with H2O, dried (MgSO4), filtered, and
evaporated to dryness. Chromatography with hexane/Et2O (95:
5) yielded eth yl 2-for m yl-2-p h en ylp r op ion a te (5.09 g, 51%)
as an oil; 1H NMR (300 MHz) δ 9.88 (s, 1H), 7.43-7.21 (m,
5H), 4.28 (q, J ) 7.1 Hz, 2H), 1.69 (s, 3H), 1.28 (t, J ) 7.1 Hz,
3H); 13C NMR (75 MHz) δ 196.9, 171.6, 136,6-126.9, 62.0, 61.8,
17.8, 14.0; IR (neat) ν 2845, 2725, 1750, 1720 cm-1; MS m/e
(%) 207 (M + 1, 1), 178 (100), 149 (33), 132 (91), 105 (80), 77
(44).
To a solution of diethyl benzhydrylphosphonate26 (3.65 g,
12 mmol) in anhyd DME (20 mL) under argon and at 0 °C
was added dropwise BuLi (7.5 mL, 1.6 M in hexane). After
the mixture was stirred for 1 h at 0 °C, a solution of ethyl
2-formyl-2-phenylpropionate (2.05 g, 10 mmol) in anhyd DME
(20 mL) was added dropwise. The resulting solution was
stirred for 2.5 h at 0 °C before quenching with H2O and
extracted with Et2O. The organic layer was washed with H2O
and saturated aq NaCl, dried (MgSO4), filtered, and evapo-
rated to dryness. Chromatography with hexane/Et2O (98:2)
yielded eth yl 2-m eth yl-2,4,4-tr ip h en yl-3-bu ten oa te (2.61
1
g, 74%) as a yellow oil; H NMR (300 MHz) δ 7.36-7.20 (m,
13H), 7.00-6.97 (m, 2H), 6.73 (s, 1H), 3.85 (q, J ) 7.1 Hz, 1H),
3.76 (q, J ) 7.1 Hz, 1H), 1.56 (s, 3H), 1.07 (t, J ) 7.1 Hz, 3H);
13C NMR (75 MHz) δ 174.8, 144.9-126.6, 61.0, 52.5, 25.1, 13.8;
IR (neat) ν 1728 cm-1; MS m/e (%) 356 (M+, 6), 341 (1), 310
(2), 283 (100), 268 (12), 205 (96), 191 (15), 178 (9), 165 (15),
105 (25), 91 (27), 77 (10).
Ethyl 2-methyl-2,4,4-triphenyl-3-butenoate (3.41 g, 9.6 mmol)
and KOH (1.60 g, 28.6 mmol) in dry EtOH (30 mL) were
refluxed for 20
h yielding 2-m et h yl-2,4,4-t r ip h en yl-3-
bu ten oic a cid (2.9 g, 92%) as a white solid: mp 155-156 °C
(hexane); 1H NMR (200 MHz) δ 7.40-7.18 (m, 10H), 7.13-
7.03 (m, 3H), 7.00-6.87 (m, 2H), 6.76 (s, 1H), 1.58 (s, 3H); 13
C
NMR (50 MHz) δ 181.0, 143.9-127.0, 52.2, 24.5; IR (KBr) ν
3500, 1697 cm-1; MS m/e (%) 328 (M+, 4), 312 (6), 283 (71),
205 (100), 191 (80), 178 (18), 167 (27), 105 (23), 91 (44), 77
(15); Anal. Calcd for C23H20O2: C, 84.15; H, 6.10. Found: C,
83.87; H, 6.18.
2-Methyl-2,4,4-triphenyl-3-butenoic acid (1.40 g, 4.3 mmol)
and SOCl2 (0.5 mL, 6.9 mmol) were refluxed for 1 h yielding
2-m eth yl-2,4,4-tr ip h en yl-3-bu ten oyl ch lor id e (1.49 g) as
a yellow oil; 1H NMR (200 MHz) δ 7.49-7.12 (m, 13H), 6.97-
6.92 (m, 2H), 6.82 (s, 1H), 1.57 (s, 3H).
2-Methyl-2,4,4-triphenyl-3-butenoyl chloride (1.49 g, 4.3
mmol), tetrabutylammonium bromide (4 mg, 0.013 mmol) in
CH2Cl2 (20 mL), and sodium azide (0.34 g, 5.2 mmol) in water
(3 mL) yielded 2-m eth yl-2,4,4-tr ip h en yl-3-bu ten oyla zid e
(1.51 g) as a yellow oil; IR (neat) ν 2135, 1711 cm-1
.
2-Methyl-2,4,4-triphenyl-3-butenoylazide (1.51 g, 4.3 mmol)
in toluene (30 mL) was refluxed for 2 h yielding 1-m eth yl-
1,3,3-tr ip h en yl-2-p r op en yl isocya n a te (1.39 g) as a yellow
oil; IR (neat) ν 2257 cm-1
.
1-Methyl-1,3,3-triphenyl-2-propenyl isocyanate (1.39 g, 4.3
mmol) and 8 M HCl (40 mL) were refluxed for 3 h yielding
1-m eth yl-1,3,3-tr ip h en yl-2-p r op en yla m in e (10d ) (0.46 g,
(E)-N-Benzhydryl-1,1-dimethyl-3-phenyl-2-propenylamine
(0.66 g, 2 mmol) and radical di-tert-butyliminoxyl in pentane
(35 mL, 0.17 M) yielded 3,3-d im eth yl-1,5,5-tr ip h en yl-2-a za -
1,4-p en ta d ien e (26b) (0.6 g, 92%) as an oil and as a 1:4
mixture of Z:E isomers: bp 150 °C (0.1 mbar); H NMR (300
MHz) δ 7.59-7.10 (m, 15H), 6.09 (s, 1.6H, E-isomer), 6.08 (d,
1
36%) as an oil: bp 140 °C (0.05 mbar); H NMR (200 MHz) δ
1
7.42-7.36 (m, 2H), 7.31-7.14 (m, 11H), 6.96-6.90 (m, 2H),
6.60 (s, 1H), 1.53 (s, 2H), 1.52 (s, 3H); 13C NMR (50 MHz) δ
150.2-125.4, 56.7, 33.6; IR (neat) ν 3383, 3306 cm-1; MS m/e
(27) Gilman, H.; Morton, J . J . Am. Chem. Soc. 1948, 70, 2514-2515.
(28) Cornejo, J . J .; Larson, K. D.; Mendenhall, G. D. J . Org. Chem.
1985, 50, 5382-5383.
(26) Zimmerman, H. E.; Klun, R. T. Tetrahedron 1978, 34, 1775-
1803.
J . Org. Chem, Vol. 68, No. 17, 2003 6669

Armesto et al.
J ) 12.0 Hz, 0.2H, Z-isomer), 5.42 (d, J ) 12.0 Hz, 0.2H,
Z-isomer), 1.43 (s, 4.8H, E-isomer), 1.36 (s, 1.2H, Z-isomer);
13C NMR (75 MHz) δ 165.6, 165.1, 141.6-125.4, 60.3, 59.7,
31.6, 30.3; IR (neat) ν 1660 cm-1; UV (CH2Cl2) λmax 256 (ꢀ 34
095); MS m/e (%) 325 (M+, 21), 310 (9), 165 (17), 145 (100),
130 (11), 91 (24), 77 (14).
elution with Et2O afforded 64 mg of highly polar material.
Final elution with EtOH yielded amine 10b (72 mg, 56%), as
a 7:3 mixture of Z:E isomers, resulting from hydrolysis of the
starting azadiene. 39a : 1H NMR (300 MHz) δ 7.58-7.09 (m,
10H), 6.96 (d, J ) 14.0 Hz, 0.33H, E-isomer), 6.07 (d, J ) 9.0
Hz, 0.67H, Z-isomer), 6.05 (d, J ) 14.0 Hz, 0.33H, E-isomer),
5.80 (d, J ) 9.0 Hz, 0.67H, Z-isomer), 2.94 (s, 0.33H, E-isomer),
2.77 (s, 0.67H, Z-isomer), 1.38 (s, 0.99H, E-isomer), 1.23 (s,
2.01H, Z-isomer), 1.11 (s, 2.01H, Z-isomer), 1.03 (s, 0.99H,
E-isomer); 13C NMR (50 MHz) δ 138.5, 138.2, 129.0-123.7,
116.0, 115.8, 54.2, 52.8, 48.6, 45.3, 21.2, 20.6, 20.3, 19.6; IR
(neat) ν 1630 cm-1; MS m/e (%) 249 (M+, 22), 248 (58), 219 (3),
193 (27), 158 (9), 144 (100), 115 (37), 91 (65), 77 (50), 51 (25).
Tr ip let-Sen sitized Ir r a d ia tion of 17. Azadiene (E)-17
(236 mg, 0.90 mmol) and m-methoxyacetophenone (550 mg,
3.7 mmol) were irradiated for 3.5 h. Chromatography with
hexane/Et2O (99:1) as eluent gave benzaldehyde (73 mg).
Further elution with Et2O afforded 64 mg of highly polar
material. Final elution with EtOH yielded a mixture of two
products that was further separated by column with chloroform/
MeOH (95:5) to give cyclopropylamine 20 (19 mg, 12%) as an
oil, resulting from hydrolysis of cyclopropylimine 19, and
amine 18 (114 mg, 71%), resulting from hydrolysis of starting
azadiene 17. 20: 1H NMR (200 MHz) δ 7.40-7.09 (m, 4H),
4.03 (s, 1H), 2.84 (td, J ) 13.5, 5.8 Hz, 1H), 2.64-2.30 (m,
4H), 1.86 (td, J ) 13.8, 5.3 Hz, 1H), 1.32 (s, 3H), 1.22 (s, 3H);
13C NMR (50 MHz) δ 137.3-126.1, 68.9, 56.7, 51.2, 27.7, 26.7,
25.8, 21.9; IR (neat) ν 3392 cm-1; MS m/e (%) 187 (M+, 1), 172
(4), 171 (6), 143 (10), 129 (9), 105 (9), 91 (14), 84 (36), 58 (100).
DCA-Sen sitized Ir r a d ia tion of 17. Azadiene (E)-17 (250
mg, 0.91 mmol), DCA (30 mg, 0.13 mmol), and biphenyl (140
mg, 0.91 mmol) were irradiated for 90 min. Chromatography
with hexane/Et2O (99:1) as eluent gave biphenyl (130 mg) and
benzaldehyde (20 mg). Further elution with Et2O afforded 35
mg of highly polar material. Final elution with EtOH yielded
amine 18 (16 mg, 7%), resulting from hydrolysis of the starting
azadiene, and amine 1-m et h yl-1-n a p h t h a len -2-yl-et h y-
la m in e (128 mg, 78%), resulting from aromatization of the
dihydronaphthalene unit. 1-Meth yl-1-n a p h th a len -2-yl-eth y-
la m in e: 1H NMR (200 MHz) δ 7.91-7.40 (m, 7H), 2.75 (br s,
2H), 1.60 (s, 6H); 13C NMR (50 MHz) δ 133.4-122.7, 53.0, 32.4;
IR (neat) ν 3285, 1599 cm-1; MS m/e (%) 186 (M + 1, 53), 185
(M+, 32), 170 (98), 169 (66), 155 (100), 141 (27), 129 (48), 128
(33), 115 (23), 105 (23), 58 (51).
Tr ip let-Sen sitized Ir r a d ia tion of 21a . Azadiene (E)-21a
(250 mg, 0.80 mmol) and m-methoxyacetophenone (5.7 g, 38
mmol) were irradiated for 10 h. Chromatography with hexane/
Et2O (99:1) as eluent gave benzaldehyde (47 mg). Further
elution with hexane/Et2O (85:15) afforded dihydropyrrol 23a
(15 mg, 6%), as a colorless oil. Final elution with Et2O yielded
amine 229 (105 mg, 66%), resulting from hydrolysis of the
starting azadiene. Compound 23a : 1H NMR (300 MHz) δ 7.95
(d, J ) 3.0 Hz, 1H), 7.71-6.81 (m, 13H), 5.83 (d, J ) 3.0 Hz,
1H), 1.36 (s, 3H), 0.75 (s, 3H); 13C NMR (75 MHz) δ 176.4,
145.0-119.4, 58.3, 79.9, 68.5, 55.8, 23.7, 21.3; IR (neat) ν 1626
cm-1; MS m/e (%) 324 (M + 1, 38), 323 (M+, 100), 308 (52),
291 (6), 280 (7), 267 (20), 254 (12), 252 (11), 219 (23), 203 (12),
191 (17), 165 (17), 145 (5), 131 (7), 117 (50), 90 (23), 77 (3).
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, the sensitizer, and
the solvent (450 mL) were purged for 1 h with argon and
irradiated under a positive pressure of argon. For the triplet-
sensitized runs m-methoxyacetophenone in dry t-BuOH was
used. After completion of the irradiation, the solvent and the
sensitizer were removed under reduced pressure. The products
were separated by flash chromatography on silica gel. In the
DCA-sensitized runs, a filter solution of 0.07 M sodium
m-vanadate in 5% sodium hydroxide was employed. Solutions
of the compounds, DCA, and the cosensitizer (biphenyl) in dry
CH3CN were used. After completion of the irradiation, the
DCA was removed by precipitation with Et2O and filtered, and
the biphenyl and the products were separated by flash chro-
matography on silica gel.
Tr ip let- and DCA-sen sitized ir r a d ia tion s of 1 were
described in a preliminary communication.9
Tr ip let-Sen sitized Ir r a d ia tion of 9a . Azadiene (E)-9a
(250 mg, 0.80 mmol) and m-methoxyacetophenone (550 mg,
3.7 mmol) were irradiated for 6 h. Chromatography with
hexane/Et2O (99:1) as eluent gave cyclopropylimine (E)-11a
(13 mg, 5%), as a colorless oil, and benzaldehyde (65 mg).
Further elution with Et2O afforded 25 mg of highly polar
material. Final elution with EtOH yielded amine 10a (148 mg,
81%), resulting from hydrolysis of the starting azadiene.
Compound (E)-11a : 1H NMR (200 MHz) δ 8.58 (s, 1 H), 7.68-
7.08 (m, 15H), 3.46 (s, 1H), 1.30 (s, 3H), 1.12 (s, 3H); 13C NMR
(50 MHz) δ 157.7, 145.1-125.6, 62.5, 48.0, 30.6, 24.8, 20.1; IR
(neat) ν 1664 cm-1; MS m/e (%) 325 (M+, 9), 310 (9), 220 (66),
205 (20), 165 (10), 117 (100), 105 (9), 90 (34).
DCA-Sen sitized Ir r a d ia tion of 9a . Azadiene (E)-9a (200
mg, 0.60 mmol), DCA (30 mg, 0.13 mmol), and biphenyl (95
mg, 0.60 mmol) were irradiated for 15 min. Chromatography
with hexane/Et2O (99:1) as eluent gave biphenyl (92 mg) and
benzaldehyde (50 mg). Further elution with Et2O afforded 15
mg of highly polar material. Final elution with EtOH yielded
amine 10a (115 mg, 79%), resulting from hydrolysis of the
starting azadiene.
Tr ip let-Sen sitized Ir r a d ia tion of 9b. Azadiene (1E,4Z)-
9b (256 mg, 1 mmol) and m-methoxyacetophenone (550 mg,
3.7 mmol) were irradiated for 9.5 h. Chromatography with
hexane/Et2O (98:2) as eluent gave cyclopropylimine 11b (10
mg, 4%) as a colorless oil and as a 3:2 mixture of (Zcyclo,EC-N):
(Ecyclo,EC-N) diastereoisomers and benzaldehyde (82 mg). Fur-
ther elution with Et2O afforded 17 mg of highly polar material.
Final elution with EtOH yielded amine 10b9 (126 mg, 78%)
as a 3:2 mixture of Z:E diastereoisomers, resulting from
hydrolysis of the starting azadiene. Compound 11b: 1H NMR
(200 MHz) δ 8.43 (s, 0.4H, E-isomer), 8.37 (s, 0.6H, Z-isomer),
7.68-7.57 (m, 2H), 7.37-7.09 (m, 8H), 3.18 (d, J ) 4.0 Hz,
0.4H, E-isomer), 3.10 (d, J ) 7.5 Hz, 0.6H, Z-isomer), 2.43 (d,
DCA-sen sitized ir r a d ia tion of 21a was described in a
preliminary communication.9
J
) 4.0 Hz, 0.4H, E-isomer), 2.19 (d, J ) 7.5 Hz, 0.6H,
Z-isomer), 1.39 (s, 1.2H, E-isomer), 1.26 (s, 1.8H, Z-isomer),
1.10 (s, 1.8H, Z-isomer), 0.88 (s, 1.2H, E-isomer); 13C NMR (50
MHz) δ 158.7, 157.9, 38.8-125.5, 59.1, 57.9, 39.4, 37.4, 28.6,
27.8, 26.4, 22.0, 20.9, 16.3; IR (neat) ν 1631 cm-1; MS m/e (%)
249 (M+, 13), 234 (26), 219 (3), 206 (5), 144 (10), 129 (16), 117
(100), 91 (22).
DCA-Sen sitized Ir r a d ia tion of 9b. Azadiene (1E,4Z)-9b
(200 mg, 0.80 mmol), DCA (30 mg, 0.13 mmol), and biphenyl
(124 mg, 0.80 mmol) were irradiated for 2 h. Chromatography
with hexane/Et2O (99:1) as eluent gave biphenyl (120 mg),
N-vinylaziridine 39a (10 mg, 5%), as a yellow oil and as a 2:1
mixture of Z:E isomers, and benzaldehyde (50 mg). Further
Tr ip let-Sen sitized Ir r a d ia tion of 21b. Azadiene (E)-21b
(200 mg, 0.6 mmol) and m-methoxyacetophenone (6.22 g, 41.5
mmol) were irradiated for 3 h. Chromatography with hexane/
Et2O (9:1) as eluent gave starting azadiene (E)-21b (32 mg,
16%) and p-cyanobenzaldehyde (33 mg). Further elution with
Et2O afforded a mixture of two products. Chromatography of
this mixture with hexane/ethyl acetate (9:1) yielded dihydro-
pyrrol 23b (31 mg, 16%), as a white solid (mp 239-240 °C
(hexane)) and amine 22 (59 mg, 43%), resulting from hydroly-
sis of the starting azadiene. 23b: 1H NMR (200 MHz) δ 7.97
(d, J ) 2.9 Hz, 1H), 7.75-6.88 (m, 12H), 5.82 (d, J ) 2.9 Hz,
1H), 1.43 (s, 3H), 0.73 (s, 3H); 13C NMR (50 MHz) δ 177.2,
6670 J . Org. Chem., Vol. 68, No. 17, 2003

Novel Photoreactions of 2-Aza-1,4-dienes
144.4-110.2, 79.2, 68.6, 56.1, 23.8, 20.8; IR (KBr) ν 2230, 1610
cm-1; MS m/e (%) 349 (M + 1, 30), 348 (M+, 100), 333 (41),
316 (4), 305 (7), 292 (20), 279 (25), 219 (36), 206 (39), 191 (48),
178 (11), 165 (31), 156 (18), 142 (47), 115 (25). Anal. Calcd for
(M+, 53), 386 (11), 345 (9), 221 (100), 207 (11), 178 (27), 165
(29), 91 (39). Anal. Calcd for C30H27N: C, 89.73; H, 6.78; N,
3.49. Found: C, 90.03; H, 7.08, N, 3.69.
Tr ip let-Sen sitized Ir r a d ia tion of 26b. A 1:4 mixture of
Z:E isomers of azadiene 26b (179 mg, 0.60 mmol) and
m-methoxyacetophenone (750 mg, 4.40 mmol) were irradiated
for 45 min. Chromatography with hexane/Et2O (98:2) as eluent
gave azadiene 26b (125 mg, 70%), as a 15:85 mixture of Z:E
diastereoisomers, and benzophenone (18 mg). Further elution
with Et2O afforded 15 mg of highly polar material. Final
elution with EtOH yielded amine (E)-10b (16 mg, 18%),
resulting from hydrolysis of the starting azadiene.
DCA-Sen sitized Ir r a d ia tion of 26b. A 1:4 mixture of Z:E
isomers of azadiene 26b (170 mg, 0.50 mmol), DCA (20 mg,
0.09 mmol), and biphenyl (80 mg, 0.50 mmol) were irradiated
for 40 min. Chromatography with hexane/Et2O (99:1) as eluent
gave biphenyl (78 mg), dihydrobenzoazepine 45b (121 mg,
71%), as a colorless oil, and benzophenone (10 mg). Further
elution with Et2O afforded 30 mg of highly polar material.
Final elution with EtOH yielded amine (E)-10b (9 mg, 11%),
resulting from hydrolysis of the starting azadiene. 45b: 1H
NMR (200 MHz) δ 7.43-7.04 (m, 14H), 6.80 (d, J ) 14.2 Hz,
1H), 6.13 (d, J ) 14.2 Hz, 1H), 1.24 (s, 6H); 13C NMR (50 MHz)
δ 140.5-118.1, 58.3, 49.5, 22.5; IR (neat) ν 3360 cm-1; MS m/e
(%) 325 (M+, 29), 310 (9), 269 (29), 191 (32), 165 (24), 145 (100),
129 (10), 103 (16), 91 (27), 77 (14).
DCA-Sen sitized Ir r a d ia tion of 40. Azadiene (E)-40 (140
mg, 0.40 mmol), DCA (12 mg, 0.05 mmol), and biphenyl (56
mg, 0.40 mmol) were irradiated for 12 min. Chromatography
with hexane/Et2O (99:1) as eluent gave biphenyl (54 mg),
N-vinylaziridine 39c (18 mg, 13%), as a colorless oil, and
benzaldehyde (25 mg). Further elution with Et2O afforded
amine 10d (72 mg, 67%), resulting from hydrolysis of the
starting azadiene. Final elution with EtOH yielded 11 mg of
highly polar material. 39c: 1H NMR (200 MHz) δ 7.29-6.98
(m, 12H), 6.90-6.82 (m, 6H), 6.76 (s, 1H), 6.64-6.60 (m, 2H),
2.72 (s, 1H), 1.66 (s, 3H); 13C NMR (50 MHz) δ 142.2-126.2,
55.9, 54.2, 22.5; IR (neat) ν 1612 cm-1; MS m/e (%) 388 (M +
1, 19), 387(M+, 54), 370 (16), 282 (34), 269 (100), 220 (12), 206
(35), 191 (61), 178 (42), 165 (24), 152 (12), 115 (22), 91 (36), 77
(14).
C
25H20N2: C, 86.17; H, 5.79; N, 8.04. Found: C, 85.97; H, 5.83,
N, 8.16. The structure assignment was established by X-ray
crystallography.19
DCA-Sen sitized Ir r a d ia tion of 21b. Azadiene (E)-21b
(250 mg, 0.70 mmol), DCA (30 mg, 0.1 mmol), and biphenyl
(111 mg, 0.70 mmol) were irradiated for 35 min. Chromatog-
raphy with hexane/Et2O (99:1) as eluent gave biphenyl (105
mg), azadiene (E)-21b (26 mg, 10%), and p-cyanobenzaldehyde
(65 mg). Further elution with Et2O afforded 20 mg of highly
polar material. Final elution with EtOH yielded amine 22 (118
mg, 70%), resulting from hydrolysis of the starting azadiene.
Tr ip let-Sen sitized Ir r a d ia tion of 25. Azadiene (E)-25 (53
mg, 0.10 mmol) and m-methoxyacetophenone (550 mg, 3.7
mmol) were irradiated for 6 h. Chromatography with hexane/
Et2O (98:2) as eluent gave benzaldehyde (10 mg) and amine
10c (31 mg, 76%), resulting from hydrolysis of the starting
material. Further elution with Et2O afforded 8 mg of highly
polar material.
DCA-Sen sitized Ir r a d ia tion of 25. Azadiene (E)-25 (197
mg, 0.50 mmol), DCA (30 mg, 0.13 mmol), and biphenyl (80
mg, 0.50 mmol) were irradiated for 15 min. Chromatography
with hexane/Et2O (99:1) as eluent gave biphenyl (78 mg),
N-vinylaziridine 39b (27 mg, 14%), and benzaldehyde (30 mg).
Further elution with Et2O afforded amine 10c (84 mg, 55%),
resulting from hydrolysis of the starting azadiene. Final
elution with EtOH yielded 35 mg of highly polar material.
39b: 1H NMR (200 MHz) δ 7.29-6.91 (m, 15H), 6.85 (s, 1H),
2.58 (s, 1H), 1.83 (sept, J ) 7.1 Hz, 1H), 1.52 (sept, J ) 7.3
Hz, 1H), 1.32 (d, J ) 7.1 Hz, 3H), 1.26 (d, J ) 7.1 Hz, 3H),
1.03 (d, J ) 7.3 Hz, 3H), 0.71 (d, J ) 7.3 Hz, 3H); 13C NMR
(50 MHz) δ 142.5-125.9, 58.9, 56.3, 35.5, 30.7, 23.1, 20.8, 20.6,
19.4; IR (neat) ν 1595 cm-1; MS m/e (%) 382 (M + 1, 4), 381
(M+, 32), 338 (24), 282 (14), 269 (100), 206 (20), 191 (56), 178
(27), 165 (15), 91 (42).
Tr ip let-Sen sitized Ir r a d ia tion of 26a . Azadiene 26a (165
mg, 0.40 mmol) and m-methoxyacetophenone (660 mg, 4.40
mmol) were irradiated for 1 h. Chromatography with hexane/
Et2O (98:2) as eluent gave azadiene 26a (98 mg, 59%) and
benzophenone (13 mg). Further elution with Et2O afforded 24
mg of highly polar material. Final elution with EtOH yielded
amine 10a (18 mg, 18%), resulting from hydrolysis of the
starting azadiene.
DCA-Sen sitized Ir r a d ia tion of 26a . Azadiene 26a (150
mg, 0.40 mmol), DCA (20 mg, 0.09 mmol), and biphenyl (57
mg, 0.40 mmol) were irradiated for 10 min. Chromatography
with hexane/Et2O (99:1) as eluent gave biphenyl (40 mg),
dihydrobenzoazepine 45a (83 mg, 55%), as a white solid (mp
142-143 °C (hexane)), azadiene 26a (13 mg, 9%), and ben-
zophenone (16 mg). Further elution with Et2O afforded 10 mg
of highly polar material. Final elution with EtOH yielded
amine 10a (21 mg, 24%), resulting from hydrolysis of the
starting azadiene. 45a : 1H NMR (200 MHz) δ 7.58-6.95 (m,
19H), 6.59 (s, 1H), 0.92 (s, 6H); 13C NMR (50 MHz) δ 142.7-
126.1, 56.7, 50.7, 22.0; IR (neat) ν 3369 cm-1; MS m/e (%) 401
Ack n ow led gm en t. O.C. and M.M-F. thank the
Ministerio de Educacion y Ciencia for postgraduate
fellowships. We thank the Subdireccion General de
Proyectos de Investigacion del Ministerio de Ciencia y
Tecnologia (grant no. BQU2001-1282) for financial
support. We acknowledge the support provided by the
Centro de Resonancia Magnetica, the Centro de Mi-
croanalisis and the Servicio de Espectrometria de Masas
of the Universidad Complutense.
Su p p or tin g In for m a tion Ava ila ble: General procedures
1
and H NMR spectra for all compounds lacking analyses. This
material is available free of charge via the Internet at
http://pubs.acs.org.
J O034452G
J . Org. Chem, Vol. 68, No. 17, 2003 6671