The photochemical reaction of vinylaziridines and vinylazetidines with chromium(0) and molybdenum(0) (fischer) carbene complexes

Article abstract of DOI:10.1002/chem.201302029

The [5+2] and [6+2] cycloaddition reactions of vinylaziridines and vinylazetidines with ketenes generated photochemically from chromium(0) and molybdenum(0) Fischer carbene complexes have been investigated. These processes constitute a straightforward and

Full text of DOI:10.1002/chem.201302029

DOI: 10.1002/chem.201302029
Full Paper
&
Cycloaddition Reactions
The Photochemical Reaction of Vinylaziridines and Vinylazetidines
with Chromium(0) and Molybdenum(0) (Fischer) Carbene
Complexes
Alexandra R. Rivero, Israel Fernꢀndez,* and Miguel A. Sierra*[a]
Abstract: The [5+2] and [6+2] cycloaddition reactions of vi-
nylaziridines and vinylazetidines with ketenes generated
photochemically from chromium(0) and molybdenum(0)
Fischer carbene complexes have been investigated. These
processes constitute a straightforward and efficient route to
azepanones and azocinones, respectively. The peculiar elec-
tronic properties of the metalated ketenes allow for the in-
troduction of electron-rich substituents in the final cycload-
ducts, a difficult task using conventional organic chemistry
procedures. The versatility of the process is demonstrated
by using Cr0 Fischer bis(carbene) complexes as metalated
bis(ketene) precursors. These species produce tethered bis(a-
zepanone)s in a single step under mild reaction conditions.
Density functional theory calculations point to a stepwise re-
action pathway through the initial nucleophilic attack of the
nitrogen atom of the aziridine on the metalated ketene, fol-
lowed by ring closure of the zwitterionic intermediate
formed.
Introduction
The ring-opening reaction of vinyl-substituted three- and four-
membered nitrogen heterocycles with cumulenes has been
little studied despite their potential to produce medium-sized
rings in an easy and efficient manner.[1] This contrasts with the
use of the strained nature of these cyclic amines to prepare
other classes of compounds in reactions involving the cleavage
of the CÀN bond.[2] For example, Alper and co-workers report-
ed the first examples of a reaction involving 2-vinylaziridines
and isocyanates, isothiocyanates, and carbodiimides.[3] Thus,
the reactions of a series of vinylaziridines 1 with cumulenes 2
under Pd catalysis yielded the corresponding five-membered
heterocycles 3 in acceptable to excellent yields (Scheme 1). Ag-
garwal and co-workers have reported a similar transformation[4]
in the Pd-catalyzed insertion of CO2 into a vinylaziridine. How-
ever, it should be noted that in both cases the double bond is
not incorporated into the final five-membered ring.[5]
Scheme 1. The reactions of vinylaziridines and cumulenes under Pd catalysis.
through
a divinylcyclopropane–cycloheptadiene-type rear-
rangement.[6] Moreover, phenyl isothiocyanate and very recent-
ly sulfonyl isocyanates have been employed as C2 units in
formal [5+2] cycloaddition reactions with 2-vinylaziridines to
smoothly produce 1,3-thiazepine derivates[7] and various cyclic
ureas,[8] respectively (Scheme 2a and b). It is remarkable that in
these cases the cycloaddition processes occurred at 08C and in
the absence of metal catalysts. A similar methodology was pre-
viously reported by the same authors in the ring-expansion re-
action of vinylazetidines with electron-deficient isocyanates (in
a formal [6+2] cycloaddition reaction).[9]
The simultaneous participation of the double bond of a vinyl-
aziridine with the concomitant three-membered ring opening
has been used to develop synthetically useful routes to the
azepane skeleton. For instance, the reaction of these substrates
with electron-poor alkynes leads to a seven-membered ring
Despite the efficiency of the aforementioned processes, the
cycloaddition reaction with vinylaziridines or vinylazetidines is
restricted to electron-deficient cumulenes, limiting the scope
of this synthetically valuable transformation. Therefore, the use
of substrates with electron-donor substituents in their struc-
tures is an unfulfilled challenge. At this point, we turned our
attention to the ability of Group 6 Cr0 and Mo0 Fischer-type
carbene complexes to form electron-rich metalated ketenes
when irradiated in the presence of visible light.[10] These spe-
cies are able to produce a wide variety of reaction products in
the presence of nucleophiles, avoiding the main shortcomings
[a] A. R. Rivero, Dr. I. Fernꢀndez, Prof. Dr. M. A. Sierra
Departamento de Quꢁmica Orgꢀnica, Facultad de Quꢁmica
Universidad Complutense, 28040 Madrid (Spain)
Fax: (+34)913944310
E-mail: israel@quim.ucm.es
sierraor@quim.ucm.es
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201302029. It contains experimental proce-
dures, compound characterization data, Cartesian coordinates, and total
1
energies of all computed stationary points and copies of the H and
13C NMR spectra of the new species prepared.
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Scheme 3. Photochemical reactions of 2-vinylpyrrolidines and -piperidines
with Cr0 carbene complexes.
Ph3P=CH2 ylide results in the desired vinylaziridines 11.
Irradiation (450 W medium pressure Hg lamp, pyrex filter
and pyrex well) of a mixture of pentacarbonyl[(ethoxy)-
(methyl)carbene]chromium(0) (15a) and aziridine 11 a (1.2:1
molar ratio) in Et2O under 60–70 psi of CO yielded N-benzyl-
Scheme 2. Formal [5+2] cycloaddition reactions of 2-vinylaziridines.
3,4-dihydroazepin-2-one
(16a)
in
quantitative
yield
(Scheme 5).[13] Thus, it became clear that the envisioned formal
[5+2] cycloaddition reaction is indeed possible, allowing for
the introduction of electron-donor substituents in the azepi-
none skeleton. Moreover, this transformation proceeds
smoothly at room temperature in the absence of Lewis acid
additives, which contrasts with the related process involving 2-
vinylpyrrolidines.[11]
of ketenes, that is, dimerization and the formation of undesired
adducts.
Interestingly, the reactions of photochemically generated ke-
tenes from Cr0 Fischer carbene complexes 8 and 2-vinylpyrroli-
dines or -piperidines 9 has been reported (Scheme 3).[11] The
final products, ten- or eleven-membered-ring amides 10, were
obtained in acceptable to good yields in the presence of
a Lewis acid. The formation of these cyclic compounds was
thought to occur through a Malherbe–Bellus variant of the
Claisen rearrangement.[12] Based on this report, we speculated
that this type of electron-rich ketene may serve as a C2 unit in
[5+2] or [6+2] cycloaddition reactions with vinylaziridines or
vinylazetidines, respectively. Herein, the successful accomplish-
ment of this hypothesis, which allows rapid access to azepa-
nones and azocinones, shall be described. In addition, the ex-
tension of this reaction to bis(carbene) complexes, as well as
the elucidation of the corre-
The reaction was then extended to 2-vinylaziridines 11 b and
11 c, which yielded 3-ethoxyazepinones 16b and 16c in excel-
lent yields. The introduction of chiral, enantiomerically pure
diastereomeric aziridines 11 d and 2-epi-11 d[14] formed the cor-
responding ethoxyazepinones 16d and 3-epi-16d with excel-
lent yields and as an inseparable mixture of diastereomers. As
expected, the diastereoselectivity of the reaction was poor
(1:2.5) and was inverted for 11 d with respect to 2-epi-11 d,
with the major product of the reaction of 11 d being the minor
product in the reaction of 2-epi-11 d (ratio 1.7:1). Clearly, the
stereochemical outcome of the reaction is controlled by the
sponding reaction mechanism
by means of computational
methods, will be reported.
Results and Discussion
Aziridines 11 were prepared in
moderate to quantitative yields
by using a standard methodolo-
gy, that is, reacting ethyl 2,3-di-
bromopropionate with amines
12 in EtOH as the solvent and in
the presence of Et3N (Scheme 4).
Reduction of aziridine esters 13
to the corresponding aldehydes
14 occurred in the presence of
DIBALH (diisobutylaluminium hy-
dride) in CH2Cl2 at À788C, fol-
lowed by quenching with an
aqueous solution of NaF. Finally,
a
Wittig reaction with the Scheme 4. Synthesis of 2-vinylaziridines 11.
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activity of Fischer carbene com-
plexes in these cycloaddition re-
actions is compatible with three-
and four-membered rings sup-
porting
the
vinyl
group
(Scheme 7).
The reaction of thermally gen-
erated electron-rich, nonmetalat-
ed ketenes and vinylaziridine
11 a was also tested to assess
the need to use ketenes derived
Scheme 5. Photochemical reactions of 2-vinylaziridines and Cr0 Fischer carbenes.
from Fischer carbene complexes.
stereochemistry of the vinylaziridine chiral center, with the exo-
cyclic chiral center as a spectator. Unfortunately, the spectro-
scopic data are inconclusive with regard to the stereochemistry
of the adduct 16d. Furthermore, we were not able to grow
crystals of any of the diastereomers of 16d and, therefore, the
stereochemistry of cycloadducts 16d remains unknown. A sim-
ilar result was obtained in the reaction of 15b and 2-epi-11 d,
which yielded 3-epi-16e as a mixture of diastereomers also
with low selectivity (1.4:1; Scheme 5).
To this end, the alkoxyketene derived from the reaction of phe-
nyloxyacetyl chloride and Et3N and the phenylketene derived
from phenylacetyl chloride and Et3N were prepared. In both
cases, conditions to ensure the generation of the ketenes[16]
(À788C/CH2Cl2, addition of Et3N to a solution of the acid chlo-
ride) were used. Both nonmetalated ketenes afford complex re-
action mixtures in their reactions with vinylaziridine 8a instead
of the clean, crude products observed when using Fischer car-
Complexes 15b and 15c also reacted smoothly with vinyl-
aziridine 11 a (1.2:1 molar ratio), yielding the expected ethoxy-
azepinones 16 f and 16g in 61% and quantitative yields, re-
spectively (Scheme 6). It is noteworthy that the diastereoselec-
tivity of the reactions between complexes 15a and 15b and 2-
epi-11 d were nearly identical, independent of the introduction
of a bulky cyclopropyl group in complex 15b compared to
a methyl group in 15a. In addition, the reaction was also ex-
tended to molybdenum(0) carbene complex 15d, which
formed the azepinone 16a in 53% yield. This result is not sur-
prising because of the known lower reactivity of Mo0 carbene
complexes compared to their Cr0 counterparts in the photocar-
bonylation reaction.[15]
Scheme 6. Reactions of Cr0 and Mo0 carbene complexes and N-benzyl-2-
Vinylazetidines 17 were tested next. These species were pre-
pared following a similar proce-
dure to that described above for
the synthesis of vinylaziridines
11. Thus, ethyl 2,4-dibromobuta-
noate was converted into the
corresponding azetidine esters
18 by reaction with amines 12.
Compounds 18 were trans-
formed into aldehydes 19
(DIBALH) and finally, into vinyl-
azetidines 17 through Wittig
methylenation
with
the
Ph3P=CH2 ylide (Scheme 7). The
photochemical reactions of aze-
tidines 17 and chromium(0) car-
bene complex 15a formed the
corresponding eight-membered-
ring
tetrahydroazocin-2-ones
20a–d in good to excellent
yields through a formal [6+2] cy-
cloaddition reaction. These re-
sults clearly indicate that the re- Scheme 7. The synthesis of 2-vinylazetidines.
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zwitterionic
complex
INT1-
a through TS1, a saddle point
associated with the formation of
the CÀN single bond (activation
barrier of 13.3 kcalmolÀ1). Com-
plex INT1-a rapidly isomerizes
into zwitterion INT1-b, which is
then able to undergo a ring-clos-
ing reaction to form the seven-
membered-ring species INT2.
This step occurs via the highly
asynchronous transition state
TS2,[18] which is associated with
the formation of the new CÀC
bond with concomitant aziridine
ring opening (i.e., CÀN bond
breaking). This process proceeds
with a very low activation barrier
Scheme 8. The reactions of Cr0 bis-carbene complexes with 2-vinylaziridines to yield bis(azepinones).
bene complex derived ketenes. This marked difference with re-
spect to the reactions involving Fischer carbene complexes
clearly illustrates the difficulties associated with the introduc-
tion of electron-donor substituents in the ketene, which can
be easily overcome when using metalated ketenes generated
by photocarbonylation of Fischer carbene complexes.
(DGa,298 =3.9 kcalmolÀ1) in a highly exergonic transformation
(DG298 =À61.6 kcalmolÀ1), which clearly reflects the ease of
this reaction step. Subsequent decoordination of the {Cr(CO)5}
fragment by use of CO or a molecule of coordinating solvent
(Et2O)[19] releases the final cycloadduct 16M. Alternatively, the
decoordination reaction may occur prior to the final ring clo-
sure in the metalated zwitterion INT1-b, producing INT1-c.
Indeed, zwitterion INT1-c can also undergo a similar, facile
ring-closure step (with an activation barrier of 5.4 kcalmolÀ1
and reaction energy of À72.9 kcalmolÀ1) to produce the seven-
membered-ring compound 16M through the highly asynchro-
nous transition state TS2-c.
From this computational study, it can be concluded that the
[5+2] cycloaddition reaction between aziridines and metalated
ketenes occurs stepwise in a process that resembles the [2+2]
cycloaddition of these metalated ketenes with imines,[10d] that
is, a process which involves the initial nucleophilic attack of
the nitrogen atom followed by ring closure of the zwitterionic
intermediate formed.
The efficiency of the aforementioned cyclization reactions
led us to assess the reaction of chromium(0) bis(carbene) com-
plexes 21a–e and vinylaziridine 11 a to produce bis(azepi-
none)s. Thus, irradiation of bis(carbene) complexes 21 with
11 a in the same reaction conditions used for the mononuclear
Fischer carbene complexes (1:2 molar ratio) afforded alkoxy-
tethered bis(azepinone)s 22a–e in moderate to good (41–
61%) yields. Complexes having aliphatic (21a and 21b) and ar-
omatic (21c–e) tethers were compatible with the transforma-
tion (Scheme 8). Bis(azepinone)s 22 resulted from a double
formal [5+2] cycloaddition reaction and were always obtained
as inseparable diastereomeric mixtures. Both the 1H and
13C NMR spectra of compounds 22 show splitting of significant
signals, especially those corresponding to the Me groups,
which confirm the formation of the racemic (RR/SS) and meso
(RS) forms. No appreciable selectivity was observed. This pro-
cess is a single reaction step route to bis(azepinone)s, which
are difficult to obtain by conventional organic chemistry proce-
dures.
Conclusion
From the joint experimental and computational study reported
herein, the following conclusions can be drawn: 1) Metalated
ketenes, photochemically generated from Fischer carbene
complexes, react with vinylaziridines and vinylazetidenes to
produce azepanones and azocinones, respectively, with high to
excellent reaction yields. 2) The peculiar electronic properties
of these metalated ketenes allow the introduction of electron-
rich substituents in the final reaction products. This constitutes
a marked difference from the reported procedures, which are
restricted to the use of electron-poor cumulenes. 3) These
transformations, which can be viewed as formal [5+2] or [6+2]
cycloaddition reactions, are compatible with chromium(0)
Fischer bis(carbene) complexes as metalated ketene precur-
sors, producing tethered bis(azepanone)s in a single step
under mild reaction conditions. 4) DFT calculations suggest
that the transformation occurs stepwise through the initial nu-
cleophilic attack of the nitrogen atom of the aziridine at the
Finally, the reaction mechanism of the above-discussed cy-
cloaddition reactions was studied by using density functional
theory (DFT) calculations at the PCM(Et2O)-B3LYP/def2-SVP
level.[17] The corresponding computed reaction profiles of the
metalated ketene 23 (generated by photocarbonylation of
a pentacarbonyl[(methoxy)(methyl)carbene]chromium(0) com-
plex following the reaction pathway previously reported by
us)[10d] with the model vinylaziridine 11 M, to produce the
[5+2] cycloadduct 16M, are shown in Figure 1 (which gathers
the respective free energies, at 298 K, in Et2O).
As can be readily seen in Figure 1, our calculations suggest
that the process begins with nucleophilic attack of the nitro-
gen atom of aziridine at the highly electrophilic carbonyl
carbon atom of metalaketene 23. This reaction leads to the
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Figure 1. Computed reaction profile of metalated ketene 23 and vinylaziridine 11 M. Relative free energy values (computed at 298 K) and bond lengths are
given in kcalmolÀ1 and ꢂ, respectively. All data have been computed at the PCM(Et2O)-B3LYP/def2-SVP level.
metalated ketene, followed by ring closure of the zwitterionic
intermediate thus formed. This reaction mechanism resembles
that proposed for the [2+2] cycloaddition reaction of these
metalated ketenes and imines.[10d]
technique. MS spectra (HRMS) were acquired on a Fourier trans-
form ion cyclone resonance mass spectrometer (4.7 T). Chromium
carbene complexes 15 and 21[20] were prepared by following previ-
ously reported procedures. Azetidines 17c and 17d were prepared
according to reported procedures.[9b]
General procedure for the photochemical cycloaddition reac-
tions: Photoreactions were carried out in oven-dried pressure
tubes that were charged with the carbene complex 15 and the
corresponding vinylaziridine 11 or vinylazetidine 18 (1.2:1 molar
ratio) and dry, degassed Et2O (3 freeze–pump–thaw cycles). The
tube was fitted with a pressure head, purged three times with CO,
and irradiated under CO (60–70 psi; medium pressure mercury
lamp 450 W, pyrex filter and pyrex well) for 16 h. The solvent was
removed under vacuum, the residue was taken up in hexane/
EtOAc (1:1), and exposed to light to oxidize the remaining metal(0)
compounds. The resulting mixture was filtered through Celite and
the solvent was removed under vacuum to obtain the desired di-
hydroazepinones 16a–f (from vinylaziridines 11) or the desired tet-
rahydroazocinones 20a–b (for vinylazetidines 18).
Experimental Section
General: All reactions were carried out under an argon atmos-
phere. All solvents used in this work were purified by distillation
and were freshly distilled immediately before use. Triethylamine
(Et3N) was distilled from calcium hydride, whereas diethyl ether
(Et2O) was purified by using a Pure Solv PS-MD-5 system. Flame-
dried glassware was used for moisture-sensitive reactions. Silica gel
(Merck: 230–400 mesh) was used as the stationary phase for purifi-
cation of crude reaction mixtures by flash column chromatography
under Ar pressure. Identification of products was made by thin-
layer chromatography (Kieselgel 60F-254). UV light (n=254 nm)
and 5% phosphomolybdic acid solution in 95% EtOH were used
to develop the plates. NMR spectra were recorded at 258C in
1-Benzyl-3-ethoxy-3-methyl-3,4-dihydroazepinone (16a): Follow-
ing the general procedure, from carbene complex 15a (66 mg,
0.25 mmol) and vinylaziridine 11 a (33 mg, 0.21 mmol), dihydroaze-
pinone 16a was obtained as an orange oil (54 mg, quantitative
1
CDCl3, on a Bruker Avance 300 spectrometer (300 MHz for H and
75 MHz for 13C). Chemical shifts are given in ppm relative to CDCl3
(1H, d=7.27 ppm and 13C, d=77.0 ppm). IR spectra were taken on
an MIR (8000–400 cmÀ1) spectrometer as solid films by slow evapo-
ration of the solvent using the attenuated total reflectance (ATR)
1
yield, 53% when using carbene complex 15d). H NMR (300 MHz,
CDCl3): d=7.35–7.21 (m, 5H), 5.71–5.53 (m, 2H), 4.73–4.61 (m, 2H),
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4.61–4.51 (m, 1H), 3.71–3.50 (m, 3H), 3.40–3.29 (m, 2H), 2.49–2.50
(m, 2H), 1.52 (s, 3H), 1.22 ppm (t, J=7.0 Hz, 3H); 13C NMR (75 MHz,
CDCl3): d=173.7, 138.1, 128.9, 128.1, 127.9, 127.6, 125.2, 80.9, 59.9,
53.5, 47.0, 38.7, 23.6, 16.4 ppm; IR (ATR): n˜ =3027, 2975, 2928,
1641, 1478, 1449, 1418, 1234 cmÀ1; HRMS (ESI): m/z calcd for
C16H21NO2: 259.1567 [M]+; found: 259.1572.
2.44 (m, 4H), 1.55 (s, 3H; m), 1.54 (s, 3H; M), 1.51 (d, J=7.0 Hz,
3H; M), 1.47 (d, J=7.0 Hz, 3H; m), 1.26 (t, J=7.0 Hz, 3H; M),
1.18 ppm (t, J=7.0 Hz, 3H; m); 13C NMR (75 MHz, CDCl3; M/m,
1.7:1): d=173.2 (M), 173.1 (m), 141.0 (m), 140.8 (M), 128.6, 128.4,
127.9, 127.5,127.4, 127.3, 127.2, 125.7 (m), 125.3 (M), 81.0 (m), 80.8
(M), 59.9 (m), 59.6 (M), 52.4 (M+m), 41.0 (M), 40.9 (m), 38.8 (m),
38.6 (M), 23.5 (M), 23.5 (m), 16.4 (M), 16.1 (M), 16.1 (m), 16.0 ppm
(m); IR (ATR): n˜ =3026, 2975, 2934, 2901, 1634, 1464, 1415, 1369,
1318, 1205, 1103, 1056, 828, 779, 753, 699, 647 cmÀ1; HRMS (ESI):
m/z calcd for C17H23NNaO2: 296.1621 [M+Na]+; found: 296.1618.
3-Ethoxy-1-(4-methoxybenzyl)-3-methyl-3,4-dihydroazepinone
(16b): Following the general procedure, from carbene complex
15a (100mg, 0.38mmol) and vinylaziridine 11 b (60mg,
0.32mmol), dihydroazepinone 16b was obtained as a yellow oil
1
(83mg, 91%). H NMR (300 MHz, CDCl3): d=7.17 (d, J=8.5 Hz, 2H),
3-Cyclopropyl-3-ethoxy-1-[(R)-1-phenylethyl]-3,4-dihydroazepi-
none, from 2-epi-11d (16e and 3-epi-16e): Following the general
procedure, from carbene complex 15b (80mg, 0.28mmol) and vi-
nylaziridine 2-epi-11 d (40mg, 0.23mmol), an inseparable mixture
of dihydroazepinone 16d and 3-epi-16d (1.4:1) was obtained as
6.83 (d, J=8.5 Hz, 2H), 5.68–5.49 (m, 2H), 4.59 (s, 2H), 4.55–4.44
(m, 1H), 3.78 (s, 3H), 3.69–3.56 (m, 1H), 3.39–3.27 (m, 2H), 2.54–
2.39 (m, 2H), 1.50 (s, 3H), 1.19 ppm (t, J=7.0 Hz, 3H); 13C NMR
(75 MHz, CDCl3): d=173.6, 159.2, 130.2, 129.5, 127.8, 125.2, 114.2,
80.9, 59.9, 55.6, 52.8, 46.7, 38.7, 23.5, 16.3 ppm; IR (ATR): n˜ =2973,
2928, 1638, 1511, 1476, 1444, 1394, 1349, 1301, 1242, 1172, 1104,
1060, 822, 639 cmÀ1; HRMS (ESI): m/z calcd for C17H24NO3: 290.1751
[M+H]+; found: 290.1747.
1
a green oil (69mg, quantitative yield). H NMR (300 MHz, CDCl3; M/
m, 1.4:1): d=7.36–7.25 (m, 5H), 6.23–6.07 (m, 1H), 5.74–5.33 (m,
2H), 4.35–4.04 (m, 1H), 3.97–3.40 (m, 2H), 3.27–3.06 (m, 1H), 2.25–
1.86 (m, 2H), 1.78–1.68 (m, 1H), 1.55–1.43 (m, 3H), 1.29–1.17 (m,
3H), 0.78–0.46 ppm (m, 4H); 13C NMR (75 MHz, CDCl3): d=173.7,
173.5, 141.3, 141.1, 128.8, 128.6, 127.7, 127.6, 127.5, 127.3, 126.9,
126.0, 125.7, 82.1, 81.9, 77.9, 59.8, 59.6, 52.8, 52.7, 41.6, 32.2, 31.9,
17.0, 16.8, 16.6, 16.4, 16.2, 4.6, 4.5 ppm; IR (ATR): n˜ =3017, 1639,
3-Ethoxy-1-(4-methoxyphenyl)-3-methyl-3,4-dihydroazepinone
(16c): Following the general procedure, from carbene complex
15a (100mg, 0.38mmol) and vinylaziridine 11 c (55mg,
0.315mmol), dihydroazepinone 16c was obtained as a yellow oil
(79mg, 91%). 1H NMR (300 MHz, CDCl3): d=7.09 (dd, J=8.6,
1.5 Hz, 2H), 6.88 (dd, J=8.6, 1.6 Hz, 2H), 5.90–5.66 (m, 2H), 5.07–
4.95 (m, 1H), 3.80 (s, 3H), 3.77–3.69 (m, 2H), 3.59–3.47 (m, 1H),
2.65–2.47 (m, 2H), 1.51 (s, 3H), 1.33 ppm (t, J=7.0 Hz, 3H);
13C NMR (75 MHz, CDCl3): d=173.6, 158.3, 139.3, 128.4, 127.7,
125.3, 114.6, 81.0, 60.0, 55.8, 50.8, 38.8, 23.3, 16.4 ppm; IR (ATR):
n˜ =2975, 2932, 2839, 1653, 1508, 1455, 1400, 1370, 1327, 1294,
1243, 1059, 1032, 828, 636 cmÀ1; HRMS (ESI): m/z calcd for
C16H22NO3: 276.1594 [M+H]+; found: 276.1600.
1496, 1061, 730 cmÀ1
; HRMS (ESI): m/z calcd for C19H26NO2:
300.1958 [M+H]+; found: 300.1964.
1-Benzyl-3-cyclopropyl-3-ethoxy-3,4-dihydroazepinone
(16 f):
Following the general procedure, from carbene complex 15b
(46mg, 0.16mmol) and vinylaziridine 11 a (21mg, 0.13mmol), dihy-
droazepinone 16e was obtained as a colorless oil (22mg, 61%).
1H NMR (300 MHz, CDCl3): d=7.35–7.22 (m, 5H), 5.70–5.52 (m, 2H),
4.76–4.63 (m, 2H), 4.57–4.46 (m, 1H), 3.93–3.83 (m, 1H), 3.47–3.36
(m, 2H), 2.24–1.96 (m, 2H), 1.74–1.63 (m, 1H), 1.23 (t, J=7.0 Hz,
3H), 0.77–0.67 (m, 1H), 0.65–0.48 ppm (m, 3H); 13C NMR (75 MHz,
CDCl3): d=173.9, 138.2, 128.9, 128.2, 127.6, 127.0, 125.4, 81.8, 59.7,
53.7, 47.4, 31.9, 16.8, 16.3, 4.4, 1.0 ppm; IR (ATR): n˜ =3084, 3032,
2974, 2920, 1643, 1476, 1450, 1350, 1230, 1167, 1089, 840,
3-Ethoxy-3-methyl-1-[(R)-1-phenylethyl]-3,4-dihydroazepinone,
from 11d (16d and 3-epi-16d): Following the general procedure,
from carbene complex 15a (43mg, 0.16mmol) and vinylaziridine
11 d (23mg, 0.13mmol), an inseparable mixture of dihydroazepi-
none 16d and 3-epi-16d (1:2.5) was obtained as a yellow oil
(35mg, quantitative yield). 1H NMR (300 MHz, CDCl3; m/M, 1:2.5):
d=7.42–7.20 (m, 10H), 6.25–5.98 (m, 2H), 5.85–5.62 (m, 1H; M),
5.65–5.50 (m, 1H; M), 5.56–5.42 (m, 1H; m), 5.40–5.30 (m, 1H; m),
4.37–4.25 (m, 1H; m), 4.21–4.04 (m, 1H; M), 3.79–3.59 (m, 2H),
3.48–3.26 (m, 2H), 3.16 (dd, J=16.7, 7.5 Hz, 1H; m), 3.07 (dd, J=
17.3, 7.6 Hz, 1H; M), 2.59–2.41 (m, 4H), 1.55 (s, 3H; M), 1.54 (s, 3H;
m), 1.50 (d, J=7.0 Hz, 3H; m), 1.46 (d, J=7.0 Hz, 3H; M), 1.25 (t,
J=7.0 Hz, 3H; m), 1.17 ppm (t, J=7.0 Hz, 3H; M); 13C NMR
(75 MHz, CDCl3; m/M, 1:2.5): d=173.5 (m), 173.3 (M), 141.3 (M),
141.1 (m), 128.8, 128.6, 128.2, 127.6, 127.5, 126.0 (M), 125.6 (m),
81.2 (M), 81.0 (m), 60.2 (M), 59.9 (m), 52.6 (M), 52.6 (m), 41.3 (m),
41.2 (M), 39.1 (M), 38.8 (m), 23.8 (m), 23.7 (M), 16.6 (m), 16.4 (M+
m), 16.3 ppm (M); IR (ATR): n˜ =3025, 2975, 2934, 2901, 1635, 1466,
1415, 1370, 1254, 1205, 1173, 1104, 1060, 920, 828, 778, 743, 700,
734 cmÀ1
; HRMS (ESI): m/z calcd for C18H23NNaO2: 308.1626
[M+Na]+; found: 308.1626.
1-Benzyl-3-butyl-3-ethoxy-3,4-dihydroazepinone (16g): Follow-
ing the general procedure, from carbene complex 15c (100mg,
0.32mmol) and vinylaziridine 11 a (42mg, 0.26mmol), dihydroaze-
pinone 16 f was obtained as a colorless oil (73mg, quantitative
yield). 1H NMR (300 MHz, CDCl3): d=7.34–7.22 (m, 5H), 5.69–5.55
(m, 2H), 4.73 (d, J=14.9 Hz, 1H), 4.64–4.54 (m, 2H), 3.55–3.46 (m,
1H), 3.39–3.25 (m, 2H), 2.60 (dt, J=18.6, 3.6 Hz, 1H), 2.38–2.27 (m,
1H), 2.20–2.08 (m, 1H), 1.81–1.72 (m, 1H), 1.42–1.33 (m, 4H), 1.22
(t, J=7.0 Hz, 3H), 0.95 ppm (t, J=6.8 Hz, 3H); 13C NMR (75 MHz,
CDCl3): d=173.9, 138.2, 128.9, 128.2, 127.7, 127.59, 125.33, 82.3,
59.2, 53.6, 47.1, 35.3, 34.1, 25.4, 23.6, 16.1, 14.6 ppm; IR (ATR): n˜ =
3026, 2957, 2827, 2869, 1642, 1475, 1450, 1417, 1232, 1166, 1106,
804, 730, 698 cmÀ1
; HRMS (ESI): m/z calcd for C19H27NNaO2:
324.1939 [M+Na]+; found: 324.1938.
648 cmÀ1
;
HRMS (ESI): m/z calcd for C17H23NNaO2: 296.1621
[M+Na]+; found: 296.1619.
1-Benzyl-3-ethoxy-3-methyl-3,4,7,8-tetrahydroazocinone (20a):
Following the general procedure, from carbene complex 15a
(120mg, 0.46mmol) and vinylazetidine 17a (66mg, 0.38mmol), tet-
rahydroazocinone 20a was obtained as a colorless oil (67mg,
64%). 1H NMR (300 MHz, CDCl3): d=7.36–7.21 (m, 5H), 5.77–5.65
(m, 1H), 5.57–5.46 (m, 1H), 5.06 (d, J=14.7 Hz, 1H), 4.67–4.54 (m,
1H), 3.95 (d, J=14.7 Hz, 1H), 3.66–3.56 (m, 1H), 3.28 (dq, J=9.0,
7.0 Hz, 1H), 3.17–3.07 (m, 1H), 2.78 (dd, J=13.6, 9.7 Hz, 1H), 2.45–
2.28 (m, 3H), 1.54 (s, 3H), 1.15 ppm (t, J=7.0 Hz, 3H); 13C NMR
(75 MHz, CDCl3): d=173.8, 138.3, 129.2, 128.8, 128.5, 127.6, 127.2,
83.3, 60.4, 49.8, 44.4, 41.9, 26.6, 25.3, 16.1 ppm; IR (ATR): n˜ =3026,
3-Ethoxy-3-methyl-1-[(R)-1-phenylethyl]-3,4-dihydroazepinone,
from 2-epi-11d (16d and 3-epi-16d): Following the general proce-
dure, from carbene complex 15a (57mg, 0.22mmol) and vinylaziri-
dine 2-epi-11 d (31mg, 0.18mmol), an inseparable mixture of dihy-
droazepinone 16d and 3-epi-16d (1.7:1) was obtained as a yellow
oil (29mg, 58%). 1H NMR (300 MHz, CDCl3; M/m, 1.7:1): d=7.39–
7.23 (m, 10H), 6.21–6.05 (m, 2H), 5.80–5.67 (m, 1H; m), 5.66–5.54
(m, 1H; m), 5.54–5.45 (m, 1H; M), 5.41–5.31 (m, 1H; M), 4.38–4.26
(m, 1H; M), 4.19–4.06 (m, 1H; m), 3.77–3.60 (m, 2H), 3.44–3.28 (m,
2H), 3.17 (dd, J=16.8, 7.7 Hz, 1H; M), 3.12–3.02 (m, 1H; m), 2.55–
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2974, 2928, 1639, 1421, 1365, 1252, 1197, 1158, 1108, 1067, 1034,
958, 702 cmÀ1; HRMS (ESI): m/z calcd for C17H23NNaO2: 296.1621
[M+Na]+; found: 296.1625.
d=173.5, 138.1, 128.9, 128.1, 127.9, 127.7, 125.1, 80.9, 61.2, 61.1,
53.6, 47.1, 47.0, 38.4, 31.8, 23.5, 23.4 ppm; IR (ATR): n˜ =3026, 2987,
2932, 1639, 1495, 1480, 1453, 1345, 1171, 1114, 1077, 733,
700 cmÀ1; HRMS (ESI): m/z calcd for C31H38N2O4: 502.2904 [M+H]+;
found: 502.2910.
3-Ethoxy-1-(4-methoxybenzyl)-3-methyl-3,4,7,8-tetrahydroazoci-
none (20b): Following the general procedure, from carbene com-
plex 15a (70mg, 0.26mmol) and vinylazetidine 17b (45mg,
0.22mmol), tetrahydroazocinone 20b was obtained as a colorless
Bis(dihydroazepinone) 22b: Following the general procedure,
from biscarbene complex 21b (279mg, 0.53mmol) and vinylaziri-
dine 11 a (170mg, 1.06mmol), biscycloadduct 22b was obtained
as a colorless oil (150mg, 55%). 1H NMR (300 MHz, CDCl3): d=
7.37–7.19 (m, 10H), 5.69–5.52 (m, 4H), 4.67 (s, 4H), 4.55–4.43 (m,
2H), 3.58–3.49 (m, 2H), 3.39–3.24 (m, 4H), 2.47 (s, 4H), 1.65–1.56
(m, 4H), 1.50 ppm (s, 6H); 13C NMR (75 MHz, CDCl3): d=173.6,
138.1, 128.9, 128.2, 127.9, 127.7, 125.2, 80.8, 64.1, 64.0, 53.6, 47.0,
38.4, 27.7, 27.6, 23.5 ppm; IR (ATR): n˜ =3026, 2985, 2936, 1639,
1
oil (62mg, 93%). H NMR (300 MHz, CDCl3): d=7.15 (d, J=8.5 Hz,
2H), 6.82 (d, J=8.5 Hz, 2H), 5.74–5.62 (m, 1H), 5.46 (dt, J=10.3,
5.1 Hz, 1H), 4.92 (d, J=14.5 Hz, 1H), 4.55 (dt, J=17.9, 9.5 Hz, 1H),
3.90 (d, J=14.5 Hz, 1H), 3.77 (s, 3H), 3.62–3.52 (m, 1H), 3.28–3.17
(m, 1H), 3.09 (dt, J=15.5, 3.8 Hz, 1H), 2.78–2.68 (m, 1H), 2.42–2.25
(m, 3H), 1.51 (s, 3H), 1.11 ppm (t, J=7.0 Hz, 3H); 13C NMR (75 MHz,
CDCl3): d=173.6, 159.2, 130.4, 129.9, 129.3, 127.1, 114.2, 83.3, 60.4,
55.6, 49.2, 44.2, 41.9, 26.7, 25.3, 16.1 ppm; IR (ATR): n˜ =2973, 2929,
2838, 1636, 1511, 1461, 1436, 1418, 1245, 1175, 1065, 1032, 983,
842, 812, 777, 755 cmÀ1; HRMS (ESI): m/z calcd for C18H25NNaO3:
326.1727 [M+Na]+; found: 326.1724.
1495, 1480, 1453, 1417, 1233, 1113, 1078, 853, 798, 733, 700 cmÀ1
;
HRMS (ESI): m/z calcd for C32H40N2O4: 517.3061 [M+H]+; found:
517.3068.
Bis(dihydroazepinone) 22c: Following the general procedure,
from biscarbene complex 21c (280mg, 0.49mmol) and vinylaziri-
dine 11 a (155mg, 0.98mmol), biscycloadduct 22c was obtained as
a colorless oil (130mg, 47%). 1H NMR (300 MHz CDCl3): d=7.34–
7.19 (m, 10H), 5.58 (d, J=4.0 Hz, 4H), 4.76–4.61 (m, 6H), 4.46–4.36
(m, 2H), 4.34–4.25 (m, 2H), 3.36–3.18 (m, 2H), 2.67–2.43 (m, 4H),
1.62 (s, 3H), 1.60 (s, 3H), 1.65–1.59 ppm (m, 6H); 13C NMR (75 MHz,
CDCl3): d=173.4, 173.3, 138.1, 136.6, 136.5, 129.0, 128.5, 128.28,
128.26, 128.17, 128.10, 127.8, 125.2, 81.39, 81.38, 64.1, 64.0, 53.71,
53.68, 47.3, 47.2, 38.6, 38.5, 23.61, 23.57 ppm; IR (ATR): n˜ =3027,
2986, 2926, 2629, 1733, 1637, 1480, 1453, 1453, 1418, 1260, 1231,
3-Ethoxy-3-methyl-1-octyl-3,4,7,8-tetrahydroazocinone
(20c):
Following the general procedure, from carbene complex 15a
(80mg, 0.31mmol) and vinylazetidine 17c (50mg, 0.25mmol), tet-
rahydroazocinone 20c was obtained as a colorless oil (45mg,
60%). 1H NMR (300 MHz, CDCl3): d=5.74–5.60 (m, 1H), 5.60–5.47
(m, 1H), 4.71–4.54 (m, 1H), 3.71–3.49 (m, 2H), 3.25–3.07 (m, 2H),
2.80–2.67 (m, 2H), 2.51–2.28 (m, 3H), 1.57–1.42 (m, 5H), 1.25 (s,
10H), 1.14 (t, J=7.3 Hz, 3H), 0.86 ppm (t, J=6.3 Hz, 3H); 13C NMR
(75 MHz, CDCl3): d=173.1, 129.1, 127.2, 83.3, 60.2, 47.4, 45.3, 41.9,
32.2, 29.8, 29.7, 28.1, 27.5, 27.1, 25.2, 23.0, 16.2, 14.5 ppm; IR (ATR):
n˜ =2927, 1641, 1466, 1369, 1066, 802, 711 cmÀ1; HRMS (ESI): m/z
calcd for C18H34NO2: 296.2584 [M+H]+; found: 296.2579.
1185, 1079, 733, 699, 644 cmÀ1
; HRMS (ESI): m/z calcd for
C36H40N2O4: 565.3061 [M+H]+; found: 565.3073.
3-Ethoxy-3-methyl-1-cyclohexyl-3,4,7,8-tetrahydroazocinone
(20d): Following the general procedure, from carbene complex
15a (95mg, 0.36mmol) and vinylazetidine 17d (50mg, 0.3mmol),
tetrahydroazocinone 20d was obtained as a colorless oil (65mg,
82%). 1H NMR (300 MHz, CDCl3): d=5.81–5.65 (m, 1H), 5.63–5.49
(m, 1H), 4.57–4.35 (m, 1H), 4.30–4.17 (m, 1H), 3.63–3.46 (m, 1H),
3.31–3.09 (m, 2H), 2.74–2.60 (m, 1H), 2.44–2.21 (m, 3H), 1.83–1.49
(m, 6H), 1.48 (s, 3H), 1.48–1.25 (m, 4H), 1.13 ppm (t, J=7.0 Hz,
3H); 13C NMR (75 MHz, CDCl3): d=172.7, 129.6, 127.5, 83.5, 60.2,
55.3, 42.1, 40.6, 31.4, 31.2, 29.4, 26.5, 26.3, 26.1, 25.5, 16.2 ppm; IR
(ATR): n˜ =2928, 1775, 1639, 1393, 1065, 1024, 712 cmÀ1; HRMS
(ESI): m/z calcd for C16H28NO2: 266.2115 [M+H]+; found: 266.2121.
Bis(azepinone) 22d: Following the general procedure, from biscar-
bene complex 21d (235mg, 0.41mmol) and vinylaziridine 11 a
(130mg, 0.82mmol), biscycloadduct 22d was obtained as a yellow
oil (137mg, 61%). 1H NMR (300 MHz, CDCl3): d=7.39–7.32 (m,
10H), 5.76–5.59 (m, 4H), 4.75 (s, 4H), 4.70 (d, J=11.0 Hz, 2H), 4.60–
4.46 (m, 2H), 4.36 (d, J=11.0 Hz, 2H), 3.44–3.32 (m, 2H), 2.74–2.53
(m, 4H), 1.69 ppm (s, 6H); 13C NMR (75 MHz, CDCl3): d=173.4,
138.1, 137.9, 128.9, 128.2, 127.9, 127.77, 127.73, 125.1, 81.4, 66.4,
53.7, 47.2, 38.5, 23.7 ppm; IR (ATR): n˜ =3026, 2987, 2932, 1639,
1495, 1480, 1453, 1345, 1173, 1078, 963, 875, 733, 700 cmÀ1; HRMS
(ESI): m/z calcd for C36H40N2O4: 565.3061 [M+H]; found: 565.3060.
Bis(azepinone) 22e: Following the general procedure, from biscar-
bene complex 21e (230mg, 0.4mmol) and vinylaziridine 11 a
(128mg, 0.8mmol), biscycloadduct 22e was obtained as a colorless
oil (114mg, 59%). 1H NMR (300 MHz, CDCl3): d=7.37–7.14 (m,
10H), 5.60 (d, J=4.3 Hz, 4H), 4.74–4.67 (m, 4H), 4.63 (d, J=11.0 Hz,
2H), 4.52–4.42 (m, 2H), 4.31 (d, J=11.0 Hz, 2H), 3.42–3.19 (m, 2H),
2.67–2.46 (m, 4H), 1.62 ppm (s, 6H); 13C NMR (75 MHz, CDCl3): d=
173.4, 138.8, 138.1, 129.0, 128.2, 127.79, 127.76, 126.94, 126.90,
125.17, 125.15, 81.4, 66.5, 53.7, 47.2, 38.5, 23.7 ppm; IR (ATR): n˜ =
3028, 2920, 2851, 1719, 1636, 1519, 1495, 1375, 1263, 1189, 1110,
895, 786, 733 cmÀ1; HRMS (ESI): m/z calcd for C36H40N2O4: 565.3061
[M+H]+; found: 565.3079.
General procedure for the photochemical cycloaddition reac-
tions involving biscarbene complexes 21: Photoreactions were
carried out in oven-dried pressure tubes that were charged with
the biscarbene complex 21 and vinylaziridine 11 a (2:1 molar ratio)
in dry, degassed Et2O (3 freeze–pump–thaw cycles). The tube was
fitted with a pressure head, purged three times with CO, and irradi-
ated under CO (60–70 psi; medium pressure mercury lamp 400 W,
pyrex filter, and pyrex well) for 20 h. The solvent from the crude re-
action mixture was removed under vacuum, the residue was taken
up in hexane/EtOAc (1:1), and exposed to light to oxidize the re-
maining chromium(0) compounds. This mixture was filtered
through Celite and purified by silica gel chromatography (hexane/
EtOAc, 4:1 to 2:1, TLC plates were developed in oleum) to produce
the desired biscycloadducts 22.
Computational details: Geometry optimizations without symmetry
constraints were carried out by using the Gaussian 09 suite of pro-
grams[21] using the B3LYP[22] functional in combination with the
double-z plus polarization def2-SVP basis sets[23] for all atoms in
Et2O as the solvent and using the polarizable continuum model
(PCM) method.[24] This level is denoted PCM(Et2O)-B3LYP/def2-SVP.
Reactants and products were characterized by frequency calcula-
tions[25] and have positive definite Hessian matrices. Transition
structures (TSs) show only one negative eigenvalue in their diagon-
alized force constant matrices, and their associated eigenvectors
Bis(dihydroazepinone) 22a: Following the general procedure,
from biscarbene complex 21a (250mg, 0.49mmol) and vinylaziri-
dine 11 a (155mg, 0.98mmol), biscycloadduct 22a was obtained as
a colorless oil (100mg, 41%). 1H NMR (300 MHz CDCl3): d=7.32–
7.22 (m, 10H), 5.70–5.50 (m, 4H), 4.72–4.58 (m, 4H), 4.54–4.43 (m,
2H), 3.66–3.54 (m, 2H), 3.41–3.26 (m, 4H), 2.46 (s, 4H), 1.90–1.76
(m, 2H), 1.50 (s, 3H), 1.48 ppm (s, 3H); 13C NMR (75 MHz, CDCl3):
Chem. Eur. J. 2014, 20, 1359 – 1366
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[11] C. J. Deur, M. W. Miller, L. S. Hegedus, J. Org. Chem. 1996, 61, 2871.
[12] a) R. Malherbe, D. Bellus, Helv. Chim. Acta 1978, 61, 3096; b) R. Mal-
herbe, G. Rist, D. Bellus, J. Org. Chem. 1983, 48, 860; c) G. Rosini, G. G.
Spineti, E. Foresti, G. Pradella, J. Org. Chem. 1981, 46, 2228; d) E. Vedejs,
R. A. Buchanan, J. Org. Chem. 1984, 49, 1841; e) E. Edstrom, J. Am.
Chem. Soc. 1991, 113, 6690.
[13] Reaction of complex 15a and vinylazetidine 11 a was tested under an
Ar atmosphere. The corresponding azepinone 16a was obtained in
53% yield. Therefore, all the reactions were carried out under a CO at-
mosphere.
were confirmed to correspond to the motion along the reaction
coordinate under consideration by using the intrinsic reaction co-
ordinate (IRC) method.[26]
Acknowledgements
The authors are grateful for financial support from the Spanish
MINECO (grants CTQ2010-20714-C02-01/BQU and Consolider-
Ingenio 2010, CSD2007-00006) and CAM (grant S2009/PPQ-
1634, AVANCAT). A.R.R. acknowledges the MINECO for an FPU
grant.
[14] Vinylaziridines 11 d and 2-epi-11 d were obtained by reaction of (R)-a-
phenylethylamine and ethyl 2,3-dibromopropionate, by following the
standard procedure depicted in Scheme 4, as a 1:1 diastereomeric mix-
ture.
[15] L. S. Hegedus, L. M. Schultze, J. Toro, C. Yijun, Tetrahedron 1985, 41,
5741.
[16] a) F. P. Cossꢃo, A. Arrieta, M. A. Sierra, Acc. Chem. Res. 2008, 41, 925;
b) T. T. Tidwell, Ketenes II, Wiley, Hoboken, 2006.
Keywords: aziridines
metal–carbenes · photochemistry
· cycloaddition · DFT calculations ·
[17] See the Computational Details.
[18] Highly asynchronous transition states have also been located for other
cycloaddition reactions; see, for example: N. C¸elebi-ꢅlÅꢆm, Y.-H. Lam, E.
Richmond, K. B. Ling, A. D. Smith, K. N. Houk, Angew. Chem. 2011, 123,
11680; Angew. Chem. Int. Ed. 2011, 50, 11478.
[19] For a related solvent-mediated release of the {Cr(CO)5} fragment, see: I.
Fernꢀndez, M. J. MancheÇo, R. Vicente, L. A. Lꢄpez, M. A. Sierra, Chem.
Eur. J. 2008, 14, 11222.
[20] a) A. Hafner, L. S. Hegedus, G. deWeck, B. Hawkins, K. H. Dçtz, J. Am.
Chem. Soc. 1988, 110, 8413; b) M. A. Sierra, J. C. del Amo, M. J. Manche-
Ço, M. Gꢄmez-Gallego, J. Am. Chem. Soc. 2001, 123, 851–861.
[21] Gaussian 09, Revision B.01, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E.
Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Men-
nucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian,
A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara,
K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O.
Kitao, H. Nakai, T. Vreven, J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro,
M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, R. Ko-
bayashi, J. Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyen-
gar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B.
Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann,
O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin,
K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg,
S. Dapprich, A. D. Daniels, ꢅ. Farkas, J. B. Foresman, J. V. Ortiz, J. Cio-
slowski, D. J. Fox, Gaussian, Inc., Wallingford CT, 2009.
[1] For the literature covering the reaction of vinylaziridines with unsaturat-
ed substrates before 1982, see: A. Hassner, W. Chau, R. de Costa, Isr. J.
Chem. 1982, 22, 76.
[2] H. Ohno, Vinylaziridines in Organic Synthesis in Aziridines and Epoxides in
Organic Synthesis (Ed.: A. K. Yudin), Wiley-VCH, Weinheim, 2006, pp. 37–
71.
[3] a) D. C. D. Butler, G. A. Inman, H. Alper, J. Org. Chem. 2000, 65, 5887;
b) C. Dong, H. Alper, Tetrahedron: Asymmetry 2004, 15, 1537.
[4] F. Fontana, C. C. Chen, V. K. Aggarwal, Org. Lett. 2011, 13, 3454.
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Received: May 27, 2013
Revised: October 17, 2013
Published online on December 16, 2013
Chem. Eur. J. 2014, 20, 1359 – 1366
www.chemeurj.org
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