Photochemically driven addition of iminyl radicals to alkynyl fischer carbene complexes

Article abstract of DOI:10.1021/om200438y

Nitrogen-centered radicals, generated by the action of UV light, are capable of reacting with alkynyl Fischer carbene complexes in two ways, 1,2- and 1,4-addition. Our results constitute the first reported example of a photochemically driven reaction of t

Full text of DOI:10.1021/om200438y

ARTICLE
pubs.acs.org/Organometallics
Photochemically Driven Addition of Iminyl Radicals to Alkynyl Fischer
Carbene Complexes†
ꢀ
Marina Blanco-Lomas, Alegria Caballero, Pedro J. Campos, Hꢀector F. Gonzꢀalez, Susana Lꢀopez-Sola,
ꢀ
Laura Rivado-Casas, Miguel A. Rodriguez,* and Diego Sampedro
ꢀ
ꢀ
ꢀ
Departamento de Quimica, Universidad de La Rioja, Grupo de Sintesis Quimica de La Rioja, Unidad Asociada al CSIC, Madre de Dios,
51, E-26006, Logro~no, Spain
ABSTRACT:
Nitrogen-centered radicals, generated by the action of UV light, are capable of reacting with alkynyl Fischer carbene complexes in
two ways, 1,2- and 1,4-addition. Our results constitute the first reported example of a photochemically driven reaction of this kind.
Scheme 1. Iminyl Radical Addition to Alkynes
’ INTRODUCTION
Radicals have shown impressive potential in synthesis.1 We
recently described2 the use of acyloximes in the photochemical
synthesis of isoquinoline derivatives in a two-step, one-pot
reaction sequence. First, the iminyl radical is easily generated
by a nitrogenꢀoxygen bond cleavage. The addition of this radical
to unsaturated moieties then gives the heterocyclic compounds
with ease in good yields.2 This reaction mechanism has been
further explored by means of theoretical calculations3 and EPR
studies.4 Several groups are able to react in the intramolecular
version, such as aryl, heteroaryl, alkenyl, or alkynyl,2 while the
intermolecular reaction works particularly well with alkynes to give
isoquinolines (Scheme 1).2a This fact, together with our experi-
ence in the photochemistry of imine Fischer carbene complexes,5
prompted us to study the reactivity of iminyl radicals with alkynyl
Fischer carbene complexes.
successful results for the photochemically induced addition of an
iminyl radical to unsaturated metalꢀcarbene complexes.
A survey of the literature showed that metal carbene com-
plexes have been extensively used as synthons in organic and
organometallic synthesis.6 However, as far as we know, only four
papers have been published on additions of radicals to unsatu-
rated Fischer carbene complexes. All of these reactions were
carried out under thermal conditions and none under photo-
chemical ones. The strategy to add alkyl radicals, generated from
epoxides and [Cp2TiCl]2, to R,β-unsaturated carbenes was
developed by Merlic7 and was also used by D€otz to prepare
carbohydrate-modified fused pyranosylidene complexes,8 while
Sierra used Et3B in the presence of traces of oxygen to produce an
ethyl radical that adds to the carbene complex.9 The lack of
examples is not surprising considering that carbenes often react
with several types of reagents for radical generation or are incom-
patible with the reaction conditions to create such species.10
Sierra also attempted to promote this kind of reaction by forming
the radical through irradiation (tungsten lamp or sunlight) of
Barton esters,11 but this process resulted in recovery of unreacted
or oxidized metalꢀcarbene complex.9 We report here the first
’ RESULTS AND DISCUSSIONS
In our first attempt we reproduced the previous reaction
conditions that successfully yielded isoquinolines. Irradiation of
a solution of benzophenone O-acetyloxime (1a) and penta-
carbonyl(1-ethoxy-3-phenyl-2-propynylidene)tungsten (2a) was
performed, at room temperature, with a 400 W medium-pressure
mercury lamp through Pyrex under an Ar atmosphere. However,
we found that the same reaction conditions were not appropriate
in this case since only decomposition of the carbene complex
occurred.
In our previous experiments, alkynes were used in excess to
easily capture the forming radical and to improve the product
yields. In this case, excess alkynyl carbene complex acts as an
internal filter, preventing formation of the iminyl radical.12 As we
were unable to irradiate the oxime derivative selectively, we
Received: May 24, 2011
Published: June 08, 2011
r
2011 American Chemical Society
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Scheme 2. Iminyl Radical Addition to Alkynylcarbene
Complexes
Scheme 4. Nucleophilic Addition of Imine 1b to Carbene
Complex 2a
Scheme 5. Reactivity of Compound 3a
Scheme 3. Radical versus Nucleophilic Addition
1
determined by the H spectrum of the crude reaction mixture.
This result demonstrates that the photochemical process is much
faster than the thermal one and supports the fact that the reaction
shown in Scheme 2 should be induced by the action of ultraviolet
light. However, as shown in Scheme 3, once the radical is formed,
it could evolve by direct radical addition to carbene 2a (path A)
or by hydrogen abstraction from the medium, followed by
nucleophilic addition of benzophenone imine 1b to 2a (path B).
In contrast to the thermal reaction of imines with Fischer
alkylcarbenes, which takes place with replacement of alkoxy by
the imino group,16 compounds with similar structures to carbene
3a can also be obtained through nucleophilic addition of imines
to alkynylcarbene complexes.14 Moreover, complexes of type 3
cyclize to 2H-pyrroles upon heating at 50ꢀ55 °C in tetrahydro-
furan solution. However, while the nucleophilic addition of
imines to chromium complexes is well known, only one example
has been described for the analogous process with a tungsten
complex bearing a tert-butyl group.14 Considering that the
reaction with the phenyl derivative tungsten complex has not
been described, we performed the reaction between carbene 2a
and benzophenone imine 1b. After 30 min stirring in diethyl
ether (de Meijere procedure)14 or 3 h in acetonitrile we observed
the formation of the seven-membered cycle 4a, which could be
isolated in 3% or 7% yield, respectively, together with a large
amount of benzophenone and various unidentified products,
but neither carbene nor starting carbene 2a was detected in the
crude reaction mixture (Scheme 4). These results rule out path
B to explain the formation of carbene 3a and, consistently, 3a
could be formed after initial addition of the iminyl radical to
carbene 2a.
modified the reaction conditions by using a 1:1 reactant ratio and
a low-pressure Hg lamp.13 Under these conditions, irradiation in
acetonitrile for 3 h led to the consumption of 1a and 2a and the
formation of the new carbene complex 3a, identified by spectro-
scopic data and comparison with similar complexes,14,15 together
with another product, identified as the seven-membered com-
pound 4a (Scheme 2).
As we were limited by the relative absorption of the two
reactants, the study of the effect of diverse reaction conditions on
the reaction outcome was limited. In all cases low-pressure Hg
lamps and a 1:1 ratio between reactants were used. Higher
carbene complex ratios led to a decrease in the reaction yields,
and higher acyloxime ratios contributed to an increase in the
formation of 4a. We also tried diverse oxime derivatives under
our best reaction conditions in order to test the influence of the
acyl moiety on the iminyl radical formation. The use of benzo-
phenone O-benzoyl- or (p-methoxybenzoyl)oxime did not affect
either of the results, the products or the yields, while the use of
benzaldehyde O-acetyloxime as the iminyl radical precursor led
only to decomposition of the starting materials. This is not
surprising, as it is known2,3 that iminyl radicals with R-hydrogen
atoms are unstable and easily yield nitriles, and we could check
that carbene 2a decomposes under the direct action of UV light.
However, the use of methoxy carbene 2b gave 3b and 4b in 10%
and 12% yields, respectively (Scheme 2).
On the other hand, 4a could also be formed from 3a either
thermally or photochemically. As additional assays, isolated 3a
was irradiated in acetonitrile for 3 h, but this resulted in
decomposition without the formation of 4a, while stirring for 3
h did not alter starting material 3a. However, heating complex 3a
in acetonitrile at 80 °C for 4 h led to 2H-pyrrole 5a in 76% yield, a
finding consistent with the literature,14 but cycle 4a was not
detected (Scheme 5).
To explore the photochemical nature of the reaction, we
performed a test at room temperature in the dark. After 3 h of
stirring only traces of 3a were obtained, together with a large
amount of unreacted starting compounds 1a and 2a, as
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In any case, it can be stated that all of the assays provide
indirect evidence for the radical addition to carbene 2. In an effort
to find direct evidence, we irradiated a mixture of 1a and 2a in the
presence of radical trappers such as TEMPO and Ph2Se2, but the
reaction yielded complex mixtures in which a carbene with a
structure like 3 could not be detected, probably due to interac-
tion of these trappers with the iminyl radical.
On the other hand, bearing in mind that a hydrogen atom
could be abstracted from the medium, the reaction in a deuter-
ated medium should give the analogous deuterated carbene.
Irradiation of 1a and 2a was performed using tetrahydrofuran-d8
or acetonitrile-d3 as solvent, but 3a was obtained once again
rather than the corresponding deuterated compound. We con-
tinued by replacing the methyl group in the carbene and
acyloxime by the trideuteromethyl one. As shown in Scheme 6,
the photoreaction of 1c and 2c in acetonitrile-d3 once again led to
3c and 4c.
These results prompted us to consider that hydrogen incor-
poration into the structure could be a polar proccess, instead of a
radical one, and traces of water present in the reaction medium
should be enough to trap a proton.17 Therefore, we performed
the irradiation of 1a and 2a in acetonitrile but in the presence of
deuterated water (9:1 ratio). This reaction gave compounds 3d
and 4d, where a deuterium has been incorporated into both
structures (Scheme 7).
Scheme 6. Irradiation in a Deuterated Medium
Although a definitive reaction pathway cannot be established
yet, tentative working proposals for the formation of 3 and 4 are
Scheme 7. Incorporation of a Deuterium Atom
Scheme 8. Proposed Mechanism for the Formation of Carbenes 3
Scheme 9. Proposed Mechanism for the Formation of Azepines 4
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Scheme 10. Deuterium Migration
(cabinet photoreactor equipped with 16 low-pressure mercury lamps of
8 W) or stirred at room temperature for the time specified for each case.
The solvent was removed in vacuo, and the products were purified by
column chromatography (silica gel, hexane/AcOEt).
Benzophenone Trideuteroacetyloxime (1c) (ref 21). Yield:
1
213 mg, 88%. H NMR: δ 7.47ꢀ7.16 (m, 10H) ppm. 13C NMR: δ
168.4, 164.3, 134.4, 132.2, 130.6, 129.4, 128.7, 128.5, 128.3, 128.1, 18.7
(m, CD3) ppm. UV: λ 210, 252 nm (ε = 9100, 16 250 Mꢀ1 cmꢀ1). Exact
mass ESI(þ) (C15H10D3NO2 þ Na): calcd 265.1025, measd 265.1027.
Bis(perdeuterophenyl)methanone acetyloxime (1d) (ref
21). Yield: 239 mg, 96%. 1H NMR: δ 2.07 (s, 3H) ppm. 13C NMR: δ
168.5, 164.3, 134.4, 132.1, 130.5ꢀ127.2 (m, CD), 19.4 ppm. UV: λ 212,
252 nm (ε = 9120, 16 330 Mꢀ1 cmꢀ1). Exact mass ESI(þ) (C15H3D10-
NO2 þ Na): calcd 272.1447, measd 272.1466.
Pentacarbonyl(1-trideuteromethoxy-3-phenyl-2-propy-
nylidene)tungsten(0) (2c) (ref 22). Yield: 452 mg, 16%. 1H NMR:
δ 7.65ꢀ7.25 (m, 5H) ppm. 13C NMR: δ 283.9 (C-1), 205.6, 197.4
(CdO), 132.9, 131.7, 129.0, 121.0 ppm. C-2, C-3, and CD3 not
observed. UV: λ 245, 290, 314, 357, 465 nm (ε = 32 450, 13 180,
9250, 3150, 12 590 Mꢀ1 cmꢀ1). Exact mass MALDI(ꢀ) (C15H5D3-
O6W): calcd 471.001, measd 471.184.
displayed in Schemes 8 and 9, respectively. First, as mentioned
above, thermal reaction between acyloxime 1a and carbene 2a
led to only traces of 3a after 3 h of stirring. Moreover, carbene 3a
was not detected in the thermal reaction between imine 1b and
2a (Scheme 4). We therefore propose that irradiation of acylox-
ime 1 should generate the iminyl radical. This would attack
carbene 2 at the alkynyl carbon (1,4-addition) to form inter-
mediate A, which can be represented by two resonance structures
(Scheme 8). A photoinduced electron transfer18 could then occur
to give carbene anion B, which is able to react with traces of H2O or
D2O to yield 3.
In relation to the seven-membered cycle, although the parti-
cipation of the thermal reaction between imine 1b (which should
be generated by a hydrogen abstraction on the iminyl radical
from the medium) and 2 cannot be ruled out (Scheme 4), hetero-
cycles 4 were obtained in up to 17% yield. As a result, we suggest a
similar mechanism to that proposed for carbenes 3. The forma-
tion of azepine 4 is thought to occur by subsequent 1,2-addition
of the iminyl radical to the carbene carbon of 2 and photoinduced
electron transfer18 to form the species C (Scheme 9). A 1,2-metal
migration, promoted by the methoxy group, would cause simul-
taneous ring closure with one of the iminic phenyl groups to form
intermediate D.17,19 A subsequent hydrogen shift regenerates the
aromaticity and 4 would form after hydrolysis or deuterolysis.
To test the effect of temperature on the addition product ratio,
the irradiation was performed at ꢀ20 °C, but, unfortunately, there
were no significant changes compared with the process at room
temperature. Finally, the proposal for the formation of azepines 4
was supported by the use of the acyloxime of benzophenone-d10
1d asthe startingmaterial(Scheme 10). Inthis case azepine 4e was
formed in 35% yield after deuterium migration from D to E. The
higher yield of 4e could be rationalized considering that an inverse
isotope effect at the position of deuteration is expected because of
the change from sp2 to sp3 hybridization.20
Pentacarbonyl{(2Z)-3-[(diphenylmethylene)amino]-1-
ethoxy-3-phenyl-2-propenylidene)}tungsten(0) (3a). Yield:
1
33 mg, 25%. H NMR: δ 7.64ꢀ7.30 (m, 15H), 7.18 (s, 1H, H-2),
4.66 (q, 2H, J = 6.0 Hz), 1.26 (t, 3H, J = 6.0 Hz) ppm. 13C NMR: δ 296.4
(C-1), 204.1, 198.2 (CdO), 164.2 (CdN), 150.0, 137.6, 136.3, 130.7,
130.6, 128.8, 128.5, 128.3, 127.9, 127.6, 125.8 (C-2), 78.8, 15.2 ppm. IR:
ν 2059, 1980, 1928 (WꢀCO), 1662 (CdC), 1604 (CdN), 1219
(CꢀO) cmꢀ1. UV: λ 246, 289, 350, 451 nm (ε = 32 910, 9880, 5430,
10 210 Mꢀ1 cmꢀ1). Exact mass MALDI(ꢀ) (C29H21NO6W): calcd
663.088, measd 663.085.
Pentacarbonyl{(2Z)-3-[(diphenylmethylene)amino]-1-
methoxy-3-phenyl-2-propenylidene)}tungsten(0) (3b). Yield:
13 mg, 10%. 1H NMR: δ 7.47ꢀ7.26 (m, 15H), 7.12 (s, 1H, H-2), 4.34 (s,
3H) ppm. 13C NMR: δ 296.5 (C-1), 204.0, 198.1 (CdO), 164.8 (CdN),
150.3, 137.8, 136.3, 130.7, 128.8, 128.7, 128.6, 128.3, 127.7, 124.5 (C-2),
68.9 ppm. Exact mass MALDI(ꢀ) (C28H19NO6W): calcd 649.072,
measd 649.013.
Pentacarbonyl{(2Z)-3-[(diphenylmethylene)amino]-1-tri-
deuteromethoxy-3-phenyl-2-propenylidene)}tungsten(0)
(3c). Yield: 11 mg, 8%. 1H NMR: δ 7.47ꢀ7.28 (m, 15H), 7.12 (s, 1H,
H-2) ppm. 13C NMR: δ 296.5 (C-1), 204.0, 198.1 (CdO), 164.8
(CdN), 150.3, 137.8, 136.3, 130.7, 128.8, 128.7, 128.6, 128.3, 127.7,
124.5 (C-2) ppm. CD3 not observed. Exact mass MALDI(ꢀ)
(C28H16D3NO6W): calcd 652.090, measd 652.014.
Pentacarbonyl{(2Z)-2-deutero-3-[(diphenylmethylene)-
amino]-1-ethoxy-3-phenyl-2-propenylidene)}tungsten(0)
(3d). Yield: 44 mg, 33%. 1H NMR: δ 7.55ꢀ7.25 (m, 15H), 4.65 (q, 2H,
J = 7.2 Hz), 1.33 (t, 3H, J = 7.2 Hz) ppm. 13C NMR: δ 296.2 (C-1),
204.1, 198.3 (CdO), 164.2 (CdN), 150.0, 137.5, 136.3, 130.7, 128.8,
128.5, 128.3, 127.9, 127.6, 126.5 (t, DC-2, J = 7 Hz), 78.7, 15.2 ppm.
Exact mass MALDI(ꢀ) (C29H20DNO6W): calcd 664.094, measd
664.031.
Pentacarbonyl{(2Z)-3-[(diperdeuterophenylmethylene)-
amino]-1-ethoxy-3-phenyl-2-propenylidene)}tungsten(0)
(3e). Yield: 39 mg, 29%. 1H NMR: δ 7.55 (d, 2H, J = 6.0 Hz), 7.40ꢀ7.27
(m, 3H), 7.18 (s, 1H, H-2), 4.66 (q, 2H, J = 6.0 Hz), 1.26 (t, 3H, J = 6.0
Hz) ppm. 13C NMR: δ 296.3 (C-1), 204.1, 198.2 (CdO), 164.2
(CdN), 149.9, 137.5, 136.0, 130.5, 129.0, 128.8, 128.5, 128.3, 127.9,
125.8 (C-2), 78.7, 15.1 ppm. Exact mass MALDI(ꢀ) (C29H11D10-
NO6W): calcd 673.148, measd 673.171.
’ CONCLUSION
In summary, it has been shown that a nitrogen-centered radical,
generated photochemically, is able to participate in a 1,4-addition
to alkynylcarbene complexes to give a 5-aza-1-metalla-1,3,5-hexa-
triene, while radical 1,2-addition leads to azepines.
’ EXPERIMENTAL SECTION
Representative Experimental Procedure. In a typical experi-
ment 0.2 mmol of the carbene complex and 0.2 mmol of the acyloxime
were dissolved in 10 mL of the appropriate solvent (commercial grade).
The solution was deoxygenated by bubbling with Ar and either irradiated
(1Z,4Z)-3-Ethoxy-1,5-diphenyl-3H-benzo[c]azepine (4a).
Yield: 6 mg, 9%. H NMR: δ 7.59ꢀ7.30 (m, 14H), 6.44 (d, 1H, J =
1
4.5 Hz), 4.43 (d, 1H, J = 4.5 Hz), 4.15ꢀ4.07 (m, 1H), 3.60ꢀ3.50 (m,
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1H), 1.38 (t, 3H, J = 7.5 Hz) ppm. 13C NMR: δ 163.5 (CdN), 140.5,
140.4, 140.2, 139.0, 136.9, 133.4 (dCH), 129.8, 129.7, 129.3, 129.0,
128.9, 128.3, 128.0, 127.8, 127.7, 126.1, 88.8, 63.1, 15.3 ppm. IR: ν 1667
(CdC), 1604 (CdN), 1196 (CꢀO) cmꢀ1. Exact mass ESI(þ)
(C24H21NO þ H): calcd 340.1701, measd 340.1689.
(3) Alonso, R.; Campos, P. J.; Rodriguez, M. A.; Sampedro, D. J. Org.
Chem. 2008, 73, 2234.
ꢀ
(4) Portela-Cubillo, F.; Alonso-Ruiz, R.; Sampedro, D.; Walton, J. C.
J. Phys. Chem. A 2009, 113, 10005.
(5) Campos, P. J.; Sampedro, D.; Rodriguez, M. A. Organometallics
2000, 19, 3082. Campos, P. J.; Sampedro, D.; Rodriguez, M. A.
Tetrahedron Lett. 2002, 43, 73. Campos, P. J.; Sampedro, D.; Rodriguez,
M. A. Organometallics 2002, 21, 4076. Campos, P. J.; Sampedro, D.;
Rodriguez, M. A. J. Org. Chem. 2003, 68, 4674. Sampedro, D.; Caro, M.;
Rodriguez, M. A.; Campos, P. J. J. Org. Chem. 2005, 70, 6705. Campos,
P. J.; Caro, M.; Lꢀopez-Sola, S.; Sampedro, D.; Rodriguez, M. A.
ꢀ
ꢀ
(1Z,4Z)-3-Methoxy-1,5-diphenyl-3H-benzo[c]azepine (4b).
Yield: 8 mg, 12%. 1H NMR: δ 7.62ꢀ7.26 (m, 14H), 6.41 (d, 1H, J = 4.5
Hz), 4.33 (d, 1H, J = 4.5 Hz), 3.61 (s, 3H) ppm. 13C NMR: δ 163.6
(CdN), 140.4, 140.4, 140.1, 139.2, 136.8, 133.0 (dCH), 130.1, 129.9,
129.8, 129.3, 129.0, 128.9, 128.6, 128.3, 128.0, 127.8, 126.1, 90.0, 55.2
ppm. Exact mass ESI(þ) (C23H19NO þ H): calcd 326.1545, measd
326.1540.
ꢀ
ꢀ
ꢀ
ꢀ
J. Organomet. Chem. 2006, 691, 1075.
(6) Selected reviews on the chemistry of Fischer carbene complexes:
D€otz, K. H.; Stendel, J., Jr. Chem. Rev. 2009, 109, 3227. Barluenga, J.;
Fernꢀandez-Rodriguez, M. A.; Aguilar, E. J. Organomet. Chem. 2005,
690, 539. Gꢀomez-Gallego, M.; Manche~no, M. J.; Sierra, M. A. Acc. Chem.
Res. 2005, 38, 44. Barluenga, J.; Santamaria, J.; Tomꢀas, M. Chem. Rev.
2004, 104, 2259. Herndon, J. W. Coord. Chem. Rev. 2004, 248, 3.
Barluenga, J.; Flꢀorez, J.; Fa~nanꢀas, F. J. J. Organomet. Chem. 2001, 624, 5.
Fletcher, A. J.; Christie, S. D. R. J. Chem. Soc., Perkin Trans. 1 2001, 1.
Sierra, M. A. Chem. Rev. 2000, 100, 3591. de Meijere, A.; Schirmer, H.;
Duestsch, M. Angew. Chem., Int. Ed. 2000, 39, 3964.Books: Metal
Carbenes in Organic Synthesis. in Topics in Organometallic Chemistry;
D€otz, K. H., Ed.; Wiley: New York, 2004; Vol. 13. Carbene Chemistry:
From Fleeting Intermediates to Powerful Reagents; Bertrand, G., Ed.;
Marcel Dekker: New York, 2002.
(1Z,4Z)-3-Trideuteromethoxy-1,5-diphenyl-3H-benzo[c]-
azepine (4c). Yield: 7 mg, 10%. 1H NMR: δ 7.62ꢀ7.24 (m, 14H), 6.41
(d, 1H, J = 4.5 Hz), 4.33 (d, 1H, J = 4.5 Hz) ppm. 13C NMR: δ 163.4
(CdN), 140.2, 140.1, 139.8, 138.8, 136.6, 132.8 (dCH), 130.1, 129.9,
129.7, 129.3, 129.0, 128.9, 128.6, 128.3, 128.0, 127.7, 125.8, 89.6 ppm.
CD3 not observed. Exact mass ESI(þ) (C23H16D3NO þ H): calcd
329.1726, measd 329.1731.
ꢀ
ꢀ
(1Z,4Z)-4-Deutero-3-ethoxy-1,5-diphenyl-3H-benzo[c]aze-
pine (4d). Yield: 12 mg, 17%. 1H NMR: δ 7.61ꢀ7.30 (m, 14H), 4.43
(s, 1H), 4.17ꢀ4.08 (m, 1H), 3.59ꢀ3.53 (m, 1H), 1.37 (t, 3H, J = 7.5 Hz)
ppm. 13C NMR: δ 163.5 (CdN), 140.4, 140.4, 140.1, 138.9, 136.9,
133.0 (t, dCD, J = 20 Hz), 129.8, 129.7, 129.3, 129.0, 128.9, 128.3,
128.0, 127.8, 126.2, 88.8, 63.1, 15.3 ppm. Exact mass ESI(þ)
(C24H20DNO þ H): calcd 341.1762, measd 341.1759.
(7) Merlic, C. A.; Xu, D. J. Am. Chem. Soc. 1991, 113, 9855.
Merlic, C. A.; Xu, D.; Nguyen, M. C.; Truong, V. Tetrahedron Lett. 1993,
34, 227.
(8) D€otz, K. H.; Gomes da Silva, E. Tetrahedron 2000, 56, 8291.
(9) Manche~no, M. J.; Ramirez-Lꢀopez, P.; Gꢀomez-Gallego, M.; Sierra,
(1Z,4Z)-3,6,7,8,9-Pentadeutero-3-ethoxy-5-(perdeutero-
phenyl)-1-phenyl-3H-benzo[c]azepine (4e). Yield: 24 mg, 35%.
1H NMR: δ 7.35ꢀ7.26 (m, 5H), 6.44 (s, 1H), 4.15ꢀ4.08 (m, 1H),
3.58ꢀ3.51 (m, 1H), 1.38 (t, 3H, J = 7.5 Hz) ppm. 13C NMR: δ 163.5
(CdN), 140.5, 140.3, 139.9, 139.0, 136.8, 133.2 (dCH), 128.9, 128.3,
127.8, 88.4 (t, CD, J = 21 Hz), 63.0, 15.2 ppm. Exact mass ESI(þ)
(C24H11D10NO þ H): calcd 350.2305, measd 350.2324.
ꢀ
M. A. Organometallics 2002, 21, 989.
(10) Examples: Merlic, C. A.; Albaneze, J. Tetrahedron Lett. 1995,
36, 1011. Merlic, C. A.; Albaneze, J. Tetrahedron Lett. 1995, 36, 1007.
Mak, C. C.; Tse, M. K.; Chan, K. S. J. Org. Chem. 1994, 59, 3585. Mak,
C. C.; Chan, K. S. J. Chem. Soc., Perkin Trans. 1 1993, 2143.
(11) Barton, D. H. R.; Crich, D.; Kretzschmar, G. J. Chem. Soc.,
Perkin Trans. 1 1986, 39. Barton, D. H. R. Tetrahedron 1992, 48,
2529.
(12) Carbene complex 2a strongly absorbs at 252 nm (ε = 32 700),
the wavelength of maximum absorption for the benzophenone acet-
yloxime 1a (ε = 16 300).
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: miguelangel.rodriguez@unirioja.es.
’ ACKNOWLEDGMENT
(13) The low-pressure Hg lamp has an emission maximum at 254 nm.
(14) Funke, F.; Duetsch, M.; Stein, F.; Noltemeyer, M.; de Meijere,
A. Chem. Ber. 1994, 127, 911.
This work was partially supported by the Spanish MEC
(CTQ2007-64197). M.B.-L., A.C., and H.F.G. thank the Spanish
MEC, CSIC, and CAR, respectively, for their fellowships.
(15) Aumann, R.; Jasper, B.; Laege, M.; Krebs, B. Organometallics
1994, 13, 3502.
(16) Knauss, L.; Fischer, E. O. Chem. Ber. 1970, 103, 3744.
(17) Some metalated zwitterionic intermediates incorporate a hy-
drogen (deuterium) atom in the presence of water (D2O). See: Barluenga,
’ DEDICATION
†This article is dedicated to Prof. J. Barluenga on the occasion of
his 70th birthday.
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J.; Tomꢀas, M.; Rubio, E.; Lꢀopez-Pelegrin, J. A.; Garcia-Granda, S.;
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Chem. 1999, 71, 1385. Barluenga, J.; Rodriguez, F.; Fa~nanꢀas, F. J.; Flꢀorez,
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Organometallics
ARTICLE
(21) Obtained from 1 mmol of oxime and 1.3 mmol of the cor-
responding acetyl chloride. See ref 2b.
(22) Obtained from 6 mmol of tungsten hexacarbonyl, using
CF3SO3CD3 as electrophile: Vꢀazquez, M. A.; Reyes, L.; Miranda, R.;
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Garcia, J. J.; Jimꢀenez-Vꢀazquez, H. A.; Tamariz, J.; Delgado, F. Organo-
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