First stepwise Dotz reaction: Isolation and characterization of a chelated metallatriene intermediate. Influence of its pattern of substitution in product partition

Article abstract of DOI:10.1021/ja991865j

A series of chelated tetracarbonyl aminovinyl carbene complexes 5 are prepared by high-yielding decarbonylation reaction. γ-Alkyl-substituted complexes 5a-d are stable in solid form while γ-aryl-substituted analogues 5e-g are stable only in solution. NMR

Full text of DOI:10.1021/ja991865j

1314
J. Am. Chem. Soc. 2000, 122, 1314-1324
First Stepwise Do¨tz Reaction: Isolation and Characterization of a
Chelated Metallatriene Intermediate. Influence of Its Pattern of
Substitution in Product Partition
Jose´ Barluenga,*,† Fernando Aznar,† Ignacio Gutie´rrez,† Alfredo Mart´ın,†,§
Santiago Garc´ıa-Granda,‡ and M. Amparo Llorca-Baragan˜o‡
Contribution from the Instituto UniVersitario de Qu´ımica Organometa´lica “Enrique Moles”, Unidad
asociada al C.S.I.C., Julia´n ClaVer´ıa 8, E-33701 OViedo, Spain, and Departamento de Qu´ımica F´ısica y
Anal´ıtica (X-ray serVice), UniVersidad de OViedo, Julia´n ClaVer´ıa 8, E-33701 OViedo, Spain
ReceiVed June 4, 1999
Abstract: A series of chelated tetracarbonyl aminovinyl carbene complexes 5 are prepared by high-yielding
decarbonylation reaction. γ-Alkyl-substituted complexes 5a-d are stable in solid form while γ-aryl-substituted
analogues 5e-g are stable only in solution. NMR studies determined that complexes 5 undergo a dynamic
process in solution, in which the unsaturated η1 species are present in low concentration. Reaction of complexes
5 with electron-deficient alkynes under controlled conditions afforded the 1,4,5-η3-dienylcarbene complexes
9 arising from the insertion of the alkyne in the metal-carbon bond. The stability and behavior of these
complexes were studied and found to be related to their electronic structure and pattern of substitution. Thermal
decomposition of carbenes 9 produced either cyclopentadienes 13 or phenol derivatives 15, the major products
in the Do¨tz reaction, thus demonstrating that they can be the actual intermediates in this reaction. The overall
process can be considered a Do¨tz reaction carried out in three separate steps at low temperature.
Introduction
Scheme 1
Despite the synthetic value of the benzannulation reaction
of Fischer carbene complexes and alkynes,1 the details of its
mechanism remain to be ascertained.2 Great efforts are being
made to establish the role of each proposed intermediate in the
outcome of the reaction. In particular, knowledge of the effect
of the structure and stereoelectronic properties of the intermedi-
ates in the product distribution would improve significantly the
ability to tune the reaction to a particular final product.
The widely accepted mechanism for the reaction is depicted
in Scheme 1. The process is initiated by the dissociation of a
CO ligand from complex I to produce the coordinatively
unsaturated carbene complex II.3 Intermediate II is trapped by
* To whom correspondence should be addressed. E-mail: Barluenga@
sauron.quimica.uniovi.es. Fax: (+) 34 8 510 34 50.
† Instituto Universitario de Qu´ımica Organometa´lica “Enrique Moles”.
‡ Universidad de Oviedo.
§ New address: Lilly, S.A., Avda de la Industria, 30, 28108-Alcobendas,
Madrid.
(1) For reviews on the synthetic applications of Fischer carbene
complexes, see: (a) Do¨tz, K. H. Angew. Chem., Int. Ed. Engl. 1984, 23,
587. (b) Wulff, W. D. In ComprehensiVe Organometallic Chemistry II; Abel,
E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon Press: Oxford, 1995;
Vol. 12, pp 469-547. (c) Hegedus, L. S. In ComprehensiVe Organometallic
Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon
Press: Oxford, 1995; Vol. 12, pp 549-576. (d) Doyle, M. In ComprehensiVe
Organometallic Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson, G.,
Eds.; Pergamon Press: Oxford, 1995; Vol. 12, pp 387-420. (e) Harvey,
D. F.; Sigano. D. M. Chem. ReV. 1996, 96, 271.
(2) For discussions of, and recent citations to mechanistic issues, see:
(a) Waters, M. L.; Brandvold, T. A.; Isaacs, L.; Wulff, W. D.; Rheingold,
A. L. Organometallics 1998, 17, 4298. (b) Hsung, R. P.; Quinn, J. F.;
Weisemberg, B. A.; Wulff, W. D.; Yap, G. P. A.; Rheingold, A. L. Chem.
Commun. 1997, 615. (c) Gross, M. F.; Finn, M. G. J. Am. Chem. Soc. 1994,
116, 10921. (d) Wulff, W. D.; Bax, B. M.; Brandvold, T. A.; Chan, K. S.;
Gilbert, A. M.; Hsung, R. P.; Mitchell, J.; Clardy, J. Organometallics 1994,
13, 102. (e) Bos, M. E.; Wulff, W. D.; Miller, R. A.; Chamberlin, S.;
Brandvold, T. A. J. Am. Chem. Soc. 1991, 113, 9293.
the alkyne present in the medium, which binds the metal in
such a way that the bulkier substituent RL is placed parallel to
the trans CO to avoid unfavorable steric interactions with the
(3) Fischer, H.; Mu¨hlemeier, J.; Ma¨rkl, R.; Do¨tz, K. H. Chem. Ber. 1982,
115, 1355.
10.1021/ja991865j CCC: $19.00 © 2000 American Chemical Society
Published on Web 02/03/2000

First Stepwise Do¨tz Reaction
J. Am. Chem. Soc., Vol. 122, No. 7, 2000 1315
Scheme 2
Table 1. Pentacarbonyl Aminovinyl Carbene Complexes Prepared
carbene ligand in complex III.4 This coordination geometry will
be ultimately responsible for the regiochemistry observed in the
final products. The next step is the insertion of the alkyne into
the metal-carbon double bond to afford metallatrienes IV. This
step can lead to two different isomers of the η3-metallatrienes,
of which only the E isomer should be able to undergo cyclization
with the terminal double bond, giving rise to the cyclopentadiene
(indene) VIII and phenol (naphthol) IX.5 On the other hand,
the Z derivative is the one responsible for the formation of furan
X.6
compd R1
R2
R3
R4
method yield (%)
1a
1b
1c
1d
1e
1f
1g
1h
1i
CH2CH2CH2
O(CH2)2CH2
CH2CH2OCH2CH2 metathesis
CH2CH2OCH2CH2 metathesis
CH2CH2OCH2CH2 metathesis
69a
41
55
75
99
99
99
99
99
CH3
H
CH3 CH2OCH3 CH2CH2OCH2CH2 metathesis
H
H
H
H
H
Ph
CH2CH2OCH2CH2 aminolysis
CH2CH2OCH2CH2 aminolysis
2-furyl
2-furyl
2-furyl
2-furyl
Me
Me
H
Me
H
H
aminolysis
aminolysis
aminolysis
Isolating the intermediates and studying their structure and
submission to the next mechanistic step in a reaction are,
theoretically, the best means of understanding them. However,
since the CO dissociation step in the benzannulation reaction
is rate limiting, the detection of subsequent intermediates has
been cumbersome. Thus, only cleverly designed stereochemi-
cally or functionally restricted analogues have been isolated and
used to estimate the structural characteristics of the actual
intermediates.7-10 To the best of our knowledge, only one
intermediate capable of undergoing the subsequent step has been
isolated and characterized, namely the last one, the metal-
complexed cyclohexadienone VII.2d
As stated above, the stereoelectronic properties of the
intermediates, especially of those situated in the branching of
the reaction pathway, are crucial for the product partition.
Unfortunately, little is known about these intermediates. Theo-
retical calculations on models for several of the intermediates
have shed some light on the energetics of the mechanism.11-13
Also, rigorous evaluation of the proportions of the final products
(including minor ones) and correlation with the electronic and
steric properties of the starting materials have allowed us to
infer the properties of the intermediates.2d,e
a See ref 17.
For instance, there is no clear reason why reactions of
arylcarbene complexes with alkynes give so many different
products and are so sensitive to changes in solvents and
concentration while reactions of alkenyl carbenes only give six-
membered rings with very few side products and are almost
unaffected by changes in reaction conditions.2d Also, the
electronic effects that have been proposed to explain the
exclusive formation of indene derivatives for arylamino carbenes
do not seem to work in the case of alkenylamino carbenes, since
the reactions of this type of carbenes with alkynes give mainly
aminophenols instead of aminocyclopentadienes.14
In the present contribution we report the first example of a
stepwise Do¨tz reaction, in which the decarbonylation step is
carried out in the absence of alkyne. This has permitted us to
isolate complexes analogous to II. We describe the insertion
of alkynes in these compounds at low temperature, which led
to the isolation and characterization of the metallatriene
intermediates of the Do¨tz reaction IV. Finally, we study the
thermal evolution of these intermediates and the effect of their
pattern of substitution in the distribution between cyclopenta-
diene and the phenol derivatives.15
Despite this, there are still some unanswered questions,
especially concerning the reaction of alkenylcarbene complexes.
Results
(4) (a) Do¨tz, K. H.; Dietz, R. Chem. Ber. 1978, 111, 2517. (b) Do¨tz, K.
H.; Pruskil, I. Chem. Ber. 1980, 113, 2876. (c) Wulff, W. D.; Tang, P. C.;
McCallum, J. S. J. Am. Chem. Soc. 1981, 103, 7677. (d) Do¨tz, K. H.;
Mu¨hlemeier, J.; Schubert, U.; Orama, O. J. Organomet. Chem. 1983, 247,
187. (e) Wulff, W. D.; Chang, K. S.; Tang, P. C. J. Org. Chem. 1984, 49,
2293. (f) Yamashita, A.; Toy, A. Tetrahedron Lett. 1986, 27, 3471.
(5) It has also been proposed for the formation of phenol (naphthol) IX
a manifold involving CO insertion in complex V followed by reductive
elimination and tautomerization: Casey, C. P. In ReactiVe Intermediates;
Jones, M., Jr., Moss, R. A., Eds.; Wiley: New York, 1981; Vol. 2, p 155.
(6) McCallum, J. S.; Kunng, F. A.; Gilbertson, S. R.; Wulff, W. D.
Organometallics 1988, 7, 2346.
(7) (a) Do¨tz, K. H.; Scha¨fer, T.; Kroll, F.; Harms, K. Angew. Chem.,
Int. Ed. Engl. 1992, 31, 1236. (b) Hohmann, F.; Siemoneit, S.; Nieger, M.;
Kotila, S.; Do¨tz, K. H. Chem. Eur. J. 1997, 3, 853.
(8) Do¨tz, K. H. Angew. Chem., Int. Ed. Engl. 1979, 18, 954.
(9) (a) Anderson, B. A.; Wulff, W. D.; Rheingold, A. L. J. Am. Chem.
Soc. 1990, 112, 8615. (b) Chelain, E.; Goumont, R.; Hamon, L.; Parlier,
A.; Rudler, M.; Rudler, H.; Daran, J. C.; Vaissermann, J. J. Am. Chem.
Soc. 1992, 114, 8088.
(10) Tang, P. C.; Wulff, W. D. J. Am. Chem. Soc. 1984, 106, 1132.
(11) Gleichmann, M. M.; Do¨tz, K. H.; Hess, B. A. J. Am. Chem. Soc.
1996, 118, 10551.
(12) (a) Hoffmann, P.; Ha¨mmerle, M. Angew. Chem., Int. Ed. Engl. 1989,
28, 908. (b) Hoffmann, P.; Ha¨mmerle, M. Unfried, G. New J. Chem. 1991,
15, 769.
(13) (a) Torrent, M.; Duran, M.; Sola´, M. Organometallics 1998, 17,
1492. (b) Torrent, M.; Duran, M.; Sola´, M. Chem. Commun. 1998, 999. (c)
Torrent, M.; Duran, M.; Sola´, M. J. Am. Chem. Soc. 1999, 121, 1309.
Aminocarbenes 1 (Scheme 2, Table 1) were prepared by two
standard methods. Aminolysis of alkoxycarbenes 2 was per-
formed on â-aryl-substituted complexes, giving rise to the
aminocarbene derivatives in almost quantitative yields. However,
in the reaction of the alkyl analogues with amines, variable
amounts of complexes (CO)5(R2NH)Cr are formed as side
products, depending on the substituents of the amine and the
carbene complex.16 Therefore, complexes 1, bearing an alkyl
or hydrogen substituent in the â-position were synthesized by
metathesis of 2-aminodienes 3 and pentacarbonylmethoxy-
(phenyl)carbene chromium 4.17 In some cases, variable amounts
(14) (a) Wulff, W. D.; Gilbert, A. M.; Hsung, R. P.; Rahm, A J. Org.
Chem. 1995, 60, 4566. (b) Barluenga, J.; Lo´pez, L. A.; Mart´ınez, S.; Toma´s,
M. J. Org. Chem. 1998, 63, 7588.
(15) A preliminary account of this report has been published: Barluenga,
J.; Aznar, F.; Mart´ın, A.; Garc´ıa-Granda, S.; Pe´rez-Carren˜o, E. J. Am. Chem.
Soc. 1994, 116, 11191.
(16) This behavior has been previously reported: (a) Anderson, B. A.;
Wulff, W. D.; Powers, T. S.; Tribbitt, S.; Rheingold, A. L. J. Am. Chem.
Soc. 1992, 114, 10784. (b) Fischer, E. O.; Heckl, B.; Werner, H. J.
Organomet. Chem. 1971, 28, 359. (c) Chelain, E.; Goumont, R.; Hamon,
L.; Parlier, A.; Rudler, M.; Rudler, H.; Daran, J.-C.; Vaissermann, J. J.
Am. Chem. Soc. 1992, 114, 8088.
(17) Barluenga, J.; Aznar, F.; Mart´ın, A. Organometallics 1995, 14, 1429.

1316 J. Am. Chem. Soc., Vol. 122, No. 7, 2000
Barluenga et al.
Scheme 3
pounds 5e-g were generated and used in subsequent reactions
without isolation.
Irradiation of complexes 1h and 1i bearing one or two N-H
bonds, respectively, did not provide the expected tetracarbonyl
η3-vinyl carbene derivatives. This behavior contrasts with that
described for the N,N-dialkyl derivatives and must be ascribed
to the presence of the N-H bonds, since this is the only
difference in the structures of 1h and 1i.21
Table 2. Complexes 5 Prepared
Complexes 5 are, in solution, in equilibrium between the
chelated (η3-vinyl carbene ligand) and nonchelated (η1-vinyl
carbene ligand) forms, probably due to the strain created by
the small chelation ring. This behavior was inferred from the
NMR analysis of complexes 5. For example, complex 5c shows
no signals in the metal-complexed carbonyl region. If the
temperature is raised to 50 °C, a single signal appears at 231.1
ppm. On the other hand, the spectrum at -20 °C showed three
signals in the carbonyl region at 224.4, 227.1, and 237.3 (double
intensity22) ppm. This type of behavior has been described before
for chelated tetracarbonyl (acylamino)carbene23 and trialkylsilyl
aminocarbene24 complexes, but, to the best of our knowledge,
it has never been observed before for a C-C double bond
chelated Fischer carbene complex. Interestingly, the signals
corresponding to the rest of the carbons of the complex remain
almost invariable throughout the temperature range. Especially
indicative are the signals for the C-C double bond which re-
main within a range of 1 ppm of 82.5 (CH) and 57.4 (CH2)
ppm.
compd
R1
R2
yielda (%)
5a
5b
5c
5d
CH2CH2CH2
O(CH2)2CH2
H
94 (90)
84
90 (77)
88 (80)
CH3
CH3
CH2OCH3
a Yields given in parentheses correspond to the thermal reaction.
of tetracarbonyl carbene complexes 5 (Scheme 3) are formed
as side products in the metathesis reaction, but these compounds
can be transformed quantitatively into their pentacarbonyl
analogues 1 by simply bubbling CO through the crude reaction
solutions. This fact suggested that the tetracarbonyl complexes
5 could be formed from 1 under thermal conditions.
Complexes 5a, 5c, and 5d (Scheme 3, Table 2) were prepared
by heating solutions of the pure pentacarbonyl complexes 1 in
THF (complex 5a) or toluene (complexes 5c and 5d) at reflux
temperature. However, to avoid the long periods of time required
to complete the reaction, that lead to partial decomposition of
the starting and final complexes, we tried to carry out this
reaction photochemically. Thus, when irradiated at -40 °C, a
carbonyl ligand dissociates from the aminovinyl carbene
complex to afford the stable tetracarbonyl species 5.18 The best
conditions found for this transformation were the irradiation of
a THF solution of the carbene complex in a Pyrex Schlenk tube
at -40 °C while a constant flow of N2 was bubbled through
the reaction in order to remove the released CO. Complexes
5a-d are stable in solid form under inert atmosphere and can
be stored at -20 °C for several months.
This observation indicates that an equilibrium between the
η3-vinyl carbene (5) and the η1-vinyl carbene (5′) complexes
occurs (Scheme 4). This η1-vinyl carbene complex 5′ is
Scheme 4
The structure of complexes 5 was postulated on the basis of
their NMR spectra. Especially relevant are their signals corre-
sponding to the double bond, which are shielded as a conse-
quence of the metal complexation (δ ) 85.7 for the CH and
86.9 for the quaternary carbon of complex 5a). The X-ray
structure17 of complex 5a shows clearly the interaction of the
double bond with the metal in a fashion similar to that reported
previously for η3-vinyl carbenes (η3-allylidenes).19 As far as
we know, no examples of η3-vinyl carbenes have been reported
in the literature for d6 group VI metals.20
pentacoordinated and probably fluxional.25 A fast interchange
of the four carbonyl ligands occurs before the η1 complex reverts
to the η3 isomer. Since no signals assignable to a nonchelated
carbene appear, the population of the η1 complex 5′ must be
necessarily low. This fact implies that the η3-vinyl carbene is
not only more stable than the η1 isomer but also more stable
than its solvent (THF)-complexed analogue 5‚S, which is, in
principle, readily accessible from it.
The behavior of 1e-g with respect to CO dissociation is
similar to that of 1a-d. Irradiation of their THF solutions at
-40 °C produced the corresponding tetracarbonyl complexes
5e-g. However, the isolation of complexes 5e-g was elusive
due to product decomposition in the solid form. To ascertain
the formation of complexes 5e-g, a solution of 1e in CD2Cl2
was irradiated at -40 °C under static vacuum. The NMR
analysis of this sample showed signals assignable to 5e along
with those corresponding to the starting material. Thus, com-
The ready availability of the unsaturated species 5′ at room
temperature prompted us to investigate the participation of
isolated complexes 5 in the Do¨tz reaction. To prove that
tetracarbonyl complexes 5 are true intermediates, we tested the
reaction of 5a with a series of alkynes. The reaction gave
unsatisfactory results in most cases when electron-rich or normal
(21) The decarbonylation reaction was also tried with some alkoxyvinyl
carbenes, but we found them inert to either photochemical or thermal
conditions. Theorethical calculations anticipated the lower stabilization
gained by chelation of the vinyl group in alkoxyvinyl carbenes, as compared
with the aminovinyl carbenes.11
(18) The main photoprocess of Fischer carbene complexes is the
decarbonylation: (a) Foley, H. C.; Strubinger, L. M.; Targos, T. S.; Geoffrey,
G. L. J. Am. Chem. Soc. 1983, 105, 3064. (b) Bell, S. E. J.; Gordon, K. C.;
McGarvey, J. J. J. Am. Chem. Soc. 1988, 110, 3107. (c) Knorr, J. R.; Brown,
F. L. Organometallics 1994, 13, 2178.
(22) The fact that the two cis carbonyl ligand 13C NMR chemical shifts
are identical is fortuitous, since both carbon atoms have different environ-
ments due to the substituents in the double bond. For example, these carbon
atoms have different chemical shifts in complex 5a (see Experimental
Section).
(19) Garret, K. E.; Sheridan, J. B.; Pourreau, D. B.; Feng, W. C.;
Geoffrey, G. L.; Staley, D. L.; Rheingold, A. L. J. Am. Chem. Soc. 1989,
111, 8383.
(23) Grotjahn, D. B.; Do¨tz, K. H. Synlett 1991, 381.
(24) Hepp, W.; Schubert, U. J. Organomet. Chem. 1990, 385, 221.
(25) Hofmann, P.; Ha¨mmerle, M. Angew. Chem., Int. Ed. Engl. 1989,
28, 908.
(20) For leading references on η3-vinyl carbenes, see: Mitsudo, T. Bull.
Chem. Soc. Jpn. 1998, 71, 1525.

First Stepwise Do¨tz Reaction
J. Am. Chem. Soc., Vol. 122, No. 7, 2000 1317
Table 3. Complexes 9 Prepared
alkynes were employed. Thus, although tetracarbonyl carbene
complexes 5 are stable at room temperature in a solution of
THF for long periods of time, they react readily with an added
acetylene such as phenylacetylene to produce the pentacarbonyl
complex 1a as the only identifiable product, in 46% yield
(Scheme 5). When the reaction is carried out at THF reflux
yield
(%)
compd R1
R2
CH2CH2CH2
OCH2CH2CH2 CH2CH2OCH2CH2 CO2Me CO2Me
CH3 CH2CH2OCH2CH2 CO2Me CO2Me
CH3 CH2OCH3 CH2CH2OCH2CH2 CO2Me CO2Me
R3
R4
R5
Z
9a
9b
9c
9d
9e
9f
CH2CH2OCH2CH2 CO2Me CO2Me
54
95
73
69
H
H
H
H
H
H
H
H
H
Ph
CH2CH2OCH2CH2 CO2Me CO2Me
CH2CH2OCH2CH2 CO2Me CO2Me
55a
50a
35a
10a,b
9a,c
48a
Scheme 5
2-furyl
2-furyl
2-furyl
2-furyl
Ph
9g
9h
9i
Me
Me
H
Me
H
H
CO2Me CO2Me
CO2Me CO2Me
CO2Me CO2Me
9j
9k
9l
CH2CH2OCH2CH2
CH2CH2OCH2CH2
CH2CH2OCH2CH2
H
H
H
CO2Me
Ph
Ph
CONMe2 54a
CN
22a
a Yield based on complex 1. b With 55% recovery of 1h. c With 80%
recovery of 1i.
ance of the starting materials lasted 22 h, and during this time,
no other signals assignable to any intermediate could be
observed. At this temperature, complex 9a is stable, and no
decomposition products were observed after 1 week.
The structure of the observed complex 9a was deduced from
its 13C NMR analysis, the most significant data being the
following. The carbene carbon chemical shift is 245.9 ppm; 10
ppm upfield from that of 5a, 257.6 ppm. It is known that
chemical shifts of carbene atoms correlate well with the electron-
donating ability of their substituents; therefore, these high-field
chemical shifts contrast with the fact that two electron-
withdrawing ester groups are placed in the dienyl system of
the complexes. The chemical shifts for two of the carbons
belonging to the diene moiety are in the range of a noncoor-
dinated C-C double bond (157.9 and 130.7 ppm) while the
other two signals are displaced to high field (93.8 and 102.1
ppm), indicating that this double bond is coordinated to the
metal. 13C-DEPT pulse sequence experiments showed that the
terminal double bond is the one actually bonded to the metal.
Finally, four signals assignable to the carbonyl carbons are
observed at room temperature in the expected chemical shift
range, indicative that chelate ring opening, if it happens, is slow
in the NMR time scale. This is what could be expected, since
ring strain in 9a is significantly lower than in complexes 5.
To test the generality of the insertion process, carbene
complexes 5a-g were reacted with a series of electron deficient
alkynes to yield the complexes 9 (Scheme 6, Table 3) as solids
after suitable workup (see Experimental Section). In these
reactions, a variable amount of complexes 1 (up to 15%) is
always recovered. Although in all cases the reaction was carried
out at -20 °C, the procedure was dependent on the stability of
the starting carbene complexes 5. Thus, in the case of complexes
9a-d, the starting materials were the corresponding previously
isolated complexes 5a-d. On the other hand, since complexes
5e-g could not be isolated (vide supra), the reactions of these
complexes were performed in one pot with the crude solutions
after the photochemical CO dissociation of carbenes 1e-g.
Finally, complexes 9h-i bearing at least one hydrogen at the
nitrogen could be prepared by irradiation in situ of a 1:1 mixture
of carbenes 1h-i and DMAD under carefully controlled
conditions.
temperature with an excess of alkyne, it is possible to isolate 6
and 7 as a 1:1 mixture in a global yield of 40%. In addition, a
mass balance in the crude reaction indicated that 4-5 equiv of
alkyne was consumed. On the other hand, when the reaction is
performed with the pentacarbonyl complex 1a instead of the
tetracarbonyl derivative 5a, it gives rise to the same mixture of
products with 80% global yield. The products isolated in the
reaction of phenylacetylene with tetracarbonyl complex 5a arise
from the decomposition of this carbene to furnish the penta-
carbonyl complex 1a in ca. 50%, which further reacts with
phenylacetylene to give the same products but in lower yield.
A possible interpretation of these results can be as follows: from
the reaction of tetracarbonyl carbene with alkyne a tetracarbonyl
species A arises that is susceptible of releasing 1 equiv of CO
in the presence of a high concentration of a CO acceptor (5a).
From this CO interchange would result 1 equiv of the penta-
carbonyl complex 1a and 1 equiv of a tricarbonyl species
capable of polymerizing the alkyne. When all the tetracarbonyl
carbene 5a has been consumed, the normal Do¨tz process takes
place from 1a. Tetracarbonyl complex 5a is regenerated from
1a, as well as the complex A arising from its reaction with
phenylacetylene. Now the concentration of both intermediates
is so low that the CO interchange process is difficult to achieve,
and then the complex A evolves into the usual Do¨tz products.
Fortunately, reaction of complexes 5 with electron-deficient
alkynes was more fruitful. When carbene complex 5a (Scheme
6, Table 3) was treated with dimethyl acetylenedicarboxylate
Scheme 6
(8) in CD2Cl2 at -80 °C, and the reaction mixture was allowed
to warm slowly while being monitored by 13C NMR analysis,
no change in the composition of the mixture was observed until
-20 °C. At this temperature the appearance of a new set of
signals could be observed corresponding to complex 9a, along
with those of the pentacarbonyl carbene 1a, which comes from
the aforementioned decomposition of 5a. The total disappear-
The thermal stability of complexes 9 is surprisingly high,
taking into account that the carbene carbon is directly attached
to an electron-withdrawing group, and must be ascribed to an
effective electron donation from the vinylogous amine. In fact,
the rotation of the amine about the N-C bond is slow at room
temperature, as can be deduced from the inequivalence of the
carbons of the amine in 13C NMR. This stability is also

1318 J. Am. Chem. Soc., Vol. 122, No. 7, 2000
Barluenga et al.
dependent on the substitution pattern at the metallatriene
complex. Thus, complexes 9a-d, in which R2 is an alkyl group
or hydrogen and R5 is an ester (Scheme 6), evolve to the
cyclopentannulation products overnight in solution at room
temperature while complexes 9e-i (R2 ) Ar, R5 ) CO2Me)
are stable for days in these conditions. On the other hand,
carbenes arising from propiolic acid derivatives 9j-l (R5 ) H;
Scheme 6) are also less stable than their DMAD analogue 9e,
and, among them, the stability decreases as the electron-
withdrawing capability of the group directly attached to carbene
carbon increases. Finally, the unstability of the carbenes 9
reaches its maximum degree when both R5 and R2 are hydrogen.
Thus, the reaction of the alkyl-substituted carbene 5c with
methyl propiolate 10 led to a carbene complex that evolves to
the Cr(CO)3 complexed phenol 11 (Scheme 7) at the reaction
temperature (-20 °C).
Scheme 7
Figure 1. Molecular structure of 12g (hydrogen atoms have been
omitted for clarity).
Table 5. Selected Bond Distances (Å) for 12g
Cr-C1
2.140(3) C1-C2
1.354(5) C12-O1
1.493(5) C14-O3
1.432(5) C16-O6
1.336(5) C17-O7
1.204(5)
1.199(4)
1.144(6)
1.146(5)
1.142(5)
1.148(5)
Cr-C16 1.884(5) C2-C3
Cr-C17 1.884(4) C3-C4
Cr-C18 1.891(4) C4-C5
Cr-C19 1.851(5) C1-C12 1.485(4) C18-O8
Cr-C20 1.887(5) C2-C14 1.481(4) C19-O9
C3-N
1.304(5) C20-O10 1.137(6)
All attempts to obtain X-ray quality crystal from carbenes 9
were unsuccessful. Therefore, to gain some insight into the
structure of these compounds, we prepared the pentacarbonyl
derivatives 12 (Scheme 8, Table 4) by reaction of some carbenes
Table 6. Selected Dihedral Angles (deg) for 12g
Cr-C1-C2-C3
C1-C2-C3-C4
C2-C3-C4-C5
N-C3-C4-C5
-5.6.1(5)
-81.7(4)
-6.5(5)
Cr-C1-C12-O1
C1-C2-C14-O3
C1-C2-C3-N
C14-C2-C3-N
-79.2(4)
-1.0(6)
99.2(4)
Scheme 8
173.3(4)
-83.1(4)
Table 7. Crystal Data and Structure Refinement for 12g
empirical formula
formula weight
temperature
C20H17NO10Cr
483.35
293(2) K
wavelength
crystal system, space group
unit cell dimensions
0.710 73 Å
triclinic, P1h
a ) 9.1582(18) Å; R ) 103.80(2)°
b ) 10.905(2) Å; â ) 100.23(2)°
c ) 14.564(5) Å; γ ) 105.08 (1)°
1318.6(6) Å3
volume
2, 1.217 Mg/m3
Table 4. Complexes 12 Prepared
Z, calculated density
absorption coefficient
F(000)
0.590 mm-1
carbene
R1
NR2
yield (%)
568
12e
12f
12g
Ph
Fu
Fu
N(CH2CH2)2O
N(CH2CH2)2O
NMe2
90
85
95
crystal size
θ range for data collection
index ranges
0.26 × 0.20 × 0.17 mm
1.49-24.98°
0 e h e 10, -12 e k e 12,
-17 e l e 17
reflections collected/unique
completeness to 2θ ) 24.98°
refinement method
4940/4622 [R(int) ) 0.0185]
100.0%
9 with CO. The structure of complexes 12 was postulated on
the base of its 1H and 13C NMR analysis. The most significant
spectroscopic finding for 12g is the following. The carbene
carbon resonance chemical shift, 224.1 ppm, for 12g is 20 ppm
upfield compared with that of its tetracarbonyl analogue 9g,
and the chemical shift for the C5-C6 double bond signals (148.4
and 122.8) is now indicative of an uncoordinated double bond.
The pentacarbonyl moiety is reflected by the two signals in the
metal-carbonyl region.
full-matrix least-squares on F2
4622/0/331
data/restraints/parameters
goodness-of-fit on F2
1.288
final R indices [I > 2σ(I)]
R indices (all data)
largest diff. peak and hole
R1 ) 0.0429, wR2 ) 0.1102
R1 ) 0.0998, wR2 ) 0.1227
0.530 and -0.522 e Å-3
plane almost perpendicular to that formed by N-C3-C4-C5
(dihedral angle C1-C2-C3-N ) 99.2°).26
The X-ray structure of 12g (Figure 1, Tables 5-7) reveals
some details about the nature of the bond between the chromium
and the carbene atom. The complex can be best described as a
zwitterion in which the nitrogen-containing conjugated system
is positively charged, since the unit Cr-C1-C2-C14 is on a
This alkyne insertion reaction has opened an easy route for
the preparation of different tetra- and pentacarbonyl carbene
complexes with an electron acceptor group directly attached to
the carbene atom. There are few reports concerning group VI
metal carbenes with this structural characteristic. In fact, to the

First Stepwise Do¨tz Reaction
J. Am. Chem. Soc., Vol. 122, No. 7, 2000 1319
Scheme 9
Scheme 10
Table 8. Cyclopentadienes 13 Prepared
compd
R1
R2
R3
R4
yield (%)
Table 9. Phenols 15 Prepared
13a
13b
13c
13d
13e
13h
13i
CH2CH2CH2
OCH2CH2CH2
CH3
CH3
H
H
H
CH2CH2OCH2CH2
CH2CH2OCH2CH2
CH2CH2OCH2CH2
CH2CH2OCH2CH2
CH2CH2OCH2CH2
CH3
H
74
62
68
65a
52b
44
35
carbene
phenol
Z
yield (%)
H
9j
9k
9l
15j
15k
15l
CO2Me
CONMe2
CN
92
45
20
CH2OCH3
Ph
2-furyl
2-furyl
H
H
14c and 14e as single stereoisomers. The stereochemistry of
14 was postulated by NOE experiments performed on the diethyl
derivative 14e′, since the signal for one of the hydrogens of the
cycle in 14e is obscured by those of the ester methoxy groups.
The reactions of Fischer aminovinyl carbene complexes and
alkynes have been reported to produce phenol derivatives as
the major product under thermal conditions,14 and, to the best
of our knowledge, there is only one example of cyclopentan-
nulation reaction of Fischer aminovinyl carbenes and alkynes.14a
Although quite a large number of pentacarbonyl dienyl carbene
complexes are known to give rise to cyclopentadienes,31 as far
as we know, no example has been reported previously with
chelated tetracarbonyl analogous.
A similar treatment was carried out with complexes arising
from propiolic acid derivatives, and surprisingly a completely
different behavior was found. As is shown in Scheme 10,
complexes 9j-l undergo CO insertion prior to cyclization to
give phenols 15 in a completely selective fashion, without
detectable traces of corresponding cyclopentadiene (Table 9).32
A possible explanation for the selectivity of this reaction will
be given in the Discussion.
These results show that metallatrienes 9j-l can be considered
as real intermediates in the Do¨tz benzannulation process.
Although a few examples of complexes similar to the intermedi-
ate IV (Scheme 1) have been described,19,33 as far as we know
there is no previous report of the thermal conversion of a well-
characterized η3-dienyl carbene or η3-vinyl carbene into a
phenol.34 This conversion has been proposed to occur via a
complexed dienylketene VI (Scheme 1)1a or a metallacyclo-
heptadienone,5 or directly.13b,c To discriminate among these
options, we monitorized the decomposition of 9j by NMR. The
reaction took place smoothly in 9 h at room temperature, but
no intermediate was observed. The only observable products
were the starting carbene 9j, the phenol 15j, and its (CO)3Cr
complex. We cannot conclude anything from this result, except
that if the reaction proceeds via any intermediate, it is
transformed faster than produced.
a As a 60:40 mixture of regioisomers. b As a 71:29 mixture of
regioisomers.
extent of our knowledge, only two other approaches to this
family of carbenes have been reported.27,28 These syntheses have
the limitation that, along with the electron attractor group, only
an amino group directly attached to the carbene atom can be
introduced in the structure of the complex. The reactions
reported herein allow the introduction, along with the acceptor
group, of a dienyl system with very different possible substit-
uents in R, γ, and δ positions and several amines in position â.
Furthermore, various acid derivatives can be introduced as
electron attractor moieties, thus expanding the range of func-
tional groups that have been attached to a carbene complex.
Even more, as far as we know, this is the first synthesis of a
stable chelated dienyl carbene complex of chromium.
The structure of complexes 9 differs from that of complexes
usually postulated as intermediates in Do¨tz reaction. In fact,
complexes 9 are isomers of IV (Scheme 1) in which the metal
has migrated from the internal to the terminal double bond in
order to be stabilized.29,30 To establish whether carbenes 9 are,
in fact, intermediates of Do¨tz reaction, we decided to study the
thermal behavior of a representative selection of them.
We started with complexes 9 prepared from DMAD insertion,
which undergo the cyclopentannulation process to afford
carbocycles 13 (Scheme 9, Table 8). Decomposition of carbenes
9a-d takes place at 25 °C while reaction of 9e, 9h, and 9i is
more sluggish and it is necessary to warm their THF solutions
to 60 °C to bring the reaction to completion in reasonable time.
Compounds 13 were obtained in some cases as an inseparable
mixture of isomers in which the double bonds are shifted
through the ring. To ascertain the identity of the cyclopenta-
dienes, 13c and 13e were hydrolyzed to afford cyclopentenones
(26) The nature of the bonding between the metal and the carbene carbon
can be seen as intermediate between that of a typical carbene and that of a
Csp2-bonded alkyl pentacarbonyl chromate. As a consequence, Cr-carbene
and Cr-CO bond distances for 12g, and the Cr-C 13C NMR chemical
shift (224 ppm), are intermediate between those of standard Fischer
aminovinyl carbene complexes and those reported for â-phosphoniumalkyl-
and R-imoniumalkylpentacarbonylchromates. (a) Aumann, R.; Jasper, B.;
La¨ge, M.; Krebs, B. Chem. Ber. 1994, 127, 2475. (b) Barluenga, J.; Toma´s,
M.; Rubio, E.; Lo´pez-Pelegr´ın, J. A.; Garc´ıa-Granda, S.; Pertierra, P. J.
Am. Chem. Soc. 1996, 118, 695.
(31) Aumann, R.; Nienaber, H. AdV. Organomet. Chem. 1997, 41, 163.
(32) (CO)3Cr adducts of the hydroxyl free phenol can be obtained with
the suitable workup of the reaction, by oxygen-free chromatography or
crystallization from the reaction crude material. Nevertheless, better yields
are obtained by oxidative cleavage of the chromium-arene bond in mild
conditions (air and sunlight) followed by silica gel chromatography to yield
the metal-free phenol.
(27) Dvora´k, D.; Ludwig, M. Organometallics 1998, 17, 3627.
(28) (a) Aumann, R.; Fischer, E. O. Angew. Chem., Int. Ed. Engl. 1967,
6, 879. (b) Aumann, R.; Fischer, E. O. Chem. Ber. 1968, 101, 954.
(29) This stabilization has been previously postulated: Harvey, D. F.;
Grenzer, E. M.; Gantzel, P. K. J. Am. Chem. Soc. 1994, 116, 6719.
(30) We are aware that, although the most stable form of tetracarbonyl
dienylcarbene complexes is 9 and not IV, it is this one which should be
formed initially from insertion of acetylene, and, if an equilibrium between
both isomers occurs, complexes IV might be also the reactive species.
(33) (a) Mitsudo, T.; Fujita, K.; Nagano, S.; Suzuki, T.; Watanabe, Y.;
Masuda, H. Organometallics 1995, 14, 4228. (b) Park, J.; Kim, J.
Organometallics 1995, 14, 4341.
(34) The thermal cyclization of an η1-dienylcarbene to a phenol has been
observed: Barluenga, J.; Aznar, F.; Palomero, M. A.; Barluenga, S. Org.
Lett. 1999, 1, 541.

1320 J. Am. Chem. Soc., Vol. 122, No. 7, 2000
Barluenga et al.
Scheme 11
The next step would consist of the coordination of the
acetylene to yield complex III, followed by insertion in the
metal-carbene bond giving rise to a new η3-allylidene complex
IV, in which the newly formed double bond can be Z or E,
depending on the stereochemistry of the process. Theoretical
calculations concerning this step conclude that this insertion is
an exothermic process with a very low energetic barrier, if any
at all. Wulff and colleagues have proposed recently that it is at
this stage where the partitioning between cyclopentadienes VIII
and phenols IX, on one side, and furans and bicyclic lactones,
on the other side, occurs.2a They stated that the product
distribution is determined by the equilibrium between both
isomers of η3-allylidene, which can interchange in the reaction
conditions. In the work described herein, only products arising
from the E isomer of complexes IV have been observed, but,
since the insertion process takes place at low temperature, we
cannot conclude whether this is the kinetic product or the only
one possible from the starting materials.
Species of type IV-E arising from alkenyl carbene complexes
can be stabilized by isomerization to the 1,4,5-η3-pentadi-
enylidene form XI. This stabilization occurs by releasing the
strain of the small chelation ring and also by liberating the
internal double bond that allows the conjugation of the lone
pairs of the heteroatom with the carbene moiety.38 It is important
to notice that this kind of complexation might not be favorable
in intermediates arising from aryl carbenes, as an η2-coordination
of the aryl moiety should be necessary.
Assuming that the energetic barrier between III and IV is
almost null,12 the one between IV and XI must be at least lower
than the barrier of alkyne coordination to the metal, since
experiments monitored by NMR spectroscopy did not show
accumulation of IV in the reaction mixture. Only a smooth
conversion of the signals of complex 5a in the signals of
complex 9a could be observed upon addition of DMAD at low
temperature.
Although an X-ray structure of none of the complexes 9 could
not be obtained, we propose the structure XI depicted in Scheme
12 according to the MNR data. In this structure there is a very
important donation from the nitrogen lone pairs to the chromium
atom.39 The terminal double bond must adopt a planar disposi-
tion toward the chromium atom in order to chelate the metal
efficiently. This disposition cannot be achieved without a
significant twisting of the metallatriene unit, which is no longer
conjugated. This folding occurs around the C3-C4 single bond
between the terminal double bond and the rest of the π system,
which would be on a plane. This disposition is essentially the
same as that which has been obtained by DFT calculations on
a similar system.13c
Table 10. Phenols 16 Prepared
carbene
R1
phenol
yield (%)
9e
9j
CO2Me
H
16e
16j
71
32
On the other hand, it is well known that acceptor-substituted
carbene complexes of late transition metals have been proposed
for a long time as very unstable intermediates in the reaction
of organic ylides with electrophilic coordinatively unsaturated
late transition metals.35 Therefore, as we have mentioned before,
it is reasonable to think that the high stability of complexes 9
has to be ascribed to the electron donor effect of the amine.
We envisioned that it could be interesting to try to modify the
nature of the metallatriene complex by exchanging the amine
group for another without electron-donating ability, such as an
alkyl group. Thus, complexes 9e and 9j were treated with
methyllithium at -80 °C to give phenols 16 (Scheme 11, Table
10) almost instantaneously. This result can be rationalized by
an initial attack of the methyllithium at the â position, followed
by amine extrusion, which furnishes the nonstabilized carbene
17. This carbene lacks the stabilization of the amine and
undergoes cyclization quickly at low temperature to afford the
phenol 16 in a fashion similar to the last steps of Do¨tz reaction
(see Discussion). As a whole, this reaction can be seen as the
equivalent of a Do¨tz reaction with a nonstabilized vinyl carbene
complex.
Discussion
It is generally accepted that the first and rate-determining
step of Do¨tz reactions is the thermal decarbonylation of the
starting pentacarbonyl carbene I to yield the tetracarbonyl
carbene complex II, which is coordinatively unsaturated (Scheme
12). This intermediate can be stabilized by intramolecular
coordination of the double bond,36 leading to a η3-allylidene
complex II′. From the NMR data of isolated carbenes of the
type II′ (complexes 5a-e) it is reasonable to conclude that there
is an equilibrium between species II and II′ in solution, which
is fast but more attracted to the more stable chelate form,
although it has never been observed.37 This mode of stabilization
can be achieved with reasonable ease by alkenyl carbene
complexes, but not by aryl ones, since it implies an η2-
coordination. It is at this early stage where the pathways of
reactions of alkenyl and aryl complexes first differ.
A slightly different structure can be proposed for those
carbenes XI, where R1 is an ester group. In this case, the
negative charge supported by the metal in the zwitterionic form
can be stabilized by retrodonation to the ester group, and
conjugation between the chromium and the imonium moiety is
no longer necessary. Now, a conjugation is possible between
the imonium and the terminal double bond maintaining the
chelation stabilization. This can happen assuming a rotation
around the bond between C2 and C3 instead of that between
C3 and C4. This structure is depicted in Scheme 12 as XI′.
The strength of the coordination of the double bond to the metal
is now increased since (a) the structural arrangement is
geometrically more accurate and (b) the double bond is more
(35) Do¨rwald, F. Z. Metal Carbenes in Organic Synthesis; Wiley-VCH:
Weinheim, 1999.
(38) This stabilization has been calculated to be 23 kcal/mol for
tetracarbonyl(3-hydroxypenta-2,4-dienylidene)chromium(0).13c
(39) This effect would explain the unexpected value for the 13C chemical
shift of the carbene carbon in these species (e.g., 246 ppm for 9a).
(36) Theoretical calculations show that this coordination is stabilizing.11
(37) This kind of equilibrium might occur not only with aminoalkenyl
carbenes but also with alkoxyalkenyl carbenes.11

First Stepwise Do¨tz Reaction
J. Am. Chem. Soc., Vol. 122, No. 7, 2000 1321
Scheme 12
electron deficient, thus leading to a greater contribution of d-π*
back-bonding. This structure has been proposed since it is
essentially the same as that which has been observed in the
X-ray structure of the related pentacarbonyl complex 12g, except
for the complexation of the terminal double bond. In this
structure, we reproduce the zwitterionic character, the conjuga-
tion of the chromium with the ester instead of the imonium
moiety, and the conjugation of this imonium with the double
bond. From the greater thermal stability of the complexes
bearing an ester in position 2, as compared to those that lack it
(9e compared with 9j) we can conclude that the overall effect
is stabilizing.
By assuming these different structures for XI and XI′, the
different outcome of the thermal progress of both structures can
be rationalized as follows: in the latter (XI′), an intramolecular
nucleophilic attack from the negatively charged chromium on
the vinyl imonium moiety could be more advantageous.40,41 This
attack yields the metallacyclohexadiene V which would undergo
reductive elimination to furnish the five-membered ring product
VIII exclusively. On the other hand, the conformer XI is less
likely to suffer this kind of attack, since the double bond is not
conjugated with the imonium cation. Thermal evolution of these
intermediates would involve a CO insertion process giving rise
to phenol IX, which is the main product of the Do¨tz reaction
of alkenyl amino carbenes.
It is worth noting that the allochemical effect proposed by
Wulff and colleagues as necessary for the CO insertion to take
place in aryl carbene complexes reactions2e cannot be claimed
in this case since the cyclization step is carried out starting from
isolated carbenes XI, in the absence of additional alkyne. It is
known that the reactions of alkenyl carbene complexes are little
or not affected by changes in the concentration of alkyne.2d This
lack of influence can be explained by a mechanism in which
CO insertion is concomitant with the complexation of the Cr-
(CO)3 moiety to all three double bonds of the dienylketene VI
just formed. The chromium maintains an 18-electron configu-
ration throughout all the CO insertion process.42 The evolution
of this dienylketene through the usually proposed electrocyclic
closure leads to Cr(CO)3-complexed cyclohexadienone VII and
then to the complexed phenol IX.
Finally, the electronic nature of the differentiation between
pathways leading to five- and six-membered ring products can
be supported by the reaction of complexes XI (and XI′) with
carbon nucleophiles. This reaction gives phenols in which the
amine group has been substituted for the nucleophile. In the
proposed mechanism for this reaction, we assume that this
substitution takes place as the first step, by nucleophilic attack
on the imonium cation of XI, followed by amine extrusion,
leading to formation of metallatriene XII. This complex is very
similar to XI except for the fact that no stabilization can be
achieved by electron donation toward the metal. Charge
separation is not produced, and a nucleophilic attack of the
(40) A similar attack has been proposed for the [4 + 1] reaction of
chromium phenylmethoxycarbene with 2-methyl-1,3-dimorpholino-1,3-
butadiene. Barluenga, J.; Aznar, F.; Ferna´ndez, M. Chem. Eur. J. 1997, 3,
1629.
(41) The formation of VIII from XI′ could also take place through a
Nazarov-type reaction. Yamashita, A. Tetrahedron Lett. 1986, 27, 5915.
(42) An alternative mechanism that accounts for the direct formation of
VII from XI without the intervention of an additional molecule of alkyne
in reactions of alkenyl carbenes has been proposed.13c

1322 J. Am. Chem. Soc., Vol. 122, No. 7, 2000
Barluenga et al.
1H NMR (300 MHz, CDCl3): δ ) 4.67 (t, 1H, J ) 3.3 Hz, dCH),
4.01-3.63 (m, 8H, N(CH2CH2)2O), 2.67-2.51 (m, 1H), 2.35-2.20 (m,
2H), 1.96 (dd, 1H, J ) 7.8, 14.0 Hz), 1.88-1.71 (m, 1H), 1.64-1.35
(m, 1H). 13C NMR (75.5 MHz, -40 °C, CD2Cl2): δ ) 257.6 (CdCr),
235.8 (CO), 234.9 (CO), 224.2 (CO), 222.0 (CO), 86.6 (dC), 85.0
(dCH), 67.5 (NCH2CH2O), 67.1 (NCH2CH2O), 58.5 (NCH2CH2O),
57.0 (NCH2CH2O), 35.4 (dCCH2), 31.1 (CH2CH2CH2), 20.5 (CH2CH2-
CH2). Anal. Calcd for C14H15NO5Cr: C, 54.36; H, 4.85; N, 4.53.
Found: C, 54.58; H, 4.64; N, 4.25.
chromium to the complexed double bond is not favorable. The
most favorable reaction pathway would be the insertion of CO
that leads, following a mechanism analogous to the one
explained above, to the final product, the phenol XIV, as a
(CO)3Cr complex. This reaction is very fast even at low
temperature, suggesting that the CO insertion process has a low
energetic barrier as well.
Conclusions
Tetracarbonyl(η3-1-morpholino-3-phenyl-2-propenylidene)chro-
mium(0) (5e). A solution of 20 mg of 1e in 1 mL of CD2Cl2 was
irradiated in a NMR tube under static vacuum for 6 h. Each hour, the
sample was degassed (two freeze-pump-thaw cycles) in order to
We report herein a comprehensive study of the thermal and
photochemical decarbonylation of alkenyl amino carbene com-
plexes. This reaction is quite general and furnishes a new type
of carbenes 5 that are valuable as low-temperature generators
of 16-electron tetracarbonyl chromium carbene complexes. The
synthesis and isolation of these complexes have allowed us to
carry out the reaction with alkynes at low temperature and to
isolate and characterize the carbene complexes 9. Since some
of these carbene complexes lead to phenols upon warming, both
complexes 5 and 9 can be considered as Do¨tz benzannulation
reaction intermediates. The overall process can be seen as a
Do¨tz reaction carried out in three separate steps at low
temperature. As far as we know, this is the first example of
such a stepwise Do¨tz reaction. On the other hand, the insertion
of alkynes into complexes 5 can be considered as a general
method for the synthesis of electron-withdrawing substituted
carbene complexes, either as η1-pentacarbonyl or as η3-
tetracarbonyl. As far as we know, this is the first synthesis of
such a chelated dienyl carbene complex. The reaction of
complexes 5 with DMAD is also the first general reaction of
cyclopentannulation of alkenylcarbene complexes with alkynes.
Finally, we have carried out a three-component Do¨tz reaction
in which we have substituted the carbene donor group for a
carbonated nucleophile.
1
remove the released CO. H and 13C NMR analyses showed a 40:60
mixture of 1e and another compound that was identified as 5e. 1H NMR
(300 MHz, CD2Cl2): δ ) 7.50-7.20 (m, 5H, Ph), 5.01 (d, 1H, J ) 12
Hz, dCH), 4.93 (d, 1H, J ) 12 Hz, dCH), 4.00-3.60 (m, 8H,
N(CH2CH2)2O). 13C NMR (75.5 MHz, CD2Cl2): δ ) 257.8 (CdCr),
229.6 (broad, 4×CO), 138.3 (C ipso), 129.3 (2×CH, Ph), 127.9 (CH,
p-Ph), 127.6 (2×CH, Ph), 75.0 (dCH), 68.1 (NCH2CH2O), 67.8
(NCH2CH2O), 64.9 (dCH), 61.2 (NCH2CH2O), 57.8 (NCH2CH2O).
Reaction of Carbene Complex 1a with Phenylacetylene. A
solution of 0.18 g (0.5 mmol) of 1a and 0.10 g (1 mmol) of
phenylacetylene in 10 mL of THF was refluxed for 1 h. The solvents
were removed under reduced pressure, and the residue was chromato-
graphed using hexane:ethyl acetate 1:1 as eluent. Two products were
obtained: 0.08 g (0.20 mmol, 40%) of tricarbonyl (η5-1,4,5,6-
tetrahydro-1-morpholino-3-phenylpentalene)chromium(0) (6) and 0.09
g (0.21 mmol, 42%) of tricarbonyl (η6-2,3-dihydro-4-hydroxy-7-
morpholino-5-phenylindene)chromium(0) (7). Spectral data for 6. Rf
1
) 0.33 (hexane:ethyl acetate 3:1). H NMR (300 MHz, CDCl3): δ )
7.50-6.91 (m, 5H, Ph), 5.69-5.40 (m, 2H), 3.80-3.55 (m, 4H,
N(CH2CH2)2O), 3.00-1.40 (m, 10H, N(CH2CH2)2O, CH2-CH2-CH2).
13C NMR (75.5 MHz, CDCl3): δ ) 238.9 (3×CO), 133.6 (C, aryl),
128.3 (2×CH, Ph), 127.5 (CH, p-Ph), 126.7 (2×CH, Ph), 106.1 (dC),
102.5 (dC), 100.3 (dCH), 87.7 (dC), 84.0 (CH), 66.1 (N(CH2CH2)2O),
50.1 (N(CH2CH2)2O), 25.6 (CH2), 24.2 (CH2), 22.2 (CH2). Anal. Calcd
for C21H21NO4Cr: C, 62.53; H, 5.25; N, 3.47. Found: C, 62.81; H,
5.52; N, 3.67. Spectral data for 7: Rf ) 0.14 (hexane:ethyl acetate
3:1). 1H NMR (300 MHz, THF-d8): δ ) 7.55-7.05 (m, 5H, Ph), 5.37
(s, 1H, aryl), 3.70-3.30 (m, 4H, N(CH2CH2)2O), 3.00-2.50 (m, 4H,
N(CH2CH2)2O), 2.20-1.80 (m, 2H, CH2-CH2-CH2), 1.75-1.45 (m,
4H, CH2-CH2-CH2). 13C NMR (75.5 MHz, THF-d8): δ ) 237.2
(3×CO), 137.5 (C, aryl), 131.6 (2×CH, Ph), 130.3 (CH, p-Ph), 130.2
(2×CH, Ph), 123.7 (C, aryl), 120.3 (C, aryl), 115.7 (C, aryl), 104.9
(C, aryl), 100.9 (C, aryl), 90.0 (CH, aryl), 68.9 (N(CH2CH2)2O), 54.2
(N(CH2CH2)2O), 33.2 (CH2), 31.8 (CH2), 27.7 (CH2). Anal. Calcd for
C22H21NO5Cr: C, 61.25; H, 4.91; N, 3.25. Found: C, 61.47; H, 5.21;
N, 3.48.
Experimental Section
All reactions were carried out under nitrogen atmosphere. Tetrahy-
drofuran (THF), toluene, and ether were dried by distillation from
sodium/benzophenone. Melting points are uncorrected. Chromato-
graphic purifications were performed on silica gel (230-400 mesh)
by flash technique. Analytical TLC plates (covered with silica gel 60
F
254) were viewed by UV light or developed by heating after treatment
with an acidic solution of Ce(IV) and Mo(VI). 1H and 13C NMR spectra
were recorded on a Bruker AC-200 or AC-300 spectrometer. Chemical
shifts refer to TMS in 1H experiments and to deuterated solvent in 13
C
experiments. IR analyses were performed on a Mattson 3000 FTIR
spectrometer. HRMS spectra were recorded on a Finnigan-Mat 95.
Elemental analyses were obtained on a Perkin-Elmer 240-B analyzer.
Photochemical reactions were carried out in Schlenk tubes (Pyrex)
equipped with external jackets for continuos coolant flow (2-propanol)
and placed 2 cm away from a 400-W medium-pressure mercury lamp.
The solutions were deoxygenated by nitrogen bubbling for 15 min prior
to irradiation. In the cases in which a loss of CO is expected, bubbling
was maintained during irradiation. The reactions were monitored by
TLC or IR techniques until disappearance of the starting materials.
General Procedure for the Preparation of η3-Aminovinyl Car-
bene Complexes 5. A 0.05 M solution of aminovinyl carbene complex
1 in degassed THF was irradiated at temperatures between -45 and
-35 °C. The reaction was monitored by IR analyses until disappearance
of the absortion signals corresponding to the starting complex. For
complexes 5a-d, the solution was then filtered through a pad of Celite,
and the solvents were evaporated under vacuum. The residue was
crystallized in deoxygenated hexane-dichloromethane. Complexes
5e-g were not isolated but were used in situ in the next reaction.
Tetracarbonyl[η3-(1-cyclopentenyl)morpholinomethylene]-
chromium(0) (5a). A 0.71 g (2 mmol) amount of 1a was irradiated
for 4 h to yield, after crystallization, 0.62 g (1.86 mmol, 94%) of 5a.
Mp: 137-139 °C (red prisms). Rf ) 0.19 (hexane:ethyl acetate 3:1).
Reaction of Carbene Complex 5a with Phenylacetylene. A
solution of 0.17 g (0.5 mmol) of 5a in 20 mL of CH2Cl2 was treated
with 0.10 g (1 mmol) of phenylacetylene at room temperature. The
reaction was monitored by TLC. When the starting material was
consumed (6 h) the solvents were removed under reduced pressure,
and the residue was chromatographed to yield 0.08 g (0.23 mmol, 46%)
of 1a as the only identifiable product. When this reaction was carried
out in refluxing THF temperature, the disappearance of the carbene
took 1 h, and the products isolated after column chromatography were
6 (0.04 g, 0.1 mmol, 20%) and 7 (0.04 g, 0.1 mmol, 20%).
General Procedure for the Preparation of 1,4,5-η3-Methoxycar-
bonyldienylcarbene Complexes 9. A 0.1 M solution of carbenes 5a-d
in CH2Cl2 was treated with 1 equiv of DMAD at -20 °C for 24 h, and
then a 2-fold volume of hexane was added. The reaction was cooled to
-40 °C, and a dark brownish solid precipitated after 1 day. The solution
was decanted under N2 at -20 °C and the resultant solid washed with
hexane to give 9a-d. These solids are thermally unstable, and
satisfactory elemental analyses could not been obtained in one case.
Complexes 9e-g and 9j-l were prepared by irradiation of a 0.05 M
solution of aminovinyl carbene complex 1e-g in degassed THF at
temperatures between -45 and -35 °C. The reaction was monitored
by IR analyses until disappearance of the absortion signals correspond-

First Stepwise Do¨tz Reaction
J. Am. Chem. Soc., Vol. 122, No. 7, 2000 1323
ing to the starting complex. DMAD (1 equiv) was added at -40 °C,
and the reaction was warmed and allowed to react overnight. Complexes
9h-i were prepared by irradiation of solutions of 1h-i in the presence
of DMAD in THF. In both cases, the solutions were evaporated under
vacuum, and the residue was chromatographed using hexane:ethyl
acetate 1:1 as eluent.
Tetracarbonyl[1,4,5-η3-(1-cyclopentenyl)-1,2-dimethoxycarbonyl-
3-morpholinopropenylidene]chromium(0) (9a). 5a (0.33 g, 1.0 mmol)
was reacted with 0.14 g (1.0 mmol) of DMAD in 10 mL of CH2Cl2 to
afford 0.25 g (0.54 mmol, 54%) of 9a as a brown powder. Rf ) 0.11
(hexane:ethyl acetate 1:1). 1H NMR (300 MHz, CD2Cl2): δ ) 4.81 (s,
1H, CdCH), 3.90 (s, 3H, CO2CH3), 3.72-4.20 (m, 8H, N(CH2CH2)2O),
3.66 (s, 3H, CO2CH3), 2.36-2.92 (m, 4H, CH2CH2CH2), 1.61-1.94
(m, 2H, CH2CH2CH2), 13C NMR (50.3 MHz, CDCl3): δ ) 245.9 (Cd
Cr), 231.1 (CO), 230.0 (CO), 220.9 (CO), 220.2 (CO), 178.1 (CO2-
CH3), 167.5 (CO2CH3), 157.9 (dC), 130.7 (dC), 102.1 (dC), 93.8
(dCH),), 67.1 (NCH2CH2O), 66.8 (NCH2CH2O), 54.2 (NCH2CH2O),
53.8 (NCH2CH2O), 52.3 (CO2CH3), 51.4 (CO2CH3), 36.7 (CH2Cd),
34.0 (CH2Cd), 20.7 (CH2CH2CH2). Anal. Calcd for C20H21NO9Cr: C,
50.96; H, 4.49; N, 2.97. Found: C, 50.80; H, 4.37; N, 2.63.
122.8 (dCH), 114.6 (CH, 3-Fu), 114.1 (CH, 4-Fu), 51.9 (CO2CH3),
50.4 (CO2CH3), 44.9 (NCH3), 41.8 (NCH3). Anal. Calcd for C20H17-
NO10Cr: C, 49.70; H, 3.54; N, 2.90. Found: C, 49.71; H, 3.64; N,
2.95.
Crystallographic Structural Determination. Data collection, crys-
tal, and refinement parameters for 12g are collected in Table 7. The
unit cell parameters were obtained from the least-squares fit of 25
reflections. On all reflections, profile analysis was performed.43 Lorentz
and polarization corrections were applied, and the data were reduced
to F2 values using THE REFLEX.44 The structures were solved by
Patterson methods using the program DIRDIF.45 Refinement on F2 was
done using SHELXL 97.46 Non-hydrogen atoms were refined aniso-
tropically. Hydrogen atoms were calculated geometrically through HFIX
and refined riding with common isotropic thermal parameters. Atomic
scattering factors were taken from International Tables for X-Ray
Crystallography.47 Geometrical calculations were made with PARST.
All calculations were made at the University of Oviedo on the Scientific
Computer Center and X-Ray Group DEC/AXP Computers.
1-(1,4,5,6-Tetrahydro-2,3-dimethoxycarbonyl-1-pentalenyl)mor-
pholine (13a). A solution of 0.42 g (0.89 mmol) of 13a in 10 mL of
CH2Cl2 was allowed to stand at room temperature for 8 h. The reaction
mixture was concentrated and the crude material chromatographed to
yield 0.20 g (0.66 mmol, 74%) of 13a as a yellow oil. Rf ) 0.40
(hexane:ethyl acetate 1:1). 1H NMR (300 MHz, CDCl3): δ ) 4.56 (s,
1H, NCH), 3.76-3.54 (m, 4H, N(CH2CH2)2O), 3.65 (s, 3H, CO2CH3),
3.61 (s, 3H, CO2CH3), 3.38-3.13 (m, 4H, N(CH2CH2)2O), 2.69-2.45
(m, 4H, CH2CH2CH2), 2.29-2.02 (m, 2H, CH2CH2CH2). 13C NMR
(75.5 MHz, CDCl3): δ ) 175.4 (CO2Me), 170.4 (CO2Me), 164.0 (d
C), 149.9 (dC), 123.6 (dC), 108.6 (dC), 66.4 (N(CH2CH2)2O), 60.5
(CH), 52.4 (CO2CH3), 50.6 (CO2CH3), 49.2 (N(CH2CH2)2O), 29.8
(CH2), 27.7 (CH2), 26.5 (CH2). Anal. Calcd for C16H21NO5: C, 62.53;
H, 6.89; N, 4.56. Found: C, 62.60; H, 6.99; N, 4.61.
Tetracarbonyl(1,4,5-η3-1,2-dimethoxycarbonyl-3-morpholino-5-
phenyl-2,4-pentadien-1-ylidene)chromium(0) (9e). 1e (1.00 g, 2.5
mmol) was irradiated in 150 mL of degassed THF at -40 °C until IR
analysis showed no absortion signals of the starting carbene. Then,
0.36 g (2.5 mmol) of DMAD was added, and the reaction mixture was
allowed to react overnight to afford, after chromatography, 0.75 g (1.4
mmol, 55%) of 9e. Mp: 139-141 (dark green prisms). Rf ) 0.14
1
(hexane:ethyl acetate 1:1). H NMR (200 MHz, CDCl3): δ ) 7.59-
7.07 (m, 5H, Ph), 4.86 (d, 1H, J ) 11.5 Hz, dCH), 4.73 (d, 1H, J )
11.5 Hz, dCH), 4.51-3.90 (m, 8H, N(CH2CH2)2O), 3.82 (s, 3H,
CO2CH3), 3.65 (s, 3H, CO2CH3). 13C NMR (50.3 MHz, CDCl3): δ )
252.5 (CdCr), 235.0 (CO), 228.8 (CO), 226.7 (CO), 222.9 (CO), 178.1
(CO2CH3), 177.3 (CO2CH3), 157.6 (dC), 138.3 (C ipso), 128.5 (2×CH,
Ph), 128.2 (CH, p-Ph), 126.2 (2×CH, Ph), 122.68 (dC), 89.8 (dCH),
68.2 (dCH), 66.4 (2×NCH2CH2O), 53.9 (NCH2CH2O), 51.8 (CO2CH3),
51.4 (NCH2CH2O), 50.9 (CO2CH3). Anal. Calcd for C23H21NO9Cr: C,
54.44; H, 4.17; N, 2.76. Found: C, 54.43; H, 4.22; N, 2.78.
Methyl 2-Hydroxy-5-morpholino-3-phenylbenzoate (15j). 9j (0.45
g, 1 mmol) was dissolved in 20 mL of THF and allowed to stand at
room temperature for 9 h and then exposed to air and sunlight for
several hours to afford, after chromatography, 0.29 g (0.92 mmol, 92%)
of 15j. Rf ) 0.35 (hexane:ethyl acetate 1:1). 1H NMR (200 MHz,
CDCl3): δ ) 10.92 (s, 1H, OH), 7.64-7.35 (m, 6H, aryl), 7.23 (d,
1H, J ) 3.2 Hz, aryl), 3.98 (s, 3H, CO2CH3), 3.89 (t, 4H, J ) 4.6 Hz,
N(CH2CH2)2O), 3.11 (t, 4H, J ) 4.6 Hz, N(CH2CH2)2O). 13C NMR
(50.3 MHz, CDCl3): δ ) 170.8 (CO2CH3), 153.5 (C, aryl), 143.7 (C,
aryl), 137.3 (C, aryl), 131.1 (C ipso), 129.2 (2×CH, Ph), 128.1 (2×CH,
Ph), 127.4 (CH, p-Ph), 127.1 (CH, aryl), 115.5 (CH, aryl), 112.3 (C,
aryl), 66.9 (N(CH2CH2)2O), 52.4 (CO2CH3), 50.7 (N(CH2CH2)2O). Anal.
Calcd for C18H19NO4: C, 68.99; H, 6.11; N, 4.47. Found: C, 69.21;
H, 6.25; N, 4.62. Chromium tricarbonyl-complexed methyl 2-hydroxy-
5-morpholino-3-phenylbenzoate 15j‚(CO)3Cr is obtained in lower
yields by chromatography without exposition to sunlight. In these
conditions, 0.36 g (0.80 mmol, 80%) of 15j‚(CO)3Cr (red prisms) was
Tetracarbonyl(1,4,5-η3-5-furyl-1,2-dimethoxycarbonyl-3-methyl-
amino-2,4-pentadien-1-ylidene)chromium(0) (9h). 1h (0.65 g, 2.0
mmol) and DMAD (0.28 g, 2 mmol) were irradiated in 150 mL of
deoxygenated Et2O at -40 °C for 6 h. The reaction crude material
was chromatographed to afford 0.09 g of 9h (0.2 mmol, 10%) and
0.04 g of 13h (0.2 mmol, 10%). In addition, 0.36 g (1.1 mmol, 55%)
of 1h was recovered unreacted. Longer reaction time did not increase
the chemical yield of 9h. Mp: 147-150 °C. Rf ) 0.52 (dichlo-
romethane:ethyl acetate 8:1). 1H NMR (300 MHz, CDCl3): δ ) 10.74
(br s, 1H, NH), 7.23 (s, 1H, 5-Fu), 6.39 (d, 1H, J ) 3.4 Hz, 4-Fu),
6.32 (d, 1H, J ) 1.5 Hz, 3-Fu), 4.93 (d, 1H, J ) 10.5 Hz, dCH), 4.78
(d, 1H, J ) 10.5 Hz, dCH), 3.78 (s, 3H, CO2CH3), 3.64 (s, 3H,
CO2CH3), 3.57 (d, 3H, J ) 4.8 Hz, NCH3). 13C NMR (75.5 MHz,
CDCl3): δ ) 271.3 (CdCr), 234.5 (CO), 227.0 (CO), 226.2 (CO),
223.3 (CO), 186.9 (CO2CH3), 177.3 (CO2CH3), 161.1 (dC), 153.7 (C,
2-Fu), 141.8 (CH, 5-Fu), 123.3 (dC), 111.9 (CH, 4-Fu), 107.4 (CH,
3-Fu), 77.4 (dCH), 63.5 (dCH), 52.0 (CO2CH3), 50.9 (CO2CH3), 32.4
(NCH3). Anal. Calcd for C18H15NO9Cr: C, 48.99; H, 3.43; N, 3.17.
Found: C, 49.18; H, 3.63; N, 3.28.
1
obtained. Mp: 152-154 °C. Rf ) 0.42 (hexane:ethyl acetate 1:1). H
NMR (300 MHz, CDCl3): δ ) 10.59 (s, 1H, OH), 7.65-7.60 (m, 2H,
Ph), 7.45-7.35 (m, 3H, Ph), 5.82 (d, 1H, J ) 2.0 Hz, aryl), 5.78 (d,
1H, J ) 2.0 Hz, aryl), 4.00 (s, 3H, OCH3), 3.83 (m, 4H, N(CH2CH2)2O),
2.92 (m, 4H, N(CH2CH2)2O). 13C NMR (75.5 MHz, CDCl3): δ ) 232.8
(3×CO), 171.5 (CO2CH3), 140.0 (C, aryl), 133.7 (C, aryl), 130.2
(2×CH, Ph), 128.6 (CH, p-Ph), 128.3 (2×CH, Ph), 120.0 (C, aryl),
97.3 (C, aryl), 86.9 (CH, aryl), 78.8 (CH, aryl), 70.8 (C, aryl), 66.0
(N(CH2CH2)2O), 53.4 (CO2CH3), 48.9 (N(CH2CH2)2O). Anal. Calcd
General Procedure for the Preparation of η1-Methoxycarbon-
yldienylcarbene Complexes 12e-g. A 0.1 M solution of carbene
complexes 9e-g was pressurized under 4 bar of CO for 2 days. The
solvent was then evaporated under vacuum and the crude mixture
chromatographed (silica gel, hexane:ethyl acetate 1:1).
(43) (a) Grant, D. F.; Gabe, E. J. J. Appl. Crystallogr. 1978, 11, 114.
(b) Lehman, M. S.; Larsen, F. K. Acta Crystallogr. 1974, A30, 580.
(44) Gutie´rrez-Rodr´ıguez, A.; Aguirre-Pe´rez, A.; Garc´ıa-Granda, S. THE
REFLEX V 1.2 E 2 Manual del usuario; Departamento de Qu´ımica F´ısica
y Anal´ıtica, Universidad de Oviedo, 19XX.
(45) Garc´ıa-Granda, S.; Gould, R. O.; Smits, J. M. M.; Smukalla, C.;
Beurkens, P. T.; Admiraall, G.; Beurskens, G.; Bosman, W. P. DIRDIF
user’s guide Technical report; Crystallography Laboratory: University of
Nijmegen, The Netherlands, 19XX.
(46) Sheldrick, G. M. SHELXS-97; University of Go¨ttingen, Germany,
19XX.
(47) International Tables for X-Ray Crystallography; Birmingham
Kynoch Press: Birmingham, UK, 1974 (present distributor, Kluwer
Academic Publishers: Dordrecht); Vol. IV.
Pentacarbonyl[3-(dimethylamino)-5-furyl-1,2-dimethoxycarbon-
yl-2,4-pentadien-1-ylidene]chromium(0) (12 g). Reaction of 0.10 g
(0.22 mmol) of 9g afforded 0.10 g (0.21 mmol, 95%) of 12g. Mp:
1
128-130 °C (black prisms). Rf ) 0.05 (hexane:ethyl acetate 1:1). H
NMR (300 MHz, CDCl3): δ ) 7.67 (s, 1H, 5-Fu), 7.60 (d, 1H, J ) 15
Hz, dCH), 7.09 (d, 1H, J ) 15 Hz, dCH), 6.96 (s, 1H, 4-Fu), 6.59 (s,
1H, 3-Fu), 3.83 (s, 3H, CO2CH3), 3.67 (s, 3H, CO2CH3), 3.61 (s, 6H,
N(CH3)2). 13C NMR (75.5 MHz, CDCl3): δ ) 224.1 (CdCr), 219.8
(CO trans), 218.4 (4×CO cis), 179.1 (CO2CH3), 178.0 (CO2CH3), 157.7
(dC), 150.5 (C, 2-Fu), 148.4 (dCH), 141.4 (CH, 5-Fu), 124.2 (dC),

1324 J. Am. Chem. Soc., Vol. 122, No. 7, 2000
Barluenga et al.
for C21H19NO7Cr: C, 56.13; H, 4.26; N, 3.12. Found: C, 56.35; H,
4.10; N, 2.96.
0.25 g (0.57 mmol, 57%) of 16e‚Cr(CO)3 (red prisms) was obtained.
1
Rf ) 0.48 (hexane:ethyl acetate 1:1). H NMR (200 MHz, CDCl3): δ
Dimethyl 3-Hydroxy-6-methyl-4-phenylphthalate (16e). A solution
of 1 mmol of methyllithium in 10 mL of diethyl ether was added
dropwise to a solution of 0.51 g (1 mmol) of 9e in 20 mL of THF at
-78 °C. The reaction mixture was then warmed to -60 °C, and a
mixture of 3 mL of saturated aqueous NH4Cl and 10 mL of THF was
added at this temperature. The reaction mixture was exposed to air
and sunlight for several hours. Et2O (20 mL) was added, and the mixture
was washed with 0.1 N HCl (2 × 20 mL) and brine (20 mL), dried
over Na2SO4, and filtrated through Celite. The volatiles were removed
in vacuo, and the residue was chromatographed to furnish 0.21 g (0.71
) 10.91 (s, 1H, OH), 7.65-7.55 (m, 2H, Ph), 7.50-7.40 (m, 3H, Ph),
5.94 (s, 1H, aryl), 4.03 (s, 3H, CO2CH3), 3.99 (s, 3H, CO2CH3), 2.15
(s, 3H, CH3). 13C NMR (50.3 MHz, CDCl3): δ ) 230.4 (3×CO), 170.7
(CO2CH3), 166.3 (CO2CH3), 140.4 (C, aryl), 132.8 (C, aryl), 130.1
(2×CH, Ph), 128.7 (CH, Ph), 128.2 (2×CH, Ph), 105.9 (C aryl), 98.4
(CH, aryl), 98.0 (C, aryl), 96.5 (C, aryl), 68.6 (C, aryl), 53.8 (CO2CH3),
53.4 (CO2CH3), 17.8 (CH3). Anal. Calcd for C20H16O8Cr: C, 55.05;
H, 3.70. Found: C, 54.91; H, 3.59.
Acknowledgment. This research was supported by the
DGICYT (Grant PB97-1271).
1
mmol, 71%) of 16e. Rf ) 0.11 (hexane:ethyl acetate 3:1). H NMR
(200 MHz, CDCl3): δ ) 11.31 (s, 1H, OH), 7.62-7.40 (m, 5H, Ph),
7.38 (s, 1H, aryl), 3.97 (s, 3H, CO2CH3), 3.94 (s, 3H, CO2CH3), 2.30
(s, 3H, CH3). 13C NMR (50.3 MHz, CDCl3): δ ) 169.7 (CO2CH3),
169.3 (CO2CH3), 157.0 (C, aryl), 138.0 (CH, aryl), 136.4 (C, aryl),
133.6 (C, aryl), 131.6 (C, aryl), 129.2 (2×CH, Ph), 128.1 (2×CH, Ph),
127.6 (CH, Ph), 125.4 (C, aryl), 109.1 (C, aryl), 53.0 (CO2CH3), 52.3
(CO2CH3), 18.4 (CH3). Anal. Calcd for C17H16O5: C, 67.99; H, 5.37.
Found: C, 68.34; H, 5.58. In a separate run, chromium tricarbonyl-
complexed dimethyl 3-hydroxy-6-methyl-4-phenylphthalate 16e‚Cr-
(CO)3 was obtained in lower yields by the same aqueous workup and
chromatography without exposition to sunlight. In these conditions,
Supporting Information Available: Experimental proce-
dures and analytical data for all new compounds and X-ray
crystallographic data for 12g, including tables of atomic
coordinates, bond lengths, bond angles, and anisotropic dis-
placement coefficients (PDF). An X-ray crystallographic file,
in CIF format, is also available. This material is available free
of charge via the Internet at http://pubs.acs.org.
JA991865J