Coupling of η3-allyl and alkyne in molybdenum carbonyl complexes

Article abstract of DOI:10.1021/om970627z

The complexes [Mo(η³allyl)(CO)₂(S₂PX₂)(NCMe)] (X = OEt (la), Ph (1b)) react with DMAD (dimethyl acetylenedicarboxylate) to give the tricarbonyl complexes [Mo(CO)₃(S₂PX₂){OC-(OMe)C(allyl)=CCO ₂Me}] (2a,b) in a reaction involving the coupling of allyl and alkyne. Subsequent addition of PEt₃ affords crystalline, air-stable dicarbonyl complexes [Mo(CO)₂-(PEt₃)(S₂PX ₂){OC(OMe)C(allyl)=CCO₂Me}] (3a,b). An X-ray structural analysis of the dithiophosphinate derivative 3b reveals that the alkenyl ligand is stabilized through intramolecular coordination of one oxygen of the ester group to the metal, forming a five-membered oxametallacycle. The alkenyl ligand shows unusual trans stereochemistry in contrast to the cis disposition usually found in previous examples of metal-mediated η³-allyl - alkyne coupling. Demetalation of the organic moiety can be easily afforded by reaction with air or HCl gas to give the corresponding 2-allyl fumarate 4 in high yield. Regioselectivity studies employing 1-methylallyl complexes reveal that the reaction is strongly influenced by the dithio ligand bonded to molybdenum. In all cases reaction at the more substituted carbon of the allyl is favored.

Full text of DOI:10.1021/om970627z

820
Organometallics 1998, 17, 820-826
Cou p lin g of η3-Allyl a n d Alk yn e in Molybd en u m
Ca r bon yl Com p lexes
Georgina Barrado, Margaret M. Hricko, Daniel Miguel,*,† V´ıctor Riera, and
Hans Wally
Departamento de Quı´mica Orga´nica e Inorga´nica/ IUQOEM-Unidad Asociada del CSIC,
Universidad de Oviedo, E-33071 Oviedo, Spain
Santiago Garc´ıa-Granda
Departamento de Quimı´ca Fisica y Analitica, Universidad de Oviedo, E-33071 Oviedo, Spain
Received J uly 23, 1997
The complexes [Mo(η3-allyl)(CO)2(S2PX2)(NCMe)] (X ) OEt (1a ), Ph (1b)) react with DMAD
(dimethyl acetylenedicarboxylate) to give the tricarbonyl complexes [Mo(CO)3(S2PX2){OC-
(OMe)C(allyl)dCCO2Me}] (2a ,b) in a reaction involving the coupling of allyl and alkyne.
Subsequent addition of PEt3 affords crystalline, air-stable dicarbonyl complexes [Mo(CO)2-
(PEt3)(S2PX2){OC(OMe)C(allyl)dCCO2Me}] (3a ,b). An X-ray structural analysis of the
dithiophosphinate derivative 3b reveals that the alkenyl ligand is stabilized through
intramolecular coordination of one oxygen of the ester group to the metal, forming a five-
membered oxametallacycle. The alkenyl ligand shows unusual trans stereochemistry in
contrast to the cis disposition usually found in previous examples of metal-mediated η3-
allyl-alkyne coupling. Demetalation of the organic moiety can be easily afforded by reaction
with air or HCl gas to give the corresponding 2-allyl fumarate 4 in high yield. Regioselectivity
studies employing 1-methylallyl complexes reveal that the reaction is strongly influenced
by the dithio ligand bonded to molybdenum. In all cases reaction at the more substituted
carbon of the allyl is favored.
In tr od u ction
resulting organic moiety remained attached to the
metal. In two cases such reaction leads to a cyclopen-
tadienyl ring bonded to the metal as a η5-ligand (A in
Chart 1),4 while in other cases an allyl-substituted
σ-alkenyl is produced.5 Recently a new reactivity pat-
tern leading to seven-membered carbocycles by insertion
of two alkynes in the allyl-metal bond has been
reported (B in Chart 1).6 Usually, the final products
contain the allyl group in a position cis to the metals,
as it can be expected for a metal-mediated allyl-alkyne
coupling. We want to report the coupling of a η3-allyl
with dimethyl acetylenedicarboxylate (DMAD) within
the coordination sphere of Mo(II) to give an intramo-
Coupling of allyl and alkyne promoted by transition
metals has been studied intensively in the last 25 years
by several research groups. Synthetically useful meth-
ods have been developed in linear as well as in cycliza-
tion coupling reactions.1,2 In most cases η1-allyl com-
pounds have been employed, whereas η3-allyls have
attracted less attention. Nevertheless, complexes con-
taining η3-allyl have been frequently used as allyl
transfer reagents in organic synthesis.3 In contrast,
there are only a few reported cases in which the
† Present address: Departamento de Quı´mica Inorga´nica, Facultad
de Ciencias, Universidad de Valladolid, 47071 Valladolid, Spain.
E-mail: dmsj@cpd.uva.es.
(2) (a) Greco, A.; Green, M.; Stone, F. G. A. J . Chem. Soc. A 1971,
3476. (b) Bottrill, M.; Green, M.; O’Brien, E.; Smart, L. E.; Woodward,
P. J . J . Chem. Soc., Dalton Trans. 1980, 292. (c) Green, M.; Taylor, S.
H. J . Chem. Soc., Dalton Trans. 1975, 1142. (d) Sbrana, G.; Brac, G.;
Benedetti, E. J . J . Chem. Soc., Dalton Trans. 1975, 74. (e) Davidson,
J . L.; Green, M.; Stone, F. G. A.; Welch, A. J . J . Chem. Soc., Dalton
Trans. 1976, 2044. (f) Fischer, R.; Herrmann, W. A. J . Organomet.
Chem. 1989, 377, 275. (g) Negishi, E.; Miller, J . A. J . Am. Chem. Soc.
1983, 105, 6761. (h) Kaneda, K.; Uchiyama, T.; Fujiwara, Y.; Imanaka,
T.; Teranishi, S. J . Org. Chem. 1979, 44, 55. (i) Yamaguchi, M.;
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Principles and Applications of Organotransition Metal Chemistry;
University Science Books: Mill Valley, CA, 1987; Chapter 19.
(4) Lutsenko, Z. L.; Aleksandrov, G. G., Petrovskii, P. V.; Shubina,
E. S.; Andrianov, V. G.; Struchkov, Y. T.; Rubezhov, A. Z. J . Organmet.
Chem. 1985, 281, 349. Schwiebert, K. E.; Stryker, J . M. Organome-
tallics 1993, 12, 600.
(1) (a) Welker, M. E. Chem. Rev. (Washington, D.C.) 1992, 92, 97.
(b) Wojcicki, A. Coord. Chem.. Rev. 1990, 105, 35. (c) Rosenblum, M.
J . Organomet. Chem. 1986, 300, 191. (d) Chiusoli, G. P. Acc. Chem..
Res. 1973, 6, 422. (e) Oppolzer, W.; Bedoya-Zurita, M.; Switzer, C. Y.
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M.; Torras, J . J . Org. Chem. 1989, 54, 1969. (g) J enny, T. A.; Ma, L.
Tetrahedron Lett. 1991, 32, 6101. (h) Camps, F.; Llebaria, A.; Moreto´,
J . M.; Pages, L. Tetrahedron 1992, 33, 109. (i) Llebaria, A.; Camps,
F.; Moreto´, J . M. Tetrahedron 1993, 49, 1283. (j) Llebaria, A.; Moreto´,
J . M. J . Organomet. Chem. 1993, 451, 1. (k) Ikeda, S.; Cui, D.; Sato,
Y. J . Org. Chem. 1994, 59, 6877. (l) Semmelhack, M. F. Org. React.
1972, 19, 115. (m) Heimback, P.; J olly, P. W.; Wilke, G. Adv.
Organomet. Chem. 1970, 8, 29. (n) Bu¨ssemeier, B.; J olly, P. W.; Wilke,
G. J . Am. Chem. Soc. 1974, 96, 4726. (o) Oppolzer, W.; Bienayme, H.,
Genevois-Borella, A. J . J . Am. Chem. Soc. 1991, 113, 9660. (p) Inoue,
Y.; Ohuchi, K.; Kawamata, T.; Ishiyama, J . I.; Imazuimi, S. Chem. Lett.
1991, 835. (q) Benn, R.; J olly, P. W.; Mynott, R., Raspel, B.; Schlencker,
G.; Schick, K. P.; Schroth, G. Organometallics 1985, 4, 1945. (r) Baker,
R.; Exon, C. M.; Rao, V. B J . Chem. Soc., Perkin. Trans 1 1982, 295.
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Appleton, T. G.; C. Clark, H.; Poller, R. C.; Puddhepatt, R. J . J .
Organomet. Chem. 1972, 39, C13.
(5) Osella, D.; Gobetto, R.; Milone, L.; Zanello, P.; Mangani, S.
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Zakrzewski, U. Organometallics 1991, 10, 3520.
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S0276-7333(97)00627-4 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 02/06/1998

Molybdenum Carbonyl Complexes
Organometallics, Vol. 17, No. 5, 1998 821
Ta ble 1. Cr ysta l Da ta a n d Refin em en t Deta ils for
[Mo(CO)2(P Et3)(S2P P h 2){OC(OMe)C(C3H5)d
CCO2Me}] (3b)
Ch a r t 1
formula
fw
C29H36MoO6P2S2
702.61
cryst syst
space group
a, Å
b, Å
c, Å
â, deg
V, Å3
Z
monoclinic
P21/n
8.999(1)
19.556(4)
18.558(4)
91.18(1)
3265(1)
4
T, K
200(2)
1.43
1448
F
calc, g cm-3
F(000)
λ(Mo KR), Å
0.710 73
0.14 × 0.13 × 0.13, orange
6.48
cryst size, mm; color
µ, cm-1
Sch em e 1
method of collcn
scan range, deg
abs corr
corr factors (min, max)
no. of reflcns measd
no of reflcns obsd, I g 3σ(I)
no. of params
data-to-param ratio
weighting scheme
g
ω/2θ scan
0 e θ e 25
empirical (ψ-scan)
0.910, 0.994
5926
2939
364
8.07
w ) [σ2(F) + gF2]-1
0.0003
goodness of fit
residuals R, Rw
1.3252
0.041, 0.040
a
a
2
R ) Σ(||Fo| - |Fc||)/Σ|Fo|; Rw ) {Σ(w(|Fo| - |Fc|)2)/Σw|Fo| }1/2
.
ing from an unstable dicarbonyl intermediate in the
course of the reaction. This means that the yield of 2a ,b
is limited by the amount of CO available, and it cannot
be higher than 66% in this case. However, when the
reaction with DMAD was carried out under CO atmo-
sphere, with continuous bubbling of CO through the
reaction mixture, no significant improvement of the
yield was observed. The crude products 2a ,b can be
purified by chomatography over silica to give an oil
which decomposes rapidly when exposed to air. Due to
some decomposition on the column, the isolated yield
is low.
Apart from the presence of the tricarbonyl grouping,
the most important feature of the spectra of complexes
2a ,b is the presence of a terminal allyl. Since on the
basis of spectroscopic data alone it was not possible to
ascertain the structural details of these tricarbonyls,
and we were unable, despite repeated attempts, to grow
crystals of these compounds which could be suitable for
a crystallographic study, we decided to attempt the
preparation of crystalline derivatives.
It was found soon that reactions of tricarbonyls 2a ,b
with triethylphosphine gave red microcrystalline dicar-
bonyl complexes 3a ,b. An X-ray determination was
carried out on a crystal of the diphenyldithiophosphi-
nate derivative 3b. Crystal and refinement data are
collected in Table 1, atomic parameters are found in the
Supporting Information, and selected bond distances
and angles are in Table 2.
As it can be seen in Figure 1, the most salient feature
of the molecule is the presence of a 2-allyl-substituted
alkenyl ligand, which originates from the coupling of
the allyl group of the parent 1b to DMAD.
lecularly stabilized σ-alkenyl complex. In contrast to
most previously known examples of η3-allyl/alkyne
coupling, the reaction affords an alkenyl displaying
trans stereochemistry which, after easy demetalation,
produces the corresponding dimethyl 2-allylfumarate in
high yield. Additionally we present here the results of
a preliminary study of the regiochemistry of the cou-
pling reaction.
Resu lts a n d Discu ssion
Com p ou n d s w ith Un su bstitu ted Allyl Liga n d s.
The reaction of the η3-allyl acetonitrile dicarbonyl
complexes 1a ,b7 with DMAD in dichloromethane pro-
duces a solution which, after chromatography, yields
tricarbonyl compounds 2a ,b as orange oils.
The structures proposed for them in Scheme 1 are
supported by analytical and spectroscopic data and,
indirectly, by the structure determination carried out
on the phosphine-substituted derivative 3b (see below).
Thus, the high ν(CO) frequencies observed in the IR
spectra of 2a ,b are in accordance with the presence of
a “Mo(CO)3” rather than a “Mo(CO)2” fragment which
was contained in the parent compounds 1a ,b. The
tricarbonyls 2a ,b are probably produced by CO scaveng-
This alkenyl is stabilized by intramolecular coordina-
tion of the oxygen atom of the ester group on the â
carbon, thus producing a five-member oxametallacycle
(7) Barrado, G.; Miguel, D.; Riera, V.; Garcia Granda, S. J . Orga-
nomet. Chem. 1995, 489, 129.

822 Organometallics, Vol. 17, No. 5, 1998
Barrado et al.
Sch em e 3
F igu r e 1. Perspective view (EUCLID Package)21 of [Mo-
(CO)2(PEt3)(S2PPh2){OC(OMe)C(C3H5)dC(CO2Me)}] (3b),
showing the atom numbering. Ethyl groups of the PEt3
ligand have been omitted for clarity.
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for [Mo(CO)2(S2P P h 2)(P Et3){OC(OMe)C-
(C3H5)dCCOOMe}] (3b)
Å is slightly shorter than that expected for a C-C bond.
All this indicates some degree of electron delocalization
around the ring. The atoms forming the oxametalla-
cycle in 3b and the atoms directly bonded to them, i.e.
C(3), C(5), and O(40), display a planar arrangement,
from which the maximum deviation of 0.057(4) Å is
found for O(4). The ester group not involved in the
bonding with the metal is nearly pependicular to the
oxametallacycle, a fact which precludes electron delo-
calization over the alkenyl-ester-metal ring. As it can
be seen in Figure 1, the allyl group in 3b is attached to
the â-carbon of the alkenyl and, quite remarkably, is
placed in a trans position relative to the metal. If the
coupling of the allyl and the alkyne is produced within
the coordination sphere of the metal, there should be
expected a cis disposition of the metal with respect to
the allyl group in the resulting alkenyl. As far as we
know there is only one other example of allyl/alkyne
coupling resulting in a trans alkenyl. Thus, the reaction
of CpMo(CO)3(η1-allyl) with excess hexafluoro-2-butyne,
under UV irradiation for 3 days, gives CpMo(CO)-
{C(CF3)dC(CF3)C(CF3)dC(CF3)CH2CHdCH2} through
a double insertion of the alkyne into the Mo-C(allyl)
bond.2e The structure of the resulting molybdenum
alkenyl complex was proposed, on the basis of spectro-
scopic data, to have a trans disposition around the
double bond in position 3.
Mo-S(1)
2.594(2)
2.503(2)
1.935(7)
2.201(4)
1.481(9)
1.522(9)
1.234(7)
1.50(1)
Mo-S(2)
2.624(2)
1.935(7)
2.181(7)
1.353(9)
1.443(9)
1.341(8)
1.460(8)
1.18(1)
Mo-P(2)
Mo-C(8)
Mo-C(9)
Mo-C(1)
Mo-O(4)
C(1)-C(2)
C(1)-C(3)
C(2)-C(4)
C(2)-C(5)
C(3)-O(30)
C(4)-O(4)
O(40)-C(40)
C(6)-C(7)
C(5)-C(6)
S(2)-Mo-S(1)
C(2)-C(1)-Mo
C(4)-C(2)-C(1)
C(5)-C(2)-C(4)
O(30)-C(3)-C(1)
C(30)-O(30)-C(3)
C(4)-O(4)-Mo
C(6)-C(5)-C(2)
77.0(1)
O(4)-Mo-C(1)
C(3)-C(1)-Mo
C(5)-C(2)-C(1)
O(3)-C(3)-C(1)
O(30)-C(3)-O(3)
O(4)-C(4)-C(2)
C(40)-O(40)-C(4)
C(7)-C(6)-C(5)
73.2(2)
116.7(5)
112.7(6)
121.6(6)
111.2(6)
115.1(6)
115.8(4)
113.4(6)
124.1(5)
125.7(6)
125.4(7)
123.4(6)
121.4(6)
115.7(5)
131.(1)
Sch em e 2
Mo-OdC-CdC, similar to that found in [Mo{C(Me)dC-
(Me)C(O)C(Me)dCHMe}(CO)2(η5-C5H5)],8 which, how-
ever, was produced by a very different route, through
the addition of two acetylenes and subsequent CO
insertion. The distance Mo-C(1) of 2.181(7) Å is shorter
than the Mo-C(alkenyl) of 2.243(3) Å found in [Mo-
{P(OMe)3}3{σ-(E)-CHdCHBut}(η-C5H5)].9 As for the
cyclopentadienyl compound mentioned above, the 13C-
{1H}NMR spectrum of the more soluble 3a shows the
signal attributable to CR in the region of δ 250 ppm.
The same feature has been found in some alkenyl
complexes, and it has been ascribed to some carbenic
character in this carbon CR, arising from the contribu-
tion of the canonic form II in Scheme 2.10
Although the available experimental data do not
permit us to propose an unambiguous mechanism, we
can offer here a rationalization for the formation of the
final product, as shown in Scheme 3.
The first step may consist in a subsitution of aceton-
trile by DMAD followed by the coupling of the allyl and
the alkyne. Precoordination of the alkyne is likely as
the reaction did not take place when acetonitrile was
employed as a solvent. Since a complete dissociation
of the allyl from the metal before the carbon-carbon
bond formation seems unlikely, it appears that the
addition of the metal and the allyl group to the alkyne
should proceed from the same side to produce initially
a cis alkenyl which would isomerize afterward to the
trans geometry observed in the final product. In the
present case, the resulting intramolecular stabilization
due to the Mo-O(ester) bond could be the driving force
for this isomerization which would be aided by the
Accordingly, the distances C(1)-C(2) of 1.353(9) Å and
C(4)-O(4) of 1.234(7) Å are somewhat longer for CdC
and CdO bonds, while the distance C(2)-C(4) of 1.443(9)
(8) Allen, S. R.; Green, M.; Norman, N. C.; Paddick, K. E.; Orpen,
A. G. J . Chem. Soc., Dalton Trans. 1983, 1625.
(9) Allen, S. R.; Baker, P. K.; Barnes, S. G.; Botrill, M.; Green, M.;
Orpen, A. G.; Williams, I. D.; Welch, A. J . J . Chem. Soc., Dalton Trans.
1983, 927.

Molybdenum Carbonyl Complexes
Organometallics, Vol. 17, No. 5, 1998 823
Sch em e 4
contribution of the canonic form of the type II displayed
in Scheme 2.
Alternatively, it could be considered that the trans
stereochemistry could be originated by the external
attack of the allyl to the activated acetylene, as proposed
to account for the reactivity of η3-allyls toward alde-
hydes found by Faller and co-workers.11 In such cases,
the attack of the allyl on the carbonyl group of the
aldehyde is favored by the easy conversion of the allyl
from η3 to η1, which is easily observed by 1H NMR
spectroscopy. However, no indication of η3 to η1-
transformation of the allyl is observed for complexes
1a ,b, even when treated with good donors such as
pyridine.7
Dem eta la tion . After we elaborated the structure of
compounds 3a ,b, it seemed interesting to us to find
methods for the clean hydrolysis of the organic moiety.
When the crude product from the reaction of DMAD and
Mo-allyls 1 is redissolved in dichloromethane, and
oxygen is bubbled through the solution for several hours
termination of the hydrazine derivative [{Mo(η3-C3-
H5)(CO)2{S2P(OEt)2}}2(µ-NH2NH2)].7 According to their
1H NMR spectra, complexes 1c,d consist mainly of the
syn isomers, as expected from the trans geometry of the
starting crotyl chloride. We have not observed any
indication of equilibration of the syn and anti isomers
either in the substituted 1c,d or in their homologues
1a ,b, containing unsubstituted allyls. The 13C{1H}
NMR spectra of the crotyl complexes 1c,d display two
signals for the CO ligands, reflecting their inequiva-
lency. In contrast, complexes 1a ,b, bearing unsubsti-
tuted allyl, exhibit only one signal for the two carbonyls.
The same occurs with other related complexes although,
according to X-ray crystallography, they contain two
inequivalent carbonyl ligands in the solid.7,12 A trigo-
nal-twist process has been invoked to account for the
equilibration of the two inequivalent CO groups in the
NMR time scale. This process consists of the rotation
of the triangular face formed by two CO’s and one allyl
ligand, this being a structural feature commonly found
in η3-allyl dicarbonyl complexes.13 The inequivalency
of the two CO’s in solution for compounds 1c,d may be
due to the presence of the methyl substituent on the
allyl, which makes the carbonyl groups diastereotopic.
Regioch em istr y. When crotyl complexes 1c,d are
reacted with DMAD, two regioisomers A and B can be
expected depending on which of the two allyl termini is
attacked by the alkyne (see Scheme 4). The complex
bearing diethyldithiophosphate 1c leads to complex 3c,
showing an 8/2 (A/B) mixture of the regioisomers,
whereas for the complex 3d containing diphenyldithio-
phosphinate a selectivity of 2/1 (A/B) was observed.
The signals for methyl group of the allyl of the two
isomers were well separated (3c: A, 1.12 ppm; B, 1.51
ppm. 3d : A, 1.21 ppm; B, 1.63 ppm) and did not overlap
with other signals. This permitted an easy evaluation
of the proportion of the regioisomers in the mixture.
The 31P spectrum of 3d shows a well-resolved pattern
with the expected four signals reflecting the isomer
distribution found in the 1H NMR spectrum. Thus, two
doublets appear for the signal of S2PPh2. One of them,
1
or the solution left for several days at air, the H NMR
spectra showed the formation of only one product. After
chromatography, the corresponding dimethyl 2-allylfu-
marate 4 (see Scheme 1) was obtained in high yield.
Experiments carried out by bubbling HCl gas through
the solution for several minutes led also to clean
demetalation without isomerization of the alkene.
The compound surprisingly turned out to be a liquid
at room temperature, in contrast to the well-known
1
dimethyl fumarate. The H NMR spectrum displays a
singlet at 6.8 ppm which is assigned to the alkenylic
proton He. Two singlets at 3.8 and 3.7 ppm are
attributed to the methyl groups of the diester. A DEPT
experiment gave unambiguous assignment of the alk-
enyl carbons CR and Câ. CR showed an upfield shift of
more than 100 ppm to δ ) 127.5 ppm whereas Câ shifted
down ca. 15 ppm to δ ) 145.9 ppm.
Com p lexes w ith Su bstitu ted Allyls. With the aim
of obtaining some information about the regiochemistry
of the reaction, the crotyl (1-methylallyl) derivatives
1c,d were prepared in two steps by reacting [Mo(CO)3-
(NCMe)3] with trans-1-chloro-2-butene (crotyl chloride)
and subsequent addition of NH4[S2P(OEt)2] or Na2[S2-
PPh2]. Crotyl derivatives 1c,d were obtained as oily
substances which decompose rapidly in air, being con-
siderably less stable than the corresponding allyl com-
plexes 1a ,b. Since the oily, air-sensitive samples of 1c,d
were not suitable for microanalysis, they were charac-
terized by high-resolution mass spectra of samples
drawn from acetonitrile solutions. Due to rapid loss of
the nitrile, M+ could not be detected. The compounds
were identified by the (M - MeCN)+ peaks, which
showed the typical isotopic pattern of molybdenum. The
spectroscopic features of 1c,d are similar to those found
for the complexes containing unsubstituted allyls 1a ,b,
and accordingly, it has been assumed for them the same
structure, which was supported by the structural de-
(10) Morran, P. D.; Mawby, R. J .; Wilson, G. D.; Moore, M. H. J .
Chem. Soc., Chem. Commun. 1996, 221. (b) Bruce, M. I.; Catlow, A.;
Cifuentes, M. P.; Snow, M. P.; Tiekink, E. R. T. J . Organomet. Chem.
1990, 397, 187. (c) J ohnson, K. A.; Vashon, M. D.; Moasser, B.;
Warmka, B. K.; Gladfelter, W. L. Organometallics 1995, 14, 461.
(11) Faller, J . W.; Linebarrier, D. L. J . Am. Chem. Soc. 1989, 111,
1937. Faller, J . W.; J ohn, J . A.; Mazzieri, M. R. Tetrahedron Lett. 1989,
30, 1769. Faller, J . W.; DiVerdi, M. J .; J ohn, J . A. Tetrahedron Lett.
1991, 32, 1271.
(12) Miguel, D.; Pe´rez-Mart´ınez, J . A.; Riera, V.; Garc´ıa-Granda, S.
Organometallics 1994, 13, 1336.
(13) Faller, J . W.; Haitko, D. A.; Adams, R. D.; Chodosh, D. F. J .
Am. Chem. Soc. 1979, 101, 865

824 Organometallics, Vol. 17, No. 5, 1998
Barrado et al.
from THF and kept under argon. NaS2PPh2 and [Mo(η3-R-
C3H4)(CO)2(NCMe)2X] (R ) H, Me; X ) Cl, Br)16 complexes
were synthesized according to published methods. Crotyl
chloride (95% predominantly trans) was purchased from
Aldrich. All other reagents were used without further puri-
fication. Column chromatography was carried out employing
silica gel (60, 230-400 mesh, Merck) or neutral alumina
(activity I). Filtering was performed using kieselgur (Merck).
1H, 31P, and 13C NMR spectra were measured on 300 and
200 MHz spectrometers. Shift values are given in ppm. 1H
NMR and 13C shifts are referenced to solvents. In 31P{1H}
spectra 85% H3PO4 is used as an external reference. High-
resolution mass spectra were recorded in the EI mode.
Compounds 2c,d were obtained as oils which were not suitable
for elemental analysis due to rapid decomposition when
exposed to air.
15
centered at 85.4 ppm, is of double intensity than the
other, being therefore assigned to isomer A. The one
at higher field (84.9 ppm) is of half intensity and is
assigned to isomer B. Interestingly, the signals due to
PEt3, at ca. 40 ppm, show reverse order. The signals
in the 31P NMR spectrum of 3c are not so well sepa-
rated. The two doublets corresponding to S2P(OEt)2
appear overlapped in the same position (103.4 ppm)
while the signals of PEt3 appear very close to each other
(40.7 ppm for isomer A, 40.6 for isomer B).
Although unambiguous signal assignment was not
possible in the 13C NMR of 3d , the easily identified
signals which are due to the carbonyl ligands, the ester
groups, and the methylene groups of triethylphosphine
resolve well for the isomers and show in all cases the
2/1 intensity ratio for the isomers A/B.
For compound 3c the signals observed in the 31C{1H}
NMR are assigned to the major isomer (A). The signals
of the minor isomer B may be obscured by those of the
major isomer A or may be lost under the noise.
At t em p t ed R ea ct ion s w it h Less Act iva t ed Al-
k yn es. Unfortunately, all attempts to extend this
reactions to less activated alkynes, such as methyl
2-butynoate, phenyl 2-propynoate, 2-butyne, and bis-
(trimethylsilyl)acetylene, have been fruitless so far.
Heating of reaction mixtures led only to extensive
decomposition. This may be due to the thermal lability
of the alkyne complexes, which dissociate upon heating,
rather than undergoing coupling with the allyl.
[Mo{η3-C3H4(Me-1)}(CO)2{S2P (OEt)2}(NCMe)] (1c). To
a solution of Mo(CO)3(CH3CN) (0.1 g, 0.33 mmol) in acetonitrile
(20 mL) was added crotyl chloride (50 µL, 0.5 mmol). The
mixture was heated at 60 °C for 1 h, and then NH4[S2P(OEt)2]
was added (0.066 g, 0.33 mmol). After the mixture was stirred
for 15 min, the precipitate of NH4Cl was removed by filtering
over kieselguhr. The filtrate was evaporated in vacuo to to
give 1c as an orange oil. Yield: 0.123 g, 76%. Anal. Calc for
C12H20MoNO4PS2: C, 33.26; H, 4.65; N, 3.23. Found: C, 32.89;
H, 5.73; N, 2.76. IR (CH2Cl2; cm-1): ν(CN) 2285 w; ν(CO) 1941
s, 1850 s. 1H NMR (acetone-d6): δ 4.1 (m, 5H, CHcentral of crotyl
and POCH2), 3.05 [d (6 Hz), 1H, Hsyn], 2.24 (s, 3H, NCCH3),
1.91 (m, 4H, CH3 and CH3CHanti of crotyl), 1.26 [t (7 Hz), 6 H,
POCH2CH3], 1.15 [d (7 Hz), 1H, Hanti]. 31P{1H} NMR (acetone-
d6): δ 103.8. 13C{1H} NMR (acetone-d6): δ 227.8, 227.0, 226.9
(2CO), 120.1 (NCCH3), 74.7, 74.6 [Ccentral of crotyl and CCH3],
62.9, 62.8 (POCH2), 52.2 (CH2 of crotyl), 18.7 (CH3 of crotyl),
15.8 and 15.7 (POCH2CH3), 1.9 (NCCH3). MS (EI): m/z 393.94
(M+ - MeCN).
Con clu sion
[Mo{η3-C3H4(Me-1)}(CO)2(S2P P h 2)(NCMe)] (1d ). The
compound was obtained as described above for 1c, from [Mo-
(CO)3(CH3CN)] (0.1 g, 0.33 mmol), crotyl chloride (50 µL, 0.5
We have described in this paper the reaction of labile
ligand allyl complexes with the activated alkyne DMAD.
The coupling between allyl and alkyne leads to an
alkenyl ligand which is stabilized through intramolecu-
lar coordination of one oxygen of the ester group to the
metal, forming a five-membered oxometallacycle. It
shows unusual trans stereochemistry in contrast to all
previously known examples of metal-mediated η3-allyl-
alkyne coupling. Demetalation of the organic moiety
can be easily effected by air or gaseous HCl to give the
corresponding 2-allylfumarate in good yield.
Regioselectivity studies employing 1-methylallyl com-
plexes reveal that the reaction is strongly influenced by
the dithio ligand bonded to molybdenum. In both cases
reaction at the more substituted carbon of the allyl is
favored.
15
mmol), and NaS2PPh2 (0.09 g, 0.33 mmol), to give 1d as an
orange oil. Yield: 0.137 g, 79%. Anal. Calc for C20H20MoNO2-
PS2: C, 48.29; H, 4.05; N, 2.82. Found: C, 47.68; H, 4.71; N,
2.34. IR (CH2Cl2; cm-1): ν(CN) 2285 w; ν(CO) 1941 s, 1848 s.
1H NMR (C6D6): δ 7.85 (m, 4H, Ph), 7.0 (m, 6H, Ph), 3.95 (m,
1H, Hcentral of crotyl), 3.29 [d (5 Hz), 1H, Hsyn], 2.01 [d (6 Hz),
3H, CH3 of crotyl), 1.85 (m, 1H, Hanti), 1.26 [d (9 Hz), 1H, Hanti],
0.3 (s, 3H, NCCH3). 31P{1H} NMR (C6D6): δ 86.3. 13C{1H}
NMR (C6D6): δ 228.9, 227.9 (2s, CO) 141.8-129.0 (m, Ph),
123.3 (s, NCCH3), 77.5 (s, Ccentral of crotyl), 75.9 (s, CCH3 of
crotyl), 53.5 (CH2 of crotyl), 19.7 (CH3 of crotyl), 1.2 (CH3CN).
MS (EI): m/z 457.95 (M+ - MeCN).
[Mo(CO)3{S2P (OE t )2}{OC(OMe)C(C3H 5)CdCCO2Me}]
(2a ). To a solution of 1a (0.2 g, 0.48 mmol) in CH2Cl2 (10 mL)
was added DMAD (58 µL, 0.48 mmol). The color of the solution
changed immediately to green and then to brown. After 15
min the solvent was removed in vacuo. The residue was
dissolved in a mixture of CH2Cl2/hexane (3:1) and chromato-
graphed over silica. The first fraction was collected. After
removal of the solvent, an orange yellow oil remained. Yield:
0.034 g (12%). Anal. Calc for C17H21MoO9PS2: C, 36.44; H,
3.78. Found: C, 36.18; H, 3.93. IR (CH2Cl2; cm-1): ν(CO) 2036
s, 1957 s, 1713 w, 1598 w. 1H NMR (CDCl3): δ 5.78 [ddt (17,
10, and 6 Hz), 1H, Hc], 5.03 [dd (17 and 2 Hz, 1H, Hb], 5.01
[dd (10 and 2 Hz), 1H, Ha], 4.19 (m, 2H, POCH2), 4.11 (m, 2H,
POCH2), 3.95 and 3.80 (s, 3H, OCH3), 3.12 [d (5 Hz), 2H, Hd],
Currently, investigations are under way to extend the
reactivity of the complexes to less activated alkynes by
proper choice of the appropriate dithio and allyl ligands.
This would give the reaction a potential use in organic
synthesis.
Exp er im en ta l Section
Gen er a l Meth od s. All manipulations were carried out
under an argon atmosphere using standard Schlenk tech-
niques or under nitrogen in a glovebox. Methylene chloride
and acetonitrile were distilled from CaH2. Methylene chloride
was degassed by one freeze-pump-thaw cycle prior to use.
THF and diethyl ether were distilled from Na/benzophenone.
Hexane was distilled from Na. All NMR solvents were stored
over 3 Å molecular sieves (Aldrich) and degassed by three
freeze-pump-thaw cycles. NH4S2P(OEt)2 was recrystallized
(14) Curtis, M. D.; Eisenstein, O. Organometallics 1984, 3, 887.
(15) Higgins, W. A.; Vogel, P. W.; Craig, W. G. J . Am. Chem. Soc.
1955, 77, 1864. Clavell, R. G.; Byers, W.; Day, E. D. Inorg. Chem. 1971,
10, 2710.
(16) Clark, D. C.; J ones, D. L.; Mawby, R. J . J . Chem. Soc., Dalton
Trans. 1980, 565. tom Dieck H.; Friedel, H. J . Organomet. Chem. 1968,
14, 375.

Molybdenum Carbonyl Complexes
Organometallics, Vol. 17, No. 5, 1998 825
1.36 [t (7 Hz), 6H, POCH2CH3]. 31P{1H} NMR (CDCl3) δ 102.9.
13C{1H} NMR (CDCl3): 229.3, 229.2, and 197.6 (s, 3CO), 177.7
and 174.0 (s, 2 CO2Me), 134.8 (s, Cb), 130.5 (s, Câ), 116.0 (s,
Ca), 63.8 and 63.6 (s, 2POCH2), 54.4 and 51.8 (s, 2CO2CH3),
34.5 (s, Cc), 15.9 (s, POCH2CH3).
refinement of a set of 25 centered reflections in the range 15
< θ < 19°. Three reflections were measured every 1 h as
orientation and intensity controls. Significant decay was not
observed. The structure was solved by Patterson methods,
phase expansion, and subsequent Fourier maps with DIRDIF.18
Full-matrix least-squares refinement was made with SHELX-
76.19 After isotropic refinement, an absorption correction was
applied with DIFABS.20 All non-hydrogen atoms were refined
anisotropically. Hydrogen atoms were geometrically posi-
tioned, with a common isotropic temperature factor which was
refined.
[Mo(CO)3(S2P P h 2){OC(OMe)C(C3H5)dCCO2Me}] (2b).
The compound was prepared from 1b (0.2 g, 0.41 mmol) and
DMAD (51 µL, 0.41 mmol) by following the procedure for 2a .
The first orange fraction which was eluted with a mixture of
CH2Cl2/hexane (5/3) contained the desired product. After
evaporation remained 0.037 g (20%) of an orange oil, which
converted into a solid after drying for several days at 40 °C.
Anal. Calc for C25H21MoO7PS2: C, 48.08; H, 3.39. Found: C,
47.46; H, 3.94. IR (CH2Cl2; cm-1): ν(CO) 2034 s, 1954 s, 1710
w, 1597 w. 1H NMR (CDCl3): δ 7.90-7.39 (m, 10H, Ph), 5.68
[ddt (17, 10, and 6 Hz), 1 H, Hc], 4.94 [dd (17 and 2 Hz), 1 H,
Hb], 4.89 [dd (10 and 2 Hz), 1 H, Ha], 3.68 and 3.25 (s, 2 × 3H,
OCH3], 3.00 [d (6 Hz), 2H, Hd]. 31P{1H} NMR (CDCl3): δ 97.3.
13C{1H} NMR (CDCl3): δ 228.9 (s, 2 CO), 197.4 (s, CO), 176.8
and 173.2 (s, 2 COOMe), 138.8-127.2 (m, C6H5), 134.0 (s, Cb),
129.1 (s, Câ), 114.9 (s, Ca), 52.8 and 50.7 (s, 2 x COOCH3), 33.5
(s, Cc).
[M o (C O )2 (P E t 3 ){S 2 P (O E t )2 }{O C (O M e )C (C 3 H 5 )d
CCO2Me}] (3a ). To a solution of 1a (0.200 g, 0.48 mmol) in
CH2Cl2 (10 mL) was added DMAD (59 µL, 0.48 mmol). The
reaction mixture was stirred for 15 min. Addition of PEt3 (71
µL, 0.48 mmol) changed the color of the solution immediately
to red. Stirring for another 15 min was followed by evapora-
tion of the solvent. The crude product was redissolved in CH2-
Cl2 and chromatographed over silica. The second orange-red
fraction contained the desired product 3a . The solvent was
removed in vacuo affording a red air-stable powder. Yield:
0.216 g (45%). Anal. Calc for C21H36MoO8P2S2: C, 39.50; H,
5.69. Found: C, 39.34; H, 5.41. IR (CH2Cl2; cm-1): ν(CO) 1935
s, 1851 s, 1704 w, 1589 w. 1H NMR (CDCl3): δ 5.74 [ddt (17,
10, and 6 Hz), 1H, Hc], 5.02 [ddt (17, 2, and 1 Hz, 1H, Hb],
4.91 [ddt (10, 2, and 1 Hz), 1H, Ha], 4.29 (m, 2H, POCH2), 4.01
(m, 2H, POCH2), 3.89 and 3.76 (s, 3H, OCH3), 3.01 [ddd (6, 1,
and 1 Hz), 2H, Hd], 1.87 [m, 6 H, PCH2], 1.39 [t (7 Hz), 3H,
POCH2CH3], 1.33 [t (7 Hz), 3H, POCH2CH3], 0.97 [m, 9H,
PCH2CH3]. 31P{1H} NMR (CDCl3): δ 102.9 [d (39 Hz),
S2P(OEt)2], 40.4 [d (39 Hz), PEt3]. 13C{1H} NMR (CDCl3): δ
253.0 (s, CR), 217.2 [d (4 Hz), CO], 217.0 [d (7 Hz), CO], 178.3
and 175.6 (s, 2 × CO2Me), 136.0 (s, Cb), 127.1 (s, Câ), 115.2 (s,
Ca), 63.7 [d (5 Hz), POCH2], 53.6 and 51.2 (s, 2 × CO2CH3),
34.2 (s, Cc), 15.9 [d (25 Hz), PCH2], 14.9 [d (8 Hz), POCH2CH3],
6.6 (s, PCH2CH3).
[Mo(CO)2(P E t 3){S2P (OE t )2}{OC(OMe )(C3H 4-Me -1)d
CCO2Me}] (3c). To a suspension of [Mo(CO)6] (0.1 g, 0.38
mmol) in acetonitrile (20 mL) was added crotyl chloride (50
µL, 0.51 mmol), and the reaction mixture was refluxed for 5
h. Subsequent addition of NH4S2P(OEt)2 (0.077 g, 0.38 mmol)
was followed by filtration over kieselguhr. The solvent was
removed, and the orange residue of 1c was redissolved in CH2-
Cl2. To the solution were successively added DMAD (47 µL,
0.38 mmol) and, after stirring for 15 min, PEt3 (56 µL, 0.38
mmol). The mixture was stirred for 15 min, and the solvent
was evaporated in vacuo to give a brown red powder. This
was purified by chromatography over silicagel (2.5 × 15 cm
column). The red band eluted with CH2Cl2 as the second
fraction was identified as the desired product. Vacuum
concentration and addition of hexane gave 3c as a microcrys-
talline powder containing a mixture of isomers. Yield: 0.106
g, 43%. Anal. Calc for C22H38MoO8P2S2: C, 40.49; H 5.87.
Found: C, 40.18; H 5.67. IR (CH2Cl2; cm-1): ν(CO) 1935 s,
1851 s, 1699 w, 1585 w. 1H NMR (CDCl3): isomer A, δ 5.82
[ddd (17, 10, and 7 Hz), 1H, Hc), 4.93 [d (17 Hz, 1H, Hb], 4.85
[d (10 Hz), 1H, Ha], 4.20 and 3.94 (m, 4H, 2 × POCH2), 3.82
and 3.66 (s, 2 × 3H, OCH3), 3.23 [qd (7 and 7 Hz),1H, Hd],
1.80 [m, 6 H, PCH2], 1.31-1.26 [m, 6H, POCH2CH3], 1.12 [d
(7 Hz), CCH3], 0.89 [m, 9H, PCH2CH3]; isomer B, δ 5.32 [m,
2H, Hb + Hc], 4.20 and 3.94 [m, 4 H, 2 × POCH2], 3.82 and
3.68 (s, 2 × 3H, OCH3), 2.85 [d (5 Hz), 2H, Hd], 1.80 [m, 6H,
PCH2], 1.51 [d (5 Hz), CCH3) 1.31-1.26 [m, 6H, POCH2CH3],
0.89 [m, PCH2CH3]. 31P{1H} NMR (CDCl3): δ 103.4 [d (39 Hz),
S2P(OEt)2 (isomer A + B)], 40.7 [d (39 Hz), PEt3 (isomer A)],
40.6 [d (39 Hz), PEt3 (isomer B)]. 13C{1H} NMR (CDCl3):
isomer A, δ 251.5 (s, CR), 215.6 [d (6 Hz), CO], 215.4 [d (6 Hz),
CO], 177.3 and 174.6 (s, 2 × CO2Me), 140.0 (s, Cb), 130.9 (s,
Câ), 112.5 (s, Ca), 62.7 [d (5 Hz), POCH2], 61.9 [d (5 Hz),
POCH2], 52.4 and 49.9 (s, 2 × CO2CH3), 38.7 (s, Cc), 15.9 [d
(25 Hz), PCH2], 14.9 [d (6 Hz), POCH2CH3), 14.3 [s, CbCH3],
6.6 (s, PCH2CH3).
[ M o ( C O ) 2 ( P E t 3 ) ( S 2 P P h 2 ) {O C ( O M e ) C ( C 3 H 5 ) d
CCO2Me}] (3b). Compound 3b was obtained as described
above for 3a , starting from 1b (0.183 g, 0.38 mmol), DMAD
(47 µL, 0.38 mmol), and PEt3 (56 µL, 0.38 mmol). Similar
workup gave 3b as orange microcrystals. Yield: 0.163 g, 61%.
Anal. Calc for C29H36MoO6P2S2: C, 49.58; H, 5.16. Found:
C, 49.41; H, 4.89. IR (CH2Cl2; cm-1): ν(CO) 1934 s, 1849 s,
1701 w, 1590 w. 1H NMR (CDCl3): δ 7.96-7.43 (m, 10H, Ph),
5.75 [ddt (17, 10, and 6 Hz), 1 H, Hc], 5.03 [dd (17 and 2 Hz),
1 H, Hb], 4.92 [dd (10 and 2 Hz), 1 H, Ha], 3.75 and 3.63 (s, 2
× 3 H, OCH3], 3.00 [d (6 Hz), 2H, Hd], 1.85 (m, 6 H, PCH2),
0.95 (m, 9 H, PCH2CH3). 31P{1H} NMR (CDCl3): δ 85.6 [d
(20 Hz), S2PPh2], 40.5 [d (20 Hz), PEt3]. 13C{1H} NMR
(CDCl3): δ 218.0 [d (7 Hz), CO], 217.9 [d (7 Hz), CO], 178.3
and 175.7 (s, 2 COOMe), 138.9-128.1 (m, C6H5), 136.1 (s, Cb),
126.8 (s, Câ), 115.1 (s, Ca), 53.5 and 51.1 (s, 2 × COOCH3),
34.1 (s, Cc), 16.6 [d (25 Hz), PCH2], 7.6 (s, PCH2CH3).
X-r a y Diffr a ction Stu d y of 3b. Crystals were grown by
slow diffusion of hexane into a concentrated solution of 3b in
diethyl ether at -20 °C. Relevant crystallographic details are
given in Table 1. The experimental temperature was 200 K.17
Unit cell parameters were determined from the least-squares
[M o (C O )2 (P E t 3 )(S 2 P P h 2 ){O C (O M e )(C 3 H 4 -M e -1)d
CCO2Me}] (3d ). Compound 3d was obtained as described
above for 3c, from [Mo(CO)6] (0.2 g, 0.76 mmol), crotyl chloride
(100 µL, 1.02 mmol), Na[S2PPh2] (0.206 g, 0.76 mmol), DMAD
(94 µL, 0.76 mmol), and PEt3 (112 µL, 0.76 mmol). Similar
workup gave 3d as red microcrystals. Yield: 0.22 g, 41%.
Anal. Calc for C30H38MoO6P2S2: C, 50.28; H, 5.34. Found:
C, 50.05; H, 5.19. IR (CH2Cl2; cm-1) ν(CO) 1934 s, 1851 s, 1698
w, 1586 w. 1H NMR (CDCl3): isomer A, δ 7.98-7.44 (m, 10H,
Ph), 5.92 [ddt (17, 10, and 6 Hz), 1 H, Hc], 5.01 [d (17 Hz), 1
H, Hb], 4.93 [d (10 Hz), 1 H, Ha], 3.75 and 3.62 (s, 2 × 3 H,
OCH3], 3.32 [m, 2H, Hd], 1.85 (m, 6 H, PCH2), 1.21 [d (7 Hz),
(18) Beurskens, P. T.; Admiraal, G.; Bosman, W. P.; Beurskens, G.;
Doesburg, H. M.; Garc´ıa-Granda, S.; Gould, R. O.; Smits, J . M. M.;
Smikalla, C. The DIRDIF Program System, Technical Report of the
Crystallography Laboratory; University of Nijmegen: Nijmegen, The
Netherlands, 1992.
(19) Sheldrick, G. M. SHELX76, Program for Crystal Structure
Determinations; University of Cambridge: Cambridge, U.K., 1976.
Local Version: Van der Maelen, F. J . Ph.D. Thesis, University of
Oviedo, Oviedo, Spain, 1991.
(20) Walker, N.; Stuart, D. Acta Crystallogr. 1983, A39, 158.
(21) Spek, A. L. The EUCLID Package. In Computational Crystal-
lography; Sayre, E., Ed.; Clarendon Press: Oxford, England, 1982; p
528.
(17) Cosier, J .; Glazer, A. M. J . Appl. Crystallogr. 1986, 19, 105.

826 Organometallics, Vol. 17, No. 5, 1998
Barrado et al.
3 H, CCH3], 0.94 (m, 9 H, PCH2CH3); isomer B, δ 7.98-7.44
(m, 10H, Ph), 5.40 [m, 2H, Ha, Hc], ], 3.73 and 3.61 (s, 2 × 3
H, OCH3], 2.92 [d (5 Hz), 2H, Hd], 1.85 (m, 6 H, PCH2), 1.63
[d (8 Hz), 3H, CCH3], 0.94 (m, 9 H, PCH2CH3). 31P{1H} NMR
(CDCl3): isomer A, δ 85.4 [d (20 Hz), S2PPh2], 40.7 [d (20 Hz),
PEt3]; isomer B, δ 84.9 [d (20 Hz), S2PPh2], 40.5 [d (20 Hz),
PEt3]. 13C{1H} NMR (C6D6): δ 255 (broad, CR), 220.4 (m, 2 ×
CO, isomer A), 219.9 (m, 2 × CO, isomer B), 179.1 (s, COOMe,
isomer B), 178.9 (s, COOMe, isomer A), and 175.4 (s, 2 ×
COOMe, isomers A + B), 141.7 (s, Cb), 141.1-128.1 (m, C6H5),
125.9 (s, Câ), 113.8 (s, Ca), 53.2 and 51.0 (s, 2 × COOCH3,
isomer B), 53.0 and 50.8 [s, 2 × COOCH3, isomer A], 40.2 (s,
Cc, isomer A), 33.6 (s, Cc, isomer B), 17.0 [d (25 Hz), PCH2,
isomer B], 16.9 [d (25 Hz), PCH2, isomer A], 7.7 [s, PCH2CH3].
Dim eth yl 2-Allylfu m a r a te (4). Complex 1b (1 g, 2.05
mmol) was dissolved in CH2Cl2 (10 mL), and DMAD (255 µL,
2.05 mmol) was added. The mixture was stirred until the IR
spectra showed the formation of the tricarbonyl complex 2b
(about 15 min). The solvent was then evaporated in vacuo,
and the residue was redissolved in CH2Cl2. The solution was
dimethyl 2-allylfumarate. Yield: 0.203 g, 81% (calculated from
the maximum yield (66%) of 2b). Anal. Calc for C9H12O4: C,
39.50; H, 5.69. Found: C, 39.34; H, 5.41. MS (EI): m/z 184.32
(M+). 1H NMR (CDCl3): δ 6.81 (s, 1H, CdCHe), 5.83 [ddt (17,
10, and 6 Hz), 1H, Hc], 5.10 [ddt (17, 2 and 1 Hz), 1 H, Hb],
5.03 [ddt (10, 2 and 1 Hz), 1H, Ha], 3.80 (s, 3H, COOCH3),
3.77 (s, 3H, COOCH3), 3.58 [d (17 Hz), 2H, Hd]. 13C{1H} NMR
(CDCl3): δ 167.6 and 166.5 (s, 2 × CO2Me), 145.9 (s, Câ), 134.7
(s, Cb), 127.5 (s, CR), 117.3 (s, Ca), 53.2 and 52.4 (s, 2 ×
CO2CH3), 32.3 (s, Cc).
Ack n ow led gm en t. This work was supported by the
Spanish DGCYT. We acknowledge the concession of
grants to G. B. (FICYT-Asturias), M. M. H. (Fulbright),
and H. W. (M. E. C.). The authors gratefully acknowl-
edge the suggestions of the reviewers, which helped to
improve the paper.
Su p p or tin g In for m a tion Ava ila ble: Complete tables of
bond length and angles, anisotropic thermal parameters, atom
parameters for all atoms, and weighted least-squares planes
for 3b (9 pages). Ordering information is given on any current
masthead page.
left open in air for several days.
A
1H NMR of the crude
product showed that the cleavage had taken place quantita-
tively. The purple solution was chromatographed over silica
with CH2Cl2 as eluent. The solvent was removed by distilla-
tion. The remaining liquid was found to be nearly pure
OM970627Z