Allylic ionization versus oxidative addition into vinyl C-X bonds by Pd with polyfunctional olefin templates

Article abstract of DOI:10.1021/ja045416h

The chemoselectivity of activation by a (PPh₃)₄Pd catalyst on a series of small, olefin-based compounds that were substituted with a variety of allylic and vinylic functional groups was studied. Of particular note, the allylic acetate of 1-acetoxy-2-bromo-2-propene (7) was selectively ionized by Pd in the presence of a malonate nucleophile, while oxidative addition of the C-Br bond to Pd occurred exclusively in the presence of a boronic acid nucleophile. When the acetate nucleophile was used, no ionization of the acetate leaving group occurred at all, which was proven by the use of deuterium-labeled substrates (e.g., 11). This report demonstrates that the nucleophile interacts in some way with Pd prior to catalyst activation of the substrate. Certainly in the case of the malonate nucleophile, this is without precedent and contradicts the central dogma of how these proposed catalytic cycles operate.

Full text of DOI:10.1021/ja045416h

Published on Web 11/18/2004
Allylic Ionization versus Oxidative Addition into Vinyl C-X
Bonds by Pd with Polyfunctional Olefin Templates
Eamon Comer, Michael G. Organ,* and Stephen J. Hynes
Contribution from the Department of Chemistry, York UniVersity, 4700 Keele Street,
Toronto, Ontario, Canada M3J 1P3
Received July 29, 2004; E-mail: organ@yorku.ca
Abstract: The chemoselectivity of activation by a (PPh3)4Pd catalyst on a series of small, olefin-based
compounds that were substituted with a variety of allylic and vinylic functional groups was studied. Of
particular note, the allylic acetate of 1-acetoxy-2-bromo-2-propene (7) was selectively ionized by Pd in the
presence of a malonate nucleophile, while oxidative addition of the C-Br bond to Pd occurred exclusively
in the presence of a boronic acid nucleophile. When the acetate nucleophile was used, no ionization of the
acetate leaving group occurred at all, which was proven by the use of deuterium-labeled substrates (e.g.,
11). This report demonstrates that the nucleophile interacts in some way with Pd prior to catalyst activation
of the substrate. Certainly in the case of the malonate nucleophile, this is without precedent and contradicts
the central dogma of how these proposed catalytic cycles operate.
Introduction
We have been working for some time on the development
of small, densely functionalized olefin building blocks (olefin
templates) whose functional groups can be activated selectively
and sequentially using metal catalysts for convergent, modular
organic synthesis.1 There are two principal functional group
activations possible by Ni or Pd catalysts involving olefins:
allylic ionization and oxidative addition.2 In a competitive
situation, allylic ionization will generally happen first because
of the bond energies involved and the stability of the resultant
π-allyl complex, relative to that of the corresponding σ-complex
resulting from oxidative addition of the vinyl halide.3 Providing
this selectivity is reliable; such substituted olefin templates can
be modified systematically into products by activating allylic
halides or pseudohalides first in the presence of vinylic ones.1
For example, the allylic Br in 1a (Figure 1) is activated cleanly
by Pd at room temperature, and allylic substitution can then be
followed by cross-coupling at the vinyl position.1a
Figure 1. Some examples of polyfunctionalized olefins, which are
substrates for Pd-catalyzed reactions.
to Suzuki reaction conditions, and that these phenoxide groups
can later be ionized by changing the reaction conditions in situ
(e.g., Figure 1, 1b).4
We were intrigued by the few reports in the literature of
selective activation of a vinyl halide or pseudohalide by Pd in
the presence of a good allylic leaving group. The bromides in
2a5 and 3a6 were activated selectively by Pd, which then
underwent Sonogashira coupling or carbonylation to provide
2b and 3b, respectively (Figure 1). Similarly, the vinyl triflate
in 4a was activated cleanly in the presence of the epoxide to
provide 4b by carbonylation.7
It is our contention that the lack of reactivity of the allylic
functional groups in these examples was the result of confor-
mational, not electronic, considerations as proposed originally
by Nwokogu5 and later supported by Heathcock.7 Indeed, Pd
failed to activate the acetate in 3c with the Br gone.6 Thus, on
the basis of these experimental data, it cannot be said that the
If an olefin template could be designed that had a vinylic
functional group that could be activated in the presence of an
allylic one, and then the allylic site activated readily later,
complementary synthetic routes could be considered that offer
considerable advantages. To this end, we have demonstrated
that certain allylic phenoxide-based leaving groups are stable
(1) (a) Organ, M. G.; Cooper, J. T.; Rogers, L. R.; Soleymanzadeh, F.; Paul,
T. J. Org. Chem. 2000, 65, 7959-7970. (b) Organ, M. G.; Mayhew, D.;
Cooper, J. T.; Dixon, C. E.; Lavorato, D. J.; Kaldor, S. W.; Siegel, M. G.
J. Comb. Chem. 2001, 3, 64-67. (c) Organ, M. G.; Bilokin, Y. V.;
Bratovanov, S. J. Org. Chem. 2002, 67, 5176-5183. (d) Organ, M. G.;
Antunes, L. M. Tetrahedron Lett. 2003, 44, 6805-6808. (e) Organ, M.
G.; Ghasemi, H. J. Org. Chem. 2004, 69, 695-700.
(4) Organ, M. G.; Arvanitis, E. A.; Dixon, C.; Cooper, J. T. J. Am. Chem.
Soc. 2002, 124, 1288-1294.
(2) For general discussions of these two processes, see: Tsuji, T. Palladium
Reagents and Catalysts: InnoVations in Organic Synthesis; John Wiley
and Sons Ltd.: Chichester, England, 1995.
(5) (a) Nwokogu, G. C. Tetrahedron Lett. 1984, 25, 3263-3266. (b) Nwokogu,
G. C. J. Org. Chem. 1985, 50, 3900-3908.
(3) (a) Rahaman, A.; Raff, L. M. J. Phys. Chem. A 2001, 105, 2156-2172.
(6) Trost, B. M.; Oslob, J. D. J. Am. Chem. Soc. 1999, 121, 3057-3064.
(7) Yamamoto, K.; Heathcock, C. H. Org. Lett. 2000, 2, 1709-1712.
(b) Tsang, W. J. Phys. Chem. 1984, 88, 2812-2817.
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J. AM. CHEM. SOC. 2004, 126, 16087-16092
16087

A R T I C L E S
Scheme 1
Comer et al.
Scheme 2
recovery as the sole product. Treatment of 7 with both malonate
nucleophile and 4-methoxyphenylboronic acid under competi-
tion conditions at room temperature led initially to the exclusive
formation of 8. Heating the reaction mixture at this stage, that
is, following the allylic substitution, led to the cross-coupled
product 10.
If one considers the presently accepted mechanistic dogma
of metal-catalyzed allylic substitution and cross-coupling reac-
tions, following Pd-olefin docking, the first step in either cycle
is the activation of the halide (or pseudohalide) by the metal,
that is, allylic ionization or oxidative addition, respectively. This
being the case, meaningful interactions that lead to product
between Pd and 7 should take place first, irrespective of the
other reaction partners present. If the acetate is the most reactive
functional group present on 7, it should activate first. The results
in Scheme 1 are suggestive that something other than the
accepted simplified mechanisms for these processes is operating.
It is possible that one of (at least) three scenarios is affecting
the chemoselectivity of the catalyst. (1) Ionization of the acetate
is happening first in every case, but the reverse reaction is
kinetically faster than transmetalation with the boronic acid to
facilitate allylic cross-coupling whereas most/all insertions of
Pd into the vinyl C-Br bond lead to product. (2) Functional
group activation is temperature-dependent. (3) Oxidative addi-
tion of the vinyl bromide occurs preferentially, except in the
presence of the malonate where the catalyst is interacting in
some way with this reagent, and this is affecting the catalyst’s
chemoselectivity. To investigate these possibilities, a series of
experiments were carried out with deuterium-labeled substrates
to track functional group activation.
Br is “electronically deactivating” the olefin in allylic substitu-
tion. Once converted to the carbonate (3d), the allylic group
ionized, albeit, at 100 °C. Such a reactive group should activate
well below this temperature, and in fact, allylic carbonates on
suitable substrates ionize with Pd at -78 °C.8 We propose that
the principal reason the allylic leaving groups in 2-4 did not
activate is that these groups could not adopt the requisite
antiperiplanar relationship between the carbon-leaving group
bond and the coordinate Pd-olefin bond that precedes allylic
ionization.9 Thus, if these conformational restrictions were
removed, these same allylic groups would activate readily and
selectively in the presence of the vinyl halide or pseudohalide
groups.
Results and Discussion
To explore the results seen by Nwokogu,5 we prepared 2a
and treated it to Pd-catalyzed allylic alkylation with sodium
dimethyl methylmalonate, an excellent nucleophile for such
substitution reactions (Scheme 1). Only starting material (2a)
and the product corresponding to hydrolyzed acetate (6) were
recovered. Thus, similar to the findings of Nwokogu, no product
resulting from apparent allylic activation of the acetate (e.g.,
5) was isolated with this cyclic system. However, when 7, an
acyclic variant of 2a, was reacted under the same conditions,
the transformation proceeded smoothly under very mild condi-
tions to provide 8. This seemed to support our hypothesis that
the Br is not necessarily electronically deactivating the olefin.
Conversely, it would, in fact, support the notion that the
compounds in Figure 1 may not have ionized due to confor-
mational constraints.
Reversibility of Acetate Ionization by Pd in Compound
7. To see whether the allylic acetate was being reversibly
ionized, compound 11 was prepared and treated with Pd and
sodium acetate nucleophile at room temperature (reaction a,
Scheme 2) and then at reflux (reaction b). In neither case was
compound 13 formed, suggesting that 11 did not ionize and
either the leaving group or the nucleophile (which are the same
in this case) attack the Pd π-allyl complex. Mechanistic studies
on allyl acetate ionization by Amatore and co-workers11 suggest
that formation of the Pd π-allyl complex occurs with complete
ion pairing in THF (i.e., no free acetate ions were produced),
while in DMF, no significant ion pairing occurred. This could
mean that ionization does occur, but that tight ion pairing in
THF is resulting in a “memory effect”12 for the leaving group;
Interestingly, treatment of 7 with anhydrous Suzuki conditions
did not lead to allylic coupling as anticipated,10 but rather, the
product of vinyl cross-coupling (9) was obtained in excellent
(8) Organ, M. G. Unpublished results.
(9) (a) Collins, D. J.; Jackson, W. R.; Timms, R. N. Tetrahedron Lett. 1976,
495-496. (b) Matsushita, H.; Negishi, E. Chem. Commun. 1982, 160-
161. (c) Temple, J. S.; Riediker, M.; Schwartz, J. J. Am. Chem. Soc. 1982,
104, 1310-1315. (d) Trost, B. M.; Schmuff, N. R. J. Am. Chem. Soc. 1985,
107, 396-405. (e) Heumann, A.; Reglier, M. Tetrahedron 1995, 51, 975-
1015. (f) Enders, D.; von Berg, S.; Jandeleit, B. Synlett 1996, 18-20.
(10) Treatment of 1-acetoxy-2-propene with the identical reaction conditions
smoothly converted the allylic acetate to the corresponding aryl derivative
in 70% isolated yield.
(11) Amatore, C.; Jutand, A.; Gilbert, M.; Mottier, L. Chem.sEur. J. 1999, 5,
466-473.
(12) Trost, B. M.; Bunt, R. C. J. Am. Chem. Soc. 1996, 118, 235-236.
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Allylic Ionization versus Oxidative Addition by Pd
A R T I C L E S
Scheme 3
In a related experiment, the same boronic acid was reacted
alongside sodium phenoxide, which is known to be a much
poorer nucleophile for Pd-catalyzed allylic substitution than is
malonate (Scheme 5).16 All the products obtained (i.e., 18-20)
resulted from ionization of the acetate moiety and attack by
the phenoxide nucleophile on the central carbon of the 2-bromo-
π-allyl Pd complex.1717-18 These results also support the notion
that ionization of the acetate is not temperature-dependent, and
that it ionizes readily in the presence of a suitable nucleophile,
even if it is a weak one. Furthermore, this ionization occurs
equally well in the presence or absence of the vinyl bromide.
What remained to be investigated more deeply was the effect
of reaction temperature on vinyl bromide oxidative addition
to Pd. All of the Suzuki reactions required heating, presum-
ably to facilitate metal-metal exchange and reductive elimina-
tion. So, it remained unclear as to whether this was impacting
on reactivity. To this end, compound 7 was reacted under
Sonogashira conditions with TMS acetylene, and enyne 21 was
obtained in suitable recovery at room temperature (Scheme 6).
Thus, either the allylic acetate or the vinyl bromide can be
activated selectively at room temperature or at elevated tem-
perature based solely on the nature of the reacting partner in
the reaction.
Effect of Halide and Olefin Structure on Selectivity of Pd
Activation. Next, a Suzuki coupling was performed on 11 at
65 °C to see if any apparent ionization of the acetate was
occurring under these conditions (Scheme 7). No product of
simple allylic coupling was observed (i.e., 26 or 27). While we
cannot say with certainty that products 22-25 did not arise from
reversible ionization of the acetate first, earlier observations with
7 and 11 and those in Scheme 8 involving 25 (vide infra) do
not support it.
We prepared 25 from the corresponding alcohol (28) and
treated it with (PPh3)4Pd and sodium acetate at reflux (Scheme
8). In this case, the products of ionization were observed,
suggesting that the formation of 24 and 25 in Scheme 7 proceeds
first by cross-coupling of the Br followed by ionization of the
acetate, which scrambles the position of the double bond. This
result clearly demonstrates that while the bromide is not tolerated
at the 2-position during ionization for allylic cross-coupling,
other substituents, even ones as large as phenyl, do not hinder
ionization.
thus, the double bond position does not scramble. To this end,
11 was treated with sodium acetate in DMF (reactions c and
d), and only starting material was recovered. This demonstrates
that simple ion pairing cannot explain the nonappearance of
product 13. Carboxylates are known to be suitable, albeit,
modest nucleophiles for Pd-catalyzed allylic substitution.13
It is difficult to argue that ionization did occur in the above
situations and that the acetate ion simply did not re-add. That
is, in the presence of catalytic Pd, the acetate ionized and Pd
remained trapped as a π-allyl complex in a small and, therefore,
undetectable amount. Even if one argued that sodium acetate
is too insoluble to act as a nucleophile, the ionized acetate itself,
which forms at least a close ion pair with the π-allyl cation,
should re-attack, and this would scramble the position of the
double bond, at least to some degree. To put this possibility to
rest, the Pd π-allyl complex derived from dimer 1414 was
prepared and treated with sodium acetate in THF (Scheme 3).
Compound 7 was produced, proving that sodium acetate does
indeed react well with the Pd π-allyl complex. Therefore, it
would appear that under the Suzuki conditions used in Scheme
1, the allylic acetate in 7 did not ionize at all and the bromide
was activated selectively.
When 11 was reacted with sodium dimethyl methylmalonate
at 55 °C (reaction e), the expected products of nucleophilic
attack were obtained, proving that 11 does ionize readily in the
presence of a “strong and suitable” nucleophile for Pd-catalyzed
allylic alkylation.15 The same result was the case when the more
soluble tetrahexylammonium counterion was used (reaction f).
Of particular note, the fact that alkylation products 12 and 13
were obtained in a 1:1 ratio further demonstrates that no memory
effect due to tight ion pair formation is operating in these
systems.11,12
Temperature Studies. In a competition experiment similar
to the one in Scheme 1, a suspension of 11, 4-methoxyboronic
acid, CsF, and the sodium dimethyl methylmalonate was
warmed to reflux, and then a solution containing the catalyst
was added (Scheme 4). The progress of the reaction was then
We then prepared a variety of labeled allyl acetates and treated
them with Pd catalyst in the presence of 1.0 equiv of sodium
acetate or tetrahexylammonium bromide (Scheme 9). In the case
of dibromide 31, ionization occurred readily, demonstrating that
in the presence of a superior leaving group, such as Br, the Pd
π-allyl complex will form regardless of the reaction conditions
(e.g., the presence of malonate, acetate, or boronic acid nucleo-
philes). In the absence of the vinyl bromide (i.e., 29), acetate,
in fact, does ionize readily. When compared to earlier results
1
followed by H NMR spectroscopy. The premise is to ensure
that if oxidative addition of the C-Br bond to Pd is temperature-
dependent (i.e., requires heat), relative to ionization of the
acetate, that the reaction’s conditions are such that both
processes could happen when the Pd is added. The products
show selective addition of the malonate to the allylic position,
while the boronic acid added only to the central bromine-bearing
carbon after allylic substitution took place. This, at least in part,
demonstrates that temperature is not a factor in the selectivity
of functional group activation by Pd, and this is addressed further
in Scheme 6.
(16) In a competition experiment, 1 equiv each of malonate and phenoxide
nucleophiles was reacted with 1-acetoxy-2-propene and (PPh3)4Pd. Only
the product of malonate substitution was obtained, and the starting acetate
reacted fully: Organ, M. G.; Arvanitis, E. A.; Hynes, S. J. Tetrahedron
Lett. 2002, 43, 8989-8992.
(13) (a) Deardorff, D. R.; Myles, D. C. Org. Synth. 1988, 67, 114-120. (b)
Deardorff, D. R.; Myles, D. C.; MacFerrin, K. D. Tetrahedron Lett. 1985,
26, 5616-5619. (c) Trost, B. M.; Organ, M. G. J. Am. Chem. Soc. 1994,
116, 10320-10321.
(14) (a) Castano, A. M.; Aranyos, A.; Szabo´, K. J.; Ba¨ckvall, J.-E. Angew. Chem.,
Int. Ed. Engl. 1995, 34, 2551-2553. (b) Aranyos, A.; Szabo´, K. J.; Castano,
A. M.; Ba¨ckvall, J.-E. Organometallics 1997, 16, 1058-1064.
(15) In a control experiment with no Pd present, no reaction took place, proving
that nucleophilic attack by malonate is Pd-catalyzed.
(17) For a discussion pertaining to the attack of the phenoxide nucleophile at
the central position of Pd π-allyl complexes, see: (a) Organ, M. G.; Miller,
M.; Konstantinou, Z. J. Am. Chem. Soc. 1998, 120, 9283-9290. (b) Organ,
M. G.; Miller, M. Tetrahedron Lett. 1997, 38, 8181-8184. (c) Kadota, J.;
Katsuragi, H.; Fukumoto, Y.; Murai, S. Organometallics 2000, 19, 979-
983.
(18) Organ, M. G.; Arvanitis, E. A.; Hynes, S. J. J. Org. Chem. 2003, 68, 3918-
3922.
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A R T I C L E S
Scheme 4
Comer et al.
Scheme 5
Scheme 6
malonate, in this case a good nucleophile, but 33a did not. These
results clearly demonstrate that electronegativity (Cl ) 2.9, Br
) 2.8, I ) 2.2) does not play a role in the ionizing ability of
the acetate. Thus, in the presence of a less efficient vinyl
oxidative addition partner, the catalyst instead activates the
allylic acetate. Additionally, when the iodoacetate 33a was
treated with 1.0 equiv of Pd(PPh3)4, selective activation of the
vinyl halide was observed, and oxidative addition product 35
precipitated from the reaction mixture. These results strongly
support the theory that oxidative addition of Pd to the vinyl
bromide occurs preferentially to π-allyl formation by acetate
ionization in templates such as 7. Furthermore, this may also
shed some light on why no products of ionization were observed
in Suzuki reactions with 11 and why 26 and 27 were never
obtained during cross-coupling reactions with 11.
with 7 or 11, this result shows that acetate ionization does not
take place in the presence of the vinyl bromide without a suitable
nucleophile for Pd (e.g., malonate) being present. This effect
could be due either to the electronegativity of the bromide, which
deactivates acetate toward ionization, or to the preferential
oxidative addition of the vinyl bromide bond to Pd.
We were curious to see whether there was a special
relationship between the position of the halide, relative to the
allylic acetate. One could imagine some complexation being
possible between the 1- and 2-position of this propene frame-
work via Pd, and that could effect where Pd inserts. To this
end, we prepared and treated 37 to Suzuki and allylic substitution
To test the former hypothesis, iodoacetate 30 was prepared
and treated to standard allylic substitution conditions with
sodium acetate, and no ionization products were observed.
Significantly, the chloro derivative, 32, smoothly ionized under
similar conditions with the same poor nucleophile. This can also
be seen in Scheme 10, where 33b ionized in the presence of
Scheme 7
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16090 J. AM. CHEM. SOC. VOL. 126, NO. 49, 2004

Allylic Ionization versus Oxidative Addition by Pd
A R T I C L E S
Scheme 8
Scheme 12
Scheme 9
Summary
This study has demonstrated that the cyclic bromo acetate
2a is deactivated toward allylic alkylation by Pd, even in the
presence of malonate nucleophile, relative to its acyclic analogue
7. We propose this to be the case because the metal cannot
adopt the requisite antiperiplanar alignment with the leaving
group to facilitate ionization in cyclic, conformationally con-
strained structures. This result has implications for the findings
of Nwokogu5 (among others)6,7 who reported selective activation
of vinyl bromides in the presence of allylic carbonates or acetate
groups. Significantly, the substrates investigated by these groups
were either hindered or cyclic, and so the chemoselectivity of
Pd activation observed may have been due to conformational
rather than electronic factors. With the use of labeling studies,
we have shown that the vinyl halogen, in fact, does deactivate
the allyl acetate toward ionization in the presence of the Pd
catalyst. However, this deactivation is not for the reasons
suggested earlier by Nwokogu5 and Heathcock.7 Rather, we
propose that the “electronic effect” is due to preferential
oxidative addition of Pd into the vinyl carbon-halogen bond.
This was demonstrated in the absence of a vinyl halogen (29)
and in the presence of a relatively poor substrate for oxidative
addition, such as vinyl chloride 32, where ionization of the
acetate occurred readily. Thus, electronegativity of the vinyl
halide, which has been implicated by others in deactivating the
allylic leaving group, likely plays no role in the chemoselectivity
of Pd activation.
Scheme 10
Scheme 11
Ionization depends not only on the vinyl moiety but also on
the nature of the allyl group. For example, while allyl acetate
failed in some cases (e.g., 7) to ionize when the vinyl bromide
was present, the analogous allyl bromide (31) ionized readily
under all reaction conditions tried. The consequences of these
results are that in the presence of a cross-coupling partner, the
vinyl Br is activated selectively alongside the allylic acetate.
Once the cross-coupling has been completed and the halogen
removed from the vinyl position, ionization can occur readily,
giving rise to allylic addition products. However, in the presence
of a suitable nucleophile (e.g., malonate or phenoxide), our
results show clearly that ionization occurs readily and indeed
takes preference over vinyl halogen activation. The accepted
mechanism of allylic alkylation with stabilized carbanions, such
as malonates, stipulates that both ionization and nucleophilic
attack proceed anti to the metal-olefin bond so that the metal
does not come into contact with the leaving group or the
incoming nucleophile.9 This has been demonstrated with ster-
eochemical studies with chiral allyl acetates, whereby alkylation
proceeds with overall retention of configuration via a double
inversion process. Our results are highly suggestive that this
dogma may not be entirely correct, and that interactions between
the certain nucleophiles and Pd take place prior to ionization,
thereby creating a new catalytic species with different properties
that are reflected in catalyst chemoselectivity. At this stage, we
reaction conditions (Scheme 11). The chemoselectivity of the
cross-coupling reaction for the bromide site was maintained as
it was for diene 39. Thus, in the presence of a readily ionizable
leaving group, oxidative addition occurred preferentially to
π-allyl formation, leading to 38 and 40. In the case of 37, which
was prepared as a single stereoisomer, the stereochemistry was
preserved in the product, proving that ionization of the acetate
did not occur in this case, as well. Alternatively, when 37 was
treated with malonate nucleophile, the acetate ionized smoothly,
leading to substitution product 36. The scrambling of the
stereochemistry of the vinyl bromide proves the intermediacy
of a Pd π-allyl complex.
In an attempt to further probe the inherent reactivity of Pd
toward a vinyl bromide relative to an allyl acetate, while
continuing to try to eliminate any possible effect that the two
centers might have on each other, a competition Suzuki experi-
ment was conducted (Scheme 12). Equal portions of 2-bro-
mopropene (41) and allyl acetate (42) were allowed to react a
limiting amount of 4-methoxyphenylboronic acid in the presence
of Pd. Only 41 reacted further, proving that the vinyl bromide
reacts fastest under these reaction conditions. Once 41 has been
consumed, then 42 would be able to react since it is known to
be a good substrate for allylic coupling with boronic acids.
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A R T I C L E S
Comer et al.
have no direct proof that this is indeed occurring, but the results
are suggestive that this is the case. Thus, while the bromine in
7 clearly switches off the allyl acetate toward ionization, the
presence of malonate switches this process back on. In other
words, the presence of the malonate alters the catalyst chemo-
selectivity and that there is a clear dependence on, or at least
an involvement of, the reaction partner (e.g., a suitable soft
nucleophile) in catalyst chemoselectivity with polyfunctional
olefins.
Acknowledgment. This work was funded by NSERC Canada
and the Ontario Research and Development Challenge Fund
(ORDCF).
Supporting Information Available: All experimental and
spectroscopic data. This material is available free of charge via
the Internet at http://pubs.acs.org.
JA045416H
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