Switchable Site-Selective Catalytic Carboxylation of Allylic Alcohols with CO2

Article abstract of DOI:10.1002/anie.201702857

A switchable site-selective catalytic carboxylation of allylic alcohols has been developed in which CO₂ is used with dual roles, both facilitating C?OH cleavage and as a C₁ source. This protocol is characterized by its mild reaction conditions, absence of stoichiometric amounts of organometallic reagents, broad scope, and exquisite regiodivergency which can be modulated by the type of ligand employed.

Full text of DOI:10.1002/anie.201702857

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Communications
Chemie
International Edition: DOI: 10.1002/anie.201702857
German Edition: DOI: 10.1002/ange.201702857
Cross-Coupling
Switchable Site-Selective Catalytic Carboxylation of Allylic Alcohols
with CO2
Manuel van Gemmeren+, Marino Bçrjesson+, Andreu Tortajada+, Shang-Zheng Sun+,
Keisho Okura, and Ruben Martin*
Abstract: A switchable site-selective catalytic carboxylation of
need for highly reactive nucleophilic entities. However, the
À
allylic alcohols has been developed in which CO2 is used with
remarkable activation barrier required for C OH scission
dual roles, both facilitating C OH cleavage and as a C1 source.
and the high polarizability of the O H bond[5] left reasonable
À
À
This protocol is characterized by its mild reaction conditions,
absence of stoichiometric amounts of organometallic reagents,
broad scope, and exquisite regiodivergency which can be
modulated by the type of ligand employed.
doubt that such a counterintuitive scenario could ever be
implemented (Scheme 1, bottom right). If successful, how-
ever, the realization of such a technique could unravel the
inherent potential of simple alcohols in cross-electrophile
events, thus constituting a unique opportunity to provide new
tactics for building up complexity from simple precursors.
Prompted by the seminal stoichiometric work of Osa-
kada,[6] we,[7] and others[8] launched a program aimed at
unraveling the potential of nickel-catalyzed reductive carbox-
ylation of organic (pseudo)halides with carbon dioxide (CO2).
At present, these endeavors unfortunately remain limited to
organic halides or particularly activated C O electrophiles.
As C O electrophiles ultimately derive from the correspond-
ing alcohol, we recently questioned whether we could
establish a design principle for promoting a more atom- and
step-economical technique by direct nickel-catalyzed carbox-
ylation of simple unprotected alcohols in the absence of either
stoichiometric amounts of, or air-sensitive organometallic
reagents.[10] To such an end, we hypothesized that CO2 could
be used with dual roles, both as a C1 source and as an
À
M
etal-catalyzed cross-coupling reactions of C O electro-
philes have recently gained considerable momentum because
of the ready availability of alcohols and the design of
orthogonal techniques in the presence of organic halides.[1]
À
Unlike common C C bond formations with activated organic
sulfonates, esters, and ethers, the use of simple alcohols as
[9]
À
À
counterparts, arguably the most accessible and simplest C O
À
derivative, has received much less attention. Despite advan-
ces realized in nucleophilic/electrophilic regimes (Scheme 1,
bottom left),[2,3] alcohols should ideally be utilized within the
realm of cross-electrophile couplings,[4] thus avoiding the
À
activating group for C O bond cleavage (Scheme 2). Our
hypothesis is driven by the known ability of CO2 to react
reversibly with alcohols en route to carbonic acids (A),[11] thus
À
lowering the activation energy for promoting C O scission
while accelerating the rate of oxidative addition to [Ni0Ln] (C
vs. B) prior to CO2 insertion.[12] Herein, we describe our
results towards this goal by designing a mild and user-friendly
nickel-catalyzed carboxylation of allylic alcohols under an
atmospheric pressure of CO2. We demonstrate that the site
selectivity at the allyl terminus can be discerned and
À
Scheme 1. Catalytic C C bond formation with alcohols as coupling
partners.
[*] M. van Gemmeren,[+] M. Bçrjesson,[+] A. Tortajada,[+] S.-Z. Sun,[+]
K. Okura, Prof. R. Martin
Institute of Chemical Research of Catalonia (ICIQ)
The Barcelona Institute of Science and Technology
Av. Paꢀsos Catalans 16, 43007 Tarragona (Spain)
E-mail: rmartinromo@iciq.es
Prof. R. Martin
ICREA
Passeig Lluꢀs Companys, 23, 08010 Barcelona (Spain)
[+] These authors contributed equally to this work.
Supporting information and the ORCID identification number(s) for
the author(s) of this article can be found under:
https://doi.org/10.1002/anie.201702857.
Scheme 2. Design principle for a carboxylation of allylic alcohols with
CO2.
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modulated at will by the ligand employed, thus leading to
either linear or a-branched carboxylic acids.[13]
Our study began by evaluating the carboxylation of 1 at an
atmospheric pressure of CO2 (Scheme 3). Interestingly,
neither 2a nor 2b were observed under reaction conditions
of the ligand exerted a profound influence in both reactivity
and site selectivity. While excellent regioselectivities towards
2a were found with 2,2’-bipyridines and 1,10-phenanthrolines
possessing substituents adjacent to the nitrogen atom, better
yields were found for the latter (entries 7–11). At present, we
hypothesize that these results account for the higher rigidity
of 1,10-phenanthrolines, likely increasing the stability of the
putative reaction intermediates within the catalytic cycle.
Interestingly, the bench-stable C6-substituted terpyridines L7
and L8, resulted in a selectivity switch en route to 2b under
identical reaction conditions to that shown for L3, albeit in
lower yields (entries 12 and 13).[16] It is worth noting that
a related 2,2’:6’.2’’:6’’,2’’’-quaterpyridine analogue (L6) failed
to provide 2b.[17] These results tacitly suggest that the
coordination geometry of the ligand dictates the selectivity
pattern, with tridentate ligands being particularly suited for
2b. Careful fine-tuning of the reaction conditions afforded 2b
in 81% yield with an excellent 3:97 2a/2b ratio when using
[Ni(COD)2] as precatalyst in DMA at room temperature, and
employing both CaCl2 and NEt3 as additives (entry 14).[18] As
anticipated, rigorous control experiments revealed that all of
the reaction parameters were critical for success.[14]
With reliable access to either 2a or 2b, we next turned our
attention to evaluate the generality of our nickel-catalyzed,
switchable site-selective carboxylation of allylic alcohols with
CO2 by using either a Ni/L3 or Ni/L8 couple (Scheme 4). In all
cases analyzed, an exquisite site selectivity was observed
regardless of whether linear or a-branched allylic alcohols
were utilized, thus indicating that a substrate-controlled site
selectivity does not come into play. Notably, the substitution
pattern on the allyl terminus was largely inconsequential for
both reactivity and site selectivity, as predominantly the linear
or a-branched carboxylic acids were obtained with the
appropriate nickel/ligand system. The presence of esters
(12a, 12b), acetals (10a, 10b), alkenes (15a, 15b) or even aryl
chlorides (13a, 13b) do not interfere, thus providing ample
room for further functionalization. Likewise, the presence of
Scheme 3. Optimization of the reaction conditions. 1 (0.20 mmol),
NiBr2·glyme (10 mol%), L3 (26 mol%), Zn (4 equiv), MgCl2
(1.20 equiv), DMF (0.10m), CO2 (1 atm) at 408C for 16 h (yields within
parentheses refer to yields of the reagents used within parentheses).
[b] Yield of 2a and 2b combined as determined by GC analysis using
anisole as internal standard. [c] Yield of isolated product. [d] No
MgCl2. [e] [Ni(COD)2] (10 mol%), L8 (10 mol%), CaCl2 (4 equiv), NEt3
(3 equiv), Zn (1.50 equiv), DMA (0.20m) at RT. COD=1,5-cycloocta-
diene, DMA=N,N-dimethylacetamide, DMF=N,N-dimethylform-
amide, NMP=N-methyl-2-pyrrolidone.
À
C O electrophilic sites susceptible to nickel-catalyzed cross-
coupling reactions such as aryl methyl ethers (8a, 8b) or aryl
pivalates (9a, 9b) does not compete with the efficacy of the
carboxylation event. Particularly noteworthy was the ability
to access quaternary centers (14b and 15b), as cross-electro-
phile endeavors have found little success with tertiary alkyl
electrophiles.[19] While a Ni/L3 regime provided predomi-
nantly E-configured isomers, we observed an intriguing
dichotomy exerted by the geometry of the starting precursor.
Specifically, naturally occurring geraniol gave rise to 15a with
a higher E/Z ratio than that obtained from the structurally
isomeric nerol and linalool. While tentative, either a subtle h1
to h3 hapticity of the intermediate allyl–nickel complex, or the
known ability of tethered alkenes on the side-chain to act as
intramolecular directing groups might account for these
results.[20] In contrast, 15b was exclusively obtained from
either geraniol, nerol, or linalool with a Ni/L8 couple. It is
worth mentioning that substituents in the a-position of the
allyl motif did not erode the site selectivity, thus giving rise to
10a and 10b in good yields. The synthetic applicability of our
nickel-catalyzed carboxylation in the context of natural
product synthesis is further illustrated in Scheme 5. Specifi-
previously developed for other carboxylation events.[7,8] After
some experimentation, a combination of NiBr2·glyme, com-
mercially available L3, Zn, MgCl2, and DMFat 408C afforded
2a in 70% yield upon isolation with exquisite site selectivity
(2a/2b = 99:1).[14] Inferior results were consistently observed
with nickel sources, additives, and solvents other than
NiBr2·glyme, MgCl2, and DMF, respectively (entries 2 and
3). Similarly, lower yields were found when either MgBr2 or
ammonium salts were used in lieu of MgCl2 (entries 4 and
5).[15] Traces of 2a, if any, were observed when using either
manganese or silanes as reducing agents (entry 6). The former
finding is particularly noteworthy given the notorious success
of manganese as reductant in cross-electrophile couplings,[4]
including carboxylation protocols.[7,8] As expected, the nature
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Scheme 5. Formal total synthesis of (+)-trans-cognac lactone.
TMS=trimethylsilyl.
TMSCHN2 and Sharpless asymmetric dihydroxylation
afforded 16 in good overall yield, thus constituting a formal
total synthesis of (+)-trans-cognac lactone[21] (17) and other
related natural products.[22] Taken together, the results
compiled in both Schemes 4 and 5 show the prospective
potential of our methodology.
While an unambiguous understanding on how these
reactions work at the molecular level should await further
investigations, we turned our attention to gather empirical
evidence about the intriguing role of the ligand by studying
the reactivity of the putative [Ni0Ln] species (Scheme 6).
Scheme 6. Mechanistic experiments.
Particularly noteworthy was the absence of reactivity when
simply exposing 18 to stoichiometric amounts of either
[Ni0(L3)2][23] or [Ni(COD)2]/L8[24], in the absence of CO2,
thus reinforcing the notion that a direct oxidative addition of
an allylic alcohol to [Ni0Ln] does not come into play.[25] More
importantly, while a [Ni0(L3)2] regime required the presence
of Zn en route to 19a,[23] the corresponding [Ni(COD)2]/L8
couple cleanly produced 19b in the absence of a reductant,
thus providing evidence for the unique role of the ligand
backbone.[26] Although speculative, these results might sug-
gest the intermediacy of h1-NiI intermediates with the
bidentate and rigid L3, and thus CO2 insertion at the a-
carbon atom (19a),[27–30] whereas the presence of the triden-
Scheme 4. Scope of the regiodivergent carboxylation of allylic alcohols
with CO2. [a] Conditions A: see Scheme 3, entry 1, at 0.25 mmol scale.
Yield is that of isolated product, and an average of at least two
independent runs. 2a–15a were all obtained in 99:1 (linear/branched)
ratio. 2a–13a were obtained in ꢀ92:8 E/Z ratio. [b] From linear
alcohol. [c] From a-branched alcohol. [d] Zn (2.50 equiv) in DMF
(0.70m). [e] E/Z=45:55. [f] From geraniol, E/Z=94:6. [g] From nerol,
E/Z=16:84. [h] From linalool, E/Z=42:58. [i] Conditions B: see
Scheme 3, entry 14, at 0.25 mmol scale. Yield is that of isolated
product, and an average of at least two independent runs. With the
exception of 3b and 10b, all products were obtained in ꢀ92:8
(branched/linear) ratio. [j] 82:18 (3b/3a). [k] 85:15 (10b/10a) and 1:1
diastereomeric ratio. [l] From geraniol. [m] From nerol. [n] From lina-
lool. Piv=pivaloyl.
tate L8 might result in h1-NiII intermediates with C C bond
À
formation occurring at the g-carbon atom (19b).[30–32]
In summary, we have documented a nickel-catalyzed,
switchable site-selective reductive carboxylation of allylic
alcohols, in which regiodivergency is exclusively dictated by
the geometry of the ligand backbone. The salient features of
this user-friendly method are the broad scope, mild reaction
conditions, exquisite site-selectivity profile, and the ability of
CO2 to act with dual roles, both as a C1 source and as
cally, a simple three-step sequence consisting of a direct
À
carboxylation of 1a, followed by esterification with
a mediator for facilitating C O scission. We anticipate that
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this method will foster systematic investigations for a more
prolific use of simple alcohols in cross-electrophile reactions.
Further work along these lines is being conducted in our
laboratories.
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Acknowledgments
[7] For selected references, see: a) T. Moragas, M. Gaydou, R.
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Chem. Soc. 2015, 137, 8924; c) X. Wang, Y. Liu, R. Martin, J. Am.
Chem. Soc. 2015, 137, 6476; d) Y. Liu, J. Cornella, R. Martin, J.
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[8] For selected references, see: a) F. Rebih, M. Andreini, A.
Moncomble, A. Harrison-Marchand, J. Maddaluno, M. Duran-
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Fujihara, K. Nogi, T. Xu, J. Terao, Y. Tsuji, J. Am. Chem. Soc.
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We thank ICIQ, the European Research Council (ERC-
277883), MINECO (Severo Ochoa Excellence Accreditation
2014–2018, SEV-2013-0319 & CTQ2015-65496-R, MINECO-
FEDER-UE), and the Cellex Foundation for support.
Johnson Matthey, Umicore, and Nippon Chemical Industrial
are acknowledged for a gift of metal and ligand sources.
M.v.G., M.B, and A.T. thank the Alexander von Humboldt
Foundation and MINECO for a postdoctoral and predoctoral
scholarships.
Conflict of interest
The authors declare no conflict of interest.
[9] M. Bçrjesson, T. Moragas, D. Gallego, R. Martin, ACS Catal.
2016, 6, 6739.
[10] For an elegant regioselective (not regiodivergent) carboxylation
with stoichiometric, air-sensitive, and pyrophoric Et2Zn as
a reducing agent, see: T. Mita, Y. Higuchi, Y. Sato, Chem. Eur.
J. 2015, 21, 16391.
Keywords: carbon dioxide · cross-coupling · nickel ·
regioselectivity · synthetic methods
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[1] a) C. Zarate, M. van Gemmeren, R. J. Somerville, R. Martin,
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[2] While activation of allylic alcohols with CO2 has been explored
using palladium, iridium, and rhodium catalysts, analogous
activation technologies using nickel catalysts are rare. For
excellent reviews dealing with cross-coupling reactions of allylic
alcohols with nucleophilic entities via the intermediacy of p-
allylic species, see: a) N. A. Butt, W. Zhang, Chem. Soc. Rev.
2015, 44, 7929; b) B. Sundararaju, M. Achard, C. Bruneau,
Chem. Soc. Rev. 2012, 41, 4467; c) Y. Tamaru, Eur. J. Org. Chem.
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[3] For selected cross-coupling reactions of alcohols with nucleo-
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Mashima, Angew. Chem. Int. Ed. 2016, 55, 1098; Angew.
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J. Am. Chem. Soc. 1981, 103, 6863, and references therein.
[13] For a selection of elegant linear-selective reductive couplings of
other allyl electrophiles, see: a) L. L. Anka-Lufford, M. R.
Prinsell, D. J. Weix, J. Org. Chem. 2012, 77, 9989; b) X. Qian,
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[14] See the Supporting information for details. The mass balance
accounts for unreacted starting material and reduction events.
[15] For the beneficial role of MgCl2 in cross-electrophile events, see:
a) C. Zhao, X. Jia, X. Wang, H. Gong, J. Am. Chem. Soc. 2014,
136, 17645; b) T. Leꢁn, A. Correa, R. Martin, J. Am. Chem. Soc.
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Lett. 2012, 14, 3044.
[16] While L7 is commercially available, L8 could easily be prepared
from simple precursors. See Ref. [14].
[17] These results are in sharp contrast with the ability of quaterpyr-
idine ligands to promote carboxylation processes of allyl ester
derivatives: T. Moragas, J. Cornella, R. Martin, J. Am. Chem.
Soc. 2014, 136, 17702.
[18] Although tentative, Lewis acids (MgCl2 or CaCl2) might react
with the corresponding carbonic acid generated in situ upon
À
exposure of 1 with CO2, thus accelerating C O bond cleavage.
Importantly, an identical regioselectivity was found regardless of
whether CaCl2 or MgCl2 were utilized, thus reinforcing the
notion that the site selectivity was dictated by the ligand
employed. As for the role of NEt3, it could potentially act as
a
proton scavenger to prevent the formation of reduced
products. See Ref. [14].
[19] a) X. Wang, S. Wang, W. Xue, H. Gong, J. Am. Chem. Soc. 2015,
137, 11562; b) see Ref. [15a]; c) M. Bçrjesson, T. Moragas, R.
Martin, J. Am. Chem. Soc. 2016, 138, 7504; d) Ref. [17].
4
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[20] K. M. Miller, T. F. Jamison, J. Am. Chem. Soc. 2004, 126, 15342.
[28] The available experimental data do not allow us to rule out the
[21] H. Takahata, Y. Uchida, T. Momose, J. Org. Chem. 1995, 60,
5628.
formation of nickel(I) intermediates by comproportionation.
See for example: a) J. Cornella, E. Gomez-Bengoa, R. Martin, J.
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[29] Recently, nickel(I) species have been shown to rapidly react with
CO2: F. S. Menges, S. M. Craig, N. Tçtsch, A. Bloomfield, S.
Ghosh, H.-J. Krꢂger, M. A. Johnson, Angew. Chem. Int. Ed.
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[23] For the synthesis of [Ni0(L3)2] see Ref. [7c]. When [Ni0(L3)2] was
used in the absence of additional L3, 19a was obtained with
a 22% yield. A similar yield was obtained upon treatment of
[Ni(COD)2] with L3. At present, we do not have a rationale for
the required 1:2.6 ratio of Ni/L3.
[30] For a mechanistic hypothesis, see Ref. [14].
[31] This mechanistic interpretation is somewhat reminiscent of the
elegant palladium-catalyzed carboxylation of allenes via h1-allyl-
PdII intermediates possessing structurally related tridentate
pincer-type ligands in which the CO2 insertion occurred at the
g-carbon atom: a) H.-W. Suh, L. M. Guard, N. Hazari, Chem.
Sci. 2014, 5, 3859; b) J. Takaya, N. Iwasawa, J. Am. Chem. Soc.
2008, 130, 15254.
[32] We cannot rule out that L8 might be redox non-innocent in our
carboxylation event. For excellent reviews about redox-active
ligands, see: a) P. Chirik, Angew. Chem. Int. Ed. 2017, 56, 5170;
Angew. Chem. 2017, 129, 5252; b) X. Hu, Chem. Sci. 2011, 2,
1867.
[24] Despite considerable synthetic efforts, we were unable to
prepare Ni0(L8) in analytically pure form.
[25] Although one might argue that allyl chloride intermediates
could be generated upon exposure of allyl alcohols to either
MgCl2 or CaCl2, control experiments in the absence of CO2 ruled
out this possibility. Additionally, we also demonstrate that allyl
chlorides are not competent as reaction intermediates en route
to either 19a or 19b. See Ref. [14].
[26] Interestingly, 48% of 19b could be obtained when reacting 18
with [Ni(COD)2]/L8 in the absence of either Zn, NEt3 or CaCl2.
[27] For the in situ generation of NiI from NiII: a) C. A. Laskowski,
D. J. Bungum, S. M. Baldwin, S. A. Del Ciello, V. M. Iluc, G. L.
Hillhouse, J. Am. Chem. Soc. 2013, 135, 18272; b) J. Breitenfeld,
J. Ruiz, M. D. Wodrich, X. Hu, J. Am. Chem. Soc. 2013, 135,
12004; c) S. Biswas, D. J. Weix, J. Am. Chem. Soc. 2013, 135,
16192; d) see Ref. [8e].
Manuscript received: March 19, 2017
Final Article published: && &&, &&&&
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Communications
Cross-Coupling
M. van Gemmeren, M. Bçrjesson,
A. Tortajada, S.-Z. Sun, K. Okura,
R. Martin*
&&&& — &&&&
Switchable Site-Selective Catalytic
Carboxylation of Allylic Alcohols with CO2
Double agent: In the title reaction CO2
absence of stoichiometric amounts of
organometallic species. The protocol has
broad scope and an exquisite regiodiver-
gency which can be modulated by the
ligand-type employed.
À
serves as both a facilitator for the C OH
cleavage and as a C1 source. This reaction
is the first example of a cross-electrophile
coupling of unprotected alcohols in the
6
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Angew. Chem. Int. Ed. 2017, 56, 1 – 6
These are not the final page numbers!