Carbonyl-Olefin Metathesis Catalyzed by Molecular Iodine

Article abstract of DOI:10.1021/acscatal.8b03769

The carbonyl-olefin metathesis reaction could facilitate rapid functional group interconversion and allow construction of complicated organic structures. Herein, we demonstrate that elemental iodine, a very simple catalyst, can efficiently promote this chemical transformation under mild reaction conditions. Our mechanistic studies revealed intriguing aspects of the activation mode via molecular iodine and the iodonium ion that could change the previously established perception of catalyst and substrate design for the carbonyl-olefin metathesis reaction.

Full text of DOI:10.1021/acscatal.8b03769

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Article
Carbonyl-Olefin Metathesis Catalyzed by Molecular Iodine
Uyen Phuoc Nhat Tran, Giulia Oss, Martin Breugst, Eric Detmar,
Domenic Paul Pace, Kevin Liyanto, and Thanh Vinh Nguyen
ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.8b03769 • Publication Date (Web): 14 Dec 2018
Downloaded from http://pubs.acs.org on December 15, 2018
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ACS Catalysis
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Carbonyl-Olefin Metathesis Catalyzed by Molecular Iodine
Uyen P. N. Tran,a Giulia Oss,a Martin Breugst,b Eric Detmar,b Domenic P. Pace,a Kevin Liyantoa and
Thanh V. Nguyena,*
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a School of Chemistry, University of New South Wales, Sydney, Australia
b Department für Chemie, Universität zu Köln, Köln, Germany
Supporting Information Placeholder
Catalytic Carbonyl-Olefin Metathesis (COM) Reaction
ABSTRACT: The carbonyl-olefin metathesis reaction
R2
R1
R2
could facilitate rapid functional group interconversion
and allow construction of complicated organic struc-
tures. Herein we demonstrate that elemental iodine, a
very simple catalyst, can efficiently promote this chemi-
cal transformation under mild reaction conditions. Our
mechanistic studies revealed intriguing aspects of activa-
tion mode via molecular iodine and iodonium ion that
could change the previously established perception of
catalyst and substrate design for the carbonyl-olefin
metathesis reaction.
This work: [cat.] = I2
R1
O
O
rt, 24 h
via iodonium catalysis
27 examples
21-96%
practical on gram scale
broad substrate scope
(all three COM reaction types)
Previously:
Franzen’s tritylium catalyst
Ar
Lambert’s hydrazine catalyst
(ref 6)
Ar
NH
NH
X
.
(ref 5)
2HCl
Ar
ring-opening COM of
cyclopropene only
intermolecular COM only
INTRODUCTION
Tiefenbacher’s catalyst
Schindler’s and Li’s catalyst
The carbonyl-olefin metathesis reaction (COM),1 an
analogue of the olefin-olefin metathesis reaction,2 is
considered to be very useful for direct carbon-carbon
bond forming transformations and functional group
interconversions. There had been a number of develop-
ments on experimental protocols3 and catalysts4 for the
COM reaction. Over the last five years, it has become
increasingly attractive after interesting studies from the
Lambert group using hydrazine5 and the Franzen group
using tritylium salts6 as organocatalysts for this reaction
(Scheme 1). More recently, the Schindler group7 and the
Li group8 reported elegant studies in which they utilized
salts of iron(III) and gallium(III) to promote COM reac-
tions. Earlier this year, the Tiefenbacher group also pub-
lished an interesting report on the cooperative effect of
hexameric resorcinarene assembly and Brønsted acid to
catalyze COM reactions.9 A recent study from our la-
boratory showed that tropylium ion10 could also be used
as an organocatalytic promoter for the COM reaction
(Scheme 1).11 The COM reaction is, however, still much
less investigated than the olefin-olefin metathesis,12
most likely due to a lack of practicability and general
knowledge about rational catalyst and substrate design
for the reaction. Herein we demonstrate that elemental
iodine, a very simple catalyst, can efficiently promote
the COM reaction on a broad range of substrates under
HCl inside hexameric
resorcinarene host
FeCl3
(ref 7a-d and 8)
(ref 9)
intramolecular COM only
intramolecular COM only
GaCl3 (ref 7e)
ring-opening COM only
Our tropylium catalyst
(ref 11)
BF4
all three types: intra/inter-molecular and ring-opening
Scheme 1. Catalytic carbonyl-olefin metathesis reaction
mild conditions with excellent outcomes.
The inspiration for our use of iodine as a promoter for
the COM reaction came from previous reports of iodine
being able to activate carbonyl substrates for a range of
chemical reactions via halogen bonding interaction.13
Elemental iodine can also serve as a pre-catalyst for
iodonium-activation of alkenes14 or alkynes15 in isomer-
ization and cyclization reactions. We predicted that io-
dine could either activate the carbonyl moiety or the
alkene moiety, or cooperatively activate both functional
groups for the carbonyl-olefin metathesis reaction. Thus,
we set out to test our hypothesis by using I2 catalyst to
promote the intramolecular COM reaction of substrate
1a1 (Scheme 2).
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ACS Catalysis
Page 2 of 9
R1
1
2
3
4
5
6
7
8
R3
R3
(
)n
R1
R2
(
)n
O
R3
R2
)n
10 mol% I2
(
R4
O
R4
R4
neat, rt, 24 h
1
2’
2
3
(see pages S5-S17 in the SI)
(*) = using 25 mol% cat. I2
(isomerized product)
(COM product)
Substrate
Products
Substrate
Products
Me
AND
Me
O
O
CO2Me
Me
Me
CO2Et
CO2Et
CO2Et
9
2a
2a’
CO2Et
2l, 23%
10
11
12
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200 mg, 93% (2a : 2a’ = 11 : 1)
1.60 g, 89% (2a : 2a’ = 38 : 1)
1l
1a1
H2C
Me
Me
Me
Me
Me
Ph
AND
O
AND
O
Me
CO2Et
CO2Et
Me
CO2Et
2m
2m’
2a
27% (2a : 2a’ = 11 : 1)
2a’
1m
1a2
94% (2m : 2m’ = 2.5 : 1)
Ph
H2C
Me
AND
O
H
Me
CO2Et
O
CO2Et
AND
Me
CO2Et
2a
2a’
Me
2n
2n’
1a3
48% (2a : 2a’ = 11 : 1)
1n
54% (2n : 2n’ = 1 : 1)
Me
O
AND
Me
Me
CO2Et
O
CO2Et
CO2Et
Me
1o
Me
2b
2b’
Me
1b
Me
76% (2b : 2b’ = 2 : 1)
2o’, 32%
Me
AND
O
Me
O
CO2iPr
Me
CO2iPr
H
CO2iPr
2c
2c’
2p, 47%
1c
58% (2c : 2c’ = 2.1 : 1)
1p
Me
Me
Me
N
Ts
O
AND
O
MeO
N
Me
Ts
MeO
Me
MeO
CO2Et
CO2Et
2q (*), 82%
1q
CO2Et
2d
2d’
1d
83% (2d : 2d’ = 4 : 1)
O
N
Ts
N
Me
Ts
Me
O
AND
Me
Me
Me
2r, 96%
Ph
Ph
O
1r
O
O
Ph
2e
2e’
Me
Ph
N
O
Ts
1e
60% (2e : 2e’ = 1 : 3)
N
Me
Ts
Me
Me
Me
Me
Me
AND
O
2s
Me
Me
Me
Me
104 mg, 92%
1.51 g, 91%
Ph
1s1
Ph
Ph
1g
2g
2g’
O
42% (2g : 2g’ = 1 : 3)
N
Me
1s2
H
N
Ts
Ts
O
Me
Me
2s, 54%
CO2Bn
CO2Bn
Me
2h, 59%
1h
N
Ts
O
N
Me
Ts
Me
Me
O
Br
Me
CO2Et
1i
Br
2t (*), 78%
1t
CO2Et
2i, 46%
Allyl
Allyl
Me
Me
O
N
Ts
N
Me
Ts
O
Me
Allyl
Me
Allyl
Me
Me
1u
2u (*), 86%
Me
2j, 58%
1j
O
Me
N
Ts
N
Me
Ts
O
Me
CO2Et
1k
CO2Et
Ph
2v, 76%
Me
Ph
Me
1v
2k, 54%
Scheme 2. Iodine-catalyzed intramolecular carbonyl-olefin metathesis reactions16
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ACS Catalysis
Substrates bearing Brønsted-basic nitrogen-centers8
RESULTS AND DISCUSSIONS
1
did not undergo this type of isomerization (Scheme 2,
2q-2v). They worked smoothly to give cyclized COM
products exclusively in high to excellent yields (2q-2v),
although substrates without substitution on the carbon
between the carbonyl and the nitrogen centres required
higher catalyst loading for efficient reactions (Scheme 2,
see products 2q, 2t and 2u, 25 mol% I2 was used).16
Apart from the driving force due to the formation of
acetone as a by-product, stabilizing effect from the con-
jugation of the aromatic ring to the carbonyl group is
also essential for this iodine-catalyzed COM reaction, as
non-aromatic substrate 1l was only converted to bicyclic
product 2l in poor yield (see page S12 in the SI for more
unproductive non-aromatic substrates).16
Gratifyingly, our preliminary investigation immediate-
ly showed very promising outcomes: within 24 hours at
50 ºC using 5 mol% of I2 as catalyst, substrate 1a1 was
converted to the cyclized COM product 2a and its isom-
erized product 2a’ in 62% total yield (~ 90% conver-
sion).16 Subsequent optimization studies (see page S3 in
the SI) revealed that the reaction could be carried out
smoothly and cleanly at ambient temperature and at-
mosphere in solvent-free conditions using 10 mol% I2
catalyst, giving the products 2a and 2a’ in 93% total
yield after purification.16 The optimal conditions were
effective for a wide range of substrates (Scheme 2).
2
3
4
5
6
7
8
9
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11
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Most of products 2 were obtained in moderate to ex-
cellent yields from generally clean intramolecular COM
reactions when substrates 1 bear the isopropylidene
moiety (i.e. when acetone is formed as a by-product,
Scheme 2, see page S5-S17 in the SI for the specific
structures of COM precursors 1).16 Substrates with ac-
tive olefin moieties bearing different substituents (such
as Ph or H) also cyclized via the COM reactions, albeit
with lower yields (Scheme 2, comparison of entries 1a1
to 1a2-1a3 and entries 1s1 to 1s2). This phenomenon
has been previously observed with transition metal Lew-
is acid catalysts7a-d,8 and our own tropylium catalytic
system. This new protocol can be practically carried out
on gram scale with very high efficiency, as demonstrat-
ed for substrates 1a1 and 1s1 to form 1.60 g of 2a and
1.51 g of 2s respectively (Scheme 2).16 The most notable
feature of this protocol is that it only required short reac-
tion time at ambient temperature to achieve similar re-
sults to the COM reactions promoted by other catalytic
systems7a-e,8-9,11 at harsher conditions.
When the distance between the carbonyl and the olefin
moieties was varied with different carbon chain linkers
(1’, Scheme 3a), the reaction outcomes changed vastly.
γ,δ-Olefin ketone (n = 1) gave the 3,4-dihydro-2H-pyran
4, presumably via a 6-endo-trig cyclization process simi-
lar to what were reported by Schindler and coworkers,17
while δ,ε-olefin ketone (n = 2) gave the normal COM
products (2a and 2a’). ε,ζ-Olefin ketone (n = 3), on the
other hand, did not convert to any cyclized products (see
page S19 in the SI for more unproductive ε,ζ-olefin
ketone substrates).16
presumably via
6-endo-trig cyclization of 4’
[see ref 17]
(a)
I
H
O
O
with n = 1
CO2Et
4, 89%
CO2Et
4’
As expected with the benign nature of the iodine cata-
lyst and the mild reaction conditions, this COM protocol
tolerates several types of functional groups. Most of the
non-nitrogen containing substrates (1a-1p) went through
the iodine-catalyzed COM reactions to give a mixture of
two regioisomeric products. When the functional group
at the α-position of the newly formed C-C double bond
is a alkoxycarbonyl group, the expected COM products
(2a-2d and 2h) were produced as major components.
When this functional group is an acyl group, phenyl ring
or methyl group, the isomerized olefins were formed as
the major products (2e’, 2g’ and 2o’). The formation of
these isomerized products can be attributed to isomeriza-
tion of the C-C double bond, generated after the COM
reactions, presumably due to traces amounts of Brønsted
acids present in the reaction mixture (Table 1, vide in-
fra). The Tiefenbacher group also reported similar ob-
servations in their Brønsted-acid catalyzed COM reac-
tions.9 These regioisomeric ratios changed with modifi-
cations of reaction conditions (Scheme 2) and we ob-
served the isomerization (2a to 2a’, see page S31 in the
SI for more details) when subjecting the pure product 2a
to the same I2-catalyzed COM reaction conditions.
with n = 2
COM
reaction
AND
O
10 mol% I2
n
CO2Et
CO2Et
neat, rt, 24 h
CO2Et
2a 93% (2a : 2a’ = 11 : 1)
2a’
1’
no COM reaction
no cyclization reaction
~ 80% recovered SM 1’
with n = 3
(see the SI page S19 for more details)
(b)
O
R
Ar
H
10 mol% I2
neat, rt, 24-72 h
Ar
O
7
5
R
3a
6
nBu
Me
Ph
CO2Me
7b, 34%
7a, 50%
7d, 31%
Me
7c, 39%
MeO
with 6 as
ring-opening
COM reaction
O
O
7f, 21%
7e, 50%
Scheme 3. (a) COM reactions with different chain
lengths; (b) Intermolecular COM reactions
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(entry 11), they only resulted in low conversion of 1a1
Page 4 of 9
This newly developed I2-catalyzed protocol was subse-
quently tested on the intermolecular COM reactions
between aromatic aldehydes 5 and isopropylidenyl ole-
fins 6 (Scheme 3b). This type of reaction were reported
previously by the Franzen group and our group using
tritylium6a and tropylium11 salts as catalysts, respective-
ly. In both cases, only low to moderate efficiencies were
obtained, most probably because the intermolecular
COM reaction is not as entropically favoured as the
intramolecular reaction. Our reactions afforded 31-50%
of the intermolecular COM adducts (7a-7d, Scheme 3b),
which were comparable results to previous studies.6a,11
The intermolecular ring-opening COM reactions with 1-
methylcyclopentene, identified as the best substrate for
this type of reaction in our previous study,11 also gave
low product yields (7e and 7f). Nevertheless, these reac-
tion outcomes are comparable with similar reactions
promoted by our tropylium catalyst11 or Schindler’s
gallium(III) catalyst,7e which potentially paves the way
for future development in this field based on the simplic-
ity of the iodine catalytic system.
1
2
3
4
5
6
7
8
to the product.
Two other iodonium sources, namely NIS and ICl, were
also tested as catalysts for this COM reactions (entries
12 and 15). These reactions gave very positive out-
comes, supporting the iodonium-catalyzed pathway with
I2 catalyst. That it was not the succinimide component
catalyzing the reaction is confirmed by entry 14 where
NBS could not convert any of 1a1 to the products. Inter-
estingly, when we added DMSO (20 mol%, 2 equiv to
NIS catalyst, entry 13, Table 1), a very good iodonium-
binding solvent,20 to the reaction, it completely turned
off the catalytic activity of NIS. Similar results were
observed with the addition of DMSO (20 mol%) to the
original I2 (10 mol%) catalyzed reaction conditions (en-
try 16, compared to entry 1), which was not too surpris-
ing as DMSO can also coordinate to I2.21 The addition of
potassium iodide (10 mol%), which could suppress the
formation of iodonium ion (I+) and combine with mo-
9
10
11
12
13
14
15
16
17
18
19
20
21
22
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48
49
50
51
52
53
54
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59
60
-
lecular iodine to form triiodide (I3 ), also negatively
affected the reaction outcomes (entry 17). These exper-
iments once again confirmed the possibility of the io-
donium ion being the actual active catalyst in this COM
reaction.
At this stage, it became very interesting to us to under-
stand how such a simple catalytic system like iodine can
promote this previously considered challenging COM
reaction. In principle, there are four potential pathways18
how this iodine-promoted reaction can proceed
through:13a,13b,13e (i) Brønsted-acid catalyzed9 pathway
with HI formed in situ from I2;13e (ii) Radical-initiated
pathway from homolytic cleavage of I2 (by light or
air);19 (iii) Halogen-bonding assisted pathway with mo-
lecular iodine I-I;18a (iv) Lewis-acid catalyzed pathway
with iodonium ion (I+) formed in situ by the heterolytic
cleavage of I2.18a A halogen-bond activation was recent-
ly proposed for the iodine-catalyzed Michael addition to
α,β-unsaturated carbonyls as both Brønsted-acid and
iodonium-ion catalysis were unlikely under the reaction
conditions.18
Due to the presence of moisture, it is possible that
some hypoiodous acid (HOI) could form from the dis-
proportionation of the molecular iodine and play some
roles in this reaction.22 However, under oxidative condi-
tions such as in entry 11, which should favor the for-
mation of HOI,23 the reaction outcomes were rather
poor. We further examined this possibility by carrying
out the COM reaction with 10 mol% I2 in the presence
of 10 mol% KOH (entry 18, Table 1), which could form
potassium hypoiodite (KOI) in situ. This reaction gave a
messy mixture with only trace amounts of the wanted
COM products, suggesting that a hypoiodous/hypoiodite
pathway is unlikely. On the other hand, although we
cannot completely rule out the possibility of activation
by direct halogen-bonding interaction from molecular
iodine based on the experimental investigations,18a en-
tries 19-22 in Table 1 were indicative that halogen-
bonding activation is unlikely to be the driving force for
this type of reaction. Indeed, the use of catalytic or stoi-
chiometric amounts of pentafluorophenyl iodide (entry
19), a frequently used halogen-bond donor,24 did not
result in any reaction. Similarly, using tri-
phenylphosphine diiodine (entry 20) and Huber’s mono-
dentate or bidentate iodoazolium salts25 (entries 21-22),
all very good halogen-bonding donors but not iodonium
sources, did not lead to formation of the COM products.
Thus, we carried out a range of mechanistic studies to
get further insights into the mode of activation by iodine
(Table 1, see page S24 in the SI for more details).16 Re-
placement of elemental iodine with HI or KI resulted in
non-productive reactions (entries 2-3, Table 1), suggest-
ing that iodide anion and Brønsted acid have no signifi-
cant role in this reaction. Carrying the reaction with I2
catalyst in the dark (entry 4) or with a radical scavenger
(BHT, see entry 8) still gave full conversions of 1a1 to
the products while BHT itself has no effect on the reac-
tion (entry 9), hinting that the radical pathway can also
be ruled out. A series of reactions with I2 catalyst, where
we excluded the presence of moisture and air (entry 5)
or just air (entries 6-7), met with significant reductions
in the conversions of 1a1. These demonstrated that air
did participate in promoting the reaction, most likely
through the oxidation of molecular iodine or iodide ion
to higher oxidation states. However, when we tried to
recreate this oxidative environment in a controlled man-
ner using m-CPBA (entry 10) or hydrogen peroxide
We furthermore carried out kinetic studies to deter-
mine the reaction order with respect to the iodine cata-
1
lyst. The kinetic studies were performed by H NMR
spectroscopy at different catalyst loadings (8 to 14
mol%), as the reaction was too slow or too fast outside
this range.16 For higher iodine loadings (>10 mol%) we
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ACS Catalysis
observed a good linear correlation with a slope of 1 in
double-logarithmic plots. The data point for low catalyst
loading (8 mol%) deviates slightly from the above and if
it was taken into account, a slope close to 2 was obtained
(see page S26 in the SI). These outcomes were reproduc-
ible from a triplicate. Based on the kinetic data, it is
rather unlikely that I3 or any other higher iodine aggre-
gate is involved in the rate-limiting transition state. Ar-
guably, the reaction order in the catalyst is around 1 and
-
1
2
3
4
5
6
Table 1. Mechanistic studies of the I2-catalyzed COM reaction with substrate 1a116
7
8
9
O
cat.
+
+
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
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42
43
44
45
46
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53
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60
O
CO2Et
CO2Et
neat, rt, 24 h
CO2Et
1a1
2a (major)
2a’ (minor)
3a
Entrya
1
Catalyst (10 mol%)
Additive
Conditionsb
air, lab light
air, lab light
air, lab light
air, in the dark
N2, lab light
N2, lab light
N2, in the dark
air, lab light
air, lab light
N2, lab light
N2, lab light
air, lab light
air, lab light
air, lab light
air, lab light
air, lab light
air, lab light
air, lab light
Conversion
100%
no reaction (8%)d
no reaction
100%
I2
-
-
-
-
-
2
KI
HI
I2
3
4
5
I2
30% (100%)d
6
I2
water (10 mol%)
water (10 mol%)
BHT (100 mol%)
BHT (100 mol%)
m-CPBA (10 mol%)
H2O2 (10 mol%)
-
10%
7
I2
16%
8
I2
100%
9
-
no reaction
7%
10
11
12c
13 c
14
15
16
17
18
I2
I2
10%
NIS
NIS
NBS
ICl
I2
48% (100%)d
no reaction
no reaction
62% (100%)d
3%
DMSO (20 mol%)
-
-
DMSO (20 mol%)
KI (10 mol%)
KOH (10 mmol%)
I2
12%
I2
messy reaction
F
F
F
I
19
-
air, lab light
no reaction
F
F
20
21
Ph3P-I2
-
-
air, lab light
air, lab light
no reaction
no reaction
nOct
N
I
N
OTf
Me
2 BArF
4
22
-
air, lab light
no reaction
N
N
N
N
I
I
nOct
nOct
aReaction conditions: substrate 1a (0.5 mmol) and catalyst/additive were stirred for 24 h at rt; bAir means the reaction was
carried out without exclusion of air. Normal lab light means fumehood lighting (4 x 13W fluorescent lamps); NIS was re-
c
crystallized; dConversion in the parentheses were recorded after 72 h.
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the iodine dissociation probably occurs only ‘partially’,
Page 6 of 9
unfavorable charge separation (see the computational SI
for more details), experimental data suggest equilibrium
constants between 1.4 × 10–5 (ΔG = +6.5 kcal mol–1) and
1.8 × 10–10 (ΔG = +13.3 kcal mol–1) for this process.26
As different solvation models (IEFPCM,27a refined
SMD,27b,c and CPCM27d–g) resulted in very similar ener-
gies, this deviation is most likely caused by charge sepa-
ration and only to a small extent by an insufficient solva-
tion model. Consequently, we decided to use the latter
experimental value for our calculations. As a conse-
quence, the calculated free energy differences will con-
stitute an upper limit for these processes and the real
number might even be smaller. Based on our calcula-
tions, the rate-limiting transition state is the nucleophilic
attack of the alkene onto the activated carbonyl (TS1,
Scheme 4), i.e., the first step of the [2+2]-cycloaddition.
All subsequent transition states are significantly lower in
energy. This energy profile is therefore slightly different
to that obtained by Schindler and coworkers for the
FeCl3-catalyzed reaction where all transition states were
comparable in energy.7a Our calculations furthermore
indicate that the addition of iodine to the double bond is
thermodynamically unfavorable (ΔG = +6.6 kcal mol–1)
and is consequently not observed under the reaction
conditions. Therefore, the computational data support
the picture of an iodonium-ion pathway as the origin of
the catalytic activity of molecular iodine in COM.
1
2
3
4
5
6
7
8
e.g., through the formation of very tight ion pairs.
Based on these mechanistic studies, we hypothesized a
mechanistic pathway in which the I+ ion acted as a Lew-
is acid to activate the carbonyl moiety and trigger the
oxetane formation event (1a1 to 10, Scheme 4). Presum-
ably, the oxetane intermediate 10 subsequently rearrang-
es to the cyclized product 2a similar to how it works
with the other acidic catalysts.6a,7a-d,8-9,11 To further
probe the reaction mechanism, we additionally em-
ployed DFT calculation at the M06-2X/aug-cc-
pVTZ/IEFPCM//M06-2X/6-311+G(d,p)/IEFPCM with
the aug-cc-pVTZ-PP for I] level to validate this pro-
posed mechanism (Scheme 4). In line with the experi-
mental observation that the reverse reaction of a mixture
of 2a and 3a (in excess) did not proceed to form 1a1
under the same catalytic conditions (see page S31 in the
SI),16, the calculations predict a substantial thermody-
namic driving force for the COM reaction (Scheme 4,
ΔG = –11.9 kcal mol–1). Furthermore, the computational
investigations indicate that a putative halogen-bond
activation by I2 requires an activation free energy of 51
kcal mol–1. Compared to the uncatalyzed reaction, this
pathway is still favourable (ΔΔG‡ = 6.7 kcal mol–1) but
very unlikely due to the high activation free energy (see
the computational SI for more details).
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Our calculations on an iodonium-ion pathway are
summarized in Scheme 4. While our calculations predict
a very endergonic splitting of molecular iodine due to
I
O
O
I
I
O
I
I2
I2
I
13
3a
I
I
O
O
TS4
O
O
TS1
TS2
TS3
+
+
Ph
Ph
Ph
Ph
Ph
Ph
Ph
MeO2C
MeO2C
CO2Me
CO2Me
MeO2C
12
MeO2C
MeO2C
8
9
10
11
14
14
ΔG / kcal mol–1
TSuncat2
+57.6
+60
TSuncat1
+50.2
+50
+40
+30
+20
+10
TS1
+29.8
TS2
+22.9
TS4
+17.8
TS3
+16.1
10
+22.1
11
+10.1
9
12
+13.3
+13.3
0
+2.7
8 + I2
13 + 14
–2.4
0.0
–10
14 + 3a + I2
–11.9
–20
Scheme 4. Gibbs free-energy profile for the uncatalyzed and the iodonium-ion-catalyzed carbonyl-olefin metathesis.
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reactions using ketones as enophiles, J. Org. Chem. 1984, 49, 3988; (c)
CONCLUSION
Khripach, V. A.; Zhabinskii, V. N.; Kuchto, A. I.; Zhiburtovich, Y. Y.;
Gromak, V. V.; Groen, M. B.; van der Louw, J.; de Groot, A.
Intramolecular cycloaddition/cycloreversion of (E)-3β,17β-diacetoxy-
5,10-secoandrost-1(10)-en-5-one, Tetrahedron Lett. 2006, 47, 6715; (d)
Schopov, I.; Jossifov, C. A carbonyl-olefin exchange reaction — new
1
2
3
4
5
6
7
8
We have developed a new practical protocol for the
intramolecular carbonyl-olefin metathesis reactions
using elemental iodine as catalyst. This method is easy
to set up with very mild reaction conditions and involves
an inexpensive and benign catalyst while offering com-
parable outcomes to previously reported procedures.
Preliminary mechanistic studies revealed the important
role of the in situ generated iodonium ion, which might
promote the COM reaction via the activation of the car-
bonyl moiety. Further applications of this new method in
organic synthesis are ongoing and will be reported short-
ly.
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R. Protic-Solvent-Mediated Cycloisomerization of Quinoline and
AUTHOR INFORMATION
Corresponding Author
T.V. Nguyen, email: t.v.nguyen@unsw.edu.au
Funding Sources
The authors declare no competing financial interests.
ASSOCIATED CONTENT
Isoquinoline
Propargylic
Alcohols:
Syntheses
of
(±)-3-
Supporting Information
Demethoxyerythratidinone and (±)-Cocculidine, Angew. Chem. Int. Ed.
2013, 52, 11129; (h) Hong, B.; Li, H.; Wu, J.; Zhang, J.; Lei, X. Total
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Carbocation catalysed ring closing aldehyde–olefin metathesis, Chem.
Commun. 2018, 54, 12982.
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S. Iron(III)-catalysed carbonyl–olefin metathesis, Nature 2016, 533, 374;
(b) Ludwig, J. R.; Phan, S.; McAtee, C. C.; Zimmerman, P. M.; Devery, J.
J.; Schindler, C. S. Mechanistic Investigations of the Iron(III)-Catalyzed
Carbonyl-Olefin Metathesis Reaction, J. Am. Chem. Soc. 2017, 139,
10832; (c) McAtee, C. C.; Riehl, P. S.; Schindler, C. S. Polycyclic
Aromatic Hydrocarbons via Iron(III)-Catalyzed Carbonyl–Olefin
Metathesis, J. Am. Chem. Soc. 2017, 139, 2960; (d) Groso, E. J.; Golonka,
A. N.; Harding, R. A.; Alexander, B. W.; Sodano, T. M.; Schindler, C. S.
3-Aryl-2,5-Dihydropyrroles via Catalytic Carbonyl-Olefin Metathesis,
ACS Catal. 2018, 8, 2006; (e) Albright, H.; Vonesh, H. L.; Becker, M. R.;
Alexander, B. W.; Ludwig, J. R.; Wiscons, R. A.; Schindler, C. S. GaCl3-
Catalyzed Ring-Opening Carbonyl–Olefin Metathesis, Org. Lett. 2018,
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Zimmerman, P. M.; Wiscons, R. A.; Schindler, C. S. Interrupted carbonyl-
olefin metathesis via oxygen atom transfer, Science 2018, 361, 1363.
(8) Ma, L.; Li, W.; Xi, H.; Bai, X.; Ma, E.; Yan, X.; Li, Z. FeCl3-
Catalyzed Ring-Closing Carbonyl–Olefin Metathesis, Angew. Chem. Int.
Ed. 2016, 55, 10410.
Experimental procedures, characterization data, NMR spectra and
details of the computational investigations are available free of
charge on the ACS Publications website.
Keywords
Carbonyl-olefin metathesis; olefination; iodine; iodonium; cataly-
sis; metal-free
ACKNOWLEDGMENT
This work is financially supported by Australian Research
Council (grant DE150100517 to TVN). Additional support
from the Fonds der chemischen Industrie (Liebig scholar-
ship to MB) and the DFG (BR 5154/2-1) is gratefully
acknowledged. We are grateful to the Regional Computing
Center of the University of Cologne for providing compu-
ting time of the DFG-funded High Performance Computing
(HPC) System CHEOPS as well as for their support.
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Carbonyl-Olefin Metathesis (COM) Reaction
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R2
R1
R2
R1
cat. I2 10 mol%
neat, rt, 24 h
O
O
27 examples
21-96%
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practical on gram-scale
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