Complementary Reactivity of 1,6-Enynes with All-Metal Aromatic Trinuclear Complexes and Carboxylic Acids

Article abstract of DOI:10.1055/s-0037-1611653

The distinct reactivity of 1,6-enynes in the presence of a trinuclear metal complex activated by a carboxylic acid is presented. The triplatinum catalyst enables the cyclization of the substrate and subsequent incorporation of a nucleophile in the final product. In contrast, sequential cyclization/double bond shift occurs under analogous conditions in the presence of the corresponding tripalladium complex.

Full text of DOI:10.1055/s-0037-1611653

SYNTHESIS
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Georg Thieme Verlag Stuttgart· New York
2019, 51, A–I
feature
A
en
C. Cecchini et al.
Feature
Synthesis
Complementary Reactivity of 1,6-Enynes with All-Metal Aromatic
Trinuclear Complexes and Carboxylic Acids
Chiara Cecchinia
Matteo Lanzia
Gianpiero Ceraa
Max Malacria*b
Giovanni Maestri*a
Me
Pt
X
S
PR'3
R'3P
Me
OAc
R1
(E)-enynes
M
S
M
H
R
S
0
0
0
0-
0
0
0
2-3
5
6
3-3
5
0
8
M
11 examples
Me
X
up to 70% yield
SbF6
0
0
0
0-
0
0
0
2-0
2
4
4-8
6
0
5
PR'3
AcOH
R1
a Università di Parma, Dipartimento di Scienze Chimiche, della Vita e
della Sostenibilità Ambientale, 17/A Parco Area delle Scienze, 43124
Parma, Italy
X
H
Pd
H
(Z)-enynes
giovanni.maestri@unipr.it
b UPMC Sorbonne Université, IPCM (UMR CNRS 8232), 4 place Jussieu,
C. 229, 75005 Paris, France
4 examples
32–70% yield
max.malacria@upmc.fr
Published as part of the 50 Years SYNTHESIS – Golden Anniversary Issue
Received: 30.11.2018
Accepted: 18.12.2018
Published online: 18.01.2019
DOI: 10.1055/s-0037-1611653; Art ID: ss-2018-z0806-fa
ry phosphine, and a disulfide in the presence of a redox ac-
tive chlorinated solvent to afford the desired C3-symmetric
trinuclear cluster. These complexes can be crystalized upon
anion metathesis with a suitable silver salt, providing a
bench- and air-stable tool for further synthetic purposes.
License terms:
Abstract The distinct reactivity of 1,6-enynes in the presence of a tri-
nuclear metal complex activated by a carboxylic acid is presented. The
triplatinum catalyst enables the cyclization of the substrate and subse-
quent incorporation of a nucleophile in the final product. In contrast, se-
quential cyclization/double bond shift occurs under analogous condi-
tions in the presence of the corresponding tripalladium complex.
Me
M
0dban
(1 equiv)
CHCl3 (0.1 M)
N2, r.t., 2 h
S
PR'3
R'3P
Me
M
S
M
PR'3 (1 equiv)
S
then
M
Me
AgSbF6 (0.33 equiv)
(MeS)2 (1 equiv)
SbF6
PR'3
Key words enynes, palladium, platinum, clusters, aromaticity, cycliza-
tion
(A): 30%
(B): 97%
M
=
=
Pt , R' = p-Tol
Pd , R' = Ph
M
All-metal aromatic clusters represent an intriguing class
of organometallic molecules characterized by delocalized
metal–metal bonds, which parallel their classical carbon-
based counterparts.1 Thanks to the variety of electronic
states offered by metal atoms compared to main group ele-
ments, it has been possible to push the known boundaries
of chemical bonding in the last two decades.2 This includes
rather exotic molecular orbitals ones such as δ- and φ-type
bonds,3 which cannot be observed in carbon-based mole-
cules, as well as examples of multidimensional electronic
delocalization that crumpled the traditionally flat land-
scape of regular aromatic rings.4 However, while an ample
mix of fascinating structures has been reported both at the
molecular level and in material sciences, their limited
bench stability has for a long time hampered thoughtful
study of the consequences of this bonding mode on organic
synthesis.1–4
Pd-Pd = 2.842 Å
Pd-S = 2.289 Å
Pd-P = 2.261 Å
Pt-Pt = 2.867 Å
Pt-S = 2.290 Å
Pt-P = 2.243 Å
Complex B':
(R' = p-Tol)
Complex A:
PdPdPd = 60.0°
PdSPd = 77.2°
PtPtPt = 60.0°
PtSPt = 77.9°
Scheme 1 One-pot synthesis of trinuclear M3+ complexes used in this
study and comparison of their main structural features at the solid state
Very recently, our group established a straightforward
synthetic approach for the synthesis of all-5d M3+ metal ar-
omatic complexes, whose synthesis is robust and can be ac-
complished in a modular fashion (Scheme 1).5 The reaction
uses a zero-valent palladium or platinum complex, a tertia-
This method allowed for a rapid yet still open investiga-
tion on the reactivity of these clusters as powerful catalysts
in synthetic organic transformations. Particularly, trinucle-
ar palladium complexes were reported to promote highly
efficient semi-reduction of alkynes under hydrogen-trans-
Georg Thieme Verlag Stuttgart · New York — Synthesis 2019, 51, A–I

B
C. Cecchini et al.
Feature
Synthesis
Biographical Sketches
Chiara Cecchini obtained her
transition metal–oxo complexes
under the supervision of Prof.
Stefano Zacchini. She then
moved to the University of Par-
ma where she began her Ph.D.
in the laboratory of Prof.
Giovanni Maestri. Her current
work focuses on transition-met-
master degree in Industrial
Chemistry in 2016 at the Uni-
versity of Bologna. She studied
the biorelevant activity of late
al-catalyzed
tions.
cycloisomeriza-
Matteo Lanzi obtained his
M.Sc. in Industrial Chemistry at
the University of Parma in 2014.
He then joined the group of G.
Maestri at the University of Par-
ma, where he is currently com-
pleting his Ph.D. thesis. During
this period he studied catalytic
methods to attain molecular
tions and he spent a research
stay at ICSN with Géraldine
Masson, working on novel pho-
tocatalyzed reactions.
complexity via domino
reac-
Gianpiero Cera studied chem-
istry at the University of Bolo-
gna and completed his Ph.D.
there in 2014 with Prof. M.
Bandini working on gold-cataly-
sis. During this period, he spent
six months in the group of Prof.
D. Toste at the University of Cal-
ifornia, Berkeley (Marco Polo fel-
low). He then moved to the
group of Prof. L. Ackermann at
the Georg-August-Universität,
Gö ttingen as an AVH fellow,
working on C–H functionaliza-
tions. He is currently a post-
doctoral researcher at the Uni-
versity of Parma with Prof. G.
Maestri. His main research ac-
tivities regard the development
of metal-catalyzed alkynes
functionalizations.
Max Malacria obtained his
Ph.D. from the University of Aix-
Marseille III with Prof. Marcel
Bertrand. He was appointed as
Assistant in 1974 at the Univer-
sity of Lyon I with Prof. J. Goré.
After almost two years as a
postdoctoral fellow with Prof. K.
P. C. Vollhardt at Berkeley, he
went back to the University of
Lyon as Maître de Conférences
in 1983. In 1988, he was ap-
pointed as Full Professor at the
UPMC. In 1991, he was elected
junior member of the Institut
Universitaire de France and pro-
moted to senior member in
2001. He directed the ICSN in
Gif sur Yvette from 2011 to
2015 and he is now member of
the European Academy of Sci-
ences.
Giovanni Maestri obtained
his Ph.D. from the University of
Parma under the guidance of
Prof. Marta Catellani. In 2011,
he began a postdoc stay at
UPMC with Louis Fensterbank
and Emmanule Lacote and then
followed Max Malacria at ICSN
as post-doctoral researcher in
2012. In 2014, he moved back
to his Alma Mater, first recruited
as Assistant Professor and cur-
rently serving as tenured Profes-
sor. His main interests swirl
around various aspects of or-
ganometallic chemistry, from
catalytic synthesis through cas-
cades to computational chemis-
try applied to mechanistic and
bonding riddles.
Georg Thieme Verlag Stuttgart · New York — Synthesis 2019, 51, A–I

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C. Cecchini et al.
Feature
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fer conditions and unconventional cycloisomerization/di-
merization of 1,6-enynes to form highly decorated tricyclic
structures, or cross-coupling reactions.6
complexes could hold potential for synthetic purposes in-
stead, thus enabling a comparison with its widely-em-
ployed mononuclear peers.
In order to provide wider applications to this family of
all-metal aromatic clusters, we now turned our attention
on trinuclear platinum clusters, whose solid-state struc-
tures evenly overlap with those of their palladium ana-
logues.5a In particular, the two clusters share nearly identi-
cal metal–metal, metal–sulfur, and metal–phosphine dis-
tances, differences remaining below 0.03 Å at the solid
states. Similarly, angles and dihedrals remain almost identi-
cal too, as witnessed by their perfectly equilateral trimetal-
lic core. An ample mix of theoretical tools and experimental
magnetic measures suggest perfect coincidence of delocal-
ized bonding, which is responsible for the aromatic charac-
ter of these complexes.
In order to fill this lack and create a parallel to precedent
contributions in the field of catalytic cycloisomerization of
enynes, we focused on the reactivity of model substrate (E)-
1a in the presence of complex A (Table 1). Preliminary in-
vestigations on solvent effect, revealed the formation of
pyrrolidine derivative 2a when using acetic acid, as an equi-
molar additive, in the presence of 0.3% of catalyst A in tolu-
ene (Table 1, entries 1–3). A reaction conducted in the ab-
sence of the acidic additive (entry 4), reflected the impor-
tance of the former. Using AcOH as the solvent, compound
2a was isolated in 42% yield (entry 5). Encouraged by these
results we continued the optimization of the reaction con-
ditions fixing AcOH as the solvent for the cycloisomeriza-
tion reaction. A strong effect was discovered by the addition
of co-catalytic amounts of the phosphine ligand which, by
ensuring a more stabilizing environment, led to the isola-
tion of 2a in 72% yield although with prolonged reaction
times (entries 6–8). Comparable efficacy was obtained in-
creasing the catalyst loading to 0.6 mol% in 16 hours (entry
9). Finally, the palladium analogue B was found to be less
competent for the reaction, leading to 2a in a meagre 16%
yield (entry 10).
We speculated that this could have been of interest for
activation of unsaturated substrates because mononuclear
platinum salts have found large application in catalytic cy-
cloisomerization reactions, with seminal contributions by
Fürstner,7 Echavarren,8 and others.9 Surprisingly, while
more than one hundred structures of trinuclear platinum
clusters have been characterized at the solid state, none of
them has been reported to trigger any C–C bond-forming
+
reaction. This led us to speculate whether aromatic Pt3
The chemoselectivity of the catalyst is highly influenced
by the nature of the carboxylic acid additive. Indeed, run-
ning the reaction in the presence of (E)-1a and equimolar
amounts of benzoic acid in toluene, bicyclic product 2a′ was
isolated as the major product in the reaction mixture
(Scheme 2).
Table 1 Optimization of Reaction Conditionsa
Me
S
Pt
PR'3
R'3P
Me
Pt
S
S
cat.
Pt
PR'3
PR'3 cat.
Me
A
Me
SbF6
OAc
TsN
TsN
S
PR'3
R'3P
Me
H
Ph
Pt
S
Pt
H
Ph
AcOH, N2, 110 °C
S
Pt
Me
1a
2a
R' = p-Tol
(0.6 mol%)
A
H
SbF6
TsN
PR'3
TsN
H
Entry
Complex A Solvent
(mol%)
PR′3 (mol%) Time
Yield
(%)b
BzOH (1.0 equiv)
toluene, N2, 110 °C
Ph
Ph
H
(h)
R' = p-Tol
1a
2a' = 36%
1
2
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.6
0.6
1,4-dioxane
–
16
16
16
16
16
16
24
44
16
16
N.R.
N.R.
29
Scheme 2 Acid-dependent cycloisomerizations of 1,6-enynes with tri-
1,2-DCE
toluene
toluene
AcOH
–
nuclear platinum complex
3
–
4c
5d
6
–
N.R.
42
Subsequently, a family of differently substituted (E)-1,6-
enynes 1 were prepared in order to prove the generality of
the methodology (Scheme 3). The tethering group ability
was then investigated. Indeed, sulfonamide 1b and dialkyl
malonyl units 1c,d were efficiently converted in moderate
to good yields, with these latter opening access to a family
of cyclopentane derivatives. Next, we found several func-
tional groups such as ether, fluoro, and trifluoro units on
the cinnamyl moiety to be tolerated (Scheme 3, 2e–g). The
aromatic phenyl ring could be replaced by naphthalene
rings as well as different alkene derivatives such as dimeth-
ylallyl, crotyl, and the geranyl scaffold, providing the corre-
–
AcOH
0.9
1.8
2.7
1.8
1.8
53
7
AcOH
57
8
AcOH
72
9
AcOH
71
10e
AcOH
16
a Reaction conditions: 1a (0.15 mmol), A (0.6 mol%), AcOH (0.15 mmol),
solvent (0.3 M), isolated yields.
b N. R.: No reaction.
c Reaction without AcOH.
d Conditions: 1a (0.15 mmol), A (0.6 mol%), AcOH (500 μL, 0.3 M).
e Reaction with complex B (0.6 mol%).
Georg Thieme Verlag Stuttgart · New York — Synthesis 2019, 51, A–I

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C. Cecchini et al.
Feature
Synthesis
sponding pyrrolidines 2h–k in synthetically useful yields.
Products 2a–c and 2e–k were obtained with high diastereo-
control (dr >20:1). Their relative configuration has been as-
signed on the basis of NOESY NMR correlation experiments,
which revealed the anti-relationship between the two pro-
tons bonded to the contiguous stereogenic carbon atoms.
We similarly observed no trace of conversion of 3a. Howev-
er, use of this substrate in combination with palladium
complex B led to the formation of bicyclic 1,4-diene scaffold
4a in good yields (Scheme 4a).10 Once again, the use of a
mild carboxylic acid proved crucial for triggering any reac-
tivity, no enyne conversion being otherwise observed.11
Me
Me
a)
S
S
PR'3
Me
PR'3
R'3P
Me
R'3P
Me
a)
M
S
M
M
S
M
(0.6 mol%)
(1.0 mol%)
S
S
M
M
Me
TsN
H
SbF6
SbF6
OAc
PR'3
PR'3
TsN
TsN
TsN
H
H
Ph
PR'3 (1.8 mol%)
AcOH, N2, 110 °C
R' = p-Tol
BzOH (1.0 equiv)
toluene, N2, 110 °C
H
Ph
1a
2a
4a
3a
M
=
=
Pt , R' = p-Tol
2a: 71%
2a: 16%
M
(A)
(B)
=
=
Pt , R' = p-Tol
(A)
(B)
4a : -
Pd , R' = Ph
M
4a : 69%
Pd , R' = Ph
M
R
R
R
b)
R
R1
b)
R1
A
(0.6 mol%)
B
(1.0 mol%)
X
X
X
X
H
OAc
R1
H
PR'3 (1.8 mol%)
AcOH, N2, 110 °C
R' = p-Tol
BzOH (1.0 equiv)
toluene, N2, 110 °C
R
R
R1
4
2
1
3
E
E
Me
OAc
OAc
Me
H
MsN
O
E
Me
E
OAc
Me
E
H
Ph
H
Ph
TsN
H
H
TsN
H
H
E
H
Me
H
H
H
O
H
2b: 40%
E = CO2Me, 2c: 70%
E = CO2Me, 2d: 56%
Ph
E = CO2Me, 4d: 70%
4b: 66%
4c: 32%
4e: 44%
OAc
H
OAc
H
OAc
OAc
H
TsN
TsN
TsN
TsN
Scheme 4 Scope of the palladium-catalyzed reaction with (Z)-enynes
H
H
H
H
H
F
CF3
This synthetic application presented a quite wide gen-
erality and a family of bicyclic compounds was synthesized
by employing different tethering units 4b–e (Scheme 4b). In
contrast to observations made using 1,6-enynes with a
trans-alkene arm,6a products 4 present a formal shift of the
olefinic double bond and no traces of the corresponding
1,3-diene have been observed. In all cases, a high level of di-
astereoselection was observed (dr >20:1), even though ra-
cemic substrates were used. The relative syn-configuration
of bridgehead CH groups has been established through
NMR correlation experiments. This structural feature paral-
lel previous observations made on enantioenriched 1,6-
enynes using mononuclear palladium catalysts.12
We then performed some labeling experiments to get
insights into the reaction mechanism. A reaction conducted
with model substrate 1a in AcOH-d4, led to a highly unusual
double incorporation of deuterium on the gem-methylene
unit to form [D]2-2a in good yield (57%, Scheme 5, top). In
particular, D-labeling occurred with 90% and 63%, respec-
tively.
OMe
2e: 44% (dr 1:1)
Me
2f: 36%
2g: 41%
2h: 43%
OAc
Me
TsN
TsN
OAc
TsN
OAc
Me
H
H
Me
Me
Me
H
Me
2i: 70%
2j: 59%
2k: 43%
Scheme 3 Scope of the platinum-catalyzed reaction with (E)-enynes
At this point, we became interested in the reactivity of
cis-1,6-enynes in cycloisomerization reactions catalyzed by
all-aromatic clusters. To this end, 3a was synthesized and
submitted to the previously optimized catalytic conditions.
Surprisingly, platinum cluster A failed to promote any
transformation. The reaction was then performed using just
one equivalent of carboxylic acid and without any addition-
al phosphine, which were the conditions adopted for the
cycloisomerization of enynes with palladium cluster B.6a
Georg Thieme Verlag Stuttgart · New York — Synthesis 2019, 51, A–I

E
C. Cecchini et al.
Feature
Synthesis
Me
demetalation would then liberate product [D]2-2a. The ab-
sence of reactivity observed using substrates 3 could be
consistent with the steric strain associated with the forma-
tion of the tricyclic intermediate corresponding to complex
D. The loss of stereocontrol observed using substrate 1e,
which has an electron-rich anisole fragment that can stabi-
lize the benzylic carbocation of intermediate G, might,
however, be more in agreement with the second manifold
instead.
S
PR'3
Me
R'3P
Me
D
Pt
S
Pt
S
(0.6 mol%)
D
Pt
TsN
SbF6
OAc
PR'3
H
H
PR'3 (1.8 mol%), 100 °C
Ph
R' = p-Tol
H
R = Ac, [D]2-2a
TsN
ROD
D
Ph
H
OMe
cat. PtCl2
H
TsN
1a
TsN
(as in Ref. 8c)
Pt
X
[D]2-2a + Pt
AcOD
AcO
H
H
Ph
Ph
1a
Pt
X
R = Me, [D]-2l
Pt
H
D
as above
Ph
Ph
TsN
TsN
OAc
TsN
TsN
X
OAc
E
Ph
H-X
H
H
Ph
Ph
Ph
AcOD
1m
2m
Pt
Scheme 5 Mechanistic probes
Pt
TsN
TsN
C
Ph
D
[2+2]
Ph
This result is in sharp contrast to previously findings in
PtCl2-catalyzed alkoxycyclizations of enynes, in which a
single deuterium atom was singularly incorporated under
similar reaction conditions.8c It is worth noting that no H/D
exchange was observed by treating 1a with AcOH-d4. Inter-
nal alkyne derivative 1m was unreactive under standard re-
action conditions (Scheme 5, bottom). These results show
that the presence of a terminal alkyne group is crucial for
triggering any reactivity with the trinuclear platinum com-
plex and that their acetylenic CH is most likely activated
during the catalytic cycle.
H
[D]2-2a Pt
AcO
Pt X
+
TsN
Ph
AcOD
Pt
X
1a
Pt
H
D
TsN
TsN
H
OAc
Ph
Ph
Pt
X
Pt
X
The reaction was finally followed by 31P NMR spectros-
copy. Interestingly, after four hours, decomposition of clus-
ter A was observed along with the formation of new, not yet
identified species. For the sake of comparison, complex B is
on the contrary stable under similar conditions.6a
Pt
X
H
X
Pt
AcOD
Pt
Pt
TsN
X
TsN
Ph
Ph
G
F
These findings, taken together, are suggestive of a com-
plimentary mood of action with respect to well established
soft electrophilic π-activation by means of gold catalysis
(Scheme 6).13 Particularly, in order to explain the deuterium
labeling experiment, we propose an initial formation of
platinum acetylide complex C. Upon this σ-activation of the
alkyne, a formal [2+2] cycloaddition forms key metalated
cyclobutene D, which further undergoes ring opening by
the acetic acid. This generates vinylplatinum complex E, in
which the first H/D scrambling has already took place. Pro-
todemetalation eventually delivers desired product [D]2-2a.
However, a dual σ,π-activation could not be excluded at this
stage of the investigation.14 In this case, the electron-rich
alkene arm of diplatinum complex F can attack the electro-
philic alkyne carbon to yield carbocationic complex G. Sub-
sequent formal quench by an acetate anion and dual proto-
Scheme 6 Plausible catalytic cycles for the synthesis of [D2]-2a
In conclusion, we have reported on the unprecedented
use of all-metal aromatic clusters in catalytic cycloisomeri-
zations of 1,6-enyne derivatives. The proper choice of the
catalyst allowed for the chemoselective synthesis of valu-
able classes of cyclic and bicyclic derivatives in good yields
and functional group tolerance. Mechanistic hints allowed
us to propose a new mode of activation for these clusters,
which will be useful for further exploration of the possibili-
ties of multinuclear complexes for catalytic synthesis.
Reactions were performed under standard Schlenk technique using
commercial reagents used as received. Solvents were dried and stored
over molecular sieves previously activated in an oven (450 °C over-
Georg Thieme Verlag Stuttgart · New York — Synthesis 2019, 51, A–I

F
C. Cecchini et al.
Feature
Synthesis
night). Catalytic reactions required the use of anhydrous solvents.
Chromatographic purifications were performed under gradient using
a Combiflash® system and prepacked disposable silica cartridges.
1H NMR (300 MHz, CDCl3): δ = 7.71 (d, J = 8.2 Hz, 2 H), 7.37–7.25 (m, 7
H), 5.71 (d, J = 7.1 Hz, 1 H), 4.92 (d, J = 2.0 Hz, 1 H), 4.53 (d, J = 2.1 Hz,
1 H), 3.87–3.73 (m, 2 H), 3.43–3.33 (m, 2 H), 3.18–3.12 (m, 1 H), 2.46
(s, 3 H), 2.01 (s, 3 H).
Complex A
[4-(Methylene-d2)-1-tosylpyrrolidin-3-yl](phenyl)methyl Acetate-
d3 ([D]2-2a)
Pt(dba)3 (90 mg, 0.1 mmol, 1 equiv) was added to a 50 mL Schlenk
flask, which underwent at least three vacuum/N2 cycles. P(p-tol)3 (31
mg, 0.1 mmol, 1 equiv) was added under N2. Then, freshly degassed
CHCl3 (10 mL) and dimethyl disulfide (9.5 mg, 0.05 mmol, 0.5 equiv)
were immediately syringed through the septum. The resulting solu-
tion was kept under stirring at r.t. for 2 h and AgSbF6 (12 mg, 0.033
mmol, 0.33 equiv) was then added under N2. The solution was kept in
the dark. Stirring was maintained for 1 h and the mixture was then
filtered under N2 through a short pad of Celite to remove traces of
black metals. The solvent was removed under vacuum to leave a deep
yellow-brown solid that was washed with a CHCl3/hexane solution
(1:30 v/v, 3 × 20 mL). Desired cluster was purified by chromatography
on silica gel using acetone/hexane under gradient as eluent. Recrys-
tallization by vapor diffusion using THF/hexane eventually provided
the pure complex as yellow crystals; yield: 15 mg (30%). Their spec-
troscopic data correspond to the literature.5a
Product [D]2-2a was isolated following GP-1 as a pale yellow oil (57%,
33 mg, 0.086 mmol) using 1a (50 mg, 0.15 mmol) and AcOH-d4 as sol-
vent.
IR (neat): 3032, 2921, 1740, 1344, 1158, 1042, 583 cm–1
.
1H NMR (300 MHz, CDCl3): δ = 7.71 (d, J = 8.2 Hz, 2 H), 7.37–7.23 (m, 7
H), 5.72 (d, J = 7.1 Hz, 1 H), 4.90 (d, J = 2.0 Hz, 0.1 H), 4.52 (d, J = 2.1 Hz,
0.37 H), 3.86–3.74 (m, 2 H), 3.43–3.34 (m, 2 H), 3.18–3.13 (m, 1 H),
2.46 (s, 3 H).
13C NMR (101 MHz, CDCl3): δ = 169.7, 143.8, 142.7, 138.4, 132.7,
129.7, 128.5, 128.3, 127.8, 126.8, 109.9, 75.3, 52.5, 49.9, 48.1, 45.5,
21.6.
LC-MS: m/z calcd for C21H18NO4SNa [M + Na]+: 413.1; found: 413.3.
[4-Methylene-1-(methylsulfonyl)pyrrolidin-3-yl](phenyl)methyl
Acetate (2b)
Complex B
Pd(dba)2 (115 mg, 0.2 mmol, 1 equiv) was added to a 100 mL Schlenk
flask, which underwent at least three vacuum/N2 cycles. PPh3 (53 mg,
0.2 mmol, 1 equiv) was added under N2. Then, freshly degassed CHCl3
(20 mL) and dimethyl disulfide (19 mg, 0.1 mmol, 0.5 equiv) were im-
mediately syringed through the septum. The resulting solution was
kept under stirring at r.t. for 2 h and AgSbF6 (12 mg, 0.033 mmol, 0.33
equiv) was then added under N2. The solution was kept in the dark.
Stirring was maintained for 1 h and the mixture was then filtered un-
der N2 through a short pad of Celite to remove traces of black metals.
The solvent was removed under vacuum to leave a deep red solid that
was washed with a CHCl3/hexane solution (1:30 v/v, 3 × 30 mL). De-
sired cluster was directly purified by recrystallization via vapor diffu-
sion using acetone/hexane, eventually providing the pure complex as
red crystals; yield: 88 mg (97%). Their spectroscopic data correspond
to the literature.5a
Product 2b was isolated following GP-1 as a colorless oil (40%, 18.5
mg, 0.06 mmol) using 1b (37 mg, 0.15 mmol) as reagent.
IR (neat): 2926, 1740, 1328, 1225, 1148, 1049, 959, 699 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.35–7.29 (m, 5 H), 5.87 (d, J = 6.9 Hz, 1
H), 5.02 (s, 1 H), 4.68 (s, 1 H), 4.01–3.88 (m, 2 H), 3.55–3.44 (m, 2 H),
3.31–3.25 (m, 1 H), 2.82 (s, 3 H), 2.09 (s, 3 H).
13C NMR (101 MHz, CDCl3): δ = 169.9, 142.8, 138.2, 128.6, 128.5,
126.8, 110.6, 75.0, 52.3, 49.7, 48.7, 35.3, 21.1.
LC-MS: m/z calcd for C15H19NO4SNa [M + Na]+: 332.093; found:
332.217.
Dimethyl 3-[Acetoxy(phenyl)methyl]-4-methylenecyclopentane-
1,1-dicarboxylate (2c)
Product 2c was isolated following GP-1 as a pale yellow oil (70%, 36
mg, 0.105 mmol) using 1c (42 mg, 0.15 mmol) as reagent.
Catalytic Synthesis of 2; General Procedure 1 (GP-1)
IR (neat): 2952, 2362, 1730, 1372, 1226, 1022, 895, 699 cm–1
.
Complex A (1.7 mg, 0.9 mmol, 0.6 mol%) and freshly degassed AcOH
(0.5 mL) were added under N2 to a Schlenk-type flask. The desired
substrate 1 (0.15 mmol, 1 equiv) and P(p-tolyl)3 (0.8 mg, 2.7 mmol,
1.8 mol%) were sequentially added. The mixture was heated at 110 °C
and the conversion was followed by analyzing samples via TLC. Upon
complete conversion of the substrate, the solution was diluted with
EtOAc (5 mL) and purified.
1H NMR (300 MHz, CDCl3): δ = 7.35–7.25 (m, 5 H), 5.91 (d, J = 5.8 Hz, 1
H), 4.98 (d, J = 2.2 Hz, 1 H), 4.64 (d, J = 2.2 Hz, 1 H), 3.73 (s, 3 H), 3.69
(s, 3 H), 3.17–3.09 (m, 1 H), 2.94 (s, 2 H), 2.48–2.41 (m, 1 H), 2.23–
2.15 (m, 1 H), 2.07 (s, 3 H).
13C NMR (75 MHz, CDCl3): δ = 171.9, 171.7, 170.1, 146.9, 139.2, 128.4,
127.9, 126.6, 109.4, 76.3, 58.3, 52.8, 52.7, 47.6, 41.8, 35.4, 21.0.
LC-MS: m/z calcd for C19H22O6Na [M + Na]+: 369.1; found: 369.2.
Catalytic Synthesis of 4; General Procedure 2 (GP-2)
Complex B (3 mg, 0.002 mmol, 1 mol%) and freshly degassed toluene
(3.5 mL) were added under N2 to a Schlenk-type flask. The desired
substrate 3 (0.2 mmol, 0.06 M) and benzoic acid (24.5 mg, 0.2 mmol,
1 equiv) were sequentially added. The mixture was heated at 100 °C
and the conversion was followed by analyzing samples via TLC. Upon
complete conversion of the substrate, the solution was diluted with
EtOAc (5 mL) and purified.
Dimethyl 3-(2-Acetoxypropan-2-yl)-4-methylenecyclopentane-
1,1-dicarboxylate (2d)
Product 2d was isolated following GP-1 as a colorless oil (56%, 25 mg,
0.084 mmol) using 1d (42 mg, 0.15 mmol) as reagent.
IR (neat): 2953, 1729, 1367, 1230, 1076, 1018, 896, 610 cm–1
.
1H NMR (300 MHz, CDCl3): δ = 5.07 (s, 1 H), 4.96 (s, 1 H), 3.73 (s, 3 H),
3.71 (s, 3 H), 3.17–3.11 (m, 1 H), 2.88 (s, 2 H), 2.64–2.56 (m, 1 H),
2.04–1.99 (m, 1 H), 1.96 (s, 3 H), 1.49 (s, 3 H), 1.45 (s, 3 H).
(4-Methylene-1-tosylpyrrolidin-3-yl)(phenyl)methyl Acetate (2a)
13C NMR (75 MHz, CDCl3): δ = 171.8, 171.7, 170.3, 147.5, 111.2, 84,
58.5, 52.8, 50.3, 43.6, 35.7, 23.6, 22.8, 22.4.
Product 2a was isolated following GP-1 as a pale yellow oil (71%, 42
mg, 0.105 mmol) using 1a (50 mg, 0.15 mmol) as reagent. Spectra
correspond to the literature.15
Georg Thieme Verlag Stuttgart · New York — Synthesis 2019, 51, A–I

G
C. Cecchini et al.
Feature
Synthesis
LC-MS: m/z calcd for C15H22O6Na [M + Na]+: 321.1; found: 321.2.
IR (neat): 2924, 1737, 1344, 1223, 1160, 1093, 814, 547 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.82–7.80 (m, 3 H), 7.70–7.68 (m, 3 H),
7.50–7.48 (m, 2 H), 7.36–7.31 (m, 3 H), 5.86 (d, J = 7.2 Hz, 1 H), 4.88 (s,
1 H), 4.51 (s, 1 H), 3.86–3.77 (m, 2 H), 3.42–3.41 (m, 2 H), 3.28–3.21
(m, 1 H), 2.44 (s, 3 H), 2.03 (s, 3 H).
13C NMR (101 MHz, CDCl3): δ = 169.7, 143.8, 142.9, 135.7, 133.2,
132.9, 132.8, 127.9, 128.4, 128.1, 127.9, 127.7, 126.4, 126.4, 126.3,
124.3, 110.4, 75.6, 52.5, 50.0, 48.0, 21.6, 21.0.
(4-Methoxyphenyl)(4-methylene-1-tosylpyrrolidin-3-yl)methyl
Acetate (2e)
Product 2e was isolated following GP-1 as a colorless oil (44%, 27 mg,
0.066 mmol, dr 6:4) using 1e (53 mg, 0.15 mmol) as reagent.
IR (neat): 2922, 1737, 1513, 1344, 1227, 1159, 1027, 661 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.69 (d, J = 8.3 Hz, 2 H), 7.63 (d, J = 8.3
Hz, 2 H), 7.33 (t, J = 7.9 Hz, 4 H), 7.16 (d, J = 7.9 Hz, 4 H), 6.85–6.82 (m,
4 H), 5.62–5.56 (m, 2 H), 5.04 (d, J = 18.2 Hz, 2 H), 4.87 (d, J = 2.0 Hz, 1
H), 4.47 (d, J = 2.1 Hz, 1 H), 3.88–3.69 (m, 4 H), 3.80 (s, 3 H), 3.78 (s, 3
H), 3.44–3.40 (m, 1 H), 3.33–3.29 (m, 1 H), 3.16–2.96 (m, 4 H), 2.44 (s,
3 H), 1.99 (s, 3 H), 1.98 (s, 3 H).
13C NMR (101 MHz, CDCl3): δ = 169.8 (da), 169.7 (db), 159.7 (da),
159.5 (db), 144.2, 143.8 (da), 143.8 (db), 142.9, 132.8 (da), 132.7 (db),
130.5 (da), 130.0 (db), 129.7 (da), 129.7 (db), 128.7 (da), 128.3 (db),
127.8, 114.0 (da), 113.8 (db), 110.6 (da), 110.3 (db), 75.3 (da), 75.3
(db), 55.3 (da), 55.3 (db), 52.5 (da), 52.1 (db), 50.2 (da), 50.0 (db), 48.3
(da), 48.0 (db), 21.6, 21.1 (da), 21.0 (db).
LC-MS: m/z calcd for C25H25NO4SNa [M + Na]+: 458.1; found: 458.3.
2-(4-Methylene-1-tosylpyrrolidin-3-yl)propan-2-yl Acetate (2i)
Product 2i was isolated following GP-1 as a pale yellow oil (70%, 35
mg, 0.105 mmol) using 1i (41 mg, 0.15 mmol) as reagent. Spectra cor-
respond to the literature.16
1H NMR (300 MHz, CDCl3): δ = 7.68 (d, J = 8.2 Hz, 2 H), 7.34 (d, J = 8.0
Hz, 2 H), 5.04 (d, J = 10.6 Hz, 1 H), 3.86 (d, J = 12.1 Hz, 1 H), 3.71 (d, J =
13.7 Hz, 1 H), 3.71 (d, J = 13.7 Hz, 1 H), 3.41 (dd, J = 9.6, 3.1 Hz, 1 H),
3.33–3.31 (m, 1 H), 3.25–3.19 (m, 1 H), 2.42 (s, 3 H), 1.91 (s, 3 H), 1.45
(s, 3 H), 1.46 (s, 3 H).
LC-MS: m/z calcd for C22H25NO5SNa [M + Na]+: 438.1; found: 438.3.
1-(4-Methylene-1-tosylpyrrolidin-3-yl)ethyl Acetate (2j)
(4-Methylene-1-tosylpyrrolidin-3-yl)[3-(trifluoromethyl)phe-
nyl]methyl Acetate (2f)
Product 2j was isolated following GP-1 as a colorless oil (59%, 28 mg,
0.087 mmol) using 1j (35 mg, 0.15 mmol) as reagent.
Product 2f was isolated following GP-1 as a colorless oil (36%, 20 mg,
0.044 mmol) using 1f (59 mg, 0.15 mmol) as reagent.
IR (neat): 2926, 1734, 1372, 1343, 1159, 1092, 662, 547 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.71 (d, J = 8.2 Hz, 2 H), 7.34 (d, J = 8.0
Hz, 2 H), 5.01 (dd, J = 18.6, 2.0 Hz, 2 H), 4.96–4.93 (m, 1 H), 3.85–3.72
(m, 2 H), 3.43 (dd, J = 9.8, 7.9 Hz, 1 H), 3.27–3.23 (m, 1 H), 2.82–2.79
(m, 1 H), 2.43 (s, 3 H), 1.92 (s, 3 H), 1.18 (dd, J = 10.2, 5.9 Hz, 3 H).
13C NMR (101 MHz, CDCl3): δ = 170.1, 143.8, 143.8, 132.8, 129.7,
127.8, 109.4, 70.1, 52.5, 49.3, 47.5, 21.5, 21.0, 17.8.
IR (neat): 2979, 1751, 1329, 1226, 1163, 903, 722, 650 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.69 (d, J = 8.2 Hz, 2 H), 7.47–7.33 (m, 6
H), 5.70 (d, J = 7.3 Hz, 1 H), 4.92 (d, J = 1.7 Hz, 1 H), 4.46 (d, J = 1.7 Hz,
1 H), 3.78 (s, J = 6.2 Hz, 2 H), 3.41–3.30 (m, 2 H), 3.12–3.08 (m, 1 H),
2.44 (s, 3 H), 2.02 (s, 3 H).
13C NMR (101 MHz, CDCl3): δ = 169.6, 144.0, 142.5, 139.5, 130.4,
LC-MS: m/z calcd for C16H21NO4SNa [M + Na]+: 346.1; found: 346.2.
129.8, 129.0, 127.8, 127.2, 126.4, 125.2 (q, 2JC,F = 3.7 Hz), 123.5 (q, 3JC,F
1
= 3.7 Hz), 123.0 (d, JC,F = 273 Hz), 110.8, 74.7, 52.3, 49.8, 48.3, 21.5,
6-Methyl-2-(4-methylene-1-tosylpyrrolidin-3-yl)hept-5-en-2-yl
Acetate (2k)
20.9.
19F NMR (376 MHz, CDCl3): δ = –62.7.
LC-MS: m/z calcd for C22H22F3NO4SNa [M + Na]+: 476.1; found: 476.1.
Product 2k was isolated following GP-1 as a pale yellow oil (43%, 26
mg, 0.065 mmol) using 1k (35 mg, 0.15 mmol) as reagent.
IR (neat): 2923, 1734, 1345, 1237, 1160, 1094, 660, 589 cm–1
.
(3-Fluoro-4-methylphenyl)(4-methylene-1-tosylpyrrolidin-3-
yl)methyl Acetate (2g)
1H NMR (300 MHz, CDCl3): δ = 7.70 (d, J = 8.3 Hz, 2 H), 7.33 (d, J = 7.9
Hz, 2 H), 5.05–4.98 (m, 2 H), 3.92–3.67 (m, 2 H), 3.54–3.48 (m, 2 H),
3.23–3.17 (m, 2 H), 2.43 (s, 3 H), 2.06–2.89 (m, 2 H), 1.96 (s, 3 H),
1.81–1.72 (m, 1 H), 1.66 (s, 3 H), 1.67 (s, 3 H), 1.46–1.38 (m, 1 H), 1.31
(s, 3 H).
Product 2g was isolated following GP-1 as a colorless oil (41%, 25 mg,
0.062 mmol) using 1g (52 mg, 0.15 mmol) as reagent.
IR (neat): 2926, 1740, 1371, 1344, 1223, 1160, 662, 588 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.69 (d, J = 8.3 Hz, 2 H), 7.33 (d, J = 8.4
Hz, 2 H), 7.11 (t, J = 7.8 Hz, 1 H), 6.90–6.84 (m, 2 H), 5.62 (d, J = 7.1 Hz,
1 H), 4.91 (s, 1 H), 4.54 (s, 1 H), 3.84–3.71 (m, 2 H), 3.39–3.30 (m, 2 H),
3.10–3.06 (m, 1 H), 2.44 (s, 3 H), 2.23 (s, 3 H), 1.99 (s, 3 H).
13C NMR (75 MHz, CDCl3): δ = 170.2, 143.7, 132.5, 132.0, 129.7, 127.8,
127.2, 123.4, 111.5, 85.4, 53.2, 49.6, 49.1, 35.3, 25.7, 22.2, 22.0, 21.5,
20.6, 17.6.
HRMS: m/z calcd for C22H31NO4SNa [M + Na]+: 428.1875; found:
428.1869.
13C NMR (101 MHz, CDCl3): δ = 169.6, 161.1 (d, 1JC,F = 245 Hz), 143.9,
4
142.7, 138.1, 132.7, 131.5 (d, JC,F = 5.3 Hz), 129.7, 127.8, 124.9 (d,
3JC,F = 17 Hz), 122.3 (d, 5JC,F = 3 Hz), 113.3 (d, 2JC,F = 23 Hz), 110.4, 74.6,
52.4, 49.8, 48.1, 21.6, 20.9, 14.3 (d, 6JC,F = 3 Hz).
(3a,7a)-3-Methylene-1-tosyl-2,3,3a,6,7,7a-hexahydro-1H-indole
(4a)
19F NMR (376 MHz, CDCl3): δ = –116.
LC-MS: m/z calcd for C22H24FNO4SNa [M + Na]+: 440.1; found: 440.2.
Product 4a was isolated following GP-2 as a colorless oil (69%, 60.1
mg, 0.21 mmol) using 3a (87 mg, 0.3 mmol) as reagent. Spectroscopic
data correspond to the literature.15
1H NMR (300 MHz, CDCl3): δ = 7.73 (d, J = 8.3 Hz, 2 H), 7.30 (d, J = 8.0
Hz, 2 H), 5.80–5.77 (m, 1 H), 5.65–5.60 (m, 1 H), 4.98 (d, J = 2.2 Hz, 1
H), 4.84 (d, J = 2.3 Hz, 1 H), 4.01–3.84 (m, 3 H), 2.73 (br s, 1 H), 2.42 (s,
3 H), 2.11–1.89 (m, 3 H), 1.63–1.51 (m, 1 H).
(4-Methylene-1-tosylpyrrolidin-3-yl)(naphthalen-2-yl)methyl
Acetate (2h)
Product 2h was isolated following GP-1 as a colorless oil (43%, 28 mg,
0.065 mmol) using 1h (56 mg, 0.15 mmol) as reagent.
Georg Thieme Verlag Stuttgart · New York — Synthesis 2019, 51, A–I

H
C. Cecchini et al.
Feature
Synthesis
The syn-configuration was determinated by NOESY NMR experiment.
3-Ethylidene-1-tosyl-2,3,3a,6,7,7a-hexahydro-1H-indole (4b)
7-Phenyl-3-tosyl-3-azabicyclo[4.1.0]hept-4-ene (2a′)
Complex A (1.7 mg, 0.9 mmol, 0.6 mol%) and freshly degassed toluene
(0.5 mL) were added under N2 to a Schlenk-type flask. Substrate 1a
(0.15 mmol) and benzoic acid (0.15 mmol, 1 equiv) were sequentially
added. The mixture was heated at 110 °C and the conversion was fol-
lowed analyzing samples via TLC. Upon complete conversion of the
substrate (24 h), the solution was diluted with EtOAc (5 mL) and puri-
fied. Product 2a′ was obtained as a yellow oil; yield: 17 mg (36%,
0.054 mmol). Spectra correspond to the literature.16
1H NMR (300 MHz, CDCl3): δ = 7.72 (d, J = 8.3 Hz, 2 H), 7.39 (d, J = 8.0
Hz, 2 H), 7.28–7.13 (m, 3 H), 6.82 (d, J = 7.1 Hz, 2 H), 6.45 (d, J = 8.0 Hz,
1 H), 5.53 (dd, J = 8.0, 5.4 Hz, 1 H), 4.06 (d, J = 12.0 Hz, 1 H), 3.18 (dd,
J = 12.0, 2.9 Hz, 1 H), 2.49 (s, 3 H), 1.96–1.90 (m, 1 H), 1.66–1.63 (m, 1
H), 1.51–1.45 (m, 1 H).
Product 4b was isolated following GP-2 as a colorless oil (66%, 60 mg,
0.2 mmol) using 3b (91 mg, 0.3 mmol) as reagent.
IR (neat): 2922, 1597, 1333, 1157, 1092, 814, 663, 545 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.73 (d, J = 8.3 Hz, 2 H), 7.30 (d, J = 8.1
Hz, 2 H), 5.77–5.75 (m, 1 H), 5.62–5.57 (m, 1 H), 5.24–5.17 (m, 1 H),
4.07–4.01 (m, 1 H), 3.86–3.79 (m, 1 H), 2.71 (br s, 1 H), 2.42 (s, 3 H),
2.20–1.86 (m, 4 H), 1.64–1.55 (m, 4 H).
13C NMR (101 MHz, CDCl3): δ = 143.3, 138.6, 129.7, 128.1, 127.3,
124.7, 117.9, 115.7, 58.8, 48.6, 42.6, 26.1, 23.3, 21.5, 14.5.
HRMS: m/z calcd for
C17H22NO2S [M +
H]+: 304.1373; found:
304.1368.
Funding Information
(3a,7a)-2,2-Dimethyl-3-methylene-1-tosyl-2,3,3a,6,7,7a-hexahy-
dro-1H-indole (4c)
Research on metal aromaticity was supported by Ministero dell’Is-
truzione, dell’Università e della Ricerca (MIUR; grant AROMA-TriP and
Product 4c was isolated following GP-2 as a colorless oil (32%, 20.3
mg, 0.06 mmol) using 3c (63.5 mg, 0.2 mmol) as reagent.
Departments of Excellence framework).
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IR (neat): 2917, 1567, 1331, 1167, 1390, 878, 623, 555 cm–1
.
1H NMR (300 MHz, CDCl3): δ = 7.78 (d, J = 8.2 Hz, 2 H), 7.27 (d, J = 4.9
Hz, 2 H), 5.90–5.50 (m, 2 H), 4.98 (d, J = 2.9 Hz, 1 H), 4.78 (d, J = 2.4 Hz,
1 H), 3.88 (dt, J = 9.0, 6.6 Hz, 1 H), 2.81 (br s, 1 H), 2.41 (s, 3 H), 2.17–
1.86 (m, 2 H), 1.73 (s, 3 H), 1.48 (s, 3 H), 1.33–1.25 (m, 2 H).
Acknowledgment
We warmly acknowledge support from UniPr and UPMC.
13C NMR (75 MHz, CDCl3): δ = 157.0, 142.6, 129.4, 129.4, 127.0, 123.9,
123.8, 103.4, 67.1, 56.4, 37.8, 30.0, 29.9, 29.2, 23.5, 21.5.
LC-MS: m/z calcd for C18H24NO2S [M + H]+: 318.1; found: 318.1.
Supporting Information
Supporting information for this article is available online at
https://doi.org/10.1055/s-0037-1611653.
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Dimethyl (3a,7a)-3-Methylene-2,3,3a,6,7,7a-hexahydro-1H-in-
dene-1,1-dicarboxylate (4d)
Product 4d was isolated following GP-2 as a colorless oil (70%, 52.3
mg, 0.21 mmol) using 3d (75 mg, 0.3 mmol) as reagent.
References
IR (neat): 2950, 1725, 1434, 1297, 1218, 1039, 895, 701 cm–1
.
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105, 3716. (b) Tsipis, C. A. Coord. Chem. Rev. 2005, 249, 2740.
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(2) (a) Boldyrev, A. I.; Popov, I. A.; Starikova, A. A.; Steglenko, D. V.
Chem. Eur. J. 2018, 24, 292. (b) Liu, C.; Popov, I. A.; Chen, Z.;
Boldyrev, A. I.; Sun, Z.-M. Chem. Eur. J. 2018, 24, 14583. (c) Cao,
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Boldyrev, A. I. Angew. Chem. Int. Ed. 2007, 46, 4277. (b) Knecht,
S.; Jensen, H. J. A.; Saue, T. Nat. Chem. 2019, 11, 40.
1H NMR (300 MHz, CDCl3): δ = 5.88–5.83 (m, 1 H), 5.77–5.72 (m, 1 H),
4.97 (d, J = 2.2 Hz, 1 H), 4.83 (d, J = 2.6 Hz, 1 H), 3.73 (s, 3 H), 3.72 (s, 3
H), 3.32 (dq, J = 17.8, 2.5 Hz, 1 H), 3.21 (br s, 1 H), 2.89–2.81 (m, 2 H),
2.04–1.99 (m, 2 H), 1.35–1.07 (m, 2 H).
13C NMR (75 MHz, CDCl3): δ = 172.3, 170.2, 151.1, 126.5, 126.4, 107.6,
62.4, 52.8, 52.5, 43.1, 42.9, 37.7, 24.5, 21.3.
LC-MS: m/z calcd for C14H19O4 [M + H]+: 251.1; found: 251.1.
(3a,7a,Z)-3-[2-(Cinnamyloxy)ethylidene]-2,3,3a,6,7,7a-hexahydro-
benzofuran (4e)
Product 4e was isolated following GP-2 as a colorless oil (44%, 37.3
mg, 0.13 mmol) using 3e (85 mg, 0.3 mmol) as reagent.
(4) (a) Soya, T.; Mori, H.; Osuka, A. Angew. Chem. Int. Ed. 2018, 57,
15882. (b) Oh, J.; Sung, Y. M.; Kim, W.; Mori, S.; Osuka, A.; Kim,
D. Angew. Chem. Int. Ed. 2016, 55, 6487. (c) Furukawa, S.; Fujita,
M.; Kanatomi, Y.; Minoura, M.; Hatanaka, M.; Morokuma, K.;
Ishimura, K.; Saito, M. Commun. Chem. 2018, 1, 60. (d) Saito, M.;
Sakaguchi, M.; Tajima, T.; Ishimura, K.; Nagase, S.; Hada, M.
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IR (neat): 2924, 1735, 1449, 1170, 1039, 963, 746, 692 cm–1
.
1H NMR (300 MHz, CDCl3): δ = 7.42–7.23 (m, 5 H), 6.63 (d, J = 15.9 Hz,
1 H), 6.31 (dt, J = 15.9, 6.0 Hz, 1 H), 5.79–5.75 (m, 1 H), 5.57–5.54 (m,
2 H), 4.53 (d, J = 13.4 Hz, 1 H), 4.38 (d, J = 12.5 Hz, 1 H), 4.23 (td, J = 5.7,
2.8 Hz, 1 H), 4.15 (d, J = 6.1 Hz, 2 H), 3.98 (d, J = 6.6 Hz, 2 H), 3.18 (s, 1
H), 2.38–2.10 (m, 1 H), 2.00–1.87 (m, 2 H), 1.74–1.64 (m, 1 H).
13C NMR (75 MHz, CDCl3): δ = 146.5, 136.6, 132.6, 128.5, 127.7, 127.0,
126.4, 126.2, 125.9, 117.2, 76.4, 70.8, 67.7, 67.4, 43.4, 24.5, 20.0.
LC-MS: m/z calcd for C19H23O2 [M + H]+: 283.2; found: 283.2.
Georg Thieme Verlag Stuttgart · New York — Synthesis 2019, 51, A–I

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Georg Thieme Verlag Stuttgart · New York — Synthesis 2019, 51, A–I