Synthesis of Fused Dihydroazepine Derivatives of Fullerenes by a Rh-Catalyzed Cascade Process

Article abstract of DOI:10.1002/adsc.202100644

A synthetic methodology is reported that functionalizes C₆₀ and C₇₀ fullerenes with dihydroazepine rings by a cascade reaction encompassing a rhodium-catalyzed cycloisomerization of 1,5-bisallenes and a [4+2] cycloaddition. This tran

Full text of DOI:10.1002/adsc.202100644

RESEARCH ARTICLE
doi.org/10.1002/adsc.202100644
Synthesis of Fused Dihydroazepine Derivatives of Fullerenes by a
Rh-Catalyzed Cascade Process
Albert Artigas,+a Cristina Castanyer,+a Nil Roig,a Agustí Lledó,a Miquel Solà,a
Anna Pla-Quintana,a,* and Anna Roglansa,*
a
Institut de Química Computacional i Catàlisi (IQCC) and Departament de Química, Universitat de Girona (UdG), Facultat de
Ciències, C/Maria Aurèlia Capmany, 69, 17003-Girona, Catalunya, Spain
E-mail: anna.plaq@udg.edu; anna.roglans@udg.edu
+
These authors contributed equally.
Manuscript received: May 26, 2021; Revised manuscript received: June 16, 2021;
Version of record online: June 29, 2021
Supporting information for this article is available on the WWW under https://doi.org/10.1002/adsc.202100644
Abstract: A synthetic methodology is reported that functionalizes C60 and C70 fullerenes with dihydroazepine
rings by a cascade reaction encompassing a rhodium-catalyzed cycloisomerization of 1,5-bisallenes and a [4+
2] cycloaddition. This transition metal-catalyzed cascade reaction provides a versatile and step-economical
approach to the synthesis of 6,7-membered polyheterocyclic fullerene adducts. Electrochemical character-
ization of the products obtained ventures their application in organic and perovskite photovoltaic devices.
Keywords: Cycloaddition; Density Functional Calculations; Fullerenes; Rhodium; Solar Cells
Introduction
(e.g. IC60BA[21] and IC70BA[22]) constitute some of the
state-of-the-art n-type semiconductor materials in or-
The functionalization of fullerenes represents one of ganic and perovskite photovoltaics.[1]
the most powerful approaches towards the develop-
On the other hand, transition metal-mediated
ment of novel carbon nanomaterials.[1] Exohedrally annulation reactions have considerably enriched the
modified fullerenes with enhanced physicochemical, synthetic toolbox available for fullerene functionaliza-
electrochemical or photophysical properties are prom- tion. In fact, radical reactions mediated by transition
ising functional molecules with potential use in a metal salts dominate the field.[23] However, other
variety of fields, ranging from biomedicine[2–4] to next- methodologies,
including
CÀ H/CÀ X
generation photovoltaics.[5–9]
functionalization[24] or [2+2+2] cycloadditions[25–28]
In the thirty years since C60 was obtained in have been reported as well. A complementary yet
macroscopic quantities for the first time,[10] synthetic convenient approach relies on the in situ generation of
organic chemists have come up with countless method- reactive intermediates, such as 1,3-dienes, by the
ologies to functionalize fullerenes.[11] In this regard, the participation of transition metal complexes or transi-
double bonds found at the junctions between the six- tion metal salts, followed by reaction with the fullerene
membered rings of fullerene cages –the so-called [6,6] (Scheme 1).[29–32] Such cascade reactions offer molec-
bonds – participate effectively in numerous chemical ular complexity from simple structures.
reactions, of which cyclopropanations[12–14] and 1,3-
When treated under transition metal-catalysis, 1,5-
dipolar cycloadditions[15–17] are amongst the most bisallenes cycloisomerize to provide a wide variety of
commonly used. The electron-deficient nature of C60, carbo- and heterocyclic compounds bearing 4-, 5-, 6-
C70, and higher fullerenes also makes [6,6] bonds and 7-membered rings.[33–39] We have recently shown
excellent
dienophiles
in
Diels-Alder
(DA) that 1,5-bisallenes 1 can be selectively transformed
cycloadditions.[18–20] Functionalization of fullerenes by into their corresponding 7-membered cycloisomers 2,
DA reactions has been used with great success in the which contain an exocyclic 1,3-diene, in the presence
field of materials science. In this sense, fullerene of cationic RhI-diphosphine catalysts (see Scheme 1).
adducts obtained through DA reactions with indene These promiscuous intermediates readily react with a
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Table 1. Optimization of the rhodium(I)-catalyzed cycloaddi-
tion of bisallene 1a with fullerene C60.[a]
Entry Ligand
Ratio
C60:1a
Solvent/T
T
Yield
°
( C)
(min) (%)
1
2
3
4
5
(R)-DTBM- 1:2
segphos
(R)-DTBM- 1.1:1
segphos
(R)-DTBM- 1.1:1
segphos
(R)-DTBM- 1.1:1
segphos
o-DCB/180 30
o-DCB/180 15
o-DCB/120 15
o-DCB/90 20
Toluene/60 30
0
<5
<5
56
0
(R)-DTBM- 1.1:1
segphos
6
7
(R)-BINAP 1.1:1
o-DCB/90 240
o-DCB/90 240
42
42
Scheme 1. Cascade reactions of C60 with in situ generated 1,3-
dienes.
(R)-H8-BI-
1.1:1
NAP
8
(R)-Tol-BI- 1.1:1
o-DCB/90 240
20
NAP
dienophile present in the reaction mixture, providing
fused dihydroazepine polycyclic systems.[40] Given that
fullerene adducts containing 7-membered rings are
scarce and challenging to prepare,[41–47] and azepane
based compounds showed a variety of pharmacological
properties,[48] we envisaged a synthetic protocol to
prepare structurally appealing fused dihydroazepine
derivatives of C60 and C70 by in situ generation of the
1,3-diene (Scheme 1).
[a] Reaction conditions: 0.06 mmol of 1a, 10 mol% of Rh
catalyst in o-DCB (1.4 mM) at the indicated temperature and
time. The 10 mol% mixture of [Rh(cod)2]BF4 and phosphine
ligand was treated with hydrogen in dichloromethane
(CH2Cl2) solution for catalyst activation prior to substrate
addition.
mixture may promote polyaddition. Given this, we
attempted the reaction using only a slight excess of C60
(1.1 equivalents) and reducing the reaction time to
Results and Discussion
We initiated our investigations by studying the reaction 15 min (entry 2, Table 1). After subjecting the reaction
conditions for the cycloaddition reaction between crude directly to column chromatography, we managed
fullerene C60 and N-tosyl-tethered bisallene 1a (see to isolate a small amount of a reaction product, which
Table 1 and Table S1 in the Supporting Information). eluted as a brown band following unreacted C60. We
In our first attempts, an equimolar mixture of a cationic then proceeded to analyze the effect of the temperature.
°
rhodium complex [Rh(cod)2]BF4 (cod=cycloocta- We first performed the reaction at 120 C but did not
diene) and (R)-DTBM-seghpos, pre-treated under observe any improvement in the yield (entry 3,
°
hydrogenation conditions, was used as a catalyst. Upon Table 1). Further lowering the temperature to 90 C
heating the reaction mixture for 30 min in refluxing o- and carefully monitoring the reaction progress by TLC
dichlorobenzene (o-DCB) and using an excess of allowed us to obtain the desired product in a 56%
bisallene 1a (2 equivalents, with respect to C60), we isolated yield after only 20 minutes of reaction (en-
did not observe the formation of the desired product try 4, Table 1). Further optimization of the reaction
3a. However, no starting materials were recovered conditions was attempted by changing the solvent to
°
(entry 1, Table 1). Conversely, complete retention at toluene and lowering the temperature to 60 C (entry 5,
the bottom of the TLC plate was observed. This Table 1). However, no reactivity was observed in this
suggested that an excess of bisallene in the reaction case. We then turned our attention to other diphosphine
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ligands (entries 6–8, Table 1). All of these turned out
to be less effective, requiring longer reaction times and
providing lower yields of the desired cycloadduct.
Finally, we attempted to reduce the catalyst load, but
employing 5 mol% of cationic rhodium/diphosphine
mixture was detrimental in terms of reaction yield.
We then proceeded to fully characterize the product
formed. The molecular formula of the new compound
was determined to be C75H17NO2S by ESI-HRMS,
indicating the formation of a monoadduct. The 13C
NMR spectra exhibited only 35 peaks of the 38
expected (30 from the fullerene core, 4 from the tosyl
group and 4 corresponding to the sp2 C atoms of the
addend) in the range of 110–160 ppm due to some
1
overlapping, and 7 signals in the sp3 region. The H
NMR spectrum displayed characteristic doublets corre-
sponding to the olefinic protons (δ=5.57 ppm and
6.97 ppm) and three signals corresponding to meth-
ylene groups (δ=2.86 ppm, 3.97 ppm and 4.04 ppm).
The absorption spectrum showed an absorption band at
435 nm, which is in accordance with the characteristic
pattern expected for a C60 monoadduct.[49] Taken
together, all these data allowed us to unambiguously
identify the product formed as 3a.
Figure 1. M06-2X-D3/cc-pVTZ(SMD=o-DCB)//B3LYP-D3/
cc-pVDZ Gibbs energy profile computed at 363.15 K of the DA
reaction involving fullerene C60 and triene 2a. Values in
parentheses correspond to electronic energies (ΔE).
It is worth noting that although 3a is particularly
sensitive to room light and atmospheric air exposure,
pure samples could be obtained and fully character- reaction was found to be exergonic by 11.8 kcal/mol,
ized. To further understand the reactivity of 3a towards with an activation energy of 27.0 kcal/mol.
light and oxygen, a CHCl3 solution of 3a was stirred
With an optimized set of conditions at hand and
under air and light exposure. After 16 hours, TLC having established a reaction mechanism, the scope of
monitoring revealed the complete consumption of 3a, the reaction was examined, as shown in Figure 2. First,
along with the appearance of a new significantly more the nature of the substituents at the phenyl ring of the
retained brown spot (Rf =0.27; toluene). ESI-HRMS sulfonamide tether in bisallene 1a was explored. The
analysis of this solution clearly showed a major peak corresponding cycloadducts 3b–h were efficiently
corresponding to [M(3a)+O2 +Na]+ (See Figure S1 obtained, indicating that the reaction proceeds well
in the Supporting Information). Unfortunately, purifi- with both electron-donating and electron-withdrawing
cation by column chromatography and 1H NMR groups. However, better yields were achieved with
analysis did not allow the identification of a defined electron-donating substituents. Substitution at the ortho
oxidation product. Conversely, a complex spectrum, position of the phenyl ring (3f) did not hamper the
representative of a complex mixture of products, was reaction. To extend our methodology to heteroaromatic
observed. Based on this, we hypothesized that a non- sulfonamide-tethered 1,5-bisallenes, we performed the
specific reaction of 3a with singlet oxygen (1O2) might reaction with 1i and 1j. The corresponding C60 adducts
have been operative. Such events have been exten- 3i and 3j were obtained in 43% and 53% yields,
sively reported in the literature.[28,50–57] In fact, the respectively. Sulfonamide-tethered reaction products
outstanding affinity of fullerenes and fullerene deriva- bearing aliphatic substituents (3k–l) could be synthe-
tives for free radicals has been exploited in medicinal sized as well with good yields.
chemistry as an approach to treat oxidative stress.[58]
We then proceeded to see if 1,5-bisallenes with a
Cycloadduct 3a is expected to form via a DA tether different from nitrogen were also efficient in the
reaction of C60 with cycloheptatriene intermediate 2a reaction. When the reaction was set up with oxygen
(that is formed through a Rh(I) catalyzed cycloisome- tethered 1,5-bisallene no hint of functionalized full-
rization as has been studied by us previously[40]). To erene could be detected. Conversely, carbon tethered
corroborate this hypothesis, we computed the Gibbs bisallenes efficiently participated in the cascade
energy profile of the DA reaction between 2a and C60 functionalization (Figure 3). Diethyl malonate as a
at the M06-2X-D3/cc-pVTZ(SMD=o-DCB)//B3LYP- tethering unit in the bisallene (1m) was initially tested
D3/cc-pVDZ level of theory (Figure 1, see SI for a providing a 27% yield of the carbocyclic analogue 3m.
more detailed description of the computational method Methyl 2-phenylacetate tethered 1,5-bisallene (1n)
used).[59] According to our computational study, the was also tested affording a 32% yield of the function-
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Figure 2. Scope of the cycloaddition of N-tethered bisallenes 1a–1l with C60.
2a has reacted to a β-C70 bond.[60–63] To ascertain the
structure of the products detected, we first computed
the Gibbs energy profile for the formation of the three
different DA adducts (Figure 4). Computations support
the selective formation of one out of the two possible
α-isomers as the major reaction product (blue path in
Figure 4), which is clearly favored both kinetically and
thermodynamically. The second most favored reaction
product would be β-4a according to our computational
study (purple path in Figure 4). To better understand
the selective formation of α-4a over α-4a’ we
analyzed the approximation of 2a to C70 on the basis
of the Activation Strain Model (ASM) (Figure 4b).[64]
The results clearly show that the lower energy of the
transition state (TS) leading to product α-4a arises
from its stabilizing interaction energy along the
Figure 3. Scope of the cycloaddition of C-tethered bisallenes
1m–p with C60. For bisallenes 1n, 1o and 1p, 2 h. of reaction
were required instead of 20 min.
alized fullerene 3n. When the carboalkoxy group in intrinsic reaction coordinate (IRC), which in turn could
bisallene 1n was replaced by a sulfo group (1o), the be attributed to favorable secondary orbital
reaction afforded a 39% of the functionalized fullerene interactions.[65–68]
3o. Finally, bisallene 1p also participated in the
In an attempt to gather more information on the
reaction to afford 3p. It is to be noted that bisallenes structure of the cycloadducts, we employed an indirect
1n, 1o and 1p reacted markedly slower than the N- method to assess the regiochemistry of the reaction
tethered bisallenes requiring 2 h of reaction time.
depicted in Scheme 2. We looked for a method that
Next, we attempted the reaction with C70 fullerene could selectively reduce the double bond vicinal to the
(Scheme 2). ESI-HRMS indicated again the formation sulfonamide group. The symmetry of the product
of a monoadduct. However, careful analysis of 2D obtained would help us to differentiate between the
NMR spectra and HPLC chromatograms evidenced formation of α-4a’ and β-4a. The reduction reaction
that a mixture of regioisomers with two major products was first optimized for C60 adduct 3a (Scheme 3, C60).
in a 3:1 ratio had been formed (See Figures S2 in the Treatment of the exohedrally modified C60 with an
Supporting Information).
excess of Et3SiH and BF3·Et2O in CH2Cl2 solution
[69]
°
UV-Vis experiments evidenced the formation of an from 0 C to room temperature
α adduct as the major reaction product, but the 82% yield, which was unambiguously characterized by
different regioisomers formed could not be separated. ESI-HRMS, UV-Vis and NMR experiments.
provided 5a in a
Plausible structures for the observed cycloadducts are:
The same reaction protocol was then applied to the
two α isomers (α-4a and α-4a’) differing in the corresponding isomeric mixture of C70 adducts. Selec-
approximation of 2a, which is not symmetric, to the tive reduction of the double bond vicinal to the
same α bond of C70 and a site-isomer (β-4a) in which sulfonamide groups in α-4a and α-4a’ would lead to a
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upon reduction of α-4a and eventually minor quanti-
ties of α-4a’, and the minor one, which showed Cs
symmetry and diastereotopic protons, was assigned as
β-6a, obtained by reduction of β-4a. Thus, reduction
of the enamine bond indirectly confirmed the forma-
tion of α-4a and β-4a, as main products in the
cycloaddition shown in Scheme 2 (as also suggested
by the DFT calculations).
Finally, the electrochemical behaviour of compound
3a was studied by cyclic voltammetry. Under the
experimental settings employed, the cycloadduct ex-
hibited two fully reversible reduction waves corre-
sponding to one-electron reductions of the fullerene
core. As expected, the reduction potentials of 3a are
negatively shifted compared with those of C60 (see
Table 2). The highest occupied molecular orbital/low-
est unoccupied molecular orbital (HOMO/LUMO)
values were estimated from the ultraviolet (UV) and
CV measurements (Table 3).[9,70] The remarkable catho-
dic shift of the cycloadduct and its excellent alignment
with perovskite bands ventures their potential applica-
tion as n-type materials in organic and hybrid photo-
voltaic devices.
Scheme 2. Cycloaddition of bisallene 1a with C70.
Conclusion
In conclusion, we have developed a method to
single product, as a consequence of the addend’s synthesize a series of fullerene adducts bearing 6,7-
symmetrization. Careful analysis of 2D NMR spectra membered polyheterocyclic addends. The reaction
of the mixture of reduced cycloadducts showed the relies in a cascade composed of the in situ generation
presence of two major products in a 3:1 molar ratio. of dienes by a selective RhI-catalyzed cycloisomeriza-
Thus, the major one was assigned as α-6a, obtained tion of 1,5-bisallenes and a DA reaction with C60 or
Figure 4. (a) M06-2X-D3/cc-pVTZ(SMD=o-DCB)//B3LYP-D3/cc-pVDZ Gibbs energy profile computed at 363.15 K of the DA
reaction involving fullerene C70 and triene 2a (blue and red paths: two different orientations of α bond; purple path: β bond). Values
in parentheses are electronic energies (ΔE). (b) M06-2X-D3/cc-pVTZ(SMD=o-DCB) //B3LYP-D3/cc-pVDZ total energy (ΔEtotal
)
along the IRC of α-4a and α-4a’ and their corresponding strain (ΔEstrain) and interaction energies (ΔEint) based on the ASM.
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on silica gel using CS2 as the eluent to provide unreacted C60.
Further elution with toluene gave compound 3a (34.1 mg, 56%
yield) as a dark brown solid.
Compound 3a. (34.1 mg, 56% yield, dark brown solid). MW
(C75H17NO2S): 996.03 g/mol; Rf: 0.75 (toluene); IR (ATR) ν
(cmÀ 1): 3082, 1344, 1159; 1H NMR (400 MHz, CDCl3) δ
(ppm): 2.39 (s, 3H), 2.86 (t, J=4.6 Hz, 2H), 3.97 (t, J=4.6 Hz,
2H), 3.99-4.12 (m, 4H), 5.57 (d, J=9.6 Hz, 1H), 6.97 (d, J=
9.6 Hz, 1H), 7.35 (d, J=8.2 Hz, 2H), 7.78 (d, J=8.2 Hz, 2H);
13C NMR (101 MHz, CDCl3) δ (ppm): 21.83, 38.33, 46.53,
47.88, 48.45, 66.37, 66.39, 111.15, 127.31, 127.80, 130.27,
131.51, 135.77, 135.87, 136.04, 138.84, 140.27, 140.32, 141.75,
141.78, 142.17, 142.23, 142.49, 142.51, 142.78, 142.79, 143.29,
144.29, 144.84, 144.91, 145.53, 145.62, 145.64, 145.67, 145.86,
146.42, 146.65, 146.67, 147.79, 147.82, 156.64, 156.71 (3
signals are not described due to overlapping); UV-vis (toluene)
λmax (nm): 435, 705; ESI-HRMS (m/z) calculated for [M+
Na]+ =1018.0872; found 1018.0837.
Scheme 3. Selective reduction of 3a and 4a.
Table 2. Redox potentials of 3a and C60.[a]
Entry
Compound
E1red
E2
E3red
red
1
2
C60
3a
À 1.13
À 1.27
À 1.52
À 1.66
À 1.98
[a]
E
1/2
in V vs.ferrocene/ferrocenium (Fc/Fc+), 0.2 mM C60/3a
Compound 3b. (33.7 mg, 56% yield, dark brown solid). MW
(C75H17NO3S): 1012.03 g/mol; Rf: 0.5 (toluene); IR (ATR) ν
and 0.05 M Bu4N+PF6 in o-dichlorobenzene, Ag/AgNO3
À
1
(cmÀ 1): 2917, 1258, 1155, 1091; H NMR (400 MHz, CDCl3) δ
reference electrode, Pt working electrode, Pt wire auxiliary
(ppm): 2.89 (t, J=4.6 Hz, 2H), 3.82 (s, 3H), 3.97 (t, J=4.6 Hz,
2H), 3.99–4.10 (m, 4H), 5.56 (d, J=9.6 Hz, 1H), 6.96 (d, J=
9.6 Hz, 1H), 7.01 (d, J=9.0 Hz, 2H), 7.83 (d, J=9.0 Hz, 2H);
13C NMR (101 MHz, CDCl3) δ (ppm): 38.35, 46.52, 47.88,
48.47, 55.75, 66.38, 66.42, 111.13, 114.78, 127.83, 129.41,
130.55, 131.54, 135.75, 135.87, 138.81, 140.26, 140.31, 141.75,
141.78, 142.17, 142.23, 142.50, 142.77, 142.78, 143.25, 144.82,
144.89, 145.51, 145.53, 145.61, 145.64, 145.67, 145.92, 146.41,
146.42, 146.66, 146.68, 147.79, 147.82, 156.69, 163.37 (3
signals are not described due to overlapping); UV-vis (toluene)
λmax (nm): 435, 706; ESI-HRMS (m/z) calculated for [M+
Na]+ =1034.0821; found 1034.0856.
°
electrode, scan rate 50 mV/s, 25 C.
Table 3. Optical bandgap, onset reduction, and lowest unoccu-
pied molecular orbital/highest occupied molecular orbital
(LUMO/HOMO) energy levels of 3a.
Compound
λmax
Eg
Eon
LUMO
(ev)
HOMO
(ev)
red
(nm)
(ev)
(V)
3a
719
1.72
À 1.15
À 3.65
À 5.37
Compound 3c. (21.6 mg, 35% yield, dark brown solid). MW
(C74H14BrNO2S): 1060.89 g/mol; Rf: 0.85 (toluene); IR (ATR) ν
C70. A combined approach involving computation and
experiments allowed us to propose the structure for the
main two isomers produced upon reaction with full-
erene C70. Electrochemical characterization of the NTs
dihydroazepine derivative 3a showed two reduction
waves with a remarkable cathodic shift as compared to
C60 that could permit their application as electron-
transporting materials in perovskite solar cells.
1
(cmÀ 1): 2946, 1352, 1161, 1087; H NMR (400 MHz, CDCl3) δ
(ppm): 2.89 (t, J=4.8 Hz, 2H), 4.00 (t, J=4.8 Hz, 2H), 4.02–
4.12 (m, 4H), 5.61 (d, J=9.6 Hz, 1H), 6.93 (d, J=9.6 Hz, 1H),
7.68–7.78 (m, 4H); 13C NMR (101 MHz, CDCl3) δ (ppm):
38.31, 46.63, 47.88, 48.43, 66.36 (x2), 112.12, 127.30, 128.67,
128.74, 131.49, 132.96, 135.70, 135.84, 138.11, 139.27, 140.31,
140.35, 141.78, 141.80, 142.20, 142.24, 142.50, 142.52, 142.80,
142.81, 143.34, 144.86, 144.91, 145.48, 145.62, 145.65, 145.68,
145.93, 146.45, 146.69, 146.71, 147.83, 147.84, 156.54, 156.60
(4 signals are not described due to overlapping); UV-vis
(toluene) λmax (nm): 436, 705; ESI-HRMS (m/z) calculated for
[M+Na]+ =1083.9806; found 1083.9783.
Experimental Section
General Procedure for the Synthesis of Fused
Dihydroazepine Derivatives of C60 (3a)
Compound 3d. (24.7 mg, 37% yield, dark brown solid). MW
(C74H14FNO2S): 999.99 g/mol; Rf: 0.75 (toluene); IR (ATR) ν
In a 10 mL capped vial under a nitrogen inert atmosphere, a
solution of [Rh(cod)2]BF4 (2.2 mg, 0.006 mmol,) and (R)-
DTBM-Segphos (7.5 mg, 0.006 mmol) in anhydrous CH2Cl2
(4 mL) was prepared. Hydrogen gas was bubbled into the
catalyst solution for 30 min before it was concentrated to
dryness, dissolved in anhydrous o-DCB and introduced into a
solution of C60 (46.3 mg, 0.064 mmol) and bisallene 1a
(17.0 mg, 0.061 mmol) in anhydrous o-DCB (1.4 mM), pre-
1
(cmÀ 1): 2916, 1340, 1151, 1089; H NMR (400 MHz, CDCl3) δ
(ppm): 2.90 (t, J=4.8 Hz, 2H), 3.99 (t, J=4.8 Hz, 2H), 4.01–
4.15 (m, 4H), 5.61 (d, J=9.6 Hz, 1H), 6.93 (d, J=9.6 Hz, 1H),
3
3
7.24 (t, JH-F =8.8, JH-H =8.8 Hz, 2H), 7.92 (dd, J=8.8 Hz,
J=4.8 Hz, 2H); 13C NMR (101 MHz, CDCl3) δ (ppm): 38.37,
2
46.54, 47.90, 48.44, 66.32, 66.33, 111.90, 117.00 (d, JC-F
=
3
22.4 Hz), 127.37, 130.00 (d, JC-F =9.4 Hz), 131.47, 135.14 (d,
4JC-F =3.4 Hz), 135.72, 135.85, 139.14, 140.31, 140.34, 141.78,
141.80, 142.19, 142.24, 142.49, 142.80, 143.33, 144.86, 144.90,
145.49, 145.59, 145.64, 145.67, 145.88, 146.44, 146.69, 146.70,
°
°
heated to 90 C. The resulting mixture was stirred at 90 C for
20 min (TLC monitoring), allowed to cool down to room
temperature, and directly subjected to column chromatography
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1
147.82, 147.84, 156.56, 156.58, 156.61, 165.50 (d, JC-F
=
48.36, 66.26, 66.28, 113.33, 124.94, 126.73, 128.45, 131.41,
135.61, 135.74, 139.77, 140.34, 140.37, 141.77, 141.79, 142.17,
142.22, 142.33, 142.41, 142.81, 142.83, 143.33, 144.76, 144.83,
144.88, 145.39, 145.55, 145.62, 145.66, 145.69, 145.80, 146.46,
146.73, 146.74, 147.83, 147.84, 150.48, 156.38, 156.44; UV-vis
(toluene) λmax (nm): 435, 705; ESI-HRMS (m/z) calculated for
[M+Na]+ =1049.0566; found 1049.0526.
254.7 Hz) (4 signals are not described due to overlapping); UV-
vis (toluene) λmax (nm): 435, 704; ESI-HRMS (m/z) calculated
for [M+Na]+ =1022.0621; found 1022.0595.
Compound 3e. (19.8 mg, 35% yield, dark brown solid). MW
(C75H14F3NO2S): 1050.00 g/mol; Rf: 0.83 (toluene); IR (ATR) ν
(cmÀ 1): 2914, 1316, 1163; 1H NMR (400 MHz, CDCl3) δ
(ppm): 2.94 (t, J=4.0 Hz, 2H), 4.02 (t, J=4.0 Hz, 2H), 4.00-
4.15 (m, 4H), 5.63 (d, J=9.6 Hz, 1H), 6.94 (d, J=9.6 Hz, 1H),
7.86 (d, J=8.2 Hz, 2H), 8.05 (d, J=8.2 Hz, 2H); 13C NMR
(101 MHz, CDCl3) δ (ppm): 38.51, 46.74, 47.85, 48.48, 66.26,
Compound 3i. (27.8 mg, 43% yield, dark brown solid). MW
(C74H16N2O2S2): 997.01 g/mol; Rf: 0.40 (toluene); IR (ATR) ν
1
(cmÀ 1): 2915, 1343, 1168, 1103; H NMR (400 MHz, CDCl3) δ
(ppm): 2.42 (s, 3H), 3.10 (t, J=4.6 Hz, 2H), 3.99-4.09 (m, 4H),
4.13 (t, J=4.6 Hz, 2H), 5.55 (d, J=9.6 Hz, 1H), 6.92 (d, J=
9.6 Hz, 1H), 7.73 (dd, J=7.6 Hz, J=1.6 Hz, 1H), 7.95 (d, J=
7.6 Hz, 1H), 8.58 (d, J=1.6 Hz, 1H); 13C NMR (101 MHz,
CDCl3) δ (ppm): 18.82, 39.12, 47.27, 47.95, 48.42, 66.36,
66.37, 111.29, 122.43, 128.12, 131.34, 135.82, 135.92, 137.93,
138.41, 139.14, 140.31, 140.33, 141.78, 141.79, 142.19, 142.24,
142.50, 142.51, 142.79, 143.31, 144.87, 144.92, 145.58, 145.60,
145.63, 145.65, 145.70, 145.87, 146.43, 146.66, 146.69, 147.81,
147.84, 151.11, 154.16, 156.75 (4 signals are not described due
to overlapping); UV-vis (toluene) λmax (nm): 435, 704; ESI-
HRMS (m/z) calculated for [M+Na]+ =1019.0825; found
1019.0808.
1
4
66.32, 112.09, 123.23 (q, JC-F =271.4 Hz), 126.82 (q, JC-F
=
=
2
3.6 Hz), 127.00, 127.79, 128.67, 131.49, 135.05 (q, JC-F
32.9 Hz), 135.70, 135.83, 139.39, 140.31, 140.34, 140.95,
141.77, 141.79, 142.18, 142.23, 142.46, 142.48, 142.61, 142.80,
143.32, 144.84, 144.89, 145.46, 145.61, 145.64, 145.67, 145.87,
146.44, 146.69, 146.71, 147.82, 147.84, 156.56 (3 signals are
not described due to overlapping; UV-vis (toluene) λmax (nm):
435, 704; ESI-HRMS (m/z) calculated for [M+Na]+ =
1072.0590; found 1072.0568.
Compound 3f. (16.6 mg, 25% yield, dark brown solid). MW
(C75H14F3NO2S): 1050.00 g/mol; Rf: 0.75 (toluene); IR (ATR) ν
(cmÀ 1): 2916, 1303, 1164; 1H NMR (400 MHz, CDCl3) δ
(ppm): 2.98 (t, J=4.6 Hz, 2H), 4.02 (t, J=4.6 Hz, 2H), 4.04-
4.15 (m, 4H), 5.63 (d, J=9.6 Hz, 1H), 6.95 (d, J=9.6 Hz, 1H),
7.73 (t, J=7.6 Hz, 1H), 7.77-7.82 (m, 1H), 7.95 (d, J=7.6 Hz,
1H), 8.19 (d, J=8.0 Hz, 1H); 13C NMR (101 MHz, CDCl3) δ
Compound 3j. (37.2 mg, 53% yield, dark brown solid). MW
(C72H13NO2S2): 988.02 g/mol; Rf: 0.75 (toluene); IR (ATR) ν
(cmÀ 1): 2917, 1349, 1158; 1H NMR (400 MHz, CDCl3) δ
(ppm): 2.96 (t, J=4.6 Hz, 2H), 4.03 (t, J=4.6 Hz, 2H), 4.03–
4.18 (m, 4H), 5.64 (d, J=9.6 Hz, 1H), 6.91 (d, J=9.6 Hz, 1H),
7.14 (dd, J=4.8 Hz, J=4.0 Hz, 1H), 7.64 (dd, J=4.8 Hz, J=
1.2 Hz, 1H), 7.67 (dd, J=4.0 Hz, J=1.2 Hz, 1H); 13C NMR
(101 MHz, CDCl3) δ (ppm): 38.25, 46.50, 47.93, 48.39, 66.18
(×2), 112.14, 127.14, 127.74, 131.38, 132.33, 132.78, 135.73,
135.81, 139.07, 139.56, 140.23, 140.27, 141.67, 141.70, 142.07,
142.13, 142.37, 142.38, 142.69, 143.22, 144.73, 144.79, 145.36,
145.51, 145.53, 145.57, 145.73, 146.32, 146.55, 146.58, 147.67,
147.70, 156.38, 156.43 (4 signals are not described due to
overlapping); UV-vis (toluene) λmax (nm): 436, 705; ESI-HRMS
(m/z) calculated for [M+Na]+ =1010.0280; found 1010.0268.
(ppm): 38.74, 46.75, 47.97, 48.45, 66.34 (×2), 111.36, 122.52
2
(q, 1JC-F =272.6 Hz), 127.51, 127.85, 128.41 (q, JC-F
=
33.4 Hz), 128.88 (q, 3JC-F =6.4 Hz), 130.68, 131.45, 131.50,
132.71, 133.40, 135.78, 135.88, 138.16 (m), 139.13, 140.31,
140.36, 141.77, 141.81, 142.19, 142.25, 142.50, 142.52, 142.79,
142.80, 143.33, 144.85, 144.92, 145.52, 145.59, 145.64, 145.66,
145.88, 146.44, 146.67, 146.70, 147.81, 147.85, 156.65 (2
signals are not described due to overlapping); UV-vis (toluene)
λmax (nm): 435, 705; ESI-HRMS (m/z) calculated for [M+
Na]+ =1072.0590; found 1072.0577.
Compound 3g. (28.3 mg, 49% yield, dark brown solid). MW
(C76H17NO4S): 1040.04 g/mol; Rf: 0.38 (toluene); IR (ATR) ν
Compound 3k. (23.3 mg, 33% yield, dark brown solid). MW
(C73H23NO2SSi): 1006.14 g/mol; Rf: 0.65 (toluene); IR (ATR) ν
(cmÀ 1): 2915, 1340, 1144; 1H NMR (400 MHz, CDCl3) δ
(ppm): 0.09 (s, 9H), 1.08–1.14 (m, 2H), 3.07–3.13 (m, 2H),
3.19 (t, J=4.6 Hz, 2H), 4.07 (t, J=4.6 Hz, 2H), 4.07–4.19 (m,
4H), 5.52 (d, J=9.6 Hz, 1H), 6.80 (d, J=9.6 Hz, 1H); 13C
NMR (101 MHz, CDCl3) δ (ppm): À 1.72, 10.53, 39.75, 46.62,
47.97, 48.54, 49.41, 66.32, 66.40, 109.71, 128.38, 131.75,
135.80, 135.88, 138.30, 140.35, 141.80, 141.81, 142.21, 142.25,
142.56, 142.80, 143.32, 144.88, 144.92, 145.59, 145.62, 145.64,
145.67, 145.69, 145.93, 146.44, 146.68, 146.71, 147.82, 147.84,
156.76 (6 signals are not described due to overlapping); UV-vis
(toluene) λmax (nm): 435, 707; ESI-HRMS (m/z) calculated for
[M+Na]+ =1028.1111; found 1028.1121.
(cmÀ 1): 2946, 2360, 1724, 1273, 1163; H NMR (400 MHz,
1
CDCl3) δ (ppm): 2.84 (t, J=4.8 Hz, 2H), 3.89 (s, 3H), 3.99–
4.10 (m, 6H), 5.64 (d, J=9.6 Hz, 1H), 6.95 (d, J=9.5 Hz, 1H),
7.96 (d, J=8.2 Hz, 2H), 8.21 (d, J=8.2 Hz, 2H); 13C NMR
(101 MHz, CDCl3) δ (ppm): 38.26, 46.65, 48.00, 48.42, 52.93,
66.41, 66.47, 112.82, 127.31, 127.37, 130.92, 131.47, 134.62,
135.76, 135.89, 139.50, 140.38, 140.43, 141.84, 141.88, 142.27,
142.33, 142.54, 142.87, 142.89, 142.97, 143.31, 144.91, 144.99,
145.55, 145.61, 145.72, 145.74, 146.02, 146.53, 146.77, 147.89,
147.92, 156.59, 156.64, 165.55 (5 signals are not described due
to overlapping); UV-vis (toluene) λmax (nm): 436, 707; ESI-
HRMS (m/z) calculated for [M+Na]+ =1062.0770; found
1062.0758.
Compound 3h. (20.3 mg, 36% yield, dark brown solid). MW
(C74H14N2O4S): 1027.00 g/mol; Rf: 0.68 (toluene); IR (ATR) ν
Compound 3l. (20.8 mg, 36% yield, dark brown solid). MW
(C72H19NO2S): 962.01 g/mol; Rf: 0.38 (toluene); IR (ATR) ν
(cmÀ 1): 2920, 1314, 1128; 1H NMR (400 MHz, CDCl3) δ
(ppm): 1.52 (s, 9H), 3.20 (t, J=4.4 Hz, 2H), 4.00-4.17 (m, 4H),
4.16 (t, J=4.4 Hz, 2H), 5.46 (d, J=9.6 Hz, 1H), 6.81 (d, J=
9.6 Hz, 1H); 13C NMR (101 MHz, CDCl3) δ (ppm): 25.07,
39.90, 47.89, 48.27, 48.54, 62.97, 66.38, 66.45, 109.06, 130.29,
1
(cmÀ 1): 2958, 1526, 1346, 1165, 1087; H NMR (400 MHz,
CDCl3) δ (ppm): 2.92 (t, J=4.4 Hz, 2H), 3.96-4.05 (m, 4H),
4.06 (t, J=4.4 Hz, 2H), 5.68 (d, J=9.6 Hz, 1H), 6.93 (d, J=
9.6 HZ, 1H), 8.09 (d, J=8.8 Hz, 2H), 8.41 (d, J=8.8 Hz, 2H);
13C NMR (101 MHz, CDCl3) δ (ppm): 38.32, 46.75, 47.87,
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131.72, 135.87, 135.92, 138.32, 140.35, 141.80, 141.81, 142.21,
142.25, 142.53, 142.54, 142.80, 143.34, 144.88, 144.92, 145.62,
145.65, 145.67, 145.72, 145.96, 146.44, 146.69, 146.72, 147.82,
147.84, 156.79 (6 signals are not described due to overlapping);
UV-vis (toluene) λmax (nm): 435, 706; ESI-HRMS (m/z)
calculated for [M+Na]+ =984.1029; found 984.1014.
Compound 3p. (13.1 mg, 22% yield, dark brown solid). MW
(C81H20O2S): 1057.11 g/mol; Rf: 0.51 (toluene); IR (ATR) ν
(cmÀ 1): 2914, 1294, 1139; 1H NMR (400 MHz, CDCl3) δ
(ppm): 2.66–3.03 (m, 3H), 3.20–3.34 (m, 1H), 3.85 (d, J=
10.6 Hz, 1H), 4.08 (d, J=11.0 Hz, 1H), 4.43 (d, J=10.6 Hz,
1H), 4.47 (d, J=11.0 Hz, 1H), 4.99 (d, J=7.6 Hz, 1H), 5.83 (d,
J=7.6 Hz, 1H), 7.28–7.39 (m, 5H), 7.62–7.72 (m, 2H), 7.73–
7.81 (m, 1H), 8.07–8.15 (m, 2H); 13C NMR (101 MHz, CDCl3)
δ (ppm): 29.80, 33.60, 48.96, 49.57, 65.54, 66.61, 74.08,
118.35, 125.45, 126.20, 126.68, 127.99, 128.38, 128.66, 129.19,
129.32, 129.69, 134.25, 135.67, 135.88, 136.01, 136.06, 138.33,
138.63, 138.66, 140.28, 140.31, 140.33, 140.40, 141.78, 141.79,
141.82, 141.84, 142.12, 142.16, 142.18, 142.21, 142.26, 142.29,
142.36, 142.39, 142.48, 142.49, 142.56, 142.61, 142.77, 142.81,
142.84, 142.86, 143.23, 143.93, 144.82, 144.85, 144.87, 144.93,
145.32, 145.51, 145.54, 145.57, 145.59, 145.72, 145.73, 145.88,
145.89, 145.92, 146.02, 146.05, 146.45, 146.67, 146.69, 146.71,
146.74, 147.80, 147.85, 148.08, 149.98, 155.95, 156.03, 156.75,
157.10 (1 signal is not described due to overlapping); UV-vis
(toluene) λmax (nm): 435, 700; ESI-HRMS (m/z) calculated for
[M+Na]+ =1079.1076; found 1079.1074.
Compound 3m. (19.7 mg, 27% yield, dark brown solid). MW
(C75H20O4): 984.98 g/mol; Rf: 0.53 (toluene); IR (ATR) ν
1
(cmÀ 1): 2916, 1723, 1423, 1225, 1040; H NMR (400 MHz,
CDCl3) δ (ppm): 1.32 (t, J=7.2 Hz, 6H), 2.68 (t, J=6.0 Hz,
2H), 3.03 (t, J=6.0 Hz, 2H), 4.05–4.14 (m, 4H), 4.26–4.34 (m,
4H), 6.15 (d, J=12.2 Hz, 1H), 6.40 (d, J=12.2 Hz, 1H); 13C
NMR (101 MHz, CDCl3) δ (ppm): 14.39, 31.40, 33.73, 47.90,
48.76, 61.23, 62.22, 66.27, 66.47, 128.73, 131.32, 131.49,
136.12, 136.13, 136.15, 136.16, 140.40, 141.90, 142.32, 142.35,
142.62, 142.67, 142.87, 143.41, 143.77, 144.98, 145.01, 145.72,
145.75, 145.84, 146.09, 146.52, 146.76, 146.79, 147.91, 147.94,
156.84, 156.88, 170.84 (5 signals are not described due to
overlapping); UV-vis (toluene) λmax (nm): 436, 707; ESI-HRMS
(m/z) calculated for [M+Na]+ =1007.1254; found 1007.1260.
Compound 3n. (17.7 mg, 32% yield, dark brown solid). MW
(C77H18O2): 974.99 g/mol; Rf: 0.79 (toluene); IR (ATR) ν
Experimental Procedure for the Synthesis of Fused
Dihydroazepine Derivatives of C70 (4a)
1
(cmÀ 1): 2916, 1725, 1425, 1214; H NMR (400 MHz, CDCl3) δ
(ppm): 2.45–2.61 (m, 1H), 2.66–2.76 (m, 2H), 2.77–2.89 (m,
1H), 3.80 (s, 3H), 3.81-3.93 (m, 1H), 3.96–4.08 (m, 1H), 4.08-
4.33 (m, 2H), 6.40 (d, J=12.2 Hz, 1H), 6.52 (d, J=12.2 Hz,
1H), 7.26 (1H, overlapped with CDCl3 signal, observable in the
COSY-NMR spectra) 7.36-7.44 (m, 4H); 13C NMR (101 MHz,
CDCl3) δ (ppm): 33.67, 34.61, 48.32, 48.46, 52.92, 58.69,
66.13, 66.66, 100.14, 127.02, 127.39, 129.08, 131.22, 131.28,
132.97, 140.18, 140.22, 140.29, 140.32, 140.36, 141.75, 141.80,
141.84, 142.17, 142.20, 142.26, 142.28, 142.49, 142.53, 142.55,
142.76, 142.79, 143.30, 143.37, 143.73 143.76, 144.88, 144.90,
144.93, 145.53, 145.62, 145.64, 145.67, 145.70, 145.74, 145.84,
145.93, 146.00, 146.39, 146.42, 146.43, 146.65, 146.68, 147.78,
147.82, 147.84, 156.64, 156.67, 175.43 (18 signals are not
described due to overlapping); UV-vis (toluene) λmax (nm): 436,
706; ESI-HRMS (m/z) calculated for [M+Na]+ =997.1199;
found 997.1178.
In a 10 mL capped vial under a nitrogen inert atmosphere, a
solution of [Rh(cod) 2]BF4 (5.3 mg, 0.01 mmol) and (R)-
DTBM-segphos (13.5 mg, 0.01 mmol) in anhydrous CH2Cl2
(4 mL) was prepared. Hydrogen gas was bubbled into the
catalyst solution for 30 min before it was concentrated to
dryness, dissolved in anhydrous o-DCB and introduced into a
solution of C70 (100 mg, 0.12 mmol) and bisallene 1a (31.1 mg,
°
0.11 mmol) in anhydrous o-DCB (1.4 mM), preheated to 90 C.
°
The resulting mixture was stirred at 90 C for 40 min (TLC
monitoring), allowed to cool down to room temperature and
directly subjected to column chromatography on silica gel using
CS2 as the eluent to provide unreacted C70. Further elution with
toluene gave the mixture compounds α-4a and β-4a (57.4 mg,
46% in a 3:1 ratio) as a dark solid.
Compound 4a (α-4a:β-4a, 3:1 ratio, 57.4 mg, 46% yield, dark
brown solid). MW (C85H17NO2S): 1116.14 g/mol; Rf: 0.63
(toluene); IR (ATR) ν (cmÀ 1): 3046, 1414, 1158, 1087; 1H NMR
(400 MHz, CDCl3) δ (ppm): 2.29 (s, 3H, α), 2.50 (s, 3H, β),
2.52–2.57 (m, 2H, α), 2.73–2.77 (m, 2H, β), 3.11–3.19 (m, 2H,
α+β), 3.52 (m, 2H, β), 3.55 (m, 2H, α), 3.79 (t, J=4.4 Hz, 2H,
α), 3.86 (t, J=4.4 Hz, 2H, β), 5.23 (d, J=9.2 Hz, 1H, β), 5.51
(d, J=9.6 Hz, 1H, α), 6.83 (d, J=9.2 Hz, 1H, β), 6.93 (d, J=
9.6 Hz, 1H, α), 7.29 (d, J=8.0 Hz, 2H, α), 7.34 (d, J=8.0 Hz,
2H, β), 7.73 (d, J=8.0 Hz, 2H, α), 7.74 (d, J=8.0 Hz, 2H, β);
13C NMR (101 MHz, CDCl3) δ (ppm): 21.77, 38.09, 44.56,
46.19, 47.77, 57.90, 59.75, 111.08, 125.44, 127.25,127.76,
130.24, 130.27, 130.32, 130.36, 131.47, 131.49, 131.58, 133.98,
134.01, 135.98, 137.17, 137.18, 140.34, 142.94, 143.15, 143.20,
143.35, 144.25, 145.95, 146.53, 147.18, 147.21, 147.20, 147.64,
149.04, 149.22, 149.60, 149.66, 150.01, 150.09, 150.12, 150.87,
151.41, 151.53, 151.55, 151.62, 155.32, 161.18 (only the major
product α-4a is identified); UV-vis (toluene) λmax (nm) α-4a:
399, 461; UV-vis (toluene) λmax (nm) β-4a: 365, 399; ESI-
HRMS (m/z) calculated for [M+Na]+ =1138.0872; found
1138.0841.
Compound 3o. (22.0 mg, 39% yield, dark brown solid). MW
(C76H18O2S): 995.04 g/mol; Rf: 0.55 (CH2Cl2); IR (ATR) ν
(cmÀ 1): 2914, 1300, 1130; 1H NMR (400 MHz, CDCl3) δ
(ppm): 2.70-2.82 (m, 2H), 2.83 (s, 3H), 2.92–3.06 (m, 1H),
3.24–3.34 (m, 1H) 3.64–3.86 (m, 1H), 3.89–4.05 (m, 1H),
4.06–4.41 (m, 2H), 6.53 (d, J=12.0 Hz, 1H), 6.69 (d, J=
12.0 Hz, 1H), 7.35 (t, J=7.5 Hz, 1H), 7.44 (t, J=7.5 Hz, 2H),
7.72 (d, J=7.5 Hz, 2H); 13C NMR (101 MHz, CDCl3) δ (ppm):
29.03, 33.63, 36.35, 47.89, 48.24, 65.88, 66.39, 74.67, 128.15,
129.33, 129.48, 129.54, 131.01, 133.23, 134.96, 135.00, 135.70,
135.76, 135.96, 140.15, 140.22, 140.30, 140.37, 141.71, 141.75,
141.79, 141.85, 142.14, 142.17, 142.24, 142.27, 142.39, 142.46,
142.51, 142.77, 142.79, 143.30, 143.33, 144.20, 144.21, 144.85,
144.86, 144.87, 145.23, 145.24, 145.33, 145.52, 145.55, 145.60,
145.62, 145.63, 145.65, 145.67, 145.73, 145.78, 145.95, 146.37,
146.41, 146.44, 146.58, 146.65, 146.69, 147.81, 155.89, 156.23,
156.25, 156.45 (9 signals are not described due to overlapping);
UV-vis (toluene) λmax (nm): 426, 700; ESI-HRMS (m/z)
calculated for [M+Na]+ =1017.0920; found 1017.0899.
Adv. Synth. Catal. 2021, 363, 3835–3844
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General Procedure for the Reduction of Fused
Dihydroazepine Derivatives (5a)
References
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In
a 25 mL round-bottom flask under a nitrogen inert
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and Physics; Springer Netherlands: Dordrecht, 2008; Vol.
1.
atmosphere and equipped with magnetic stirrer, a solution of 3a
(100.0 mg, 0.10 mmol) in anhydrous CH2Cl2 (10 mL) was
°
stirred and cooled at 0 C. Et3SiH (0.15 mL, 0.9 mmol) and
BF3·Et2O (0.1 mL, 0.81 mmol) was then added and the resulting
mixture was stirred for 5 h at room temperature (TLC
monitoring) and directly subjected to column chromatography
on silica using toluene as the eluent to provide compound 5a
(82.1 mg, 82%) as a dark brown solid.
[4] N. Panwar, A. M. Soehartono, K. K. Chan, S. Zeng, G.
Xu, J. Qu, P. Coquet, K. T. Yong, X. Chen, Chem. Rev.
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[6] E. Castro, J. Murillo, O. Fernandez-Delgado, L. Eche-
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[10] W. Krätschmer, L. D. Lamb, K. Fostiropoulos, D. R.
Huffman, Nature 1990, 347, 354–358.
Compound 5a. (82.1 mg, 82% yield, dark brown solid). MW
(C75H19NO2S): 998.04 g/mol; Rf: 0.20 (toluene); IR (ATR) ν
1
(cmÀ 1): 2917, 1424, 1150, 1090; H NMR (400 MHz, CDCl3) δ
(ppm): 2.38 (s, 3H), 2.91 (t, J=4.8 Hz, 4H), 3.66–3.71 (m,
4H), 3.95 (s, 4H), 7.31 (d, J=8.0 Hz, 2H), 7.75 (d, J=8.0 Hz,
2H); 13C NMR (101 MHz, CDCl3) δ (ppm): 21.72, 35.91, 47.81,
48.41, 66.40, 127.39, 129.99, 135.75, 135.85, 137.41, 140.30,
141.76, 142.20, 142.53, 142.79, 143.27, 143.52, 144.85, 145.56,
145.63, 145.90, 146.42, 146.67, 147.80, 156.80 (one signal is
not described due to overlapping); UV-vis (toluene) λmax (nm):
434, 705; ESI-HRMS (m/z) calculated for [M+Na]+ =
1020.1029; found 1020.1005.
Compound 6a (α-6a:β-6a, 3:1 ratio, 42.0 mg, 69% yield, dark
brown solid). MW (C85H19NO2S); 1118.15 g/mol; Rf: 0.25
1
(toluene); IR (ATR) ν (cmÀ 1): 2904, 1423, 1154, 10889; H
NMR (400 MHz, CDCl3) δ (ppm): 2.35 (s, 3H, α), 2.50 (s, 3H,
β), 2.51 (m, 2H, β), 2.61 (t, J=5.2 Hz, 2H, α), 2.61 (m, 2H, β),
2.81 (t, J=5.2 Hz, 2H, α), 2.93 (d, J=14 Hz, 2H, β), 3.07 (s,
2H, α), 3.09 (d, J=14 Hz, 2H, β), 3.40 (m, 2H, β), 3.45 (s, 2H,
α), 3.49 (m, 2H, β), 3.52 (m, 2H, α), 3.62 (m, 2H, α), 7.29 (d,
J=8.0 Hz, 2H, α), 7.38 (d, J=8.0 Hz, 2H, β), 7.71 (d, J=
8.0 Hz, 2H+2H, α+β); 13C NMR (101 MHz, CDCl3) δ (ppm):
21.75, 35.70, 35.86, 44.53, 47.46, 47.68, 48.30, 57.88, 59.77,
127.36, 128.37, 129.19, 129.98, 131.49, 131.60, 133.97, 134.04,
135.73, 135.86, 136.31, 137.18, 140.41, 140.66, 142.28, 142.94,
143.16, 143.20, 143.37, 143.55, 145.95, 146.45, 146.57, 147.19,
147.23, 147.65, 148.31, 149.04, 149.22, 149.60, 149.66, 150.07,
150.10, 150.86, 150.89, 151.38, 151.61, 155.25, 161.40 (only
the major product α-6a is identified); UV-vis (toluene) λmax
(nm): 398, 449 (only the major product α-6a is identified); ESI-
HRMS (m/z) calculated for [M+Na]+ =1140,1029; found
1140.0985.
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Acknowledgements
We are grateful for the financial support by the Spanish
Ministry of Economy and Competitivity (MINECO) (Projects
CTQ2017-85341-P and CTQ2017-83587-P, FPI predoctoral
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