Palladium-catalyzed cycloisomerizations of (Z)-1-iodo-1,6-dienes: Iodine atom transfer and mechanistic insight to alkyl iodide reductive elimination

Article abstract of DOI:10.1021/ja201204g

A palladium-catalyzed iodine atom transfer cycloisomerization of (Z)-1-iodo-1,6-diene has been developed, which provides a facile method to construct six-memebered heterocycles bearing an alkyl iodide group. The ligand screening shows that both the type and the quantity of ligand impose significant influences on this transformation, and the combination of 30 mol % 1,1′-bis(diphenylphosphino)ferrocene (DPPF) and 10 mol % Pd(OAc) ₂ is the optimal choice. The catalytic cycle, consisting of oxidative addition of Pd(0) to vinyl iodide, intramolecular alkene insertion, and alkyl iodide reductive elimination, has been proposed and eventually supported by convincing evidence from a series of control experiments. More importantly, these control experiments disclose some features of the event of alkyl iodide reductive elimination: (1) this reductive elimination is proved to be a stereospecific process; and (2) both alkyl iodide oxidative addition and reductive elimination are not effected by a TEMPO additive. Besides its ability to undergo oxidative addition, the catalyst (palladium + DPPF) could also promote a radical transfer process. The findings described in this paper will be helpful for further development of the metal-catalyzed formation of a carbon-halide bond.

Full text of DOI:10.1021/ja201204g

ARTICLE
pubs.acs.org/JACS
Palladium-Catalyzed Cycloisomerizations of (Z)-1-Iodo-1,6-dienes:
Iodine Atom Transfer and Mechanistic Insight to Alkyl Iodide
Reductive Elimination
Hui Liu,† Chaolong Li,† Dong Qiu,*,‡ and Xiaofeng Tong*,†
†Key Laboratory for Advanced Materials and Institute of Fine Chemicals, East China University of Science and Technology (ECUST),
Shanghai 200237, China
‡Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Polymer Physics and Chemistry,
Institute of Chemistry, Chinese Academy of Sciences (ICCAS), Beijing 100190, China
S Supporting Information
b
ABSTRACT: A palladium-catalyzed iodine atom transfer cycloisome-
rization of (Z)-1-iodo-1,6-diene has been developed, which provides a
facile method to construct six-memebered heterocycles bearing an alkyl
iodide group. The ligand screening shows that both the type and the
quantity of ligand impose significant influences on this transformation,
and the combination of 30 mol % 1,10-bis(diphenylphosphino)ferrocene
(DPPF) and 10 mol % Pd(OAc)2 is the optimal choice. The catalytic
cycle, consisting of oxidative addition of Pd(0) to vinyl iodide, intramo-
lecular alkene insertion, and alkyl iodide reductive elimination, has been
proposed and eventually supported by convincing evidence from a series
of control experiments. More importantly, these control experiments
disclose some features of the event of alkyl iodide reductive elimination: (1) this reductive elimination is proved to be a stereospecific
process; and (2) both alkyl iodide oxidative addition and reductive elimination are not effected by a TEMPO additive. Besides its
ability to undergo oxidative addition, the catalyst (palladium þ DPPF) could also promote a radical transfer process. The findings
described in this paper will be helpful for further development of the metal-catalyzed formation of a carbonꢀhalide bond.
XeF2.9 In 2006, Milstein et al. showed that the CH3ꢀI reductive
1. INTRODUCTION
elimination could take place in a sterically encumbered Rh(III)
Oxidative addition and reductive eliminations are fundamental
pincer-type complex, representing the first direct observation of the
transformations in numerous catalytic and stoichiometric pro-
C(sp3)-X reductive elimination in a Croup 9 metal center.10
cesses.1 In this context, oxidative addition of organic halides has
Despite all the advances in stoichiometric carbon halide
reductive elimination, the catalytic variants are still remarkably
rare and remain to be formidable challenges probably because the
free energy favors oxidative addition, while reductive elimination
received incredibly large amount of attention, as the initial step for
most transition-metal-catalyzed formations of carbonꢀcarbon2 or
carbonꢀX (X = N, O)3 bonds. In contrast to the well established
oxidative addition of organic halides, the reverse reaction, carbon
is thermodynamically uphill. In light of their importance in both
halide reductive elimination from a transition-metal center, is
theoretical consideration and synthetic practice, metal-catalyzed
substantially less documented.4 In 1969, Ruddick et al. reported
reactions for carbonꢀhalide bond formation are highly desirable.11
the thermolysis of the isomeric [(PR3)2Pt(Me)2(I)2] complexes to
yield mixtures of CꢀC and CꢀI reductive elimination products,
tion.5 Since then, continuous efforts have been dedicated to the
Pt(IV) center related carbon halide reductive elimination, and great
A famous example of rhodium-catalyzed acyl-I reductive elimination
comes from the Monsanto methanol carbonylation process, where
representing an early example of C(sp3)-halide reductive elimina-
the rapid hydrolysis of acyl iodide toward a carboxylic acid renders
this reductive elimination irreversible, thus promoting the catalytic
effects.12 Very recently, Buchwald and co-workers have reported the
developments have been achieved, especially for mechanism eluci-
Pd(0)-catalyzedconversionofaryltriflates to aryl halides, which high-
lighted the contribution of sterically demanding, electron-rich biaryl
dation6 and its extension to C(sp2)-halide analogues.7 With respec-
tive to Pd(II) center, Hartwig et al. observed stoichiometric
monophosphine ligand to aryl-X (X = F, Cl, Br) reductive elimina-
reductive elimination of arylpalladium halide induced by an excess
tion.13 While preparing for this manuscript, Lautens et al. reported an
of P(t-Bu)3.8 Interestingly, the reactivity of halide ligands followed
the trend I > Br > Cl, suggesting the importance of kinetic factors in
interesting palladium-catalyzed cross-coupling of polyhalogenated
aryl halide reductive elimination. A few years later, Vigalok et al. also
reported an elegant example of reductive elimination of iodoarene
from the reaction of chelating arylpalladium iodide complexes with
Received: September 1, 2010
Published: April 01, 2011
r
2011 American Chemical Society
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Scheme 1. Design Plan (R2 ¼ H)
Table 1. Initial Screeninga
entry
ligand
x
T (oC)
yield (%)b
c
1
2
P(t-Bu)3
100
100
120
60
80
34
41
P(t-Bu)3
P(t-Bu)3
P(t-Bu)3
P(t-Bu)3
P(t-Bu)3
ꢀ
reflux
reflux
reflux
reflux
reflux
reflux
reflux
reflux
reflux
reflux
reflux
reflux
reflux
reflux
reflux
reflux
reflux
reflux
reflux
reflux
3
39
4
27
5
30
trace
NDg
NDg
NDg
23
6d
7e
8f
100
ꢀ
substrates to synthesize brominated indoles, which, for the first time,
demonstrated that P(t-Bu)3 induced reductive elimination of aryl-
palladium bromides could have catalytic features.14 Although catalytic
carbon halide reductive elimination in a low-valent Pd(II) metal
center has not been widely reported so far, in contrast to the case of a
Pd(IV) center,15 it still provides a novel conceptual alternative.
However, to the best of our knowledge, there has been no report
on catalytic reactions involving the step of alkyl iodide reductive
elimination from a Pd(II) center.
ꢀ
PPh3
ꢀ
9
100
100
50
10
11
12
13
14
15
16
17
18
19
20
21
P(n-Bu)3
DPPE
BINAP
DPPP
DPPB
DPPF
DPPF
DPPF
DPPF
DPPF
DPPF
DPPF
15
trace
10
50
50
25
50
36
50
74
As part of our research on metal-catalyzed cyclizations of
1,6-enynes,16 we have recently become interested in the substrate
of (Z)-1-iodo-1,6-diene 1 (Scheme 1). It has been reported that
substrate 1 offers an unique opportunity to form alkyl-Pd(II)
intermediate B without a β-hydrogen (R2 ¼ H) via oxidative
addition of Pd(0) species to vinyl iodide followed by alkene
insertion (scheme 1).17 Inspired by a recent report where bulky
phosphine P(t-Bu)3 can readily promote aryl-X (X = F, Cl, Br)
reductive elimination from arylꢀPd(II) halides,8,14 we envision
that the alkylꢀPd(II) intermediate B would potentially undergo
a similar alkyl iodide reductive elimination imposed by the same
ligand effect. Herein, we report a palladium-catalyzed iodine
atom transfer cycloisomerization of 1 to yield alkyl iodide 2 (first
reaction, Scheme 1), where the alkyl iodide reductive elimination
from intermediate B is proposed as the product-forming step in
the catalytic cycle (Scheme 1).
70
75
100
20
73
trace
43
25
30
84
40
71
a Reaction Conditions: 1a (0.2 mmol, 83.8 mg), Pd(OAc)2 (0.02 mmol,
4.5 mg), 4 mL toluene, 16 h. b Isolated yield. c [(t-Bu)3PH]BF4/K2CO3
(1:2) was used. d Without Pd(OAc)2. Without ligand. Without Pd-
e
f
(OAc)2 and ligand. g ND = not detected. Compound 1a was recovered.
(BINAP), 1,2-bis(diphenylphosphino)ethane (DPPE), and 1,3-bis-
(diphenylphosphino)propane (DPPP) as well as 1,2-bis(diphenyl-
phosphino)benzene (DPPB), which, however, did not exhibit any
superior performance than P(t-Bu)3 (Table 1, entries 11ꢀ14). For-
tunately, the use of 50 mol % 1,10-bis(diphenylphosphino)ferrocene
(DPPF) as ligand enabled a promising result with a 74% isolated yield
(Table 1, entry 15). Once again, the quantity of DPPF was found to
be an important factor, but its influence on the product yields is not
monotonous (Table 1, entries 16ꢀ21). Nevertheless, the combina-
tion of 30 mol % DPPF and 10 mol % Pd(OAc)2 was identified as the
best choice, delivering 2a in 84% yield (Table 1, entry 20). It should
be noted that some classical radical initiators, such as (Bu3Sn)2, 2,20-
azobisisobutyronitrile (AIBN), or Et3B/O2, did not promote this
cycloisomeration, and the starting material 1a was recovered almost
quantitatively in these cases.
Table 2 summarizes the scope of this reaction under the
optimized conditions as discussed above. In general, the palladium-
catalyzed iodine atom transfer cycloisomerizations can be efficiently
achieved with a considerably wide range of (Z)-1-iodo-1,6-dienes
irrespective of nitrogen or oxygen linkage, delivering alkyl iodide
derivatives 2 in moderate to high yields. Both alkyl and aryl sub-
stituents at C2 position are well tolerated. But the C1-position
functionalized substrate 1c was completely inert under the optimized
conditions (Table 2, entry 3). This problematic issue can be
partially resolved by using activated vinyl iodide as the substrate.
2. RESULTS AND DISCUSSION
2.1. Reaction Optimization and Scope. To test our postula-
tions outlined in Scheme 1, an initial attempt using substrate 1a was
conducted in toluene at 80 °C with the combination of 10 mol %
Pd(OAc)2 and 100 mol % P(t-Bu)3 as catalyst, which really delivered
the anticipated product 2a, albeit only in 34% isolated yield (Table 1,
entry 1). The structural assignment was initially supported by NMR
and high-resolution mass spectrometry (HRMS) and later corrobo-
rated by X-ray crystallography of product 2b (vide infra).18 The yield
of 2a could increase to 41% when the reaction temperature was
elevated to 120 °C (Table 1, entry 2). Moreover, the quantity of P(t-
Bu)3 had great impact on the reaction yield (Table 1, entries 3ꢀ5). It
was found that the combination of Pd(OAc)2 and phosphine ligand
was essential for this transformation; no desired product was obtained
in the absence of either Pd(OAc)2 or ligand or both (Table 1, entries
6 and 8). Encouraged by these findings, different ligands were further
evaluated. Other two monophosphine ligands, PPh3 and P(n-Bu)3,
gave inferior results with yields of 23 and 15%, respectively (Table 1,
entries 9 and 10). We therefore examined a variety of biphos-
phine ligands, such as 2,20-bis(diphenylphosphino)-1,10-binaphthyl
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Table 2. Substrate Scopea
even the bulky isobutyl group was compatible in terms of reaction
rate and yield (Table 2, entry 7). Furthermore, oxygen-functiona-
lized tether could also be introduced into C6-position (Table 2,
entries 8ꢀ10). It was worth noting that the reaction of (E)-1a did
not give 2a on the base of thin-layer chromatography (TLC)
monitor and 1H NMR analysis of the crud reaction mixture, although
it was completely consumed within 16 h (Table 2, entry 12).
2.2. Mechanistic Consideration. Although elegant mecha-
nistic analysis has uncovered several fundamental principles
related to aryl-halide reductive elimination so far,8ꢀ14 the alkylꢀ
halide analogue still remains untouched. We believe that the
reactions described above, especially the alkyl-I bond formation,
would be a simple platform for mechanistic investigation, leading to
a basic understanding for the further development of the transition-
metal-catalyzed formation of carbonꢀhalogen bond.
2.2.1. Catalytic Cycle. As mentioned in the Introduction
Section, this transformation is initiated by oxidative addition of
Pd(0) to vinyl iodide to yield vinylꢀpalladium intermediate A,
which is followed by alkene insertion to form alkylꢀPd(II)
intermediate B (Scheme 2, Cycle I). The lack of β-hydrogen and
the presence of excess DPPF ligand might enforce intermediate B to
undergo alkyl iodide reductive elimination. Thus, the alkyl iodide
product 2 is obtained, and the Pd(0) catalyst is regenerated.
However, in light of the structural relationship between 1 and 2,
an alternative possibility, the classic metal-catalyzed radical cycliza-
tion, should also be considered (Scheme 2, Cycle II).19 At the initial
stage, the Pd(0) species abstracts20 the iodine atom from the vinyl
iodide to generate a vinyl radical intermediate C and the metallic
species LnPdI.21 According to Nagashima’s finding,22 the interactions
between the radical species C and metallic species LnPdI are not so
strong. Thus, intermediate C will undergo radical addition in
6-exotrig fashion to form intermediate D, which abstracts the iodine
atom from LnPdI to yield product 2. However, the fact that (Z)-1a
and (E)-1a (Table 2, entries 1 and 12) presented completely
different behavior under the same conditions primarily indicated
the pathway of Cycle II to be unlikely. Further evidence against Cycle
II has been obtained from the following experiment.
When the reaction of 1b was performed by using a chiral ligand
(S)-BINAP instead of DPPF, as expected, 2b was obtained with
56% ee, albeit only in 10% yield (Scheme 3). These results
strongly suggested the existence of vinylꢀPd(II) intermediate
A*, which induced asymmetric alkene insertion to realize the
enantioselectivity. Obviously, the pathway of Cycle II, if possible,
is unlikely to produce the enantioriched 2b because the interac-
tion between LnPdI and intermediate C is too weak to promote
asymmetric induction.22
The above results lead us to conclude that vinyl iodide 1 and
Pd(0) species are prone to the formation of a regular oxidative
addition adduct, such as intermediate A, rather than a radical pair
(intermediate C þ LnPdI). One more evidence to support this
argument comes from the results of HCO2H NEt3 testing
3
(Scheme 4). In fact, compound 3 could be isolated in 48% yield
when the reaction of 1b was conducted with HCO2H NEt3 (5
3
equiv) as the additive; while under the same conditions, product
4 was obtained in the yield of 56% starting from substrate (E)-1a
(Scheme 4). Therefore, the oxidative addition adduct (E)-A-1a
was supposed to be involved, which was subsequently reduced by
a Reaction Conditions: 1 (0.2 mmol), Pd(OAc)2 (0.02 mmol, 4.6 mg),
DPPF (0.06 mmol, 34 mg), 4 mL toluene, 120 °C, 16 h. b Isolated yield.
c NR = no reaction.
the reagent HCO2H NEt3 to generate compound 4 (Scheme 4).
3
Indeed, compound 1d with electron-deficient vinyl iodide was found
to be a suitable substrate although the corresponding product 2d was
isolated in a lower yield (Table 2, entry 4). On the contrary,
substitution at the C6-position showed a much wider tolerance;
The configuration of vinyl-Pd(II) intermediate (E)-A-1a is
believed to be the reason for the failed conversion of (E)-A-1a
into 2a (Table 2, entry 12), thus the possibility of cycle II in
scheme 2 can be further precluded.
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Scheme 2. Proposed Reaction Mechanisms
Scheme 3. Asymmetric Induction
Scheme 5. Investigation of the Mechanism of Alkyl Iodide RE
Scheme 4. HCO2H NEt3 Testing
3
Scheme 6. Effect of Reaction Time on Deuterium
Scrambling
2.2.2. Mechanism of Alkyl Iodide Reductive Elimination.
While the reaction mechanism depicted in Scheme 2 is a lack
of direct evidence at this stage and still needs to be further
verified, the pathway of Cycle I seems to be more consistent with
the current experimental findings. After the establishment of the
steps of oxidative addition and alkene insertion in Cycle I, we
then focus on the subsequent step of alkyl iodide reductive
elimination (RE).
To this purpose, we synthesized the deuterated substrate 1e-D
(75% D) with (Z)-configuration terminal olefin. The reaction of
deuterated substrate 1e-D would involve intermediate F with
well-defined stereochemistry resulted from stereospecifically
intramolecular insertion of olefin to vinylꢀpalladium bond in
intermediate A-1e-D via a transition state E17 (Scheme 5).
Intermediate F will then undergo an alkyl iodide RE process
to afford product 5. In turn, the stereochemical information of
5 can be used to deduce the corresponding mechanism of
alkyl iodide RE process.
Initially, we subjected compound 1e-D to the optimized
conditions and ran this reaction for 16 h. To our delight, deu-
terated product 5d was obtained in 79% yield without deuterium
erosion but with deuterium scrambling (17% and 58%) (entry 4,
Scheme 6). Apparently, the observation of deuterium scrambling
seems to support a radical-involved process. However, the fact
that only partial deuterium scrambling was observed in 5d needs
to be further elucidated. This finding inspired us to examine the
reaction of 1e-D more carefully. Surprisingly, compound 5e with
more even deuterium scrambling (35 and 40%) was obtained
when the reaction time was prolonged to 24 h (entry 5,
Scheme 6), implying a great effect of reaction time on deuterium
scrambling. Thus, a series of control experiments with different
reaction times was tested. When the reaction of 1e-D was
interrupted at 2 h, compound 5a was unexpectedly isolated in
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Scheme 7. Reaction of 2b and HCO2H NEt3
Scheme 8. Reaction of 2b and HCO2H NEt3 in the Presence
of TEMPO
3
3
60% yield without deuterium scrambling; meanwhile 1e-D was
recovered in 33% yield (entry 1, Scheme 6). With the reaction
time increased to 6 and 10 h, the corresponding products were
isolated at higher yields, but the deuterium scrambling was still
negligible (entries 2 and 3, Scheme 6). Furthermore, we found
that 5a could be readily converted into 5e under the optimized
conditions (eq 1).23 These results strongly indicated that the
event of deuterium scrambling should be promoted by the
reaction of the newly formed product 5a with Pd(0) catalyst,
rather than the palladium-catalyzed cycloisomerization. Thus, we
conclude that alkyl iodide reductive elimination in this palladium
catalysis is a stereospecific process.
Scheme 9. TEMPO Testing
could be improved by increasing the catalyst loading to 20 mol %
(Scheme 8, entry 2). Theses results strongly indicated that
TEMPO might impose a negative effect on the catalyst itself
rather than the process of alkyl iodide oxidative addition.
The above results inspired us to investigate the effect of
TEMPO on the reaction of 5a under the optimized conditions. In
fact, compound 5a could be recovered quantitatively with 200 mol %
TEMPO as additive under the optimized conditions for 24 h
(Scheme 9a), which was completely different from the case in the
absence of TEMPO (eq 1). With combination of the results from
2.2.3. Explanation for the Observed Deuterium Scrambling.
The control experiments as outlined in Scheme 6 and eq 1 have
established that alkyl iodide reductive elimination in this palla-
dium catalysis is a stereospecific step. Based on the principle of
microscopic reversibility, it is reasonable to deduce that the
reverse reaction, alkyl iodide oxidative addition, if possible under
the same conditions, should also be a stereospecific process.
Thus, it seems that the observed deuterium scrambling should be
caused by a process other than the oxidative addition reaction of
the newly formed product 5a and Pd(0) catalyst.
both HCO2H NEt3 and TEMPO testing (Schemes 8 and 9), the
3
following conclusions can be drawn: (1) alkyl iodide oxidative
addition and the deuterium scrambling of 5a are two separate
processes, both of which can be initiated by the combination of
Pd(0) and DPPF; and (2) the reaction accounting for the deuterium
scrambling seems to be a standard process of radical transfer,20,26
which can be completely inhibited by a radical scavenger (TEMPO).
As expected, TEMPO additive also ensured the reaction of
1e-D to produce compound 5a without deuterium scrambling
under the optimized conditions even for 24 h (Scheme 9b). More
importantly, the isolated yield of 5a was 71%. The negligible
effect of TEMPO on the yield of the deuterated product 5a
suggests that the TEMPO additive does not disturb the process
of alkyl iodide reductive elimination, which is consistent with the
observation from alkyl iodide oxidative addition (Scheme 8).
Thus, it is believed that alkyl iodide reductive elimination and
oxidative addition in this palladium catalysis is more likely to be a
nonradical process.
To address the event of deuterium scrambling more clearly, we
first sought to determine what actually happened to the newly
formed alkyl iodides under the optimized conditions. We em-
ployed HCO2H NEt3 (500 mol %) as an additive24 to probe the
3
chemical behavior of 2b (Scheme 7). To our delight, compound
3 was isolated in 92% yield, which was postulated to be formed
via the route as depicted in Scheme 7. Additionally, it was found
that the reagent HCO2H NEt3 could not realize this transfor-
3
mation without Pd(OAc)2 or DPPF. These results suggest the
facile oxidative addition of Pd(0) to the newly formed alkylꢀI
bond, resulting in alkylꢀPd(II) intermediate B-2b (Scheme 7).
Furthermore, we found that TEMPO imposed some effects on
3. CONCLUSIONS
We have found a Pd(0)-catalyzed cycloisomerization of (Z)-1-
iodo-1,6-diene with an iodine atom transfer. This reaction
provides a facile entry to 1,2,3,6-tetrahydropyridines with a
quaternary carbon center. The reaction mechanism, consisting
of oxidative addition of vinyl iodide, alkene insertion, and alkyl
iodide reductive elimination, has been established on the basis of
the reaction of 2b and HCO2H NEt3 (Scheme 8). Indeed, when
3
the reaction of 2b and HCO2H NEt3 was conducted in the
3
presence of 200 mol % TEMPO, the corresponding yield of
compound 3 was dropped to 63% with 27% of 2b recovered
(Scheme 8, entry 1), although it failed to isolate any adducts
derived from radicals and TEMPO. However, the performance
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the results of a series of control experiments. More importantly,
these control experiments disclose some features of the event of
alkyl iodide reductive elimination: (1) this reductive elimination
is proved to be a stereospecific process; and (2) both alkyl iodide
oxidative addition and reductive elimination are not effected by
TEMPO additive. Furthermore, it was found that the combina-
tion of palladium and DPPF might promote the process of radical
transfer, which could make the scrambling of stereochemistry of
alkyl iodide. We believe that the findings described in this paper
will be helpful for further development of metal-catalyzed for-
mation of carbonꢀhalide bond.
(d) Culkin, D. A.; Hartwig, J. F. Acc. Chem. Res. 2003, 36, 234. (e) Fu,
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4. EXPERIMENTAL SECTION
General Procedure for Pd-Catalyzed Cycloisomerization.
In a 25 mL Schlenk tube, the mixture of 1a (0.2 mmol, 84 mg),
Pd(OAc)2 (0.02 mmol, 4.6 mg), and DPPF (0.06 mmol, 34 mg) were
dissolved in toluene (4 mL). Then, the reaction mixture was heated to
reflux under nitrogen atmosphere. The reaction was monitored by TLC.
When compound 1a disappeared, the mixture was cooled to room
temperature and directly subjected to column chromatography (silica
gel, petroleum ether/EtOAc 50:1 to 5:1 gradient) to give a yellow oil (70
mg, 84% yield). See also Supporting Information.
2a: 1H NMR (400 MHz, CDCl3): δ 0.99 (t, J = 7.2 Hz, 3H), 1.08 (s,
3H), 1.96 (q, J = 7.2 Hz, 2H), 2.43 (s, 3H), 2.54 (d, J = 11.2 Hz, 1H),
3.16ꢀ3.22 (m, 2H), 3.28 (d, J = 10.0 Hz, 1H), 3.33 (d, J = 11.2 Hz, 1H),
3.55 (d, J = 15.6 Hz, 1H), 5.20 (s, 1H), 7.34 (d, J = 8.4 Hz, 2H), 7.69 (d,
J = 8.4 Hz, 2H); 13C NMR (100 MHz, CDCl3): 12.0, 18.2, 21.5, 25.4,
27.0, 36.0, 47.5, 52.4, 124.3, 127.7, 129.7, 133.1, 136.3, 143.6; MS (m/z):
419 (Mþ); HRMS calcd for C16H22INO2S: 419.0416, found: 419.0414.
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’ ASSOCIATED CONTENT
S
Supporting Information. Preparative methods and spec-
b
tral and analytical data for all new compounds and X-ray crystal-
lographic data for 2b (CIF). This material is available free of
charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
tongxf@ecust.edu.cn; dqiu@iccas.ac.cn
’ ACKNOWLEDGMENT
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This work is supported by Shanghai Municipal Committee of
Science and Technology (09ZR1408500) and the Fundamental
Research Funds for the Central Universities. Special gratitude
goes to Professor Limin Wang and Ms. Shuzhen Jiang for their
long-term support. We also thank Professors Guosheng Liu
(SIOC) and Zengming Shen (SJTU) for helpful discussions.
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