Experimental and theoretical investigation of hydrogenative cyclization of allenynes

Article abstract of DOI:10.1002/ejoc.201100280

Upon platinum-catalyzed hydrogenation, allenynes underwent reductive cyclization to provide hetero- and carbocycles with completely controlled regio- and stereoselectivity. By employing hydrogen as a reductant, the use of stoichiometric amounts of toxic o

Full text of DOI:10.1002/ejoc.201100280

FULL PAPER
DOI: 10.1002/ejoc.201100280
Experimental and Theoretical Investigation of Hydrogenative Cyclization of
Allenynes
Hyo-Tong Kim,[a] Hyo-Sang Yoon,[a] Woo-Young Jang,[a] Youn K. Kang,*[b] and
Hye-Young Jang*[a]
Keywords: Cumulenes / Allenes / Alkynes / Platinum / Hydrogenation / Reductive cyclization / Density functional calculations
Upon platinum-catalyzed hydrogenation, allenynes under-
went reductive cyclization to provide hetero- and carbo-
cycles with completely controlled regio- and stereoselecti-
vity. By employing hydrogen as a reductant, the use of stoi-
chiometric amounts of toxic organometallic reductants was
avoided, leading to clean and cost-effective synthesis. A pos-
sible catalytic cycle is proposed on the basis of a deuterium-
labeling study and theoretical calculations.
product was realized. In addition, the use of a large excess
of organometallic reductants was avoided, and the amounts
of byproducts were reduced by using hydrogen, leading to
an atom-economical and clean process. As reaction mecha-
nisms, the hydrometalation of the alkyne or the allene and
the metallacycle formation are considered. On the basis of
theoretical calculations, a catalytic cycle initiated with hy-
drometalation of the alkyne is proposed, implying that the
alkyne shows higher reactivity toward the platinum–hydride
complex than the allene. The mechanism involving a metalla-
cyclic intermediate appears to be an energetically difficult
route.
Introduction
The transition-metal-catalyzed reductive cyclization of π-
unsaturated compounds has been studied extensively as a
convenient route for producing synthetically useful carbo-
and heterocycles.[1–3] Among the π-unsaturated compounds
used for reductive cyclization, alkynes have often been em-
ployed because they are subjected to facile hydrometalation
at the onset of the catalytic cycle. On the other hand, allenes
are less preferred for reductive cyclization because of their
poor selectivity and reactivity. Accordingly, studies on re-
ductive cyclization of allenynes that aim to assess the prod-
uct distribution and the related reaction mechanism are of
interest.[3–6] We expect that our experimental results and
theoretical calculations on reductive cyclization of allenynes
will contribute to a better understanding of the reactivity
and selectivity of allenyne cyclization under hydrogenative
conditions.
Results and Discussion
Table 1 lists the optimization results of the hydrogenative
Recently, our research group studied platinum-catalyzed, cyclization of allenyne 1a. Initially, compound 1a was sub-
hydrogen-mediated, reductive cyclization by using a wide jected to reaction conditions involving [PtCl2(cod)] (5 mol-
range of π-functional groups: bis(enones), enone–aldehydes, %), P[2,4,6-(OMe)3C6H2]3 (5 mol-%), and SnCl2 (25 mol-
alkyne–alkenes, alkyne–α,β-unsaturated carbonyl com- %) in dichloroethane (DCE) under 1 atm of H2 at 80 °C
pounds, alkyne–dienes, alkyne–aldehydes, and allene–hy- to afford the five-membered ring product 1b in 47% yield
drazones.[7] As part of an ongoing effort to extend the scope (Table 1, entry 1). The indicated alkene geometry was con-
of platinum-catalyzed hydrogenative cyclization and to gain firmed by a NOESY experiment. The yield was increased
mechanistic insights, investigations on the reductive cycliza- significantly by increasing the stoichiometry of the phos-
tion of allenynes and related theoretical calculations were phane ligand to 10 mol-% (Table 1, entry 2). The electronic
carried out. A remarkable achievement pertaining to the effect of the phosphane ligands was then evaluated: elec-
reductive cyclization of allenynes was that complete control tron-rich phosphanes tended to form the desired reductive
of the regiochemistry and alkene stereochemistry of the cyclization products (Table 1, entries 2–5). Interestingly, the
NHC carbene ligand, which is a strong σ donor, showed a
[a] Division of Energy Systems Research, Ajou University,
yield that was lower than the yield of the reaction involving
P[2,4,6-(OMe)3C6H2]3 (Table 1, entry 6). The reaction did
not occur in the presence of 10 mol-% NHC ligand. The
Pt complex without the COD ligand produced a reductive
cyclization product with a yield (69%) similar to that of the
[PtCl2]-catalyzed reaction (Table 1, entry 7).
Suwon, 443-749, South Korea
Fax: +82-31-219-1615
E-mail: hyjang2@ajou.ac.kr
[b] Department of Chemistry, Sangmyung University,
Seoul, 110-743, Korea
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201100280.
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Hydrogenative Cyclization of Allenynes
Table 1. Optimization of reductive cyclization of allenyne 1a.
Table 2. Cycloreduction of allenynes.[a]
Entry Pt complex[a] Ligand
(5 mol-%)
Yield
[%]
1
2
3
4
5
6
7
[PtCl2(cod)] P[2,4,6-(OMe)3C6H2]3 (5 mol-%)
[PtCl2(cod)] P[2,4,6-(OMe)3C6H2]3 (10 mol-%) 71
[PtCl2(cod)] P(p-OMeC6H4)3 (10 mol-%)
[PtCl2(cod)] P(p-CF3C6H4)3 (10 mol-%)
[PtCl2(cod)] P(2-furyl)3 (10 mol-%)
[PtCl2(cod)] NHC (5 mol-%)[c]
47
44
n.r.[b]
10
45
[PtCl2]
P[2,4,6-(OMe)3C6H2]3 (10 mol-%) 69
[a] COD = 1,5-cyclooctadiene. [b] n.r. = no reaction. [c] NHC =
1,3-bis(2,4,6-trimethylphenyl)-1,3-dihydro-2H-imidazol-2-ylidene.
A range of allenynes were evaluated under the indicated
conditions (Table 2). From the results for compounds 1b,
2b, and 3b, the allenyne possessing additional methyl groups
at the allene terminal was found to provide a higher yield
(Table 2, entries 1–3).[8] Next, the effect of the substituent
at the alkyne was assessed. Allenynes with 2-naphthyl, 2-
anisol, and 3-anisol groups underwent cyclization and pro-
vided the corresponding products in 73, 65, and 72% yield,
respectively (Table 2, entries 4–6). The cyclization of TMS-
substituted compound 7a gave a lower yield (33%) com-
pared with the aromatic substituted substrates (Table 2, en-
try 7). In the case of compound 8b, the gem-dimethyl group
proximal to the alkyne affected the yield of the cyclization,
resulting in a slightly decreased yield (56%; Table 2, entry
8). In addition to the reductive cyclization of nitrogen-
tethered compounds, the reductive cyclization of carbon-
tethered compound 9a was attempted, and it was found to
provide the product 9b in 57% yield (Table 2, entry 9).
A deuterium-labeling experiment was carried out by
using allenyne 1a to gain some insights into the reaction
mechanism (Scheme 1). Under 1 atm of D2, the reaction af-
forded 1b, in which 100% deuteration occurred at both al-
kenes. It is apparent that hydrogen gas is the source of pro-
tons at the two vinyl positions and that the hydrogenation
process is indeed occurring through Pt catalysts, which in
turn implies that the reaction pathway is most probably by
hydrometalation or oxidative cyclization of Pt catalysts.[7,9]
Scheme 1. A deuterium-labeling study.
[a] Reagents and conditions: starting materials (0.25 mmol), Pt
complex (5 mol-%), ligand (indicated mol-%), SnCl2 (25 mol-%),
DCE (0.1 m), H2 (1 atm), 80°C; Ts = tosyl, TMS = trimethylsilyl.
[b] [PtCl2(cod)], P[2,4,6-(OMe)3C6H2]3 (10 mol-%). [c] [PtCl2(cod)],
P(2-furyl)3 (5 mol-%). [d] [PtCl2], P[2,4,6-(OMe)3C6H2]3 (5 mol-%).
[e] PtCl2, P[2,4,6-(OMe)3C6H2]3 (10 mol-%). [f] [PtCl2(cod)],
P[2,4,6-(OMe)3C6H2]3 (5 mol-%).
To delineate the reaction mechanism further, we per-
formed DFT calculations.[10,11] On the basis of previously
reported studies, as well as the deuterium-labeling experi-
ment shown above, we focused on two major reaction path-
ways that included hydrometalation and oxidative cycliza-
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FULL PAPER
Scheme 2. Proposed mechanism involving hydrometalation.
tion, as schematically shown in Schemes 2 and 3, respec-
Before pursuing the catalytic pathway, we needed to de-
tively. Other possible routes involving cycloisomerization of fine the active catalyst species first. On the basis of many
allene–enes and enynes, which can be formed by partial re- past studies, including our previous work, we presumed that
duction of allenynes, are excluded, based on the control ex- [PtH(PR3)2(SnCl3)] [R = 2,4,6-(OMe)3C6H2] was formed
periments.[12,13] Separately prepared allene–ene and enyne when a [PtCl2(cod)] or [PtCl2] catalyst precursor was treated
compounds were not converted to 1,4-diene products under with phosphane ligands and SnCl2 under an H2 atmo-
platinum-catalyzed hydrogenation conditions.[14]
sphere.[7,15] The optimized geometry of the compound’s
structure is square planar with two phosphane ligands in
the trans position. Owing to the sterically congested nature
of tris(2,4,6-trimethoxyphenyl)phosphane, the axial posi-
tion of the Pt ion is barely accessible, inhibiting the ap-
proach of additional ligands. Consequently, the optimiza-
tion process starts by forcefully positioning alkyne or allene
groups at the axial position of the Pt ion in a square pyram-
idal geometry, which leads to the detachment of one of the
phosphane ligands. Therefore, we adopted [PtH(PR3)-
(SnCl3)] as the real catalyst species. We then considered the
conformation of a catalyst–substrate adduct. Compound 3a
was chosen as the substrate for its structural simplicity.
Since it was not clear which unsaturated π bond (alkyne or
allene) was more favorable for binding with the Pt ion, we
built four different conformational representations, as illus-
trated in Scheme 4. The calculation results indicated that
while the alkyne-bound adduct (E02) had the most stable
conformation, its stabilization energy was only
Scheme 3. Proposed mechanism involving oxidative cyclization.
Scheme 4. Five different conformational representations of possible reactant states. Numbers in parentheses are relative zero-point energy
(ZPE)-corrected free energies in units of kcalmolϪ1, obtained by frequency calculations for the gas phase. R denotes the 2,4,6-trimethoxy-
1-phenyl group.
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Hydrogenative Cyclization of Allenynes
5.4 kcalmolϪ1; this implied that the thermal energy at the other hand, the cyclized intermediate IE0 needs to over-
experimental reaction temperature (80 °C) could easily ex- come an activation barrier of 29 kcalmolϪ1 to proceed to
ceed the stabilization energy. Thus, we decided to consider IE01. This activation barrier is quite large and cannot be
the reaction pathways starting from both the alkyne-bound overcome by the conventional thermal reaction carried out
geometry (E02) and allene-bound one (A02). When both at 80 °C. Moreover, the activation barrier for the forward
alkyne and allene groups were coordinated to the reaction at the IE0 state rather higher than that for the re-
[PtH(PR3)(SnCl3)] catalyst species, the optimized geometry verse reaction by 6.6 kcalmolϪ1, which would retard the re-
turned out to be M01. The five-coordinate stationary state action. For these reasons, the pathway via IE0 is less favor-
could not be located. Moreover, the free energy of M01 was able than that via IE1. After the oxidative addition of a
higher than that of E02 by 40.5 kcalmolϪ1. Therefore, it hydrogenation molecule to the Pt ion (IE121), reductive eli-
was thought to be reasonable to remove the five-coordinate mination leads to the product state PE3.
stationary state from the list of suitable reactant states.
Besides the mechanism involving hydrometalation, we
Once two reactant states were defined with the full geom- examined the route involving metallacycle IE2. The geome-
etry, for further calculations and to save computational try of the transition state that leads E2 to IE2 is a five-
cost, we used simplified models in which the PR3 (R = coordinate square pyramid in which the alkyne and the al-
2,4,6-trimethoxy-1-phenyl) ligand was replaced by PH3 and lene groups occupy two coordination sites in cis conforma-
the tosyl group at the nitrogen atom was replaced with H. tion and the hydride is at the pyramidal vertex. The energy
The simplified models are labeled A2 and E2 and are shown of this state is extremely high (47.9 kcalmolϪ1) and thus the
in Figure 1. The thermodynamic free energies of these two reaction through this transition state is practically unfavor-
reactant states are coincidently isoenergetic.
able.
The allene-bound reactant state, A2, showed a different
We examined the pathway starting from E2. The reaction
pathways could be further partitioned to (1) 5-exo cycliza- reaction pattern. Importantly, despite our extensive search,
tion (occurring first) and hydrometalation, or (2) vice versa. the pathway involving hydrometalation from A2 could not
The E2-IE0-IE01 pathway corresponds to 5-exo cyclization be found due to the lack of appropriate transition states.
followed by hydrometalation, whereas the E2-IE1-IE12 However, the metallacyclic intermediate IA2 and the transi-
pathway corresponds to hydrometalation followed by cycli- tion state leading to it were successfully located. The reac-
zation. The reaction barrier for the 5-exo cyclization from tion from A2 to IA2 is exothermic by 13.5 kcalmolϪ1. IA2
the E2 state was 20.7 kcalmolϪ1 and that for the hydromet- can evolve to IA01, which is geometrically and energetically
alation was only 8.8 kcalmolϪ1. The latter is more favor- similar to IE12. The reaction barrier for this process is only
able. The hydrometallated intermediate IE1 proceeds to 5.1 kcalmolϪ1. Upon oxidative addition of a hydrogen mo-
IE12 via TS_IE1_IE12 with
a reaction barrier of lecule to the Pt ion of IA01, hydrometalation to the vinyl
14 kcalmolϪ1. Although this barrier is only 1 kcalmolϪ1 group occurs, leading to the product state PA2. However, it
lower than that for the reverse reaction, the forward reac- should be noted that the activation barrier of the first step
tion toward IE12 is highly exothermic, and thus, the overall (A2ǞIA2) is 34.6 kcalmolϪ1, which is 25.8 kcalmolϪ1
process from E2 to IE12 appears to be very smooth. On the higher than that of the E2ǞIE1 counterpart. Therefore,
Figure 1. Free energy reaction profile of platinum-catalyzed reductive cyclization reactions of 1,6-allenyne. Numbers in red denote ZPE-
corrected free energies in kcalmolϪ1 calculated by DFT at the B3LYP/6-31G(d) and LANL2DZ levels. Green dotted lines signify most
probable reaction pathways. For details of structures of all compounds listed in this diagram, see the Supporting Information.
Eur. J. Org. Chem. 2011, 3748–3754
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H.-T. Kim, H.-S. Yoon, W.-Y. Jang, Y. K. Kang, H.-Y. Jang
FULL PAPER
1 H, aromatic H), 7.12 (d, J = 7.2 Hz, 2 H, aromatic H), 4.39 (d,
J = 14.8 Hz, 1 H, CH2-NTs), 3.91 (d, J = 15.2 Hz, 1 H, CH2-NTs),
3.65 (m, 2 H, CH2-NTs), 2.60 (t, J = 8.0 Hz, 1 H, allylic H), 2.40
(s, 3 H, CH3Ts), 1.76 (s, 3 H, CH3), 1.66 (s, 3 H, CH3) ppm.
the working mechanism would most likely consist of i. cata-
lyst binding to the alkyne group of 1,6-allenyne (E2), ii.
hydrometalation (E2ǞTS_E2_IE1ǞIE1), iii. 5-exo cycli-
zation (IE1ǞTS_IE1_IE12ǞIE12), iv. oxidative addition
of a hydrogen molecule (IE12ǞIE121), and v. reductive
elimination (IE121ǞTS_IE121_PE3ǞPE3). It is impor-
tant to note that the model calculation indicates the confor-
mation required for the hydrometalation of the alkyne and
the stereochemical outcome of the exomethylene alkene as
a Z type (TS_E2_IE1), which accounts for the experimental
results .
(Z)-3-Benzylidene-1-tosyl-4-vinylpyrrolidine (3b): The representative
experimental procedure was applied to compound 3a (84 mg,
0.25 mmol) to yield product 1b (13.6 mg, 16%). 1H NMR
(400 MHz, CDCl3): δ = 7.72 (m, 2 H, aromatic H), 7.27 (m, 5 H,
aromatic H), 7.08 (m, 2 H, aromatic H), 6.18 (s, 1 H, =CHPh),
5.57 (m, 1 H, CH=CH2), 5.18 (m, 2 H, CH=CH2), 4.30 (d, J =
14.8 Hz, 1 H, CH2-NTs), 3.98 (d, J = 15.2 Hz, 1 H, CH2-NTs),
3.63 (m, 1 H, CH2-NTs), 3.43 (d, J = 7.6 Hz, 1 H, CH2-NTs), 2.84
(m, 1 H, allylic H), 2.42 (s, 3 H, CH3) ppm. 13C NMR (100 MHz,
CDCl3): δ = 143.8, 139.0, 136.4, 136.0, 129.9, 128.7, 128.6, 128.2,
127.9, 127.3, 124.3, 118.7, 52.3, 51.0, 49.6, 21.9 ppm. HRMS:
calcd. for C20H21NO2S [M + H]+ 340.1371; found 340.1366. IR
Conclusions
We have found that allenynes participate in reductive cy-
clization to afford cyclic compounds with good stereoselec-
tivity and reasonable yield under hydrogenation conditions.
Depending on the substitution pattern of the substrates, the
yields are variable. Allenynes with an aromatic group at the
alkyne and a dimethyl group at the allene show good yield.
On the basis of a deuterium-labeling study and theoretical
calculations, a tentative mechanism beginning with hydro-
metalation of the alkyne by a [PtHLn] complex has been
proposed.
(KBr): ν = 2955, 2924, 2853, 1598, 1493, 1447, 1347, 1163, 1093,
˜
1041 cm–1.
(Z)-3-(2-Methylprop-1-enyl)-4-(naphthalen-2-ylmethylene)-1-tosyl-
pyrrolidine (4b): The representative experimental procedure was ap-
plied to compound 4a (51 mg, 0.12 mmol) to yield product 4b
1
(37.7 mg, 73%). H NMR (400 MHz, CDCl3): δ = 7.77 (m, 5 H,
aromatic H), 7.57 (s, 1 H, aromatic H), 7.47 (m, 2 H, aromatic H),
7.29 (m, 3 H, aromatic H), 6.25 (s, 1 H, =CHNaph), 4.93 (d, J =
7.4 Hz, 1 H, =CH), 4.53 (d, J = 15.2 Hz, 1 H, CH2-NTs), 4.01 (d,
J = 14.8 Hz, 1 H, CH2-NTs), 3.70 (m, 2 H, CH2-NTs), 2.64 (m, 1
H, allylic H), 2.39 (s, 3 H, CH3Ts), 1.79 (s, 3 H, CH3), 1.69 (s, 3
H, CH3) ppm. 13C NMR (100 MHz, CDCl3): δ = 143.8, 140.5,
136.8, 134.2, 133.5, 132.8, 132.3, 129.9, 128.3, 128.2, 127.9, 127.7,
127.2, 126.5, 126.3, 126.2, 123.2, 122.0, 52.7, 51.2, 44.4, 26.3, 21.9,
18.6 ppm. HRMS: calcd. for C26H27NO2S [M+] 417.1763; found
Experimental Section
General: All reactions were run under an atmosphere of argon,
unless otherwise indicated. Anhydrous solvents were transferred by
an oven-dried syringe. Flasks were flame-dried and cooled under a
stream of nitrogen. DCE was distilled from calcium hydride. Prod-
uct 2b[7c] exhibited spectral properties consistent with previous lit-
erature reports.
417.1764. IR (KBr): ν = 2971, 2920, 2851, 1597, 1347, 1165, 1093,
˜
1037 cm–1.
(Z)-3-(2-Methoxybenzylidene)-4-(2-methylprop-1-enyl)-1-tosylpyr-
rolidine (5b): The representative experimental procedure was ap-
plied to compound 5a (99 mg, 0.25 mmol) to yield product 5b
(65 mg, 65 %). 1H NMR (400 MHz, CDCl3): δ = 7.69 (d, J =
8.4 Hz, 2 H, aromatic H), 7.25 (m, 3 H, aromatic H), 7.05 (d, J =
6.8 Hz, 1 H, aromatic H), 6.93 (m, 1 H, aromatic H), 6.84 (d, J =
8.4 Hz, 1 H, aromatic H), 6.36 (s, 1 H, =CHanisol), 4.94 (d, J =
8.4 Hz, 1 H, =CH), 4.30 (d, J = 14.8 Hz, 1 H, CH2-NTs), 3.88 (d,
J = 16.0 Hz, 1 H, CH2-NTs), 3.79 (s, 3 H, OCH3), 3.65 (m, 2 H,
CH2-NTs), 2.66 (m, 1 H, allylic H), 2.41 (s, 3 H, CH3Ts), 1.75 (s,
3 H, CH3), 1.67 (s, 3 H, CH3) ppm. 13C NMR (100 MHz, CDCl3):
δ = 156.5, 143.6, 140.0, 136.2, 132.9, 129.7, 128.6, 128.5, 127.8,
125.6, 122.2, 120.5, 117.8, 110.6, 55.7, 52.8, 50.9, 44.1, 26.1, 21.8,
18.6 ppm. HRMS: calcd. for C23H27NO3S [M+] 397.1712; found
Representative Experimental Procedure for the Cyclization of 1a:
The starting material was added to a premixed solution of PtII
(5 mol-%), phosphane (indicated mol-% in Table 2), and SnCl2
(25 mol-%) under H2 (1 atm) in DCE (0.1 m) at room temperature.
The resulting mixture was allowed to react at 80 °C under H2
(1 atm) until the starting material was completely consumed.
(Z)-3-Benzylidene-4-(2-methylprop-1-enyl)-1-tosylpyrrolidine (1b):
The representative experimental procedure was applied to com-
pound 1a (91 mg, 0.25 mmol) to yield product 1b (65.4 mg, 71%).
1H NMR (400 MHz, CDCl3): δ = 7.70 (d, J = 8.0 Hz, 2 H, aro-
matic H), 7.31 (m, 4 H, aromatic H), 7.21 (m, 1 H, aromatic H),
7.12 (d, J = 7.6 Hz, 2 H, aromatic H), 6.07 (s, 1 H, =CHPh), 4.87
(d, J = 8.4 Hz, 1 H, =CH), 4.39 (d, J = 15.1 Hz, 1 H, CH2-NTs),
3.91 (d, J = 15.0 Hz, 1 H, CH2-NTs), 3.65 (m, 2 H, CH2-NTs),
2.60 (t, J = 8.8 Hz, 1 H, allylic H), 2.40 (s, 3 H, CH3Ts), 1.76 (s, 3
H, CH3), 1.66 (s, 3 H, CH3) ppm. 13C NMR (100 MHz, CDCl3):
δ = 143.7, 140.0, 136.6, 136.5, 132.8, 129.8, 128.6, 128.1, 127.8,
127.0, 123.1, 122.0, 52.6, 51.0, 44.2, 26.1, 21.8, 18.5 ppm. HRMS:
calcd. for C22H25NO2S [M+] 367.1606; found 367.1602. IR (KBr):
397.1716. IR (KBr): ν = 2962, 2927, 2853, 1598, 1489, 1463, 1347,
˜
1289, 1246, 1164, 1106, 1093, 1028 cm–1.
(Z)-3-(3-Methoxybenzylidene)-4-(2-methylprop-1-enyl)-1-tosylpyr-
rolidine (6b): The representative experimental procedure was ap-
plied to compound 6a (99 mg, 0.25 mmol) to yield product 6b
(72 mg, 72 %). 1H NMR (400 MHz, CDCl3): δ = 7.72 (d, J =
8.0 Hz, 2 H, aromatic H), 7.27 (m, 3 H, aromatic H), 6.76 (m, 2
H, aromatic H), 6.66 (s, 1 H, aromatic H), 6.06 (s, 1 H, =CHanisol),
4.88 (d, J = 8.6 Hz, 1 H, =CH), 4.38 (d, J = 15.2 Hz, 1 H, CH2-
NTs), 3.91 (d, J = 16.0 Hz, 1 H, CH2-NTs), 3.80 (s, 3 H, OCH3),
3.65 (m, 2 H, CH2-NTs), 2.61 (m, 1 H, allylic H), 2.41 (s, 3 H,
CH3Ts), 1.77 (s, 3 H, CH3), 1.67 (s, 3 H, CH3) ppm. 13C NMR
(100 MHz, CDCl3): δ = 159.6, 143.7, 140.4, 137.9, 136.6, 132.7,
129.8, 129.5, 127.8, 123.0, 121.9, 120.5, 114.0, 112.4, 55.4, 52.6,
51.0, 44.1, 26.1, 21.8, 18.5 ppm. HRMS: calcd. for C23H27NO3S
ν = 3055, 2925, 2853, 1598, 1447, 1376, 1348, 1165, 1094, 815, 754,
˜
697, 664 cm–1.
Deuterio-(Z)-3-Benzylidene-4-(2-methylprop-1-enyl)-1-tosylpyrrolid-
ine (deuterio-1b): The representative experimental procedure was
applied to compound 1a (91 mg, 0.25 mmol) to yield product de-
uterio-1b (56 mg, 61%). 1H NMR (400 MHz, CDCl3): δ = 7.70 (d,
J = 8.4 Hz, 2 H, aromatic H), 7.3 (m, 4 H, aromatic H), 7.21 (m,
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Hydrogenative Cyclization of Allenynes
[M+] 397.1712; found 397.1714. IR (KBr): ν = 2965, 2926, 2852,
385–388; b) H.-Y. Jang, M. J. Krische, J. Am. Chem. Soc. 2004,
126, 7875–7880; c) I. G. Jung, J. Seo, S. Y. Choi, Y. K. Chung,
Organometallics 2006, 25, 4240–4242; d) K. T. Sylvester, P. J.
Chirik, J. Am. Chem. Soc. 2009, 131, 8772–8774.
For selected articles for reductive cyclization of allenynes, see:
a) C. H. Oh, S. H. Jung, D. I. Park, J. H. Choi, Tetrahedron
Lett. 2004, 45, 2499–2502; b) C. H. Oh, S. H. Jung, C. Y. Rhim,
Tetrahedron Lett. 2001, 42, 8669–8671.
˜
1598, 1578, 1492, 1453, 1377, 1347, 1292, 1272, 1165, 1094,
1040 cm–1.
(Z)-3-(2-Methylprop-1-enyl)-1-tosyl-4-[(trimethylsilyl)methylene]-
pyrrolidine (7b): The representative experimental procedure was ap-
plied to compound 7a (90 mg, 0.25 mmol) to yield product 7b
(31 mg, 33%). 1H NMR (400 MHz, CDCl3): δ = 7.71 (d, J = 8 Hz,
2 H, aromatic H), 7.34 (d, J = 7.2 Hz, 2 H, aromatic H), 5.23 (s, 1
H, =CHTMS), 4.75 (d, J = 5.6 Hz, 1 H, =CH), 4.07 (d, J =
15.2 Hz, 1 H, CH2-NTs), 3.63 (m, 2 H, CH2-NTs), 3.43 (m, 1 H,
CH2-NTs), 2.54 (t, J = 9.8 Hz, 1 H, allylic H), 2.45 (s, 3 H, CH3Ts),
1.72 (s, 3 H, CH3), 1.60 (s, 3 H, CH3) ppm. 13C NMR (100 MHz,
CDCl3): δ = 155.2, 146.7, 136.5, 132.5, 129.7, 127.8, 122.0, 120.9,
53.0, 51.6, 45.3, 29.9, 26.0, 21.8, 18.5 ppm. HRMS: calcd. for
[3]
[4]
For selected articles for Pd-catalyzed cyclization of allenynes,
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8416–8417; b) R. Kumareswaran, S. Shin, I. Gallou, T. V. Ra-
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Kozak, C. Aubert, L. Fensterbank, M. Malacria, Angew.
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Marco-Contelles, J. Am. Chem. Soc. 2004, 126, 3408–3409; b)
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Chem. Soc. 2002, 124, 15186–15187; for Ru-catalyzed reactions
of allenynes, see: d) N. Saito, Y. Tanaka, Y. Sato, Organometal-
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see: e) D. Lierena, C. Aubert, M. Malacria, Tetrahedron Lett.
1996, 37, 7027–7030; for Mo-catalyzed reactions of allenynes,
see: f) Q. Shen, G. B. Hammond, J. Am. Chem. Soc. 2002, 124,
6534–6535; for Hg-catalyzed reactions of allenynes, see: g)
S. H. Sim, S. I. Lee, J. Seo, Y. K. Chung, J. Org. Chem. 2007,
72, 9818–9821; for Ga-catalyzed reactions of allenynes, see: h)
S. I. Lee, S. H. Sim, S. M. Kim, K. Kim, Y. K. Chung, J. Org.
Chem. 2006, 71, 7120–7123; for Ir-catalyzed reactions of al-
lenynes, see: i) T. Shibata, S. Kadowaki, M. Hirase, K. Takagi,
Synlett 2003, 573–575; for thermal reactions of allenynes, see:
j) H. Ohno, T. Mizutani, Y. Kadoh, A. Aso, K. Miyamura, N.
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Y. Ja n g , Adv. Synth. Catal. 2010, 352, 2949–2954.
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C
19H29NO SSi [M+] 363.1688; found 363.1685. IR (KBr): ν =
˜
2
[5]
2955, 2926, 2855, 1933, 1633, 1598, 1452, 1377, 1351, 1249, 1165,
1092, 1031, 872, 840 cm–1.
(Z)-3-Benzylidene-2,2-dimethyl-4-(2-methylprop-1-enyl)-1-tosylpyr-
rolidine (8b): The representative experimental procedure was ap-
plied to compound 8a (98 mg, 0.25 mmol) to yield product 8b
(56 mg, 56%). 1H NMR (400 MHz, CDCl3): δ = 7.70 (d, J =
8.4 Hz, 2 H, aromatic H), 7.23 (m, 5 H, aromatic H), 7.09 (d, J =
7.2 Hz, 2 H, aromatic H), 6.20 (s, 1 H, =CHPh), 4.94 (d, J =
8.8 Hz, 1 H, =CH), 3.66 (m, 2 H, CH2-NTs), 2.85 (m, 1 H, allylic
H), 2.40 (s, 3 H, CH3Ts), 1.72 (m, 9 H, gem-dimethyl and CH3),
1.28 (s, 3 H, CH3) ppm. 13C NMR (100 MHz, CDCl3): δ = 150.6,
142.8, 138.1, 137.4, 136.6, 129.4, 128.8, 128.0, 127.4, 126.6, 122.7,
122.5, 68.2, 52.2, 42.4, 30.5, 26.2, 26.0, 21.8, 18.5 ppm. HRMS:
calcd. for C24H29NO2S [M+] 395.1919; found 395.1920. IR (KBr):
[6]
ν = 2974, 2928, 2856, 1599, 1442, 1363, 1338, 1159, 1093, 1026,
˜
815, 739, 704, 670, 582, 550 cm–1.
Dimethyl (E)-3-Benzylidene-4-(2-methylprop-1-enyl)cyclopentane-
1,1-dicarboxylate (9b): The representative experimental procedure
was applied to compound 9a (81 mg, 0.25 mmol) to yield product
1
9b (47 mg, 57%). H NMR (400 MHz, CDCl3): δ = 7.23 (m, 5 H,
aromatic H), 6.09 (d, J = 2.4 Hz, 1 H, =CHPh), 5.03 (d, J = 8.8 Hz,
1 H, =CH), 3.74 (s, 3 H, CO2CH3), 3.72 (s, 3 H, CO2CH3), 3.54
(m, 1 H), 3.40 (d, J = 16.8 Hz, 1 H), 3.20 (dt, J = 2.8, 17.6 Hz, 1
H), 2.57 (dd, J = 7.2, 12.4 Hz, 1 H), 1.85 (t, J = 12.4 Hz, 1 H),1.79
(s, 3 H, CH3), 1.70 (s, 3 H, CH3) ppm. 13C NMR (100 MHz,
CDCl3): δ = 172.3, 172.1, 144.3, 137.9, 134.3, 128.4, 126.3, 125.8,
122.9, 59.4, 53.5, 53.1, 44.5, 40.4, 39.0, 26.1, 18.6 ppm. HRMS:
calcd. for C H O [M+] 328.1675; found 328.1675. IR (KBr): ν =
˜
[7]
20 24
4
3057, 2955, 2928, 1735, 1436, 1268, 1203, 1164, 1064, 738,
699 cm–1.
Supporting Information (see footnote on the first page of this arti-
cle): 2D-NOESY data for compound 1b and computational results.
Acknowledgments
[8]
[9]
This study was supported by the Korean Government, National
Research Foundation of Korea (grant numbers 2010-0029617,
2010-0016079, and 2010-0002396). We also wish to thank the Ko-
rean Basic Science Institute (Deagu) for providing the mass spectra.
[10]
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Eur. J. Org. Chem. 2011, 3748–3754
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3753

H.-T. Kim, H.-S. Yoon, W.-Y. Jang, Y. K. Kang, H.-Y. Jang
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Received: February 28, 2011
Published Online: May 12, 2011
3754
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2011, 3748–3754