Rhodium N-heterocyclic carbene-catalyzed [4 + 2] and [5 + 2] cycloaddition reactions

Article abstract of DOI:10.1021/jo051685u

A rhodium complex of N-heterocyclic carbene (NHC) has been developed for intra- and intermolecular [4 + 2] and intramolecular [5 + 2] cycloaddition reactions. This is the first use of a transition-metal NHC complex in a Diels-Alder-type reaction. For the

Full text of DOI:10.1021/jo051685u

Rhodium N-Heterocyclic Carbene-Catalyzed [4 + 2] and [5 + 2]
Cycloaddition Reactions
Sang Ick Lee, Se Yeoun Park, Ji Hoon Park, Il Gu Jung, Soo Young Choi, and
Young Keun Chung*
Intelligent Textile System Research Center, Department of Chemistry, College of Natural Sciences, Seoul
National UniVersity, Seoul 151-747, Korea
Bun Yeoul Lee
Department of Molecular Science and Technology, Ajou UniVersity, Suwon 442-749, Korea
ykchung@plaza.snu.ac.kr
ReceiVed August 10, 2005
A rhodium complex of N-heterocyclic carbene (NHC) has been developed for intra- and intermolecular
[4 + 2] and intramolecular [5 + 2] cycloaddition reactions. This is the first use of a transition-metal
NHC complex in a Diels-Alder-type reaction. For the intramolecular [4 + 2] cycloaddition reactions,
all the dienynes studied were converted to their corresponding cycloadducts in 91-99% yields within 10
min. Moreover, up to 1900 turnovers have been obtained for the intramolecular [4 + 2] cycloaddition at
15- 20 °C. For the intermolecular [4 + 2] cycloadditions, high yields (71-99%) of the corresponding
cycloaddition products were obtained. The reaction time and yield were highly dependent upon the diene
and the dienophile. For the intramolecular [5 + 2] cycloaddition reactions, all the alkyne vinylcyclopropanes
studied were converted to their corresponding cycloadducts in 91-98% yields within 10 min. However,
the catalytic system was not effective for an intermolecular [5 + 2] cycloaddition reaction.
Introduction
However, considerable effort is still being devoted to the
development of more efficient and practical methods of
Development of effective cyclization reactions for the syn-
thesis of carbocycles and heterocycles has been the subject of
extensive study because of their relevance to medicines and other
functional materials.1 Among the numerous methods available,
the transition-metal-promoted cyclization reaction has attracted
a lot of attention and has become one of the most popular.2
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10.1021/jo051685u CCC: $33.50 © 2006 American Chemical Society
Published on Web 11/19/2005
J. Org. Chem. 2006, 71, 91-96
91

Lee et al.
SCHEME 1
synthesizing polycyclic organic compounds from readily avail-
able starting materials.
Recently, N-heterocyclic carbenes (NHCs) have emerged as
a group of promising materials for the design of new homoge-
neous catalysts.3 The promise of being able to predetermine the
structure and chemical properties of a metal complex has been
the main driving force in the design of new ligand systems.
Moreover, the donor power of NHC ligands is considered to
be even greater than that of phosphines, prompting a range of
investigations seeking to exploit their properties in homogeneous
catalysis. Carbene ligand precursors are easy to prepare, and
their chemical and topological versatility allows the preparation
of a wide variety of complexes whose chemical properties can
be easily modulated. Despite the intense interest in the catalytic
properties of NHC complexes,4 reports of the use of transition
metal NHC complexes in cyclization, other than in metathesis,5
are still rare.6 Until now, the Rh NHC complex (Rh-NHC)
catalyzed cycloaddition reactions such as Diels-Alder-type
reactions have not been reported. Very recently, Evans reported7
a diastereoselective Rh-NHC-catalyzed [4 + 2 + 2] carbocy-
clization. Some years ago, in situ generated Ni(II)-NHC had
been used as a catalyst in the reaction of 1,3-dienes and
aldehydes.8 As a further step in our program toward the
development of cycloaddition reactions catalyzed by transition-
metal complexes,9 we initiated a study on the use of transition-
metal NHC complexes in cyclization. Here, we report on Rh-
NHC-catalyzed intra- and intermolecular [4 + 2] and intra-
molecular [5 + 2] cycloaddition reactions. This catalytic system
has several advantages, such as mild reaction conditions, high
yields, and high TON.
TABLE 1. Rh(NHC)-Catalyzed Intramolecular [4 + 2]
Cycloadditiona
Results and Discussion
Complex 1, RhCl(IPMes)(COD) (IPMes) N,N′-bis(2,6-
diisopropyl)imidazole-2-yilidene), showed a high catalytic activ-
(3) (a) Wang, A. E.; Xie, H. H.; Wang, L. X.; Zhou, Q. L. Tetrahedron
2005, 61, 259-266. (b) Crudden, C. M.; Allen, D. P. Coord. Chem. ReV.
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Chem. Soc. Rev. 2004, 33, 619-636. (d) Cavell, K. J.; McGuinness, D. S.
Coord. Chem. ReV. 2004, 248, 671-681. (e) Lebel, H.; Janes, M. K.;
Charette, A. B.; Nolan, S. P. J. Am. Chem. Soc. 2004, 126, 5046-5047. (f)
Herrmann, W. A.; Kocher, C. Angew. Chem., Int. Ed. Engl. 1997, 36, 2163.
(g) Bourissou, D.; Guerret, O.; Gabbai, F. P.; Bertrand, G. Chem. ReV. 2000,
100, 39-92. (h) Crabtree, R. H. Pure Appl. Chem. 2003, 75, 435. (i)
Arduengo, A. J. Acc. Chem. Res. 1999, 32, 913-921.
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J. Organomet. Chem. 2003, 687, 229-248. (c) Perry, M. C.; Burgess, K.
Tetrahedron: Asymmetry 2003, 14, 951-961. (d) Herrmann, W. A. Angew.
Chem., Int. Ed. 2002, 41, 1290-1309.
a 0.52 mmol of substrate, 2 mol % of catalyst, and 3 mol % of AgSbF6
were used. b Isolated yield. c 2.5 mol % of [Rh(dppb)(solvent)]+ was used;
see ref 11.
ity in hydrosilylation10 and was used as a precatalyst for our
reactions. The catalyst [Rh(IPMes)(COD)(solvent)]+ was gener-
ated in situ by the reaction of 1 with AgSbF6 at 15-20 °C for
5 min. Without a silver salt, the reaction did not proceed. Using
2a as a dienyne model compound, we studied an intramolecular
[4 + 2] cycloaddition reaction (Scheme 1).
When 2 mol % of 1/AgSbF6 was used at 15-20 °C, the
reaction went to completion within several minutes, although
the exact reaction time was not determined. The yield was up
to 95∼98%. Thus, we cut down the amount of catalyst to 0.1
mol %. In this case, the reaction went to completion within 30
min and the yield was 95%. When the catalyst was cut down
to 0.05 mol %, the reaction went to completion within 5 h and
the yield was 95%. Thus, the maximum TON should be higher
than 1900. For practical purposes, when 1.0 g of the substrate
(2a) was reacted under the same reaction conditions, a 91%
yield of the corresponding product was obtained within 45 min.
Several years ago, Zhang et al.11 reported on rhodium diphos-
(5) (a) Despagnet-Ayoub, E.; Grubbs, R. H. Organometallics 2005, 24,
338-340. (b) Yang, L.; Mayr, M.; Wurst, K.; Buchmeiser, M. R. Chem.
Eur. J. 2004, 10, 5761-5770. (c) Choi, T.-L.; Grubbs, R. H. Angew. Chem.,
Int. Ed. 2003, 42, 1743-1746. (d) Trnka, T. M.; Morgan, J. P.; Sanford,
M. S.; Wilhelm, T. E.; Scholl, M.; Choi, T.-L.; Ding, S.; Day, M. W.;
Grubbs, R. H. J. Am. Chem. Soc. 2003, 125, 2546-2558. (e) Trnka, T. M.;
Grubbs, R. H. Acc. Chem. Res. 2001, 34, 18-29. (f) Weskamp, T.;
Schattenmann, W. C.; Spiegler, M.; Herrmann, W. A. Angew. Chem., Int.
Ed. Engl. 1998, 37, 2490-2493.
(6) (a) Louie, J.; Gibby, J. E.; Farnworth, M. V.; Tekavec, T. N. J. Am.
Chem. Soc. 2002, 124, 15188-15189. (b) Tekavec, T. N.; Arif, A. M.;
Louie, J. Tetrahedron 2004, 60, 7431-7437.
(7) Evans, P. A.; Baum, E. W.; Fazal, A. N.; Pink, M. Chem. Commun.
2005, 63-65.
(8) Sato, Y.; Sawaki, R.; Mori, M. Organometallics 2001, 20, 5510-
5512.
(9) (a) Lee, S. I.; Park, J. H.; Chung, Y. K.; Lee, S.-G. J. Am. Chem.
Soc. 2004, 126, 10190. (b) Park, K. H.; Jung, I. G.; Kim, S. Y.; Chung, Y.
K. Org. Lett. 2003, 5, 4967-4970. (c) Son, S. U.; Park, K, H.; Lee, S. J.;
Kim, B. M.; Chung, Y. K. Synlett 2003, 1101-1104. (d) Lee, S. I.; Son, S.
U.; Choi, M. R.; Chung, Y. K. Tetrahedron Lett. 2003, 44, 4705-4709.
(10) Park, K. H.; Kim, S. Y.; Son, S. U.; Chung, Y. K. Eur. J. Org.
Chem. 2003, 4341-4345.
92 J. Org. Chem., Vol. 71, No. 1, 2006

Rh-NHC-Catalyzed [4 + 2] and[5 + 2] Cycloaddition Reactions
TABLE 2. Rh(NHC)-Catalyzed Intermolecular [4 + 2] Cycloadditiona
a 0.52 mmol of dienophile, 3 mol % of catalyst, and 4 mol % of AgSbF6 were used. b 2 equiv of diene was used. c Isolated yield. d ,eRatio was determined
1
by H NMR. f 1 equiv of diene was used. g,h Yields for dehydrated products are shown in parentheses.
phine cationic complex-catalyzed intramolecular [4 + 2] cy-
cloaddition. Among them, they obtained the best results when
they used [Rh(dppb)(solvent)]+ (dppb) 1,4-bis(diphenylphos-
phino)butane) as a catalyst. Using [Rh(dppb)(solvent)]+ (gener-
ated in situ by the reaction of [Rh(dppb)Cl]2 and AgSbF6) as a
catalyst at room temperature for 4 h, up to 1000 turnovers were
observed. They did not obtain the maximum turnovers under
the optimized reaction conditions. Thus, it was not simple to
compare directly our turnovers with theirs.
As shown in Table 1, all the dienynes studied were converted
to their corresponding cycloadducts in 91-99% yields within
10 min. Our results show that the catalytic system can tolerate
the oxygen and nitrogen tether in the substrate. Any change of
terminal substituents in the alkyne (entries 5 and 6) and in the
diene (entries 1-4) has little effect on the efficiency of the
cycloaddition reaction. When the reaction of 1-prop-2-ynyloxy-
hexa-2,4-diene (entry 3) in Table 1 was carried out using 2.5
mol % of [Rh(dppb)(solvent)]+ as a catalyst at room temper-
ature, the time taken to reach 90% completion of the reaction
was ca. 5 h.11
(entry 2) had no effect on either the reaction time or the yield
(15 min and 99%). Due to the unsymmetric nature of a diene,
an isomeric mixture was obtained in the ratio of 3.2:1.12
However, the use of an internal alkene (entry 3) resulted in an
isomeric mixture (5.7:1) with a diminished yield of 76% and a
lengthening of the reaction time to 45 min.13 Substitution of a
hydrogen on the nitrogen with a Boc group (entry 4) had no
effect on the reaction time and yield (15 min and 99%).
Interestingly, the increase of the chain length between an alkyne
and a nitrogen atom of an amine (entry 5) led to a decrease of
the yield (71%) and an increase of the reaction time (45 min).
When an internal alkyne (entry 6) was used as a dienophile,
the yield decreased to 80% and the reaction time increased to
2 h.
When enynes were reacted with dienes in the presence of
Rh-NHC, it was known that [4 + 2 + 2] cycloaddition reactions
proceeded.7 Similarly, we first expected [4 + 2 + 2] cycload-
diton between diyne and diene. However, we could get the [4
+ 2] cycloaddition reaction product only (entry 7). These results
agreed with entries 1 and 6. The structure of 13A was confirmed
by X-ray structure.14 When an enyne with a terminal alkyne
(entry 8) was used as a dienophile the terminal alkyne reacted
We also investigated an intermolecular [4 + 2] cycloaddition
reaction (Table 2). In general, high yields of the corresponding
cycloaddition products were obtained. Interestingly, the reaction
time and yield were highly dependent upon the diene and the
dienophile. When the reaction between 2,3-dimethyl-1,3-buta-
diene and 9a (a reaction time of 15 min and a yield of 98%)
was studied as a model reaction, the use of a terminal alkene
(12) Paik, S.-J.; Son, S. U.; Chung, Y. K. Org. Lett. 1999, 1, 2045-
2047.
(13) [(η6-C10H8)Rh(COD)]BF4 showed similar selectivities for the
intermolecular [4 + 2] cycloaddition. See ref 11.
(14) Crystal system, triclinic, P1, unit cell dimensions, a ) 9.42870(40)
Å, b ) 11.28010(40) Å, c ) 11.75760(50) Å, R ) 93.0232(21)°, â )
111.2617(20)°, γ ) 98.4089(23)°. Final R indices [I > 2σ(I)], R1 ) 0.0223,
wR2 ) 0.0320. CCDC reference no.: 271994.
(11) Wang, B.; Cao, P.; Zhang, X. Tetrahedron Lett. 2000, 41, 8041-
8044.
J. Org. Chem, Vol. 71, No. 1, 2006 93

Lee et al.
TABLE 3. Rh(NHC)-Catalyzed Intermolecular [5 + 2]
SCHEME 2
Cycloadditiona
catalytic systems went to completion within 10 min under our
reaction conditions. Thus, our catalytic system seems to be quite
effective for the intramolecular [5 + 2] cycloaddition reaction.
We attempted to develop an intermolecular version of the [5
+ 2] cycloaddition reaction (Scheme 2). However, after workup,
the reactant was recovered. Unfortunately, the catalytic system
has not proved to be effective for an intermolecular reaction.
Further study will hopefully disclose a catalytic system that is
effective for an intermolecular reaction.
Conclusion
a 0.52 mmol of substrate, 2 mol % of catalyst, and 3 mol % of AgSbF6
were used. b Isolated yield.
We have found a useful catalytic system that is especially
active for the intra- and intermolecular [4 + 2] and intra-
molecular [5 + 2] cycloaddition reactions. Up to 1900 turnovers
have been obtained for the intramolecular [4 + 2] cycloaddition
at 15 °C∼ 20 °C. Compared to other rhodium catalytic systems,
the Rh-NHC system is a preferred catalyst for the intramolecular
[5 + 2] cycloaddition of tethered alkyne vinylcyclopropanes.
We are currently investigating asymmetric catalysts based on
NHC ligands and tandem [4 + 2]/[5 + 2] cyclization using
Rh-NHC.
with a diene to give a cyclohexadiene bearing a side chain with
a double bond in 72% yield within 1 h. Interestingly, when a
terminal alkyne having a linear alkyl chain or a TMS group
(entry 9 and 10) was used as a dienophile, the reaction time
increased to 2 h and the reaction product was obtained as a
mixture of a cycloadduct and an arene, a dehydrogenated
cycloadduct, in a ratio of 2:1-3.6:1. The generation of aromatic
compounds via oxidation of the Diels-Alder reaction product
is not unusual.15 When the reaction of entry 10 in Table 2 was
carried out in the presence of 1 mol % of [(η6-C10H8)Rh(COD)]-
BF4 at 15-20 °C for 15 min, the corresponding cycloaddition
product was obtained in 94% yield without any dehydrogenated
compounds.12 When a diester-substituted alkyne (entry 11) was
used as a dienophile, the reaction time increased to 30 min with
a quantitative yield. However, all of the reactions went to
completion within 2 h.
Next we examined an intramolecular [5 + 2] cycloaddition
reaction (Table 3). We used Wender’s alkyne vinylcyclopro-
panes as substrates.16 Heteroatom (O and NTs) tethers are good
substrates. The presence of a substitutent on the alkyne did no
harm to either the yield or the reaction time. The Rh-NHC
catalytic system displayed a greatly enhanced cycloaddition
activity compared to other rhodium catalytic systems11,17 in the
cycloaddition reaction of the substrate. For example, in the
cycloaddition of the substrate (entry 3), the time taken to reach
complete conversion to a bicyclic diene was less than 10 min
in the presence of Rh-NHC. However, no other rhodium
Experimental Section
A Typical Procedure for the Synthesis of Rh-NHC Complex
(1). 1,3-Bis(2,6-diisopropylphenyl)-1H-imidazole chloride (0.72 g,
0.41 mmol) and Ag2O (0.1 g, 0.4 mmol) were dissolved in a flame-
dried 100 mL of Schlenk flask, covered with aluminum foil,
containing anhydrous dichloromethane (20 mL) at room temperature
(rt). After the solution was stirred for 4 h, the solution was filtered
through the vacuum-dried Celite. The filtrate was evaporated under
reduced pressure. The obtained crude Ag-carbene salt and [RhCl-
(cod)]2 (cod ) 1,5-cyclooctadiene) (0.2 g, 0.4 mmol) were added
to a flask containing 30 mL of dichloromethane. The resulting
solution was stirred at room temperature for 4 h. Removal of the
solvent followed by chromatography on a silica gel eluting with
hexane and diethyl ether (v/v, 10:1) gave yellow solid 1 (0.216 g,
0.34 mmol) in 85% yield: 1H NMR (CDCl3, 300 MHz) δ 1.11 (d,
J ) 6.8 Hz, 6H, CH3), 1.24-1.54 (br, 6H, CH3), 1.40-1.60 (m,
2H, CH2), 1.66-1.78 (m, 1H, COD), 1.78-1.92 (m, 1H, COD),
2.40-2.70 (br, 1 H, CH), 3.26 (s, 1H, COD), 3.46-3.76 (br, 1 H,
CH), 4.38 (s, 1H, COD), 7.03 (s, 1H, dCH), 7.20-7.50 (br, 2H,
m-iPr2C6), 7.51 (t, J ) 7.6 Hz, 1H, p-iPr2C6); 13C{1H} NMR
(C6D6): δ 22.68 (br, CH), 24.02 (br, CH), 26.97 (br, CH3), 28.85
(COD), 29.35 (CH3), 33.36 (COD), 67.55 (d, 2JCRh ) 14 Hz, COD),
(15) (a) Hilt, G.; du Mesnil, F.-X. Tetrahedron Lett. 2000, 41, 6757-
6761. (b) Levy, L. A. J. Org. Chem. 1978, 43, 3068-3069.
(16) (a) Wender, P. A.; Takahashi, H.; Witulski, B. J. Am. Chem. Soc.
1995, 117, 4720-4721. (b) Wender, P. A.; Husfeld, C. O.; Langkopf, E.;
Love, J. A. J. Am. Chem. Soc. 1998, 120, 1940-1941. (c) Wender, P. A.;
Glorius, F.; Husfeld, C. O.; Langkopf, E.; Love, J. A. J. Am. Chem. Soc.
1999, 121, 5348-5349. (d) Wender, P. A.; Dyckman, A. J.; Husfeld, C.
O.; Kadereit, D.; Love, J. A. J. Am. Chem. Soc. 1999, 121, 10442-10443.
(e) Wender, P A.; Dyckman, A J. Org. Lett. 1999, 1, 2089-2092. (f)
Wender, P A.; Zhang, L. Org. Lett. 2000, 2, 2323-2326. (g) Wender, P
A.; Barzilay, C M.; Dyckman, A J. J. Am. Chem. Soc. 2001, 123, 179-
180. (h) Wender, P A.; Pedersen, T M.; Scanio, M J. C. J. Am. Chem. Soc.
2002, 124, 15154-15155.
2
96.44 (d, JCRh ) 7.6 Hz, COD), 122.92 (br, m-iPr2C6), 124.69
(dCH), 125.22 (br, m-iPr2C6), 130.15 (p-iPr2C6), 136.85 (ipso-
iPr2C6), 145.56 (br, o-iPr2C6), 148.44 (br, o-iPr2C6), 187.51 (d, 2JCRh
) 52 Hz, CdRh). Anal. found (calcd for C37H48N2Rh1Cl1): C,
66.41 (66.22); H, 7.59 (7.63); N, 4.37 (4.42).
General Procedure for Rh-NHC-Catalyzed Intramolecular
[4 + 2] and [5 + 2] Cycloaddition. To a flame-dried 15 mL
Schlenk flask capped with a rubber septum was added 5 mL of
dichloromethane via syringe under N2 flow. Then, Rh-NHC (8 mg,
2 mol %) and AgSbF6 (7 mg, 3 mol %) were added sequentially.
After the solution was stirred for 10 min, a substrate (0.52 mmol)
was added to the solution under N2 flow. The reaction was
(17) Wender, P. A.; Williams, T. J. Angew. Chem., Int. Ed. 2002, 41,
4550-4552.
94 J. Org. Chem., Vol. 71, No. 1, 2006

Rh-NHC-Catalyzed [4 + 2] and[5 + 2] Cycloaddition Reactions
monitored by thin-layer chromatography (TLC). After the reactant
completely disappeared, the solvent was removed under reduced
pressure. Flash chromatography on silica gel eluting with hexane
and ethyl acetate (or diethyl ether) gave a product.
(br), 2884, 2056 (s), 1792 (w), 1635 (w), 1462 (m), 1382 (m);
HRMS (EI) calcd for (C14H14O1) 198.1045, found 198.1044.
(2-Methyl-5-prop-2-ynyloxypenta-1,3-dienyl)benzene (6a). To
a solution of anhydrous THF (30 mL) were added 1.1 equiv of
HMPT (1.16 mL, 6.31 mmol), 1.2 equiv of NaH (0.28 g, 6.9 mmol,
60 wt % stabilized mineral oil), and 4-methyl-5-phenylpenta-2,
4-dien-1-ol (1.0 g, 5.7 mmol) at 0 °C. After the solution was stirred
for 1 h, 1.3 equiv of propargyl bromide (0.80 mL, 7.5 mmol, 80
wt % in toluene) was added at 0 °C. After the resulting solution
was stirred at room temperature for 6 h, the reaction mixture was
extracted with aqueous NH4Cl solution and Et2O. Flash column
chromatography gave colorless oil 6a (1.0 g, 4.9 mmol) in 85%
yield (TLC: Rf ) 0.75, hexane/Et2O ) 2:1): 1H NMR (CDCl3,
300 MHz) δ 2.02 (s, 3 H), 2.47 (s, 1 H), 4.19 (m, 4 H), 5.89 (m,
1 H), 6.46 (s, 1 H), 6.53 (d, 10.3 Hz, 1 H), 7.33 (m, 5 H); 13C
NMR (CDCl3, 75 MHz) δ 14.0, 57.1, 70.5, 74.6, 79.9, 124.3, 126.8,
128.3, 129.3, 132.2, 135.0, 137.7, 139.0; IR (cm-1, in CHCl3): 3313
(s), 3040, 2864, 2256 (s), 1642 (w), 1446 (m), 1382 (m); HRMS
(EI) calcd for (C15H16O1) 212.1201, found 212.1200.
General Procedure for Rh-NHC-Catalyzed Intermolecular
[4 + 2] Cycloaddition. To a flame-dried 15 mL Schlenk flask
capped with a rubber septum was added 5 mL of dichloromethane
via syringe under N2 flow. Rh-NHC (10 mg, 3 mol %) and AgSbF6
(9 mg, 4 mol %) were added sequentially to the above solution.
After the resulting solution was stirred for 10 min, diene (1 mmol,
2 equiv) was added by syringe (1 mL). The color of solution turned
to orange. Dienophile (0.52 mmol) was added to the above solution
under N2 flow. The reaction was monitored by TLC. After the
reactant was completely disappeared, the solvent was removed
under reduced pressure. Flash chromatography on a silica gel
column eluting with hexane and ethyl acetate (or diethyl ether) gave
a product.
4-Methyl-N-penta-2,4-dienyl-N-prop-2-ynylbenzenesulfon-
amide (2a). To a solution of anhydrous DMF (30 mL) were added
NaH (0.2 g, 5.0 mmol, 60 wt % stabilized mineral oil) and 4-methyl-
N-penta-2, 4-dienyl-benzenesulfonamide (1.0 g, 4.2 mmol) at 0 °C.
After the solution was stirred for 1 h, 1.3 equiv of propargyl bromide
(0.58 mL, 5.4 mmol, 80 wt % in toluene) was added at 0 °C. After
the resulting solution was stirred at room temperature for 6 h, the
reaction mixture was extracted with saturated NaCl aqueous solution
and diethyl ether. Flash column chromatography gave 2a (6.35 g,
2.3 mmol) in 55% yield as a white solid (TLC Rf ) 0.8, hexane/
ethyl acetate ) 3:1): 1H NMR (CDCl3, 300 MHz) δ 2.42 (s, 3 H),
3.85 (d, 6.9 Hz, 2 H), 4.08 (d, 2.0 Hz, 2 H), 5.12 (d, 9.8 Hz, 1 H),
5.22 (d, 16.7 Hz, 1 H), 5.57 (m, 1 H), 6.28 (m, 2 H), 7.29 (d, 7.9
Hz, 2 H), 7.73 (d, 7.9 Hz, 2 H); 13C NMR (CDCl3, 75 MHz) δ
21.8, 36.0, 48.2, 74.0, 76.3, 118.7, 127.0, 128.0, 129.7, 135.8, 135.9,
136.1, 143.8; IR (in CHCl3) 3296 (w), 3152 (w), 2968 (w), 2256
(s), 1795 (w), 1595 (br); HRMS (EI) calcd for (C15H17S1O2N1)
275.0980, found 275. 0981.
5-Methyl-6-phenyl-1,3,3a,6-tetrahydroisobenzofuran (6A): 1H
NMR (CDCl3, 300 MHz) δ 1.48 (s, 3 H), 3.25 (m, 1 H), 3.38 (dd,
11 Hz, 7 Hz, 1 H), 3.88 (d, 9.7 Hz, 1 H), 4.30 (dd, 14 Hz, 6.8 Hz,
2 H), 4.46 (ddt, 11.8 Hz, 3.3 Hz, 1.7 Hz, 1 H), 5.49 (s, 1 H), 5.64
(s, 1 H), 7.26 (m, 5 H); 13C NMR (CDCl3, 75 MHz) δ 22.3, 40.7,
62.3, 73.5, 118.3, 120.0, 126.6, 128.3, 128.6, 128.7, 137.0, 144.5;
IR (cm-1, in CHCl3) 3056 (s), 2976 (s), 2303 (m), 1600 (w), 1424
(s), 1260 (s); HRMS (EI) calcd for (C15H16O1) 212.1201, found
212.1201.
N-(4,5-Dimethylcyclohexa-1,4-dienylmethyl)-4-methylben-
1
zenesulfonamide (9A): H NMR (CDCl3, 300 MHz) δ 1.58 (s, 6
H), 2.42 (s, 3 H), 2.43 (m, 2 H), 2.53 (m, 2 H), 3.47 (m, 2 H), 4.33
(m, 1 H), 5.53 (m, 1 H), 7.28 (d, 7.9 Hz, 2 H), 7.74 (d, 7.9 Hz, 2
H); 13C NMR (CDCl3, 75 MHz) δ 18.3, 18.5, 21.6, 33.8, 34.1,
49.1, 122.8, 123.1, 127.4, 129.8, 131.0, 137.7, 143.4; IR (cm-1, in
CHCl3) 3376 (w), 3152 (w), 2978 (w), 2256 (s), 1808 (w), 1795
(w), 1635 (w), 1465 (m), 1382 (m), 1324 (br), 1155 (s), 1091 (s);
HRMS (EI) calcd for (C16H21S1O2N1) 290.1294, found 290.1293.
4-Methyl-N-(4-methylcyclohexa-1,4-dienylmethyl)benzene-
sulfonamide (9B): 1H NMR (CDCl3, 300 MHz) δ 1.62 (s, 3 H),
2.38 (s, 3 H), 2.4 (m, 4 H), 3.48 (m, 2 H), 4.5 (m, 1 H), 5.34 (m,
1 H), 5.55 (m, 1 H), 7.28 (m, 2 H), 7.73 (m, 2 H); 13C NMR (CDCl3,
75 MHz) δ 20.9, 21.9, 31.4, 31.6, 48.2, 117.2, 118.1, 125.7, 129.6,
135.7, 136.8, 141.2; HRMS (EI) calcd for (C15H19S1O2N1) 277.1136,
found 277.1136.
2-(Toluene-4-sulfonyl)-2,3,3a,6-tetrahydro-1H-isoindole
(2A): 1H NMR (CDCl3, 300 MHz) δ 2.10 (m, 3 H), 2.42 (s, 3 H),
2.44 (m, 1 H), 2.90 (t, 10.6 Hz, 1 H), 3.20 (m, 1 H), 3.88 (t, 9.96
Hz, 1 H), 5.42 (d, 9.96 Hz, 1 H), 5.60 (m, 1 H), 6.10 (s, 1 H), 7.28
(d, 7.9 Hz, 2 H), 7.66 (d, 7.9 Hz, 2H); 13C NMR (CDCl3, 75
MHz): δ 21.6, 26.9, 51.0, 53.1, 117.3, 123.5, 126.9, 127.7, 129.9,
135.2, 143.6; IR (in CHCl3) 3296 (w), 3152 (w), 2968 (w), 2256
(s), 1795 (w), 1595 (br); HRMS (EI) calcd for (C15H17S1O2N1)
275.0980, found 275. 0982
4-Methyl-N-(5-methylcyclohexa-1,4-dienylmethyl)benzene-
sulfonamide (9C): 1H NMR (CDCl3, 300 MHz) δ 1.62 (s, 3 H),
2.38 (s, 3 H), 2.4 (m, 4 H), 3.48 (m, 2 H), 4.5 (m, 1 H), 5.34 (m,
1 H), 5.55 (m, 1 H), 7.28 (d, 7.9 Hz, 2 H), 7.73 (d, 7.9 Hz, 2 H);
13C NMR (CDCl3, 75 MHz) δ 20.9, 23.2, 29.2, 38.9, 48.5, 116.9,
117.9, 125.4, 129.5, 134.7, 136.3, 140.9; HRMS (EI) calcd for
(C15H19S1O2N1) 277.1136, found 277.1138.
4-Methyl-N-(3-methylcyclohexa-1,4-dienylmethyl)benzene-
sulfonamide (9D): 1H NMR (CDCl3, 300 MHz) δ 1.61 (s, 3 H),
2.45 (s, 3 H), 2.50 (m, 4 H), 3.45 (m, 2 H), 4.90 (m, 1 H), 5.35 (m,
1 H), 5.54 (s, 1 H), 7.27 (d, 7.9 Hz, 2 H), 7.74 (d, 7.9 Hz, 2 H);
13C NMR (CDCl3, 75 MHz) δ 20.8, 21.2, 31.4, 31.7, 48.5, 121.9,
124.8, 125.7, 129.9, 135.9, 137.3, 141.00; HRMS (EI) calcd for
(C15H19S1O2N1) 277.1136, found 277.1138.
4-Methyl-N-(6-methylcyclohexa-1,4-dienylmethyl)benzene-
sulfonamide (9E): 1H NMR (CDCl3, 300 MHz) δ 1.61 (s, 3 H),
2.45 (s, 3 H), 2.50 (m, 4 H), 3.45(m, 2H), 4.90 (m, 1 H), 5.35 (m,
1 H), 5.54 (s, 1 H), 7.27 (d, 7.9 Hz, 2 H), 7.74 (d, 7.9 Hz, 2 H);
13C NMR (CDCl3, 75 MHz) δ 17.3, 20.8, 30.1, 32.3, 45.8, 116.7,
124.8, 125.7, 129.9, 136.6, 140.2, 140.9, 141.2; HRMS (EI) calcd
for (C15H19S1O2N1) calcd 277.1136, found 277.1138.
N-Boc-N-(4,5-dimethylcyclohexa-1,4-dienylmethyl)-4-methyl-
N-(3-phenylprop-2-ynyl)benzenesulfonamide (10A): 1H NMR
(CDCl3, 300 MHz) δ 1.32 (s, 9 H), 1.58 (s, 3 H), 1.61 (s, 3 H),
2.39 (s, 3 H), 2.45 (t, 7.5 Hz, 2 H), 2.62 (s, 2 H), 4.36 (s, 2 H),
(5-Prop-2-ynyloxypenta-1,3-dienyl)benzene (5a). To a solution
of anhydrous THF (30 mL) were added 1.1 equiv (1.16 mL, 6.31
mmol) of HMPT (hexamethylphosphorus triamide), 1.2 equiv of
NaH (0.30 g, 7.49 mmol, 60 wt % stabilized mineral oil), and
5-phenylpenta-2, 4-dien-1-ol (1.0 g, 6.2 mmol) at 0 °C. After the
solution was stirred for 1 h, 1.3 equiv of propargyl bromide (0.88
mL, 8.11 mmol, 80 wt % in toluene) was added at 0 °C. After the
resulting solution was stirred at room temperature for 6 h, the
reaction mixture was extracted with aqueous NH4Cl solution and
Et2O. Flash column chromatography gave colorless oil 5a (1.0 g,
5.3 mmol) in 85% yield (TLC Rf ) 0.75, hexane/Et2O ) 2:1): 1H
NMR (CDCl3, 300 MHz) δ 2.48 (m, 1 H), 4.19 (d, 1.0 Hz, 2 H),
4.21 (d, 2.4 Hz, 2 H), 5.90 (dt, 15.2 Hz, 6.3 Hz, 1 H), 6.48 (dd,
15.2 Hz, 10.4 Hz, 1 H), 6.60 (d, 15.6 Hz, 1 H), 6.82 (dd, 15.6 Hz,
10.4 Hz, 1 H), 7.27 (m, 1 H), 7.35 (m, 1 H), 7.42 (m, 1 H); 13C
NMR (CDCl3, 75 MHz): δ 57.2, 70.1, 74.7, 79.9, 126.6, 127.9,
128.3, 128.8, 129.2, 133.3, 134.0, 137.3; IR (cm-1, in CHCl3) 3313
(s), 3040, 2864, 2256 (s), 1642 (w), 1446 (m), 1382 (m); HRMS
(EI) calcd for (C14H14O1) 198.1045, found 198.1044.
6-Phenyl-1,3,3a,6-tetrahydroisobenzofuran (5A): 1H NMR
(CDCl3, 300 MHz) δ 3.21 (m, 1 H), 3.38 (dd, 11.1 Hz, 7.3 Hz, 1
H), 4.05 (m, 1 H), 4.31 (m, 2 H), 4.49 (m, 1 H), 5.57 (m, 1 H),
5.88 (m, 2 H), 7.22 (m, 2 H), 7.29 (m, 1 H), 7.36 (m, 2H); 13C
NMR (CDCl3, 75 MHz) δ 39.4, 43.5, 69.5, 72.4, 119.5, 122.4,
126.7, 128.2, 128.8, 131.9, 138.9, 145.2; IR (cm-1, in CHCl3) 3360
J. Org. Chem, Vol. 71, No. 1, 2006 95

Lee et al.
5.62 (s, 1 H), 7.23 (d, 8 Hz, 2 H), 7.76(d, 8 Hz, 2 H); 13C NMR
(CDCl3, 75 MHz) δ 18.3, 18.6, 21.7, 28.0, 33.7, 33.9, 51.6, 81.2,
122.1, 122.5, 122.8, 128.3, 129.7, 130.9, 137.2, 144.2, 151.2; IR
(cm-1, NaCl) 2312 (s), 1723 (s), 1548 (w), 1419 (br); HRMS (EI)
calcd for (C21H29S1O4N1) 391.1817, obsd 391.1818.
N-[2-(4,5-Dimethylcyclohexa-1,4-dienyl)ethyl]-4-methylben-
zenesulfonamide (11A): 1H NMR (CDCl3, 300 MHz) δ 1.56 (s, 3
H), 1.60 (s, 3 H), 2.10 (t, 6.5 Hz, 2 H), 2.20 (m, 2 H), 2.42 (s, 3
H), 2.56 (m, 2 H), 3.03 (dd, 12 Hz, 6 Hz, 2 H), 4.50 (t, 5.5 Hz, 1
H), 5.38 (s, 1 H), 7.28 (d, 8 Hz, 2 H), 7.72(d, 8 Hz, 2 H); 13C
NMR (CDCl3, 75 MHz) δ 18.3, 18.5, 21.7, 33.9, 35.4, 36.5, 40.6,
122.5, 122.7, 123.1, 127.3, 129.8, 131.2, 137.1, 143.5; HRMS (EI)
calcd for (C17H23S1O2N1) 305.1449, obsd 305.1448.
4-Methyl-N-(2,4,5-trimethylcyclohexa-1,4-dienylmethyl)ben-
zenesulfonamide (12A): 1H NMR (CDCl3, 300 MHz) δ 1.53 (s,
3 H), 1.54 (s, 3 H), 1.56 (s, 3 H), 2.42 (s, 3 H), 2.44 (s, 4 H), 3.54
(d, 5.8 Hz, 2 H), 4.49 (t, 5.8 Hz, 1 H), 7.30 (d, 8 Hz, 2 H), 7.75 (d,
8 Hz, 2 H); 13C NMR (CDCl3, 75 MHz) δ 17.9, 18.0, 18.1, 21.7,
36.1, 40.2, 44.3, 122.7, 122.9, 123.2, 127.3, 129.7, 130.3, 137.1,
143.5; HRMS (EI) calcd for (C17H23S1O2N1) (EI, m/z) 305.1449,
obsd 305.1448.
benzenesulfonamide (2.85 g, 10 mmol) and NaH (12 mmol, 0.48
g, 60 wt % in mineral oil). To a second flame-dried 100 mL Schlenk
flask charged with 4-methyl-N-(3-phenylprop-2-ynyl)benzene-
sulfonamide (2.85 g, 10 mmol) was added NaH (12 mmol, 0.48 g,
60 wt % in mineral oil) slowly at 0 °C. After the solution was
stirred for 30 min at room temperature, the solution was cooled to
-78 °C. The bromide solution prepared above was transferred via
cannula into the second flask. The resulting solution was stirred at
-78 °C for 2 h and at room temperature for 4 h. Quenching with
NaCl solution, extraction with diethyl ether, drying over MgSO4,
and evaporation gave a crude product. Flash chromatography on a
silica gel eluting with hexane and ethyl acetate (v/v, 10:1) gave
white solid 21a (TLC: Rf ) 0.7, hexane/ethyl acetate ) 2:1): 1H
NMR (CDCl3, 300 MHz) δ 0.36 (m, 2 H), 0.72 (m, 2 H), 1.44 (m,
1 H), 2.32 (s, 3 H), 3.80 (d, 6.7 Hz, 2 H), 4.29 (s, 2 H), 5.21 (m,
1 H), 5.46 (m, 1 H), 7.02 (d, 7.9 Hz, 2 H), 7.24 (m, 5 H), 7.74 (d,
7.9 Hz, 2 H); 13C NMR (CDCl3, 75 MHz) δ 7.1, 13.7, 21.6, 36.6,
46.7, 82.0, 85.7, 120.8, 122.5, 128.0, 128.3, 128.5, 129.7, 131.6,
136.1, 140.9, 143.6; IR (cm-1, in CHCl3) 3064 (s), 2304 (m), 1419
(s), 1344 (w), 1264 (s), 1161 (m); HRMS (EI) calcd for
(C22H23S1O2N1) 365.1449, obsd 365.1450.
N-(4,5-Dimethylcyclohexa-1,4-dienylmethyl)-4-methyl-N-(3-
phenylprop-2-ynyl)benzenesulfonamide (13A): H NMR (CDCl3,
8-Phenyl-2-(toluene-4-sulfonyl)-1,2,3,3a,6,7-hexahydrocyclo-
hepta[c]pyrrole (21A): 1H NMR (CDCl3, 300 MHz) δ 2.25 (m,
3 H), 2.45s, 3 H), 2.78 (dd, 9 Hz, 9 Hz, 1 H), 2.87 (m, 1 H), 3.60
(d, 14 Hz, 1 H), 3.73 (dd, 9 Hz, 9 Hz, 1 H), 3.85 (d, 14 Hz, 1 H),
3.93 (m. 1 H), 5.64 (m, 1 H), 6.65(m, 1 H), 7.08 (d, 8.0 Hz, 2 H),
7.30 (m, 5 H), 7.65 (d, 8.0 Hz, 2 H); 13C NMR (CDCl3, 75 MHz)
δ 21.8, 26.7, 32.8, 40.6, 52.4, 55.0, 127.1, 127.2, 128.2, 128.3,
1
300 MHz) δ 1.63 (s, 3 H), 1.65 (s, 3 H), 2.31 (s, 3 H), 2.63 (s, 4
H), 3.78 (s, 2 H), 4.23 (s, 2 H), 5.70 (s, 1 H), 7.03 (d, 8.0 Hz, 2
H), 7.22 (m, 5 H), 7.77 (d, 8.0 Hz, 2 H); 13C NMR (CDCl3, 75
MHz) δ 18.3, 18.6, 34.0, 34.1, 52.6, 82.2, 85.8, 122.6, 123.4, 128.0,
128.2, 128.7, 129.6, 131.7, 136.6, 143.5; HRMS (EI) calcd for
(C25H27S1O2N1) 405.1762, obsd 405.1764.
128.6, 129.8, 131.0, 131.9, 135.6, 136.9, 142.6, 144.0; IR (cm-1
,
4-Methyl-N-pent-2-en-4-ynylbenzenesulfonamide (14a). To a
flame-dried 50 mL Schlenk flask capped with a rubber septum were
added N-Boc-4-methyl-N-pent-2-en-4-ynylbenzenesulfonamide (1.0
g, 3.0 mmol) and 5 equiv of TFA (1.11 mL, 14.9 mmol)
sequentially. After the solution was stirred for 3 h at room
temperature, the solution was evaporated under reduced pressure.
Flash chromatography on a silica gel column eluting with hexane
and ethyl acetate (v/v, 10:1) gave brown solid 14a (0.35 g, 1.5
mmol) in 50% yield (TLC Rf ) 0.55, hexane/ethyl acetate ) 3:1):
1H NMR (CDCl3, 300 MHz) δ 2.35 (s, 3 H), 2.98 (s, 1 H), 3.83
(m, 2 H), 4.32 (m, 1 H), 5.62 (s, 1 H), 6.12 (m, 1 H), 7.34 (d, 8.0
Hz, 2 H), 7.81 (d, 8.0 Hz, 2 H); 13C NMR (CDCl3, 75 MHz) δ
20.9, 42.5, 80.0, 82.8, 113.9, 125.4, 129.5, 136.3, 140.2, 140.9; IR
(cm-1, in CHCl3) 3408 (br), 3296 (s), 3168 (w), 3008 (w), 2240
(s), 1916 (w), 1792 (w), 1593 (m), 1465 (br), 1408 (br), 1328 (s),
1158 (s), 1092 (s); HRMS (EI) calcd for (C12H13S1O2N1) 235.0667,
obsd 235.0667.
N-[3-(4,5-Dimethylcyclohexa-1,4-dienyl)allyl]-4-methylben-
zenesulfonamide (14A): 1H NMR (CDCl3, 300 MHz) δ 1.71 (s,
6 H), 2.35 (m, 4 H), 2.63 (s, 3 H), 5.29 (m, 1 H), 5.74 (m, 1 H),
6.15 (m, 1 H), 7.24 (m, 2 H), 7.81 (m, 2 H); 13C NMR (CDCl3, 75
MHz) δ 16.4, 16.8, 20.9, 36.5, 41.3, 44.1, 118.3, 125.4, 127.3,
129.5, 128.5, 136.3, 140.9; IR (cm-1, in CHCl3) 3360 (br), 2256
(m), 1808 (w), 1459 (m), 1155 (s), 1094 (s); HRMS (EI) calcd for
(C18H23S1O2N1) 317.1449, obsd 317.1450.
in CHCl3) 3056 (s), 2970 (s), 2304 (m), 1420 (s), 1264 (s), 1158
(m); HRMS (EI) calcd for (C22H23S1O2N1) 365.1449, obsd 365.1448.
N-(3-Cyclopropyl-allyl)-4-methyl-N-pent-2-ynylbenzenesulfon-
1
amide (23a): H NMR (CDCl3, 300 MHz) δ 0.34 (m, 2 H), 0.70
(m, 2 H), 0.88 (t, 7.4 Hz, 3 H), 1.40 (m, 1 H), 1.90 (m, 2 H), 2.40
(s, 3 H), 3.72 (d, 6.7 Hz, 2 H), 4.30 (t, 2.2 Hz, 2 H), 5.21 (m, 1 H),
5.38 (m.1 H), 7.27 (d. 7.9 Hz, 2 H), 7.72 (d, 7.9 Hz, 2 H); 13C
NMR (CDCl3, 75 MHz) δ 6.9, 12.2, 13.4, 13.6, 21.6, 36.1, 48.3,
72.1, 87.4, 117.2, 121.0, 127.9, 129.3, 136.6, 140.3, 143.2; IR
(cm-1, in CHCl3) 3408 (br), 3168 (m), 2960 (s), 1795 (w), 1596
(m), 1459 (s), 1340 (s); HRMS (EI) calcd for (C18H23S1O2N1)
317.1449, obsd 317.1449.
8-Ethyl-2-(toluene-4-sulfonyl)-1,2,3,3a,6,7-hexahydrocyclohepta-
[c]pyrrole (23A): 1H NMR (CDCl3, 300 MHz) δ 0.95 (t, 7.5 Hz,
3 H), 1.93 (m, 3 H), 1.97 (m, 1 H), 2.21 (m, 1 H), 2.44 (s, 3 H),
2.49 (m, 1 H), 2.63 (m, 1 H), 3.53 (d, 13.1 Hz, 1 H), 3.69 (m, 2
H), 3.98 (d, 13.1 Hz, 1 H), 5.30 (m, 1 H), 5.61 (m, 1 H), 7.34 (d,
7.9 Hz, 2 H), 7.70 (d, 7.9 Hz, 2 H); 13C NMR (CDCl3, 75 MHz)
δ 12.0, 21.6, 26.5, 28.5, 29.5, 40.2, 51.1, 54.8, 128.1, 129.7, 130.9,
131.6, 132.1, 135.8, 143.8; HRMS (EI) calcd for (C18H23S1O2N1)
(EI, m/z) 317.1449, found 317.1448.
Acknowledgment. This work was supported by the Korean
Research Foundation Grant funded by the Korean Government
(MOEHRD) (R02-2004-000-10005-0). S.I.L, S.Y.P., and J.H.P.
acknowledge BK21 fellowships. J.H.P. acknowledges a GSI-1
fellowship.
N-(3-Cyclopropylallyl)-4-methyl-N-(3-phenylprop-2-ynyl)ben-
zenesulfonamide (21a). To a flame-dried 100 mL Schlenk flask
containing 3-cyclopropylprop-2-en-1-ol (1.0 g, 10 mmol) and THF
(30 mL) at -78 °C was added 1.2 equiv of n-BuLi (4.8 mL, 2.5 M
in hexane). After the solution was stirred for 10 min, 1.2 equiv of
methanesulfonyl chloride (0.95 mL, 12 mmol) and 1.3 equiv of
lithium bromide (1.11 g, 13 mmol) were added in one portion. After
the solution was stirred for 30 min, it was transferred via cannula
to the DMF solution containing 4-methyl-N-(3-phenyl-prop-2-ynyl)-
Supporting Information Available: Procedures, spectral data
for new compounds, and details for the crystal structures of 1, 5A,
and 13A. This material is available free of charge via the Internet
at http://pubs.acs.org.
JO051685U
96 J. Org. Chem., Vol. 71, No. 1, 2006