5-Exo versus 6-Endo cyclization of primary aminyl radicals: An experimental and theoretical investigation

Article abstract of DOI:10.1021/jo7015967

(Chemical Equation Presented) The cyclization of neutral primary pent-4-enylaminyl radicals was investigated experimentally and theoretically. Unlike the corresponding secondary aminyl radicals, primary pent-4-enylaminyl radicals underwent efficient cyclization to afford the pyrrolidine and/or piperidine products in good to high yields. While the simple pent-4-enylaminyl radical gave predominately the 5-exo cyclization product, 4-chloropent-4- enylaminyl radicals led to the formation of the corresponding 6-endo cyclization products in excellent regioselectivity. Theoretical calculations revealed that the 5-exo cyclization rate of primary aminyl radicals is about 3-4 orders of magnitude higher than that of secondary aminyl radicals.

Full text of DOI:10.1021/jo7015967

toward electron-rich CdC double bonds,3 neutral secondary
aminyl radicals are much less reactive and rather nucleophilic.
Kinetic study by Newcomb et al. showed that the rate constant
for 5-exo cyclization of N-alkylpent-4-enamidyl radicals is
5-Exo versus 6-Endo Cyclization of Primary
Aminyl Radicals: An Experimental and
Theoretical Investigation
around 2 × 109 s-1 3a
.
As a comparison, the rate constant for
5-exo cyclization of the N-butylpent-4-enylaminyl radical is in
Feng Liu, Kun Liu, Xinting Yuan, and Chaozhong Li*
the range of 3 × 103 to 4 × 104 s-1 4,5
.
However, the rate of
Joint Laboratory of Green Synthetic Chemistry,
Shanghai Institute of Organic Chemistry, Chinese
Academy of Sciences, 354 Fenglin Road,
secondary aminyl radical cyclization can be increased signifi-
cantly by the addition of a Bro¨nsted or Lewis acid.6
Despite the relatively slow addition of neutral secondary
aminyl radicals to CdC bonds, they provide a direct entry to
N-alkyl pyrrolidines and piperidines and thus have attracted
considerable attention.1,7 However, to our surprise, the cycliza-
tion of neutral primary aminyl radicals is far less explored. In
fact, only a few separated examples were reported in the
literature.8 The possible difference between primary and second-
ary aminyl radicals in reactivity remains virtually unknown.
During our investigation on the cyclizations of unsaturated
amidyl radicals,9 we found that the activation energies for 6-exo
cyclization of N-alkyl-substituted hex-5-enamidyl radicals are
significantly higher than that of the primary hex-5-enamidyl
radical.9b More recently, we demonstrated that the regioselec-
tivity of amidyl and sulfonamidyl radical cyclization could be
excellently controlled by the vinylic halogen substitution.9d,f We
were thus motivated to find if (1) primary aminyl radicals would
exhibit significantly higher cyclization rates than the corre-
sponding secondary aminyl radicals and (2) the regioselectivity
of cyclization of pent-4-enylaminyl radicals could be controlled
by vinylic halogen substitution. We report here that, unlike
N-alkylpent-4-enylaminyl radicals, primary aminyl radicals
underwent efficient 5-exo and/or 6-endo cyclization to furnish
the corresponding pyrrolidine and/or piperidine products in good
to high yields. Furthermore, the internal vinylic substitution
played an important role in controlling the regioselectivity of
Shanghai 200032, People’s Republic of China
clig@mail.sioc.ac.cn
ReceiVed July 22, 2007
The cyclization of neutral primary pent-4-enylaminyl radicals
was investigated experimentally and theoretically. Unlike the
corresponding secondary aminyl radicals, primary pent-4-
enylaminyl radicals underwent efficient cyclization to afford
the pyrrolidine and/or piperidine products in good to high
yields. While the simple pent-4-enylaminyl radical gave
predominately the 5-exo cyclization product, 4-chloropent-
4-enylaminyl radicals led to the formation of the correspond-
ing 6-endo cyclization products in excellent regioselectivity.
Theoretical calculations revealed that the 5-exo cyclization
rate of primary aminyl radicals is about 3-4 orders of
magnitude higher than that of secondary aminyl radicals.
(3) (a) Horner, J. H.; Musa, O. M.; Bouvier, A.; Newcomb, M. J. Am.
Chem. Soc. 1998, 120, 7738. (b) Nicolaou, K. C.; Baran, P. S.; Zhong,
Y.-L.; Barluenga, S.; Hunt, K. W.; Kranich, R.; Vega, J. A. J. Am. Chem.
Soc. 2002, 124, 2233. (c) Gagosz, F.; Moutrille, C.; Zard, S. Z. Org. Lett.
2002, 4, 2707. (d) Martinez, E., II; Newcomb, M. J. Org. Chem. 2006, 71,
557.
(4) (a) Musa, O. S.; Horner, J. H.; Shahin, H.; Newcomb, M. J. Am.
Chem. Soc. 1996, 118, 3862. (b) Newcomb, M.; Musa, O. M.; Martinez, F.
N.; Horner, J. H. J. Am. Chem. Soc. 1997, 119, 4569.
(5) (a) Wagner, G. D.; Ruel, G.; Lusztyk, J. J. Am. Chem. Soc. 1996,
118, 13. (b) Maxwell, B. J.; Tsanaktsidis, J. J. Am. Chem. Soc. 1996, 118,
4276. (c) Maxwell, B. J.; Smith, B. J.; Tsanaktsidis, J. J. Chem. Soc., Perkin
Trans. 2 2000, 425.
(6) (a) Horner, J. H.; Martinez, F. N.; Musa, O. M.; Newcomb, M.;
Shahin, H. E. J. Am. Chem. Soc. 1995, 117, 11124. (b) Ha, C.; Musa, O.
M.; Martinez, F. N.; Newcomb, M. J. Org. Chem. 1997, 62, 2704.
(7) For recent examples, see: (a) Sjoholm, A.; Hemmerling, M.; Pradeille,
N.; Somfai, P. J. Chem. Soc., Perkin Trans. 1 2001, 891. (b) Hasegawa,
H.; Senboku, H.; Kajizuka, Y.; Orito, K.; Tokuda, M. Tetrahedron 2003,
59, 827. (c) Benati, L.; Bencivenni, G.; Leardini, R.; Minozzi, M.; Nanni,
D.; Scialpi, R.; Spagnolo, P.; Zanardi, G.; Rizzoli, C. Org. Lett. 2004, 6,
417. (d) Benati, L.; Bencivenni, G.; Leardini, R.; Nanni, D.; Minozzi, M.;
Spagnolo, P.; Scialpi, R.; Zanardi, G. Org. Lett. 2006, 8, 2499.
(8) (a) Bowman, W. R.; Coghlan, D. R.; Shah, H. C. R. Chim. 2001, 4,
625. (b) Bowman, W. R.; Clark, D. N.; Marmon, R. J. Tetrahedron 1994,
50, 1275. (c) Guindon, Y.; Guerin, B.; Landry, S. R. Org. Lett. 2001, 3,
2293.
Nitrogen-centered radicals are involved in a number of useful
organic transformations.1 Intramolecular addition of N-centered
radicals to CdC double bonds offers a unique entry to
N-hetereocycles such as lactams and cyclic amines. In particular,
the cyclization in a 5-exo mode has been widely investigated
and has found important application in natural product synthe-
sis.2 Different types of N-centered radicals exhibit dramatically
different reactivities in these cyclization reactions. While amidyl
and sulfonamidyl radicals are electrophilic and highly reactive
(1) For reviews, see: (a) Neale, R. S. Synthesis 1971, 1. (b) Stella, L.
Angew. Chem., Int. Ed. Engl. 1983, 22, 337. (c) Esker, J.; Newcomb, M.
In AdVances in Heterocyclic Chemistry; Katritzky, A. R., Ed.; Academic
Press: New York, 1993; Vol. 58, p 1. (d) Zard, S. Z. Synlett 1996, 1148.
(e) Fallis, A. G.; Brinza, I. M. Tetrahedron 1997, 53, 17543. (f) Stella, L.
In Radicals in Organic Synthesis; Renaud, P., Sibi, M. P., Eds.; Wiley-
VCH: Weinheim, Germany, 2001; Vol. 2, p 407. (g) Bowman, W. R.;
Bridge, C. F.; Brookes, P. J. Chem. Soc., Perkin Trans. 1 2000, 1.
(2) (a) Cassayre, J.; Gagosz, F.; Zard, S. Z. Angew. Chem., Int. Ed. 2002,
41, 1783. (b) Sharp, L. A.; Zard, S. M. Org. Lett. 2006, 8, 831.
(9) (a) Tang, Y.; Li, C. Org. Lett. 2004, 6, 3229. (b) Chen, Q.; Shen,
M.; Tang, Y.; Li, C. Org. Lett. 2005, 7, 1625. (c) Lu, H.; Li, C. Tetrahedron
Lett. 2005, 46, 5983. (d) Hu, T.; Shen, M.; Chen, Q.; Li, C. Org. Lett.
2006, 8, 2647. (e) Tang, Y.; Li, C. Tetrahedron Lett. 2006, 47, 3823. (f)
Lu, H.; Chen, Q.; Li, C. J. Org. Chem. 2007, 72, 2564.
10.1021/jo7015967 CCC: $37.00 © 2007 American Chemical Society
Published on Web 11/15/2007
J. Org. Chem. 2007, 72, 10231-10234
10231

TABLE 1. Cyclization of Pent-4-enylaminyl Radicals
SCHEME 1
yield (%)a
radical derived form 1a is much faster than that of the
corresponding secondary aminyl radical.
entry
substrate
R
2
3
4
1
2
3
4
5
6
1a
1b
1c
1d
1e
1f
H
Me
n-Bu
i-Pr
t-Bu
Ph
66
46
37
43
33
0
6
22
29
32
20
17
4
As also can be seen from the reaction of 1a, 5-exo cyclization
(2a) predominated over 6-endo cyclization (3a) for the pent-
4-enylaminyl radical and the product ratio was about 92:8. It is
foreseeable that the terminal vinylic substitution will further
increase the regioselectivity and efficiency of the 5-exo aminyl
radical cyclization because of the radical-stabilizing effect of
the substituent (also vide infra). Such a trend has been widely
observed in radical cyclization reactions. Of interest to us was
the internal vinylic substitution effect, which varies dramatically
in different cyclization systems. Thus, the 4-alkyl- or phenyl-
substituted sulfenamides 1b-f were prepared and subjected to
the same procedures indicated above. The results are sum-
marized in Table 1. In all cases, the cyclized products were
obtained in good yields. The 4-methylpent-4-enylamine 1b
afforded the mixture of 5-exo cyclization product 2b (46%) and
6-endo cyclization product 3b (17%) (entry 2, Table 1).
Although 5-exo cyclization was again preferred, the ratio of 2:3
was decreased from 92:8 (R ) H) to 73:27 (R ) Me). Changing
the methyl group to a butyl or isopropyl moiety further lowered
the regioselectivity to ∼65:35 (entries 3 and 4, Table 1).
However, with the 4-tert-butyl substitution, the regioselectivity
of the aminyl radical cyclization was reversed (44:56) to be in
favor of 6-endo cyclization (entry 5, Table 1). On the other hand,
the 4-phenyl-substitutited substrate 1f gave exclusively 6-endo
cyclization product 3f in 84% yield (entry 6, Table 1). The above
alkyl-substitution effect is in sharp contrast to that in amidyl
radical cyclization9d but similar to that in pent-4-enoxyl radical
cyclization.14
Although the 4-alkyl-substitution encourages the 6-endo
cyclization, the regioselectivity was poor. We then moved on
to test the effect of halogen substitution, which has showed a
remarkable control of regioselectivity in the cyclization of
amidyl9d and sulfonamidyl9f radicals. Thus, 4-chloro-substituted
amine 5a was prepared and subjected to the same reaction
indicated above. Three products were isolated, the piperidine
7a (56%) as the 6-endo cyclization product, the vinyl chloride
8a (25%) as the direct reduction product, and the ketone 6a
(∼4%) apparently generated from the hydrolysis of the 5-exo
cyclization product 2-methylenepyrrolidine (Scheme 1). The
ratio of 5-exo versus 6-endo cyclization products (6a:7a) was
therefore determined by HPLC to be 7:93, indicating the
overwhelming predominance of 6-endo cyclization.
17
20
25
42
84
a Isolated yield based on 1.
cyclization. Theoretical calculations in combination with the
experimental results offer a detailed understanding of the
mechanism of the primary aminyl radical cyclization.
Several methods are available for the generation of aminyl
radicals. The older and widely used method is the photolysis
or metal-induced reduction of N-chloroamines.1b However, the
radical reactions of N-chloroamines are prone to the contamina-
tion of ionic processes such as electrophilic halocyclization. The
use of N-hydroxypyridine-2-thione carbamates (PTOC carbam-
ates) developed by Newcomb and co-workers has served as good
precursors for secondary aminyl radicals.10 Unfortunately, the
PTOC carbamates derived from primary amines are very
unstable in solution.11 Therefore, we chose the benzenesulfe-
namide derivatives as the precursors for primary aminyl
radicals.8b,12 Benzenesulfenamides could be easily prepared in
good yield by reaction between amines and N-(benzenesulfenyl)-
phathalimide.13 Besides, they were found to be fairly stable and
their purification could be carried out with column chromatog-
raphy on netrual or basic alumina.8b Thus, we synthesized
N-(benzenesulfenyl)pent-4-enylamine (1a) according to the
above method. It was then subjected to treatment with Bu3SnH
(1.5 equiv) and AIBN (0.2 equiv) in refluxing benzene according
to the standard literature procedure.8b To facilitate product
characterization, the resulting product amines were then trapped
by benzoyl chloride with triethylamine as the base to give the
corresponding benzamides, which were readily purified by
column chromatography on silica gel. We were delighted to
find that the cyclization products 2a and 3a were achieved in a
combined 72% yield along with the direct reduction product
4a in 22% yield (Table 1). This result is in sharp contrast to
that of secondary aminyl radicals as the N-butylpent-4-eny-
laminyl radical gave very poor yield of cyclized product.8b It
also implied that the cyclization rate of the primary aminyl
(10) Newcomb, M.; Deeb, T. M.; Marquardt, D. J. Tetrahedron 1990,
46, 2317.
We then tested a number of 4-halogen-substituted substrates
and the results are listed in Table 2. The reactions of 5a-e
with different substitutions all exhibited high preference of
6-endo cyclization with the ratio of endo/exo ranging from 6:1
(11) Newcomb, M.; Weber, K. A. J. Org. Chem. 1991, 56, 1309.
(12) (a) Bowman, W. R.; Clark, D. N.; Marmon, R. J. Tetrahedron Lett.
1991, 32, 6441. (b) Beckwith, A. L. J.; Maxwell, B. J.; Tsanakatsidis, J.
Aust. J. Chem. 1991, 44, 1809. (c) Bowman, W. R.; Clark, D. N.; Marmon,
R. J. Tetrahedron Lett. 1992, 33, 4993. (d) Maxwell, B. J.; Tsanaktsidis, J.
J. Chem. Soc., Chem. Commun. 1994, 533.
(14) Hartung, J.; Kneuer, R.; Rummey, C.; Bringmann, G. J. Am. Chem.
Soc. 2004, 126, 12121.
(13) Behforouz, M.; Kerwood, J. E. J. Org. Chem. 1969, 34, 51.
10232 J. Org. Chem., Vol. 72, No. 26, 2007

TABLE 2. Cyclization of 4-Halopent-4-enylaminyl Radicals
TABLE 3. Calculated (UB3LYP/6-311++G**//UB3LYP/6-31G*)
Activation Energies
∆Gq (kcal/mol)
5-exo 6-endo
B:C (at 80 °C)
entry
R
calcd
expt
1
2
3
4
5
6
7
8
H
10.2
11.0
10.6
10.8
11.3
13.2
13.2
13.5
12.1
11.4
10.7
10.9
10.5
9.4
94:6
64:36
54:46
54:46
24:76
<1:99
4:96
92:8
73:27
65:35
63:37
44:56
<1:99
7:93
Me
n-Bu
i-Pr
t-Bu
Ph
Cl
Br
10.9
10.9
2:98
confirm the geometry obtained to be a true minimum or first-
order saddle point. The enthalpies and free energies were then
calculated at the UB3LYP/6-311++G** level. The zero-point
vibrational energy and thermal corrections were also obtained
at the UB3LYP/6-311++G** level. The computed activation
free energies (∆Gq) for 5-exo and 6-endo cyclization are
summarized in Table 3. By assuming that the cyclizations are
kinetically controlled, the regioselectivities, which are also
included in Table 3, could be calculated based on the transition
state theory.
As can be seen in Table 3, the activation energies for both
5-exo and 6-endo cyclization of aminyl radicals A (R ) H or
alkyl) are around 10-12 kcal/mol. With the increase of
bulkiness of the alkyl substituent, the energy differences between
the two modes of cyclization become smaller. This can be well
interpreted in terms of steric effect. For the phenyl-substituted
radical A, the activation energy for 6-endo cyclization is lowered
by 2.6 kcal/mol compared to that of the unsubstituted radical
A (R ) H), apparently resulting from the powerful radical-
stabilizing effect of the phenyl moiety. The calculated ratios of
5-exo versus 6-endo cyclization products are in good agreement
with the experimental data.
a Isolated yield based on 5. b Trans:cis ) 3:1. c Not detected.
to 33:1. The regioselectivity was decreased by the 1-alkyl
substitution but increased by the 3-alkyl substitution. This
substituent effect parallels that in alkyl radical cyclization and
can be well explained analogously according to the work of
Beckwith and Schiesser.15 For the 4-bromo-substituted substrate
5f (entry 6, Table 2), no desired cyclization product could be
obtained probably because of the contamination of the easy
reduction of the vinyl bromide by Bu3SnH.
As a comparison, the 5-chloro-substituted substrate 9a led
to the exclusive formation of the 5-exo cyclization product 10a
in 83% yield (eq 1). The 5-methyl or 5,5-dimethyl substitution
also enhanced the efficiency and regioselectivity of cyclization
and the expected pyrrolidines 10b and 10c were also obtained
in 87% and 90% yield, respectively (eq 1).
As a comparison, the activation free energy for 5-exo
cyclization of a typical secondary aminyl radical, N-butylpent-
4-enylaminyl radical, was also computed at the UB3LYP/6-
311++G**//UB3LYP/6-31G* level to be 16.5 kcal/mol, about
6.3 kcal/mol higher than that of the corresponding primary
aminyl radical A (R ) H). This strongly implies a 3-4 orders
of magnitude increase of 5-exo cyclization rate from secondary
to primary aminyl radicals. For secondary aminyl radicals, the
rate of cyclization is very similar to the rate of reduction of
aminyl radicals by Bu3SnH.5b,10,11 Poor yield of cyclization is
generally obtained. However, for primary aminyl radicals, the
dramatic acceleration of the rate of cyclization allows it to
compete efficiently with the rate of direct reduction. As a result,
a high yield of cyclization can be achieved.
The above results clearly demonstrated the efficiency of
primary aminyl radical cyclization and the unique effect of Cl
substitution in controlling the regioselectivity. To gain more
insight into the reactivity of primary aminyl radicals, we turned
to density functional calculations for help, which have been
shown to be an increasingly important tool in modeling radical
reactions and mechanisms.16,17 All the structures were fully
optimized at the UB3LYP/6-31G* level. Once the geometry
was reached, the harmonic frequencies were examined to
When the alkyl group is switched to the chlorine atom, the
activation energy for 5-exo cyclization is increased by >2 kcal/
(17) For the recent selected examples, see: (a) Itoh, Y.; Houk, K. N.;
Mikami, K. J. Org. Chem. 2006, 71, 8918. (b) O’Neil, L. L.; Wiest, O. J.
Org. Chem. 2006, 71, 8926. (c) Hartung, J.; Daniel, K.; Rummey, C.;
Bringmann, G. Org. Biomol. Chem. 2006, 4, 4089. (d) Lin, H.; Chen, Q.;
Cao, L.; Yang, L.; Wu, Y.-D.; Li, C. J. Org. Chem. 2006, 71, 3328. (e)
Liu, L.; Chen, Q.; Wu, Y.-D.; Li, C. J. Org. Chem. 2005, 70, 1539. (f)
Speybroeck, V. V.; De Kimpe, N.; Waroquier, M. J. Org. Chem. 2005, 70,
3674. (g) References 9d and 9f.
(15) Beckwith, A. L. J.; Schiesser, C. H. Tetrahedron 1985, 41, 3925.
(16) For review articles on use of calculations in radical reactions, see:
(a) Eksterowicz, J. E.; Houk, K. N. Chem. ReV. 1993, 93, 2439. (b)
Schiesser, C. H.; Skidmore, M. A. In Radicals in Organic Synthesis; Renaud,
P., Sibi, M. P., Eds.; Wiley-VCH: Weinheim, Germany, 2001; Vol. 1, p
337.
J. Org. Chem, Vol. 72, No. 26, 2007 10233

enylamine (234 mg, 2.74 mmol) and the solution was stirred for 2
h at rt. The resulting mixture was then concentrated under reduced
pressure and the residue was poured into hexane (20 mL). The
mixture was filtered and the precipitate was washed with hexane
(3 × 10 mL). The filtrate was concentrated in vacuo and the crude
product was purified by flash chromatography on basic alumina
with hexane-ethyl acetate (10:1, v:v) as the eluent to give
N-(benzenesulfenyl)pent-4-enylamine (1a) as a yellowish liquid.
Yield: 264 mg (55%). 1H NMR (300 MHz, CDCl3) δ 1.66 (2H, q,
J ) 7.1 Hz), 2.11 (2H, q, J ) 7.1 Hz), 2.86 (1H, br), 2.96 (2H, t,
J ) 6.4 Hz), 4.95-5.06 (2H, m), 5.73-5.85 (1H, m), 7.12-7.35
(5H, m); 13C NMR (CDCl3) δ 29.3, 30.9, 51.4, 114.9, 123.7 125.2,
128.6, 138.0, 141.6; EIMS m/z (rel intensity) 193 (M+, 13), 160
(22), 138 (54), 109 (100), 84 (14), 77 (15), 65 (26), 39 (18); HRMS
calcd for C11H16NS (M + H: 194.0998, found 194.1000.
Typical Procedure for the Cyclization of Pent-4-enylaminyl
Radicals. The benzene (10 mL) solution of Bu3SnH (213 mg, 0.732
mmol) and AIBN (16 mg, 0.097 mmol) was added via the aid of
a syringe pump over a period of 5 h into the benzene (20 mL)
solution of N-(benzenesulfenyl)pent-4-enylamine (1a, 94 mg, 0.487
mmol) at reflux. After the addition was complete, the mixture was
allowed to cool to room temperature and triethylamine (0.20 mL,
1.30 mmol) was added. The solution was further cooled to 0 °C
and benzoyl chloride (102 mg, 0.73 mmol) was added. The mixture
was then stirred at rt overnight. After the usual workup, the crude
products were separated by column chromatography on silica gel
with ethyl acetate-hexane (1:3, v:v) as the eluent to give 2a (61
mg, 66%),11 3a (5.4 mg, 6%),19 and 4a (20 mg, 22%).20
mol while the activation energy for 6-endo cyclization remains
almost unchanged. Since chlorine is smaller in size than a methyl
group and the radical-stabilizing energy of Cl is only slighter
higher than that of Me,18 the above two effects (steric and
radical-stabilizing effects) are not enough to account for the
difference between Cl and Me in controlling the regioselectivity.
The third effect, the lone pair-lone pair repulsion between
chlorine and nitrogen atoms, should add an additional weight
to the improvement of regioselectivity. This can be further
evidenced from the calculated structures. The computed transi-
tion state structures for 5-exo and 6-endo cyclization of radical
A (R ) Cl) are shown as TS-1 and TS-2, respectively. TS-1 is
in a half-chair conformation while TS-2 is in a chair conforma-
tion. The NH proton is in the axial position in both cases. The
N-Cl distance is 2.94 Å in TS-1 but 3.76 Å in TS-2. Moreover,
the chlorine atom and the lone pair electron of the nitrogen atom
are at the same side in TS-1 but in the opposite directions in
TS-2. Therefore, the lone pair-lone pair repulsion is much
stronger for 5-exo cyclization than for 6-endo cyclization.
Acknowledgment. This project was supported by the
National NSF of China (Grant Nos. 20325207, 20472109, and
20702060) and by the Shanghai Municipal Committee of
Science and Technology (Grant No. 07XD14038).
In summary, the chemistry detailed above has clearly
demonstrated the efficiency of 5-exo and 6-endo cyclization of
neutral primary aminyl radicals and the remarkable chlorine
substitution effect in controlling the regioselectivity. This finding
should encourage the further development of primary aminyl
radical-based strategy in organic synthesis.
Supporting Information Available: Characterizations of 1-10
and the computational results on the cyclizations of radicals A and
N-butylpent-4-enylaminyl radical. This material is available free
of charge via the Internet at http://pubs.acs.org.
Experimental Section
Typical Procedure for the Synthesis of N-(Benzenesulfenyl)-
pent-4-enylamines. N-(Benzenesulfenyl)phthalimide (636 mg, 2.49
mmol) was added into the CH2Cl2 (8 mL) solution of pent-4-
JO7015967
(19) Kazuaki, I.; Takayuki, Y. Org. Lett. 2004, 6, 1983.
(20) Albert, P.; David, J. A.; Alan, T. P.; David, W. M. Tetrahedron
1996, 52, 3247.
(18) Henry, D. J.; Parkinson, C. J.; Mayer, P. M.; Radom, L. J. Phys.
Chem. A 2001, 105, 6750.
10234 J. Org. Chem., Vol. 72, No. 26, 2007