Construction of linked nitrogen heterocycles by palladium(0)-catalyzed intramolecular domino cyclization of 2-alkynylaziridines bearing a 2-aminoethyl group via ring expansion with Isocyanate

Article abstract of DOI:10.1021/jo100462w

A novel palladium(0)-catalyzed domino cyclization of 2-alkynylaziridines with isocyanates through ring expansion is described. Treatment of N-protected 2-(4-aminobut-1-ynyl)aziridine derivatives with a catalytic amount of Pd(PPh₃)₄ and aryl isocyanates in THF at room temperature affords 4-(4,5-dihydropyrrol-2-yl)imidazolidin-2-one derivatives in good yields. Interestingly, bis-adducts were selectively obtained by use of excess isocyanate (5 equiv) at lower reaction temperature.

Full text of DOI:10.1021/jo100462w

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Construction of Linked Nitrogen Heterocycles by Palladium(0)-
Catalyzed Intramolecular Domino Cyclization of 2-Alkynylaziridines
Bearing a 2-Aminoethyl Group via Ring Expansion with Isocyanate
Akinori Okano,† Shinya Oishi,† Tetsuaki Tanaka,‡ Nobutaka Fujii,*,† and Hiroaki Ohno*,†
†Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan, and
‡Graduate School of Pharmaceutical Sciences, Osaka University, 1-6 Yamadaoka, Suita, Osaka 565-0871, Japan
nfujii@pharm.kyoto-u.ac.jp; hohno@pharm.kyoto-u.ac.jp
Received March 13, 2010
A novel palladium(0)-catalyzed domino cyclization of 2-alkynylaziridines with isocyanates through
ring expansion is described. Treatment of N-protected 2-(4-aminobut-1-ynyl)aziridine derivatives
with a catalytic amount of Pd(PPh3)4 and aryl isocyanates in THF at room temperature affords
4-(4,5-dihydropyrrol-2-yl)imidazolidin-2-one derivatives in good yields. Interestingly, bis-adducts
were selectively obtained by use of excess isocyanate (5 equiv) at lower reaction temperature.
Introduction
intermediate A by a stereoselective ring-opening reaction
with palladium(0). Quite recently, efficient syntheses of pyr-
roles 5 by reaction with a gold catalyst or iodine were also
reported.4 However, to the best of our knowledge, there have
been no precedents for domino cyclization with 2-alkynylazir-
idines.
2-Alkynylaziridines 1 are valuable intermediates for the syn-
thesis of nitrogen-containing compounds due to the presence of
a strained three-membered ring at the propargylic position
(Scheme 1). Previously we reported a stereoselective synthesis
of R-amino allenes 2 by an anti-SN20 ring-opening reaction of
2-ethynylaziridines with an organocopper reagent.1 SN2-type
ring-opening of 2-ethynylaziridines with phenol derivatives to
give 3 is useful for stereoselective construction of a tertiary ether
motifinustiloxinD.2 We have also demonstrated that 2-ethynyl-
aziridines can function as a chiral carbon nucleophile by
umpolung with InI in the presence of a palladium(0) catalyst
and water, to produce 2-ethynyl-1,3-amino alcohols 4 stereo-
selectively by reaction with an aldehyde.3 This reaction clearly
shows that 2-ethynylaziridines can form allenylpalladium(II)
SCHEME 1. Synthetic Utility of 2-Alkynylaziridines
(1) (a) Ohno, H.; Toda, A.; Miwa, Y.; Taga, T.; Fujii, N.; Ibuka, T.
Tetrahedron Lett. 1999, 40, 349–352. (b) Ohno, H.; Toda, A.; Fujii, N.;
Takemoto, Y.; Tanaka, T.; Ibuka, T. Tetrahedron 2000, 56, 2811–2820.
Quite recently, Yudin reported a highly related allene synthesis by SN20
reduction of unprotected 2-ethynylaziridines with 9-BBN, see: (c) He, Z.;
Yudin, A. K. Angew. Chem., Int. Ed. 2010, 49, 1607–1610.
ꢀ
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(b) Li, P.; Forbeck, E. M.; Evans, C. D.; Joullie, M. M. Org. Lett. 2006, 8,
ꢀ
5105–5107.
(4) (a) Davies, P. W.; Martin, N. Org. Lett. 2009, 11, 2293–2296.
(b) Yoshida, M.; Al-Amin, M.; Shishido, K. Tetrahedron Lett. 2009, 50,
6268–6270. (c) Chen, D.-D.; Hou, X.-L.; Dai, L.-X. Tetrahedron Lett. 2009,
50, 6944–6946. (d) Du, X.; Xie, X.; Liu, Y. J. Org. Chem. 2010, 75, 510–513.
(3) (a) Ohno, H.; Hamaguchi, H.; Tanaka, T. Org. Lett. 2000, 2, 2161–
2163. (b) Ohno, H.; Hamaguchi, H.; Tanaka, T. J. Org. Chem. 2001, 66,
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3396 J. Org. Chem. 2010, 75, 3396–3400
Published on Web 04/20/2010
DOI: 10.1021/jo100462w
r
2010 American Chemical Society

Okano et al.
JOCArticle
SCHEME 3. Preparation of 2-Alkynylaziridine 11aa
SCHEME 2. Domino Cyclization of 2-Alkynylaziridines 6 with
Aryl Isocyanates in the Presence of a Palladium(0) Catalyst
aAbbreviation: DIAD = diisopropyl azodicarboxylate.
of 2-alkynylaziridines with palladium(0), we envisioned that
2-alkynylaziridines 6, bearing nucleophilic functional groups on
the alkyne terminus, would facilitate palladium(0)-catalyzed
ring-opening followed by domino cyclization through allenyl-
palladium(II) intermediate B, an equivalent of allyl dication C
(Scheme 2). In this paper, we describe a novel synthesis of linked
heterocycles 710 by palladium(0)-catalyzed domino cyclization
of 6, via ring-expansion by addition with an aryl isocyanate.11
A bis-addition cascade with an excess amount of isocyanate to
form linked cyclic ureas 8 selectively is also presented.
It is well-known that palladium(0)-catalyzed reactions of
propargylic compounds developed by Tsuji and co-workers
provide an efficient approach to not only introduce two nucleo-
philes into a substrate5 but also construct various heterocyclic
compounds.6 Furthermore, our recent studies on bromoallenes
and propargyl bromides have demonstrated that this type of
reactivity is extremely useful for construction of medium-sized
heterocycles,7 bicyclic sulfamides,8 and pyrrolo[3,2-b]pyridine
derivatives.9 Thus allenic/propargylic compounds can act as
allylic dication equivalents in the presence of a palladium(0)
catalyst. On the basis of these findings and sufficient reactivity
Results and Discussion
2-Alkynylaziridine 11a, a representative substrate for the
domino cyclization, was readily prepared as follows (Scheme 3).
Addition of lithium acetylide derived from N-tosylbut-3-yn-
1-amine to commercially available N-Boc-glycinal 9followed by
removal of the Boc group and tosylation provided propargyl
alcohol 10a. Aziridination under the Mitsunobu conditions
afforded the desired alkynylaziridine 11a bearing a nucleophilic
functional group. Other aziridines were prepared in a similar
manner.
(5) (a) Tsuji, J.; Watanabe, H.; Minami, I.; Shimizu, I. J. Am. Chem. Soc.
1985, 107, 2196–2198. (b) Minami, I.; Yuhara, M.; Watanabe, H.; Tsuji, J.
J. Organomet. Chem. 1987, 334, 225–242. For a review, see: (c) Tsuji, J.;
Mandai, T. Angew. Chem., Int. Ed. 1995, 34, 2589–2612.
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Tetrahedron Lett. 1987, 28, 629–632. (b) Geng, L.; Lu, X. Tetrahedron Lett.
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2, 527–529. (d) Yoshida, M.; Ihara, M. Angew. Chem., Int. Ed. 2001, 40, 616–
619. (e) Kozawa, Y.; Mori, M. Tetrahedron Lett. 2001, 42, 4869–4873.
(f) Yoshida, M.; Fujita, M.; Ishii, T.; Ihara, M. J. Am. Chem. Soc. 2003,
125, 4874–4881. (g) Kozawa, Y.; Mori, M. J. Org. Chem. 2003, 68, 8068–
8074. (h) Zong, K.; Abboud, K. A.; Reynolds, J. R. Tetrahedron Lett. 2004,
45, 4973–4975. (i) Ambrogio, I.; Cacchi, S.; Fabrizi, G. Org. Lett. 2006, 8,
2083–2086. (j) Duan, X.-H.; Guo, L.-N.; Bi, H.-P.; Liu, X.-Y.; Liang, Y.-M.
Org. Lett. 2006, 8, 5777–5780.
TABLE 1. Domino Reaction of Alkynylaziridine 11a with Phenyl
Isocyanate 12a under Various Reaction Conditions
(7) (a) Ohno, H.; Hamaguchi, H.; Ohata, M.; Tanaka, T. Angew. Chem.,
Int. Ed. 2003, 42, 1749–1753. (b) Ohno, H.; Hamaguchi, H.; Ohata, M.;
Kosaka, S.; Tanaka, T. J. Am. Chem. Soc. 2004, 126, 8744–8754.
(8) (a) Hamaguchi, H.; Kosaka, S.; Ohno, H.; Tanaka, T. Angew. Chem.,
Int. Ed. 2005, 44, 1513–1517. (b) Hamaguchi, H.; Kosaka, S.; Ohno, H.;
Fujii, N.; Tanaka, T. Chem.;Eur. J. 2007, 13, 1692–1708.
(9) (a) Ohno, H.; Okano, A.; Kosaka, S.; Tsukamoto, K.; Ohata, M.;
Ishihara, K.; Maeda, H.; Tanaka, T.; Fujii, N. Org. Lett. 2008, 10, 1171–1174.
(b) Okano, A.; Tsukamoto, K.; Kosaka, S.; Maeda, H.; Oishi, S.; Tanaka, T.; Fujii,
N.; Ohno, H. Chem.;Eur. J. 2010, 16, in press (chem.201000653).
(10) For biologically active compounds bearing a related linked hetero-
cyclic structure, see: (a) Watjen, F.; Baker, R.; Engelstoff, M.; Herbert, R.;
MacLeod, A.; Knight, A.; Merchant, K.; Moseley, J.; Saunders, J.; Swain,
C. J.; Wong, E.; Springer, J. P. J. Med. Chem. 1989, 32, 2282–2291. (b) Gu,
Z.-Q.; Wong, G.; Dominguez, C.; de Costa, B. R.; Rice, K. C.; Skolnick, P.
J. Med. Chem. 1993, 36, 1001–1006. (c) Mehta, A. K.; Shank, R. P. Life Sci.
1995, 57, 2215–2222. (d) Artico, M.; Silvestri, R.; Pagnozzi, E.; Stefancich,
G.; Massa, S.; Loi, A. G.; Putzolu, M.; Corrias, S.; Spiga, M. G.; La Colla, P.
Bioorg. Med. Chem. 1996, 4, 837–850. (e) Li, X.; Morrow, D.; Witkin, J. M.
yield (%)b
temp time
solvent (°C) (min)
entrya
catalyst system
Pd(OAc)2, PPh3
PdCl2(dppf) CH2Cl2 THF
13a
14a
1c
2
THF
rt
rt
rt
rt
rt
rt
20
180
240
1
45
60
20
40
15
40
40
40
40
4
0
0
0
3
3d
4
Pd2(dba)3 CHCl3
THF
THF
trace
82
22
39
80
37
59
17
0
0
13
4
0
6
24
44
3
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
5
6
7
8
MeCN
DMF
dioxane rt
CH2Cl2 rt
ꢀ
Life Sci. 2006, 78, 1933–1939. (f) Faugeroux, V.; Genisson, Y.; Salma, Y.;
9
THF
THF
THF
THF
THF
0
Constant, P.; Baltas, M. Bioorg. Med. Chem. 2007, 15, 5866–5876.
(11) Related palladium-catalyzed cycloaddition of vinylaziridines with
heterocumulenes to give monocyclization product was extensively investi-
gated by Alper and co-workers, see: (a) Butler, C. D.; Inman, A. G.; Alper,
H. J. Org. Chem. 2000, 65, 5887–5890. For asymmetric reaction, see:
(b) Trost, B. M.; Fandrick, D. R. J. Am. Chem. Soc. 2003, 125, 11836–
11837. For related reactions of arylaziridines, see: (c) Baeg, J. O.; Alper, H.
J. Org. Chem. 1992, 57, 157–162. (d) Baeg, J. O.; Alper, H. J. Am. Chem. Soc.
1994, 116, 1220–1224. (e) Baeg, J. O.; Bensimon, C.; Alper, H. J. Am. Chem.
Soc. 1995, 117, 4700–4701. (f) Wu, J.-Y.; Luo, Z.-B.; Dai, L.-X.; Hou, X.-L.
J. Org. Chem. 2008, 73, 9137–9139.
10
11
12e
13f
-40
-78
-40
-40
No reaction
18
7
82
93
aUnless otherwise stated, all reactions were carried out with palla-
dium catalyst (5 mol %) and PhNCO (1.1 equiv). bYields of isolated
products. cPPh3 (10 mol %) was used. dPd2(dba)3 CHCl3 (2.5 mol %)
3
was used. ePhNCO (2.0 equiv) was used. fPhNCO (5.0 equiv) was used.
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TABLE 2. Domino Cyclization of Various Alkynylaziridines and Aryl Isocyanates
product (yieldb, %)
entry
substrate
isocyanate (Ar)
conditiona
time (min)
13
14
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
11a
11b
11c
11d
11a
11a
11a
11a
11a
11a
11a
11a
11b
11c
11d
11a
11a
11a
11a
11a
11a
11a
12a (Ph)
12a (Ph)
12a (Ph)
12a (Ph)
12b (4-MeC6H4)
12c (4-iPrC6H4)
12d (4-FC6H4)
12e (4-ClC6H4)
12f [3-(CF3)C6H4]
12g [3-(NO2)C6H4]
12h (2-MeC6H4)
12a (Ph)
12a (Ph)
12a (Ph)
12a (Ph)
12b (4-MeC6H4)
12c (4-iPrC6H4)
12d (4-FC6H4)
12e (4-ClC6H4)
12f [3-(CF3)C6H4]
12g [3-(NO2)C6H4]
12h (2-MeC6H4)
A
A
A
A
A
A
A
A
A
A
A
B
B
B
B
B
B
B
B
B
B
B
1
1
1
1
1
1
1
1
1
13a (82)
13b (0)
14a (0)
14b (73)c
14c (0)
14d (0)
14e (2)
14f (0)
14g (11)
14h (8)
14i (13)
14j (0)
14k (0)
14a (93)
14b (99)
14c (0)
14d (0)
14e (89)
14f (99)
14g (92)
14h (74)
14i (54)
14j (0)
13c (75)
13d (89)
13e (73)
13f (86)
13g (71)
13h (84)
13i (80)
13j (93)
13k (83)
13a (7)
1
1
40
25
30
30
40
25
35
40
30
30
40
13b (0)
13c (62)
13d (67)
13e (8)
13f (0)
13g (6)
13h (trace)
13i (45)
13j (76)
13k (14)
14k (80)
aConditions A: Pd(PPh3)4 (5 mol %), ArNCO (1.1 equiv), THF, rt. Conditions B: Pd(PPh3)4 (5 mol %), ArNCO (5.0 equiv), THF, -40 °C. bYields of
isolated products based on 11 unless otherwise noted. cBased on isocyanate.
We started our investigation of the domino cyclization with
2-alkynylaziridine 11a and phenyl isocyanate 12a (1.1 equiv)
under various reaction conditions (Table 1). The reaction in the
presence of Pd(OAc)2 and PPh3 at room temperature, standard
conditions for vinylaziridine cycloaddition,11a gave only 4%
yield of the desired product 13a (entry 1). Similarly, PdCl2-
investigated the domino cyclization using various 2-alkynyl-
aziridines and aryl isocyanates under two sets of reaction
conditions [conditions A: Pd(PPh3)4 (5 mol %), aryl isocya-
nate (1.1 equiv), THF, rt; conditions B: Pd(PPh3)4 (5 mol %),
aryl isocyanate (5.0 equiv), THF, -40 °C]. The results are
summarized in Table 2. Interestingly, the reaction of N-mesyl-
alkynylaziridine 11b under conditions A, monoaddition condi-
tions for the N-tosylaziridine 11a (entry 1), selectively afforded
the bis-adduct 14b in 73% yield (based on isocyanate, entry 2).
In sharp contrast, alkynylaziridines 11c and 11d bearing a 2,4,6-
trimethylphenylsulfonyl (Mts) group on the aziridine nitrogen
were efficiently converted into the corresponding monoadducts
13c (75%) and 13d (89%), respectively, under conditions A
(entries 3 and 4). We next investigated the substitution effect of
the aryl isocyanates using the aziridine 11a (entries 5-11). The
reaction with 4-methylphenyl or 4-isopropylphenyl isocyanates
12b and 12c under conditions A gave bicyclic products 13e and
13f in good yields (73% and 86%, entries 5 and 6). Similarly,
exposure of 11a to aryl isocyanates 12d and 12e containing a
halogen atom (F or Cl) at the 4-position under conditions A
afforded the desired bicyclic products 13g (71%) and 13h
(84%), respectively (entries 7 and 8). The reaction with iso-
cyanates 12f-hcontaining an electron-withdrawing group (CF3
or NO2) at the 3-position or a methyl group at the 2-position also
afforded monoadducts 13i-k in 80-93% yields (entries 9-11).
Next, the reaction under conditions B was investigated.
When the reaction of the N-mesylaziridine 11b was carried
(dppf) CH2Cl2 was ineffective for the desired reaction (entry 2).
3
After screening several palladium catalysts, we found that Pd-
(PPh3)4 (5 mol %) was the most effective catalyst for the domino
cyclization to provide the desired bicyclic product 13a in 82%
yield (entry 4). Next, we examined the influence of reaction
solvent and temperature. MeCN, DMF, and CH2Cl2 were
ineffective as the solvent (entries 5, 6, and 8). Interestingly, the
reaction at 0 °C afforded bis-adduct 14a in 24% yield along with
the monoadduct 13a (59%, entry 9).12 The selectivity for bis-
addition was improved by conducting the reaction at -40 °C
(entry 10, 13a:14a=17:44), while the reaction did not proceed at
-78 °C (entry 11). As we expected, the reaction with an
increased amount of isocyanate 12a (5.0 equiv) at -40 °C more
efficiently promoted bis-addition to give 14a selectively in 93%
yield (entry 13).
Having established the optimal reaction conditions for
selective formation of 13a (entry 4) and 14a (entry 13), we
(12) Structures of bicyclic heterocycles 13a and 14a were characterized by
COSY, HMQC and HMBC spectroscopic analysis and NOE experiment (see
the Supporting Information).
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SCHEME 4. Plausible Reaction Mechanism of Palladium(0)-
Catalyzed Domino Cyclization of 2-Alkynylaziridines in the
Presence of Aryl Isocyanates
Plausible reaction mechanisms for the formation of the linked
nitrogen heterocycles 13 and 14 are shown in Scheme 4. Oxi-
dative addition of alkynylaziridine 11 to palladium(0) followed
by nucleophilic addition of the resulting η3-propargylpalladium
complex 1514 to aryl isocyanates forms η3-propargylpalladium
complex 16, which is in equilibrium with 17. The first cyclization
onto the central carbon atom of 17 and the second cyclization of
the resulting η3-allylpalladium complex 18 produces the mono-
adducts 13. On the other hand, addition of 17 to a second
molecule of aryl isocyanate before the successive cyclization
will afford the bis-adducts 14 via 19 and 20.15 Excess isocyanate
(5.0 equiv, conditions B) will apparently promote the second
addition of 17 to form 19, which will increase the ratio of the bis-
adducts 14. Another pathway to form the intermediate 20 would
be conversion of 15 to 21 by proton transfer, addition of 21
to aryl isocyanate, cyclization to form 23, and addition to the
second molecule of aryl isocyanate. Selective formation of bis-
adduct 14b from N-mesylaziridine 11b (R1=Ms,R2=Ts) canbe
rationalized as follows. The intermediate 15 bearing an N-mesyl
group as R1 will be rapidly converted to 21 because of the weaker
electron-withdrawing effect of a mesyl group than that of a tosyl
group (as R2).16 This can assist the reaction of 21 with isocyanate
to produce 22, a precursor of the bis-adduct 14.17,18
Conclusion
In conclusion, we have developed a novel synthesis of
linked nitrogen heterocycles by palladium(0)-catalyzed dom-
ino cyclization of 2-alkynylaziridines via addition with an
aryl isocyanate. This reaction selectively provides mono- and
bis-adducts by simply changing the reaction conditions.
Further investigation for the construction of other hetero-
cycles is in progress in our laboratory.
Experimental Section
General Procedure for Preparation of Propargyl Alcohols 10:
Synthesis of N,N0-(2-Hydroxyhex-3-yne-1,6-diyl)bis(4-methylphenyl-
sulfonamide) (10a). To a stirred mixture of N-(but-3-ynyl)-
4-methylphenylsulfonamide (1.51 g, 6.78 mmol) in dry THF (20
mL) under nitrogen was added n-BuLi (1.65 mol/L; 8.03 mL, 13.2
mmol) at -78 °C, and the mixture was stirred at the same
temperature for 20 min. N-Boc glycinal 9 (502 mg, 3.15 mmol) in
THF (10 mL) was added to the above stirred reagent at -78 °C, and
the mixture was stirred at 0 °C for 2 h, followed by quenching with
saturated NH4Cl (2 mL). The whole was extracted with EtOAc,
out under conditions B, bis-adduct 14b was obtained in 99%
yield (entry 13), similar to the reaction of N-tosylaziridine
11a (entry 12). On the other hand, treatment of the aziridines
11c and 11d bearing an N-Mts group under conditions B
afforded the monoadducts 13c (62%, entry 14) and 13d
(67%, entry 15), respectively, the same products produced
by the reaction under conditions A (entries 3 and 4). Further-
more, the bis-adducts 14e-h and 14k were selectively obta-
ined in 74-99% yields from 11a when using 4-substituted
aryl isocyanates 12b-e or the 2-methyl one 12h (entries
16-19 and 22). For a reason that is unclear, substitution
with an electron-withdrawing group at the 3-position of
phenyl isocyanate increased formation of monoadducts 13i
and 13j (entries 20 and 21). These observations have revealed
that N-arylsulfonylaziridines allow selective formation of the
linked heterocycles 13 through monoaddition under conditions
A, while the selectivity of the bis-adduct under conditions B
depends on the substituent on the phenyl isocyanates as well as
the aziridine nitrogen.13
(14) (a) Ogoshi, S.; Tsutsumi, K.; Nishiguchi, S.; Kurosawa, H. J.
Organomet. Chem. 1995, 493, C19–C21. (b) Tsutsumi, K.; Ogoshi, S.;
Nishiguchi, S.; Kurosawa, H. J. Am. Chem. Soc. 1998, 120, 1938–1939. (c)
Tsutsumi, K.; Kawase, T.; Kakiuchi, K.; Ogoshi, S.; Okada, Y.; Kurosawa,
H. Bull. Chem. Soc. Jpn. 1999, 72, 2687–2692.
(15) We previously reported that medium-sized rings easily formed from
η3-propargylpalladium complexes; see ref 7.
(16) In other words, the higher basicity of the anionic mesylamide
nitrogen in 15 (R1 =Ms, R2 =Ts) in comparison to the anionic tosylamide
nitrogen in 21 would shift the equilibrium in the direction of 21 thus favoring
the formation of 14b. The following pKa values were reported. PhSO2NH2:
pKa=16.1 (DMSO); MeSO2NH2: pKa=17.5 (DMSO), see: Bordwell, F. G.
Acc. Chem. Res. 1988, 21, 456–463.
(17) Although the exact reason for the temperature effect on the selecti-
vity (entry 4 vs 10) is unclear, a lower reaction temperature might decrease the
impact of the entropy loss (-TΔS) in the intermolecular addition to a second
molecule of isocyanate. This effect can promote formation of the bis-adduct
14a. Because the entropy loss in the intramolecular cyclization reaction to
form 13a would be smaller than that in the intermolecular addition reaction,
the cyclization reaction will receive less benefit of the effect of lower reaction
temperature than the intermolecular addition reaction.
(13) Unfortunately, the reaction with N-benzyl or N-tosyl isocyanates
gave a mixture of unindentified products without producing the desired bis-
cyclization products.
(18) At present, the effect of the electron-withdrawing group at the
3-position of the aryl isocyanate 12f and 12g on the selectivity is unclear.
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and the extract was washed successively with water and brine, and
dried over Na2SO4. The filtrate was concentrated and purified by
flash chromatography over silica gel with n-hexane/EtOAc (1:1) to
give a crude propargyl alcohol as an oil. This crude propargyl
alcohol was dissolved in 4 N HCl/dioxane (1 mL) at room
temperature, and the mixture was stirred at the same temperature
for 30 min. TsCl (230 mg, 1.21 mmol) in CHCl3 (2 mL) was added
to the mixture. The mixture was cooled to 0 °C and Et3N (1.5 mL)
was added to the mixture, and the resulting mixture was stirred at
room temperature for 30 min. The mixture was partitioned between
EtOAc and water. The organic layer was separated, washed with
water and brine, and dried over Na2SO4. The filtrate was concen-
trated under reduced pressure to give an oily residue, which was
purified by column chromatography over silica gel with n-hexane/
EtOAc (1:1 to 1:2) to give 10a (120 mg, 69% yield, 3 steps): colorless
oil; IR (neat) (cm-1) 3482 (OH), 3282 (NHSO2), 2237 (CtC), 1324
(NHSO2), 1159 (NHSO2); 1H NMR (400 MHz, CDCl3) δ 2.36 (td,
J=6.0, 1.6 Hz, 2H), 2.42 (s, 6H), 3.05-3.11 (m, 4H), 3.67 (ddd, J=
9.2, 6.8, 4.0 Hz, 1H), 4.38-4.43 (m, 1H), 5.43-5.49 (m, 1H),
7.29-7.31 (m, 4H), 7.75-7.77 (m, 4H); 13C NMR (75 MHz,
CDCl3) δ 20.3, 21.5 (2C), 41.6, 48.7, 61.4, 80.5, 83.4, 127.0 (2C),
127.1 (2C), 129.8 (4C), 136.9, 137.1, 143.57, 143.61; MS (FAB) m/z
(%) 437 (MHþ, 100); HRMS (FAB) calcd for C20H25N2O5S2
(MHþ) 437.1205, found 437.1225.
82% yield): colorless oil; IR (neat) (cm-1) 1736 (CdO), 1598
(CdC), 1364 (NSO2), 1171 (NSO2); 1H NMR (500 MHz,
CDCl3) δ 1.96-2.04 (m, 1H), 2.10-2.17 (m, 1H), 2.42 (s, 3H),
2.44 (s, 3H), 3.76 (ddd, J=11.5, 10.5, 6.5 Hz, 1H), 3.84-3.90 (m,
1H), 4.05 (dd, J=9.5, 9.0 Hz, 1H), 4.20 (dd, J=9.5, 2.5 Hz, 1H),
5.09-5.11 (m, 1H), 5.41-5.43 (m, 1H), 7.09-7.12 (m, 1H),
7.24-7.29 (m, 4H), 7.33 (d, J=8.5 Hz, 2H), 7.37 (d, J=8.5 Hz,
2H), 7.65 (d, J=8.5 Hz, 2H), 7.96 (d, J=8.5 Hz, 2H); 13C NMR
(125 MHz, CDCl3) δ 21.6 (2C), 27.5, 47.5, 51.2, 52.4, 116.1,
120.2 (2C), 124.7, 127.5 (2C), 128.2 (2C), 129.0 (2C), 139.7 (2C),
130.0 (2C), 134.3, 134.7, 137.4, 140.7, 144.5, 145.0, 151.5; MS
(FAB) m/z (%) 538 (MHþ, 100); HRMS (FAB) calcd for
C27H28N3O5S2 (MHþ) 538.1470, found 538.1470.
General Procedure for Domino Cyclization of 2-Alkynylazir-
idines and Aryl Isocyanates (Conditions B): Synthesis of 3-(4-Methyl-
phenylsulfonyl)-7-[1-(4-methylphenylsulfonyl)-2-oxo-3-phenylimi-
dazolidin-4-yl]-1-phenyl-4,5-dihydro-1H-1,3-diazepin-2(3H)-one
(14a) (Table 1, Entry 13). To a stirred mixture of 2-alkynylazir-
idine 11a (26.8 mg, 0.0641 mmol) and PhNCO 12a (34.9 μL,
0.321 mmol) in THF (0.6 mL) was added Pd(PPh3)4 (3.7 mg,
0.00320 mmol) at -40 °C, and the resulting mixture was stirred
at the same temperature for 40 min. Concentration under
reduced pressure gave an oily residue, which was purified by
column chromatography over silica gel with n-hexane/EtOAc
(5:2 to 3:2) to give 14a (39.0 mg, 93% yield) and 13a (2.4 mg, 7%
yield).
General Procedure for Preparation of 2-Alkynylaziridines 11:
N-{4-[1-(4-Methylphenylsulfonyl)aziridin-2-yl]but-3-ynyl}-4-methyl-
phenylsulfonamide (11a). To a stirred mixture of the propargyl
alcohol 10a (323 mg, 0.488 mmol) and PPh3 (233 mg, 0.888
mmol) in THF (5 mL) was added diisopropyl azodicarboxylate
(386 μL, 1.15 mmol; 40% in toluene solution) at room tempera-
ture, and the resulting mixture was stirred at the same tempera-
ture for 1 min. Concentration under reduced pressure gave an
oily residue, which was purified by column chromatography
over silica gel with n-hexane/EtOAc (5:4) to give 11a (249 mg,
82% yield): colorless oil; IR (neat) (cm-1) 3300 (NHSO2), 2253
Compound 14a: colorless oil; IR (neat) (cm-1) 1736 (CdO),
1697 (CdO), 1597 (CdC), 1358 (NSO2), 1170 (NSO2); 1H NMR
(500 MHz, CDCl3) δ 2.33-2.44 (m, 2H), 2.41 (s, 3H), 2.44 (s,
3H), 3.65-3.69 (m, 1H), 3.87-3.93 (m, 2H), 4.00 (dd, J=10.0,
3.5 Hz, 1H), 4.40 (dd, J=10.0, 3.5 Hz, 1H), 5.76 (dd, J=6.5, 6.5
Hz, 1H), 7.06-7.09 (m, 1H), 7.15-7.17 (m, 1H), 7.20-7.26 (m,
5H), 7.30-7.40 (m, 7H), 7.96 (d, J=8.5 Hz, 2H), 8.02 (d, J=8.5
Hz, 2H); 13C NMR (125 MHz, CDCl3) δ 21.6, 21.7, 24.6, 47.2,
51.8, 54.2, 119.8 (2C), 120.1, 124.7, 127.6 (2C), 128.5 (2C), 128.6,
128.9 (2C), 129.0 (2C), 129.4 (2C), 129.5 (2C), 129.8 (2C), 134.9,
135.1, 136.8, 137.4, 138.3, 144.5, 145.0, 151.5, 154.8; MS (FAB)
m/z (%) 657 (MHþ, 45), 154 (100); HRMS (FAB) calcd for
C34H33N4O6S2 (MHþ) 657.1842, found 657.1846.
1
(CtC), 1329 (NHSO2), 1161 (NHSO2); H NMR (500 MHz,
CDCl3) δ: 2.32 (td, J=6.5, 1.5 Hz, 2H), 2.34 (d, J=4.5 Hz, 1H),
2.43 (s, 3H), 2.46 (s, 3H), 2.67-2.68 (m, 1H), 3.05 (td, J=6.5, 6.5
Hz, 2H), 3.17-3.20 (m, 1H), 4.77-4.87 (m, 1H), 7.30 (d, J=8.5
Hz, 2H), 7.36 (d, J=8.5 Hz, 2H), 7.73 (d, J=8.5 Hz, 2H), 7.83
(d, J=8.5 Hz, 2H); 13C NMR (125 MHz, CDCl3) δ 20.2, 21.5,
21.7, 28.1, 34.7, 41.4, 77.2, 79.8, 127.0 (2C), 128.0 (2C), 129.8
(2C), 129.9 (2C), 134.4, 136.9, 143.6, 145.1; MS (FAB) m/z (%)
419 (MHþ, 54), 154 (100); HRMS (FAB) calcd for C20H23N2-
O4S2 (MHþ) 419.1099, found 419.1112.
General Procedure for Domino Cyclization of 2-Alkynylazir-
idines and Aryl Isocyanates (Conditions A): Synthesis of 1-(4-Methyl-
phenylsulfonyl)-4-[1-(4-methylphenylsulfonyl)-4,5-dihydro-1H-
pyrrol-2-yl]-3-phenylimidazolidin-2-one (13a) (Table 1, Entry 4). To
a stirred mixture of 2-alkynylaziridine 11a (25.2 mg, 0.0603
mmol) and PhNCO 12a (7.2 μL, 0.0663 mmol) in THF (0.6 mL)
was added Pd(PPh3)4 (3.5 mg, 0.00301 mmol) at room tempera-
ture, and the resulting mixture was stirred at the same tempera-
ture for 1 min. Concentration under reduced pressure gave an
oily residue, which was purified by column chromatography over
silica gel with n-hexane/EtOAc (5:2 to 3:2) to give 13a (26.5 mg,
Acknowledgment. This work was supported in part by
Grants-in-Aid for Encouragement of Young Scientists (A)
(H.O.) and for Scientific Research (B) (T.T.) from the
Ministry of Education, Culture, Sports, Science and Techno-
logy of Japan, and Targeted Proteins Research Program.
A.O. is grateful for Research Fellowships from the Japan
Society for the Promotion of Science (JSPS) for Young
Scientist. Appreciation is expressed to Fundamental Studies
in Health Sciences of the National Institute of Biomedical
Innovation (NIBIO).
Supporting Information Available: Experimental proce-
dures and characterization data for all new compounds. This
material is available free of charge via the Internet at http://
pubs.acs.org.
3400 J. Org. Chem. Vol. 75, No. 10, 2010