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H. Yamamoto et al.
LETTER
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ing pyrroles were obtained in excellent yields without sig-
nificant leaching of the metal.17 However, the reaction of
the cyclohexyl derivative 17 required 30 mol% of 10 in
order to consume the starting material within acceptable
reaction periods (Table 3, entry 4). The cyclization of sub-
strates with an alkyl substituent on the terminal alkyne
smoothly produced the corresponding pyrrole derivatives
in very good yields (Table 3, entries 5–7); even when us-
ing the sterically hindered tert-butyl-substituted 22, the
desired pyrrole 23 was obtained in 91% yield within five
minutes.
A free hydroxy moiety did not affect the course of the re-
action, giving rise to 25 in 74% yield after 15 minutes. The
TBS ether 26 underwent cleavage of the siloxy group un-
der the reaction conditions to again afford 25 in quantita-
tive yield. In contrast, the TBDPS ether as well as the
acetyl and benzyl alkynes remained intact (Table 3, en-
tries 10–12), affording the desired derivatives in high
yields (92–99%).
In many respects, the conversion of homopropargyl azide
derivatives catalyzed by mercuric reagents such as
PhHgOTf or silaphenylmercuric triflate constitutes a rea-
sonable alternative for the preparation of various pyrroles.
Indeed, in all cases, the procedure can be carried out at
room temperature and is applicable to a wide range of ho-
mopropargyl azides, giving the corresponding pyrroles in
excellent yields.
(8) Hiroya, K.; Matsumoto, S.; Ashikawa, M.; Ogiwara, K.;
Sakamoto, T. Org. Lett. 2006, 8, 5349.
(9) Wyrębek, P.; Sniady, A.; Bewick, N.; Li, Y.; Mikus, A.;
Wheeler, K. A.; Dembinski, R. Tetrahedron 2009, 65, 1268.
(10) Nishizawa, M.; Skwarczynski, M.; Imagawa, H.; Sugihara,
T. Chem. Lett. 2002, 12.
(11) Nishizawa, M.; Imagawa, H.; Yamamoto, H. Org. Biomol.
Chem. 2010, 8, 511.
(12) Yamamoto, H.; Sasaki, I.; Namba, K.; Imagawa, H.;
Nishizawa, M. Org. Lett. 2007, 9, 1399.
(13) When the cyclization reaction of 1 with Hg(OTf)2 was
quenched using Et3N and NaCl at –20 °C, the formation of
pyrrolic mercury chloride corresponds to 7 was confirmed
by 1H NMR spectroscopy. However, pyrrolic mercury
chloride was unstable under acidic conditions. During
column chromatography on silica gel pyrrolic mercury
chloride decomposed into 2.
(14) Yamamoto, H.; Sasaki, I.; Hirai, Y.; Namba, K.; Imagawa,
H.; Nishizawa, M. Angew. Chem. Int. Ed. 2009, 48, 1244.
(15) (a) Rahmatpour, A.; Aalaie, J. Heteroat. Chem. 2011, 22,
85. (b) Veisi, H. Tetrahedron Lett. 2010, 51, 2109.
(c) Kumar, M. A.; Krishna, A. B.; Babu, B. H.; Reddy, C. B.;
Reddy, C. S. Synth. Commun. 2008, 38, 3456. (d) Nad, S.;
Roler, S.; Haag, R.; Breinbauer, R. Org. Lett. 2006, 8, 403.
(e) Curini, M.; Montanari, F.; Rosati, O.; Lioy, E.;
Margarita, R. Tetrahedron Lett. 2003, 44, 3923.
Supporting Information for this article is available online at
Acknowledgment
This study was financially supported by a Grant-in-Aid [Young Sci-
entists (B) and the Senryaku project] from MEXT (the Ministry of
Education, Culture, Sports, Science, and Technology of the Japa-
nese Government).
References and Notes
(1) (a) Jones, A. Pyrroles; Jones, R. A., Ed.; Wiley: New York,
1990, 105. (b) Sundberg, R. J. Comprehensive Heterocyclic
Chemistry II, Vol. 2; Katritzky, A. R.; Rees, C. W.; Scriven,
E. F. V., Eds.; Elsevier: Oxford, 1996, 119. (c) Eicher, T.;
Hauptmann, S.; Speicher, A. The Chemistry of Heterocycles,
2nd ed.; Wiley-VCH: Weinheim, 2003, 97. (d) Fan, H.;
Peng, J.; Hamann, M. T.; Hu, J.-F. Chem. Rev. 2008, 108,
264.
(2) (a) Patil, N. T.; Yamamoto, Y. Chem. Rev. 2008, 108, 3395.
(b) Patil, N. T.; Yamamoto, Y. ARKIVOC 2007, (x), 121.
(3) (a) Knorr, L. Ber. Dtsch. Chem. Ges. 1884, 17, 1635.
(b) Paal, C. Ber. Dtsch. Chem. Ges. 1884, 17, 2756.
(c) Amarnath, V.; Anthony, D. C.; Amarnath, K.; Valentine,
W. M. J. Org. Chem. 1991, 56, 6924. (d) Pridmore, S. J.;
Slatford, P. A.; Taylor, J. E.; Whittlesey, M. K.; Williams,
J. M. J. Tetrahedron 2009, 65, 8981. (e) Azizi, N.; Khajeh-
Amiri, A.; Ghafuri, H.; Bolourtchian, M.; Saidi, M. R.
Synlett 2009, 2245. (f) Rivera, S.; Bandyopadhyay, D.;
Banik, B. K. Tetrahedron Lett. 2009, 50, 5445. (g)Chen, J.;
Wu, H.; Zheng, Z.; Jin, C.; Zhang, X.; Su, W. Tetrahedron
Lett. 2006, 47, 5383.
(16) Preparation of Silaphenylmercuric Triflate (10) and a
Typical Experimental Procedure for a Silaphenyl-
mercuric Triflate Catalyzed Cyclization
To a suspension of dried silaphenylmercuric acetate 9 (0.2
mmol/g, 500 mg, 0.1 mmol) in MeNO2 (5 mL) was added
TfOH (17.4 mL, 0.2 mmol), and the mixture was stirred for
10 min at r.t. The filtered residue was washed with MeNO2
(10 mL) and dried to give silaphenylmercuric triflate 10.
Next, MeNO2 (4 mL) and prepared 10 were added to a dried
two-neck flask. To the stirred suspension of 10 was added a
solution of 1 (86 mg, 0.5 mmol) in MeNO2 (1 mL) at r.t.
under argon. The mixture was stirred at r.t. for 5 min, and the
catalyst was then removed by filtration and washed with
MeNO2 (10 mL). The combined filtrates were concentrated
under reduced pressure. Purification by column chromatog-
raphy on silica gel using hexane and EtOAc (10:1) gave
pyrrole 2 (70 mg, 97%).
(17) In all cases (Table 3), recovery of 10 was between 99.29%
and 99.89%.
Synlett 2011, No. 19, 2815–2818 © Thieme Stuttgart · New York