Organic Letters
Letter
nylphosphaneyl)ethane (5 mol %) provided an azirine as major product
in 55% yield rather than the targeted pyridine (20%).
REFERENCES
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(
1) Murphree, S. S. In Modern Heterocyclic Chemistry; Alvarez-Builla, J.,
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(14) The structure of this pyridine is equal to 3 as depicted in Scheme 3.
(15) For comparison, we have also investigated the use of commercial
1
(
2
61.
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[
Ir(coe) Cl] (0.25 mol %). In the absence or presence of bipy in either
2 2
toluene or CPME, 2a was not detected after 24 h at 100 °C.
2
(
16) Substrates with R = H did not form 2H-azirines in significant
amounts. In this case, substrate dimerization was noticed.
(
(17)Calculated thermodynamicparameters for thereaction typeof1to
2
have been reported. It was found that the reaction is not only
(
entropically favorable but also exothermically favorable as a result of the
Tetrahedron 1980, 36, 877. (b) Nakamura, S.; Hayama, D. Angew. Chem.,
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large energy gain upon CO formation (see ref 10).
2
(18) (a) Synthesis of highly enantioenriched isoxazolinones by
asymmetric direct 1,4-additions: Hellmuth, T.; Frey, W.; Peters, R.
Angew. Chem., Int. Ed. 2015, 54, 2788. For related studies, see, e.g.:
(
(b) Hellmuth, T.; Rieckhoff, S.; Weiss, M.; Dorst, K.; Frey, W.; Peters, R.
(
ACS Catal. 2014, 4, 1850. (c) Peters, R.; Fischer, D. F.; Jautze, S. Top.
Organomet. Chem. 2011, 33, 139.
(19) The intensity of the signal was too low for precise high-resolution
ESI-MS measurements.
(20) For a Au-catalyzed transformation of alkyne-substituted azirines
into pyridines, see ref 5n.
(21) Selected review: Hill, M. D. Chem. - Eur. J. 2010, 16, 12052.
(22) For alternative approaches toward this compound class, see, e.g.:
Weiss, M.;Peters, R. ACSCatal. 2015, 5,310andreferencescitedtherein.
2
010, 12, 3312. (j) Okamoto, K.; Mashida, A.; Watanabe, M.; Ohe, K.
̈
(23) Eller, K.; Henkes, E.; Rossbacher, R.; Hoke, H. In Ullmann’s
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(24) Crystallographic data have been deposited with the Cambridge
Crystallographic Data Centre (no. 1538203).
(25) The price of Ru metal is about 15 times lower than that of Ir
according to the Engelhard Industrial Bullion (EIB) prices for one troy
(
n) Prechter, A.; Henrion, G.; dit Bel, P. F.; Gagosz, F. Angew. Chem., Int.
Ed. 2014, 53, 4959. (o) Loy, N. S. Y.; Kim, S.; Park, C.-M. Org. Lett. 2015,
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1
(
2
1
Chem. Ber. 1989, 122, 1175. (e) Pinho eMelo, T. M. V. D.; Lopes, C. S. J.;
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(
5
f) Sjoholm Timen, A.; Risberg, E.; Somfai, P. Tetrahedron Lett. 2003, 44,
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7) Examples for the Neber-type reactions: (a) Sakamoto, S.; Inokuma,
(
T.; Takemoto, Y. Org. Lett. 2011, 13, 6374. (b) Skepper, C. K. C. K.;
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8
491. (d) Azirine intermediates: Ooi, T.; Takahashi, M.; Doda, K.;
Maruoka, K. J. Am. Chem. Soc. 2002, 124, 7640.
8) For alternative recently reported protocols, see, e.g.: (a) Enamines
(
plus hypervalent iodine reagents: Li, X.; Du, Y.; Liang, Z.; Li, X.; Pan, Y.;
Zhao, K. Org. Lett. 2009, 11, 2643. (b) Sun, X.; Lyu, Y.; Zhang-Negrerie,
D.; Du, Y.; Zhao, K. Org. Lett. 2013, 15, 6222. (c) Via transition-metal
catalysis: Jiang, Y.; Chan, W. C.; Park, C.-M. J. Am. Chem. Soc. 2012, 134,
4
104. (d) From isoxazoles: Auricchio, S.; Bini, A.; Pastormerlo, E.;
Truscello, A. M. Tetrahedron 1997, 53, 10911.
(
9) Rieckhoff, S.; Hellmuth, T.; Peters, R. J. Org. Chem. 2015, 80, 6822.
(
10) Okamoto, K.; Shimbayashi, T.; Yoshida, M.; Nanya, A.; Ohe, K.
Angew. Chem., Int. Ed. 2016, 55, 7199.
11) The Ohe research group has recently reported elegant studies for
(
transition-metal-catalyzed decarboxylative transformations of isoxazoli-
nones which are likely to involve vinylnitrene intermediates:
(
a) Okamoto, K.; Oda, T.; Kohigashi, S.; Ohe, K. Angew. Chem., Int.
Ed. 2011, 50, 11470. (b) Okamoto, K.; Shimbayashi, T.; Tamura, E.;
Ohe, K. Chem. - Eur. J. 2014, 20, 1490.
(
2
(
12) Okamoto, K.; Sasakura, K.; Shimbayashi, T.; Ohe, K. Chem. Lett.
016, 45, 988.
13) Ohe et al. observed in this study that 2H-azirines were formed as
reactive intermediates, which were suggested to undergo an oxidative
addition of their C−N bond to the Ru(II) catalyst to generate Ru(IV)
species which further react to the final pyridines. They also found that
[
RuCl (p-cymene)] (2.5 mol %) in combination with 1,2-bis(diphe-
2 2
D
Org. Lett. XXXX, XXX, XXX−XXX