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A. Yanagisawa et al.
Letter
Synlett
(5) Yanagisawa, A.; Sawae, T.; Yamafuji, S.; Heima, T.; Yoshida, K.
Synlett 2015, 26, 1073.
(14) Exactly what causes propargylic barium reagent 6 to react
selectively at the -carbon with azo compound 2 is not clear;
however, the unusually long barium–carbon bond (2.76–2.88 Å)
might prevent the formation of a six-membered cyclic transi-
tion-state model 10 leading to the -adduct, see: Kaupp, M.;
Schleyer, P. v. R. J. Am. Chem. Soc. 1992, 114, 491.
(15) Typical Experimental Procedure for the Barbier-Type Selec-
tive Propargylation of Diaryl Azo Compounds: Synthesis of
1-(6,6-Dimethylhept-4-yn-3-yl)-1,2-diphenylhydrazine (3ea,
Table 2, Entry 2)
(6) (a) Ma, G.; Xu, Z.; Zhang, P.; Liu, J.; Hao, X.; Ouyang, J.; Liang, P.;
You, S.; Jia, X. Org. Process Res. Dev. 2014, 18, 1169. (b) Fonseca,
T. S.; da Silva, M. R.; de Oliveira, M. C. F.; de Lemos, T. L. G.;
Marques, R. A.; de Mattos, M. C. Appl. Catal., A 2015, 492, 76.
(7) (a) Fowler, J. S. J. Org. Chem. 1977, 42, 2637. (b) Divya, K.;
Narayana, B. ISRN Spectrosc. 2014, 541970/1.
(8) Yanagisawa, A.; Yamafuji, S.; Sawae, T. Synlett 2016, 27, 2019.
(9) Prof. Miyoshi and co-workers have reported various reactions
promoted by metallic strontium, see: (a) Miyoshi, N. In Science
of Synthesis, Vol. 7; Yamamoto, H., Ed.; Thieme: Stuttgart, 2004,
685. (b) Miyoshi, N.; Ikehara, D.; Matsuo, T.; Kohno, T.; Matsui,
A.; Wada, M. J. Synth. Org. Chem., Jpn. 2006, 64, 845. (c) Miyoshi,
N.; Matsuo, T.; Kikuchi, M.; Wada, M. J. Synth. Org. Chem., Jpn.
2009, 67, 1274. (d) Miyoshi, N.; Kohno, T.; Wada, M.;
Matsunaga, S.; Mizota, I.; Shimizu, M. Chem. Lett. 2009, 38, 984.
(e) Miyoshi, N.; Matsuo, T.; Mori, M.; Matsui, A.; Kikuchi, M.;
Wada, M.; Hayashi, M. Chem. Lett. 2009, 38, 996. (f) Miyoshi, N.;
Asaoka, M.; Miyazaki, Y.; Tajima, T.; Kikuchi, M.; Wada, M.
Chem. Lett. 2012, 41, 35.
(10) For a review of reductive N–N bond cleavage of hydrazines, see:
Gilchrist, T. L. In Comprehensive Organic Synthesis, Vol. 8; Trost,
B. M.; Fleming, I., Ed.; Pergamon Press: Oxford, 1991, 388.
(11) Sapountzis, I.; Knochel, P. Angew. Chem. Int. Ed. 2004, 43, 897.
(12) Bunton, C. A.; Rubin, R. J. J. Am. Chem. Soc. 1976, 98, 4236.
(13) For reviews, see: (a) Epsztein, R. In Comprehensive Carbanion
Chemistry, Chap. 3; Buncel, E.; Durst, T., Ed.; Elsevier: New York,
1984, 107. (b) Yamamoto, H. In Comprehensive Organic Synthe-
sis, Vol. 2; Trost, B. M.; Fleming, I.; Heathcock, C. H., Ed.; Perga-
mon Press: Oxford, 1991, 81.
Freshly cut barium (small pieces, 103.0 mg, 0.75 mmol), propar-
gylic tosylate 1h (220.8 mg, 0.75 mmol), and azobenzene (45.6
mg, 0.25 mmol) were placed in a Schlenk tube (25 mL) under an
argon atmosphere and covered with dry THF (1 mL). The
mixture was stirred for 14 h at room temperature. The mixture
was treated with sat. aq NH4Cl (10 mL), and the aqueous layer
was extracted three times with Et2O (10 mL each). The com-
bined organic extracts were washed with brine, dried over
Na2SO4, and concentrated in vacuo after filtration. The residual
crude product was purified by column chromatography on
silica gel (hexane–MeOH, 50:1) to afford propargylic hydrazine
3ea (65.5 mg, 85% yield).
1H NMR (400 MHz, CDCl3): = 7.25–7.15 (m, 4 H, Ar–H), 7.05–
7.03 (d, 2 H, J = 8.2 Hz, Ar–H), 6.91–6.85 (m, 3 H, Ar–H), 6.77–
6.74 (t, 1 H, J = 7.3 Hz, Ar–H), 5.67 (br, 1 H, NH), 4.43–4.39 (t, 1
H, J = 7.5 Hz, CH), 1.89–1.66 (m, 2 H, CH2), 1.16 (s, 9 H, 3 CH3),
1.04–1.00 (t, 3 H, J = 7.4 Hz, CH3). 13C NMR (99.5 MHz, CDCl3):
= 150.8, 149.0, 129.1, 128.9, 120.7, 118.9, 116.2, 112.1, 94.9,
75.1, 58.1, 31.4, 31.1, 27.4, 11.4. IR (neat): 3311, 2965, 2359,
1600, 1496, 1362, 1308, 1239, 1170, 1092, 1025, 992, 857, 819,
745, 691, 628 cm–1. MS (ESI): m/z calcd for [C21H27N2]+ [M + H]+:
307.2169; found: 307.2170; mp 57–60 °C..
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