Abstract
A mild and efficient general method for the deoxygenation of organic N -oxides such as azoxybenzenes, N -arylnitrones, and N -heteroarene N -oxides using Zn(OTf)2 and Cu(OTf)2 in excellent yields is described.
Key words
deoxygenation - metal triflates - nitrones -
N -heteroarene N -oxides - azoxybenzenes
References and Notes
1a Ollevier T.
Nadeau E.
J. Org. Chem.
2005,
70:
9292
1b Deng X.-M.
Sun X.-L.
Tang Y.
J. Org. Chem.
2005,
70:
6537
1c Yang C.-G.
Reich NW.
Shi Z.
He C.
Org. Lett.
2005,
7:
4553
1d Nakamura M.
Endo K.
Nakamura E.
Org. Lett.
2005,
7:
3279
1e Curini M.
Epifano F.
Genovese S.
Marcotullio MA.
Rosati O.
Org. Lett.
2005,
7:
1331
1f Morris WJ.
Custar DW.
Scheidt KA.
Org. Lett.
2005,
7:
1113
1g Anderson ED.
Ernat JJ.
Nguyen MP.
Palma AC.
Mohan RS.
Tetrahedron Lett.
2005,
46:
7747
1h Temelli B.
Unaleroglu C.
Tetrahedron Lett.
2005,
46:
7941
1i Su W.
Li J.
Zheng Z.
Shen Y.
Tetrahedron Lett.
2005,
46:
6037
1j Yanai H.
Saito A.
Taguchi T.
Tetrahedron
2005,
61:
7087
1k De S K.
Gibbs RA.
Tetrahedron Lett.
2005,
46:
1811
1l Jiang H.
Zhu S.
Tetrahedron Lett.
2005,
46:
517
1m Liu L.-Y.
Tang L.
Yu L.
Chang W.-X.
Li J.
Tetrahedron
2005,
61:
10930
1n Cheng K.
Lin L.
Chen S.
Feng X.
Tetrahedron
2005,
61:
9594
1o Zhang J.
Blazecka PG.
Angell P.
Lovdahl M.
Curran TT.
Tetrahedron
2005,
61:
7807
2 Kobayashi S.
Sugiura M.
Kitgawa H.
Lam WW.-L.
Chem. Rev.
2002,
102:
2227 ; and references cited therein
3a Kobayashi S.
Synlett
1994,
689
3b Marshman RW.
Aldrichimica Acta
1995,
28:
77
4a Kobayashi S.
Chem. Lett.
1991,
2187
4b Kobayashi S.
Hachiya I.
Tetrahedron Lett.
1992,
33:
1625
4c Kobayashi S.
Hachiya I.
J. Org. Chem.
1994,
59:
3590
4d Kobayashi S.
Araki M.
Ishitani H.
Nagayama S.
Hachiya I.
Synlett
1995,
233
4e Kobayashi S.
Ishitani H.
Komiyama S.
Oniciu DC.
Katritzky AR.
Tetrahedron Lett.
1996,
37:
3731
4f Kobayashi S.
Araki M.
Yasuda M.
Tetrahedron Lett.
1995,
36:
5773
4g Kobayashi S.
Basujima T.
Nagayama S.
Synlett
1999,
545
4h Aspinall HC.
Browning AF.
Greeves N.
Ravenscroft P.
Tetrahedron Lett.
1994,
35:
9283
4i Kagoshima H.
Hashimoto Y.
Saigo K.
Tetrahedron Lett.
1998,
39:
8465
4j Shen Y.
Qi M.
J. Chem. Res., Synop.
1993,
222
5a Kobayashi S.
Hachiya I.
Araki M.
Ishitani H.
Tetrahedron Lett.
1993,
34:
3755
5b Kobayashi S.
Hachiya I.
Takahori T.
Araki M.
Ishitani H.
Tetrahedron Lett.
1992,
33:
6815
5c Kobayashi S.
Ishitani H.
Nagayama S.
Chem. Lett.
1995,
423
5d Kobayashi S.
Ishitani H.
Nagayama S.
Synthesis
1995,
1195
5e Batey RA.
Simoncic PD.
Lin D.
Smyj RP.
Lough AJ.
Chem. Commun.
1999,
651
5f Gothelf KV.
Hazell RG.
Jørgensen KA.
J. Org. Chem.
1996,
61:
346
5g Sanchez-Blanco AI.
Gothelf KV.
Jørgensen KA.
Tetrahedron Lett.
1997,
38:
7923
5h Minakata S.
Ezoe T.
Nakamura K.
Ryu I.
Komatsu M.
Tetrahedron Lett.
1998,
39:
5205
5i Kobayashi S.
Akiyama R.
Kawaura M.
Ishitani H.
Chem. Lett.
1997,
1039
6a Barrett AGM.
Braddock DC.
McKinnell RM.
Waller FJ.
Synlett
1999,
1489
6b Kotsuki H.
Arimura K.
Araki T.
Shinohara T.
Synlett
1999,
462
6c Tsuda A.
Osuka A.
Science (Washington, D.C.)
2001,
293:
79
7a Kamachi Y.
Kudo T.
Tetrahedron Lett.
2000,
41:
341
7b Castellani CB.
Carugo O.
Perotti A.
Sacchi D.
Invernizzi AG.
Vidari G.
J. Mol. Catal.
1993,
85:
65
7c Gillespie KM.
Munslow IJ.
Scott P.
Tetrahedron Lett.
1999,
40:
9371
8a Gadwal S.
Sandhu JS.
J. Chem. Soc., Perkin Trans. 1
2000,
2827
8b Laskar DD.
Prajapati D.
Sandhu JS.
Tetrahedron Lett.
2000,
41:
8639
8c Barman DC.
Gohain M.
Prajapati D.
Sandhu JS.
Indian J. Chem., Sect. B: Org. Chem. Incl. Med. Chem.
2002,
41:
154
9a Ochiai E. In Aromatic Amine Oxides
Elsevier;
Amsterdam:
1967.
p.184
9b Hisahiro H.
Hideyuki I.
Masakazu F.
Takashi H.
Toshio S.
Synlett
2005,
2388
10a Hamer J.
Macaluso A.
Chem. Rev.
1964,
64:
473
10b Padwa A.
1,3-Dipolar Cycloaddition Chemistry
Vol. I:
Wiley-Interscience;
New York:
1984.
10c Padwa A.
1,3-Dipolar Cycloaddition Chemistry
Vol II:
Wiley-Interscience;
New York:
1984.
11a Nicolaou KC.
Koumbis AE.
Snyder SA.
Simosen KB.
Angew. Chem. Int. Ed.
2000,
41:
2663
11b Chandrashekhar S.
Reddy CR.
Rao JM.
Synlett
2002,
349
12 Barton DHR.
Fekih A.
Lusinchi X.
Tetrahedron Lett.
1985,
26:
4603
13a Olah GA.
Gupta BGB.
Narang SC.
J. Org. Chem.
1978,
43:
4503
13b Howard E.
Olszewski WF.
J. Am. Chem. Soc.
1959,
81:
1483
13c Lunn G.
Sansone EB.
Keefer LK.
Synthesis
1985,
1104
14a Bjorsvik H.-R.
Gambarotti C.
Jensen VR.
Gonzalez RR.
J. Org. Chem.
2005,
70:
3218 ; and references cited therein
14b Bjorsvik H.-R.
Conzalez RR.
Liguori L.
J. Org. Chem.
2004,
69:
7720
14c Baliki R.
Chem. Ber.
1990,
647
14d Malinoswaki M.
Synthesis
1987,
732
15a Hwu JR.
Tseng WN.
Patel HV.
Wong FF.
Horng D.-N.
Liaw BR.
Lin LC.
J. Org. Chem.
1999,
61:
2211
15b Naumann K.
Zon G.
Mislow K.
J. Am. Chem. Soc.
1969,
91:
7012
15c Vorbrüggen H.
Krolikiewicz K.
Tetrahedron Lett.
1983,
24:
5337
16a Kano S.
Tanaka Y.
Hibino S.
Heterocycles
1980,
14:
39
16b Kano S.
Tanaka Y.
Sugino E.
Hibino S.
Synthesis
1980,
695
17a Kozuka S.
Akasaka T.
Furumai S.
Chem. Ind. (London)
1924,
452
17b Jousseaume B.
Chanson E.
Synthesis
1987,
55
17c Newumann WP.
Heymann E.
Ann. Chem.
1965,
683:
24
18 Ilias M.
Barman DC.
Prajapati D.
Sandhu JS.
Tetrahedron Lett.
2002,
43:
1877
19a Abramovitch RA.
Saha JG.
Adv. Heterocycl. Chem.
1966,
6:
229
19b Grimmett MR.
Adv. Heterocycl. Chem.
1993,
58:
271
19c Morimoto Y.
Kurihara H.
Yokoe C.
Kinoshita T.
Chem. Lett.
1989,
829
20 Roberto S.
Jaime E.
Yolanda F.
Rafael A.
Maria RP.
Francisco JA.
Synlett
2005,
1389
21 Jeevanandam A.
Ling Y.-C.
Tetrahedron Lett.
2001,
42:
4361
22 Kalyanam N.
Rao GV.
Tetrahedron Lett.
1993,
34:
1647
23 Vorbrüggen H.
Krolikiewicz K.
Tetrahedron Lett.
1983,
24:
5337
24
Deoxygenation of Nitrones; Typical Procedure
N -phenylnitrone (3a , 0.39 g, 2 mmol) in CH3 CN (15 mL) was added Zn(OTf)2 (2 mmol, 1 equiv) and the resulting mixture was stirred at 80 °C for 70 min. After completion of the reaction (monitored by TLC), the solvent was removed under reduced pressure, and the residue was treated with H2 O (3 × 30 mL). The resultant mixture was extracted with CH2 Cl2 , the organic layer was dried (Na2 SO4 ), and the solvent removed by distillation to give the crude product, which was purified by column chromatography (silica, hexane-EtOAc) to afford benzylidine aniline 4a , in 74% yield; mp 51-52 °C (Lit.26 mp 52 °C). 1 H NMR (200 MHz): δ = 8.35 (s, 1 H, CH=N), 7.30-7.60 (m, 10 H, Ar). 13 C NMR (50 MHz): δ = 122.0, 12.3, 127.0, 128.4, 128.6, 129.0, 129.1, 129.6, 129.8, 130.8, 131.2, 153.2 (Ar), 163.4 (CH).
25 Vogel AI.
A Textbook of Practical Organic Chemistry
3rd ed.:
Longmans;
London:
1956.
26 Sekiya M.
Chem. Pharm. Bull.
1970,
18:
2146
27 Bigelow LA.
Eatough H.
Org. Synth., Coll. Vol. I
Wiley;
New York:
1941.
p.80
28 Dictionary of Organic Compounds
4th ed.:
Pollock JRA.
Stevens R.
Eyre & Spottiswoode;
London:
1965.
29 30 Hantzsch A.
Ber. Dtsch. Chem. Ges.
1901,
34:
822
31
Deoxygenation of Heteroarene
N
-Oxides: Typical Procedure
N -oxide (5a , 0.19g, 2 mmol) in CH3 CN (15 mL) was added Zn(OTf)2 (2 mmol, 1 equiv) and the resulting mixture was stirred at 80 °C for 60 min. The solvent was removed under reduced pressure and H2 O (50 mL) was added. The pH was adjusted to >7 by the addition of 25% aq NH3 and the product extracted with Et2 O (3 × 50 mL). The organic layer was dried (Na2 CO3 ) and evaporated to give the crude product, which after purification afforded pyridine 6a in 89% yield; bp 113-115 °C (Lit.27 bp 115.5 °C); picrate mp 163-164 °C (Lit.27 mp 164-65 °C). 1 H NMR (200 MHz): δ = 7.20 (dd, 2 H, J = 8.2 Hz), 7.55 (dd, 1 H, J = 8.2 Hz), 8.50 (d, 2 H, J = 6.2 Hz). 13 C NMR (50 MHz): δ = 123.2, 123.7, 135.4, 149.6, 149.7.
