m-C₂B₁₀H₁₁HgCl/AgOTf-Catalyzed Reaction for Reductive Deoxygenation

Abstract

A m-C₂B₁₀H₁₁HgCl/AgOTf-catalyzed reaction of allyl silyl ethers with N-Boc-N′-tosylhydrazine has been developed. Under mild conditions, the resulting allyl hydrazine products were transformed into naked alkenes in good yield. Furthermore, the used m-C₂B₁₀H₁₁HgCl could be recovered quantitatively.

Key words

deoxygenation - N-Boc-N′-tosylhydrazine - allylic amination - allylic diazene - carbaborane - mercury - catalytic reaction

• References and Notes

• 1a Myers AG. Zheng B. Tetrahedron Lett. 1996; 37: 4841
• 1b Myers AG. Zheng B. J. Am. Chem. Soc. 1996; 118: 4492

For example, see:
• 2a Siegel DS. Piizzi G. Piersanti G. Movassaghi M. J. Org. Chem. 2009; 74: 9292
• 2b Haukaas MH. O’Doherty GA. Org. Lett. 2002; 4: 1771
• 2c Ott GR. Heathcock CH. Org. Lett. 1999; 1: 1475
• 2d Myers AG. Movassaghi M. Zheng B. J. Am. Chem. Soc. 1997; 119: 8572
• 2e Wood JL. Porco JA. Jr. Taunton J. Lee AY. Clardy J. Schreiber SL. J. Am. Chem. Soc. 1992; 114: 5898
• 3 Movassaghi M. Piizzi G. Siegel DS. Piersanti G. Angew. Chem. Int. Ed. 2006; 45: 5859
• 4 Movassaghi M. Ahmad OK. J. Org. Chem. 2007; 72: 1838
• 5 Kumara Swamy KC. Bhuvan Kumar NN. Balaraman E. Pavan Kumar KV. P. Chem. Rev. 2009; 109: 2551
• 6 Yang Z. Kiran Kumar R. Liao P. Liu Z. Li X. Bi X. Chem. Commun. 2016; 52: 5936
• 7a Yamamoto H. Ho E. Sasaki I. Mitsutake M. Takagi Y. Imagawa H. Nishizawa M. Eur. J. Org. Chem. 2011; 2417
• 7b Yamamoto H. Yamasaki N. Yoshidome S. Sasaki I. Namba K. Imagawa H. Nishizawa M. Synlett 2012; 1069
• 8a Hutchins RO. Kacher M. Rua L. J. Org. Chem. 1975; 40: 923
• 8b Kabalka GW. Yang DT. C. Baker JD. Jr. J. Org. Chem. 1976; 41: 574
• 8c Harapanhalli RS. J. Chem. Soc., Perkin Trans. 1 1988; 3149
• 8d Chu M. Coates RM. J. Org. Chem. 1992; 57: 4590
• 8e Greco MN. Maryanoff BE. Tetrahedron Lett. 1992; 33: 5009
• 8f Chai Y. Vicic DA. McIntosh MC. Org. Lett. 2003; 5: 1039
• 9 Iwai Y. Ozaki T. Takita R. Uchiyama M. Shimokawa J. Fukuyama T. Chem. Sci. 2013; 4: 1111
• 10 The structure of the byproduct was indicated in the Supporting Information.
• 11 The reaction of 15a with 12 in CH₃CN and toluene at r.t. for 1440 min gave 16 in 23% and 17% yield, respectively.
• 12 Nishizawa M. Imagawa H. Yamamoto H. Org. Biomol. Chem. 2010; 8: 511
• 13 Yamamoto H. Sasaki I. Imagawa H. Nishizawa M. Org. Lett. 2007; 9: 1399
• 14 Yamamoto H. Sasaki I. Hirai Y. Namba K. Imagawa H. Nishizawa M. Angew. Chem. Int. Ed. 2009; 48: 1244
• 15a Yamamoto H. Sasaki I. Shiomi S. Yamasaki N. Imagawa H. Org. Lett. 2012; 14: 2266
• 15b Yamamoto H. Yamasaki N. Hamauchi H. Shiomi S. Sasaki I. Seyama K. Mima Y. Nakano M. Kawakami T. Miyataka H. Kasai Y. Imagawa H. RSC Adv. 2015; 5: 94737
• 16 Product 16 was obtained as the mixture of rotamers; see Supporting Information.
• 17 Preparation of 0.1 M CH₂Cl₂ Solution of m-C₂B₁₀H₁₁HgCl/AgOTf To a suspension of AgOTf (38.5 mg, 0.150 mmol) in CH₂Cl₂ (1.5 mL) was added m-C₂B₁₀H₁₁HgCl (56.9 mg, 0.150 mmol) at r.t., and the mixture was stirred at r.t. for 30 min. Typical Procedure for the m-C₂B₁₀H₁₁HgCl/AgOTf-Catalyzed Allylic Amination (Table 1, Entry 12) A solution of (E)-tert-butyldiphenyl(undec-6-en-5-yloxy)silane (15b, 1.08 g, 2.64 mmol) and tert-butyl 2-tosylhydrazine-1-carboxylate (12, 755 mg, 3.96 mmol) in CH₂Cl₂ (8.7 mL) was added to a dried two-neck flask under an atmosphere of argon. m-C₂B₁₀H₁₁HgCl/AgOTf in 0.1 M CH₂Cl₂ (1.32 mL) was added dropwise to the solution at 0 °C, and the mixture was stirred at 0 °C for 10 min. The reaction was quenched with sat. NaCl aq, and the organic phase was separated. The aqueous phase was extracted with CH₂Cl₂ (3 ×). The combined organic phase was dried over MgSO₄ and concentrated in vacuo. The residue was purified by silica gel chromatography (hexane/AcOEt = 20:1 to 4:1) to give 16 (902 mg, 2.06 mmol, 78%) along with m-C₂B₁₀H₁₁HgCl (48.2 mg, 0.127 mmol, 96%). Analytical Data for Compound 16 Colorless syrup. FT-IR (neat): 3313, 3238, 3138, 2957, 2929, 2857, 2856 cm^–1. ¹H NMR (500 MHz, DMSO, 70 °C): δ = 0.85 (6 H, m), 1.25 (20 H, m), 1.93 (3 H, m), 2.43 (3 H, s), 4.18 (1 H, br d, J = 6.0 Hz), 5.27 (1 H, m), 5.47 (1 H, m), 7.36 (2 H, d, J = 7.5 Hz), 7.79 (2 H, d, J = 7.5 Hz), 8.59 (NH, br s). ¹³C NMR (125 MHz, DMSO, 70 °C): δ = 14.06, 21.36, 21.96, 22.18, 27.92, 28.13, 28.25, 28.47, 30.92, 31.68, 32.38, 62.06, 80.09, 128.22, 128.60, 129.55, 129.67, 143.80, 155.48. MS (CI): m/z = 437 [M – H]⁺. HRMS (CI⁺): m/z calcd for C₂₃H₃₉N₂O₄S: 437.2474; found: 437.2479.
• 18 Corma A. Leyva-Pérez A. Sabater MJ. Chem. Rev. 2011; 111: 1657
• 19 Tsuchimoto T. Iwabuchi M. Nagase Y. Oki K. Takahashi H. Angew. Chem. Int. Ed. 2011; 50: 1375
• 20 Trost BM. Zhang T. Sieber JD. Chem. Sci. 2010; 1: 427
• 21 Typical Procedure for the Selective Cleavage of Boc-Protecting Group and the Transformation into Alkene (Scheme 3, a) A 1.0 M HCl in AcOEt (6.2 mmol, 6 mL) was added to a solution of 16 (156 mg, 0.310 mmol) in AcOEt (0.31 mL) at r.t. The reaction mixture was stirred for 5 h at r.t. It was diluted with Et₂O and then quenched with sat. NaHCO₃ aqueous solution. The aqueous phase was extracted with Et₂O (3 ×). The combined organic phase was dried over Na₂SO₄, and concentrated in vacuo to give 17 (105 mg, 0.310 mmol, quant.) as a crude product. Analytical Data for Compound 17 Yellow syrup. FT-IR (neat): 3368, 3029, 2956, 2928, 2870, 2858 cm^–1. ¹H NMR (300 MHz, CDCl₃): δ = 0.87 (6 H, m), 1.13–1.33 (8 H, m), 1.52–1.67 (2 H, m), 1.86 (2 H, q, J = 6.6 Hz), 2.42 (3 H, s), 3.40 (NH₂, s), 4.39, (1 H, q, J = 7.5 Hz), 5.18 (1 H, ddd, J = 1.5 Hz, 7.5 Hz, 15.6 Hz), 5.50 (1 H, dt, J = 6.6 Hz, 15.6 Hz), 7.29 (2 H, d, J = 7.8 Hz), 7.73 (2 H, d, J = 7.8 Hz). ¹³C NMR (75 MHz, CDCl₃): δ = 13.86, 14.00, 21.48, 22.11, 22.28, 28.28, 31.05, 31.65, 31.95, 60.35, 125.44, 128.25, 128.37, 134.54, 134.94, 143.51. MS (Cl): m/z = 339 [M + H]⁺. HRMS (CI⁺): m/z calcd for C₁₈H₃₁N₂O₂S: 339.3006; found: 339.2907. Next, neutral silica gel (3.0 g) was added to a solution of 17 (105 mg, 0.310 mmol) in AcOEt (6 mL), and it was stirred for 6 h at r.t. It was filtrated and washed with hexane/AcOEt (100:1), and the filtrate was concentrated in vacuo. The residue was purified by silica gel chromatography (hexane/AcOEt = 100:1) to give (E)-undec-5-ene (19, 39.2 mg, 0.254 mmol, 82% from 16). Analytical Data for Compound 19 Colorless syrup. FT-IR (neat): 2957, 2931, 2871 cm^–1. ¹H NMR (400 MHz, CDCl₃): δ = 0.88 (6 H, m), 1.27 (10 H, m), 1.97 (4 H, m), 5.39 (2 H, m). ¹³C NMR (100 MHz, CDCl₃): δ = 14.31, 14.43, 22.54, 22.90, 29.689, 31.75, 32.18, 32.64, 32.93, 130.64, 130.71. MS (Cl): m/z = 154 [M]⁺. HRMS (CI⁺): m/z calcd for C₁₁H₂₂: 154.1722; found: 154.1720.
• 22 One-Pot Synthesis of Alkene 19 from 15b (Scheme 3, b) A solution of 15b (129 mg, 0.316 mmol) and 12 (136 mg, 0.474 mmol) in CH₂Cl₂ (0.85 mL) was added to a dried two-neck flask under an atmosphere of argon. m-C₂B₁₀H₁₁HgCl/AgOTf in 0.1 M CH₂Cl₂ (158 μL) was added dropwise to the solution at 0 °C, and it was stirred at 0 °C for 10 min. Subsequently, a 1.0 M HCl in AcOEt (5.0 mL) was added to the mixture at r.t., and it was stirred at r.t. until disappearance of 16. Next, neutral silica gel (3.0 g) was added to the mixture, which was stirred for 24 h at r.t. The suspension was filtrated and washed with hexane/AcOEt (4:1). The filtrate was concentrated in vacuo. The residue was purified by silica gel chromatography (hexane/AcOEt = 100:1 to 4:1) to give 19 (31.2 mg, 0.202 mmol, 64% from 15b) along with m-C₂B₁₀H₁₁HgCl (5.9 mg, 15.6 μmol, 99%).

See Supporting Information. For review of NHK reaction, see:
• 23a Tian Q. Zhang G. Synthesis 2016; 48: 4038
• 23b Cintas P. Synthesis 1992; 248
• 24 CCDC 1556661 contains the supplementary crystallographic data for this paper. The data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/getstructures.
• 25 Myers AG. Kukkola PJ. J. Am. Chem. Soc. 1990; 112: 8208