The Oxidative Acylnitroso Hetero-Diels–Alder Reaction Catalyzed by Dirhodium Caprolactamate

Abstract

An effective protocol is described for the generation and in situ Diels–Alder trapping of acylnitroso derivatives. In this procedure, the oxidation of hydroxamic acid is efficiently catalyzed by dirhodium(II) caprolactamate with tert-butyl hydroperoxide (TBHP) in the presence of dienes at room temperature. Using this approach we obtained a variety of hetero-Diels–Alder cycloadducts in yields of up to 96% at 0.1 mol% catalyst loading.

Key words

catalysis - oxidation - acylnitroso - Diels–Alder reaction - dirhodium(II)

• References

• 1 Kirby GW, Sweeny JG. J. Chem. Soc., Chem. Commun. 1973; 704
• 2 For a recent review, see: Bodnar BS, Miller MJ. Angew. Chem. Int. Ed. 2011; 50: 5630
• 3 Kirby GW. Chem. Soc. Rev. 1977; 6: 1
• 4 Gowenlock BG, Richter-Addo GB. Chem. Rev. 2004; 104: 3315
• 5 Flower KR, Lightfoot AP, Wan H, Whiting A. Chem. Commun. 2001; 1812
• 6 Flower KR, Lightfoot AP, Wan H, Whiting A. J. Chem. Soc., Perkin Trans. 1 2002; 2058
• 7 Chow CP, Shea KJ. J. Am. Chem. Soc. 2005; 127: 3678
• 8 Howard JA. K, Ilyashenko G, Sparks H, Whiting A. Dalton Trans. 2007; 2108
• 9 Howard JA. K, Ilyashenko G, Sparkes HA, Whiting A, Wright AR. Adv. Synth. Catal. 2008; 350: 869
• 10 Iwasa S, Tajima K, Tsushima S, Nishiyama H. Tetrahedron Lett. 2001; 42: 5897
• 11 Iwasa S, Fakhruddin A, Tsukamoto Y, Kameyama M, Nishiyama H. Tetrahedron Lett. 2002; 43: 6159
• 12 Adamo MF. A, Bruschi S. J. Org. Chem. 2007; 72: 2666
• 13 Atkinson D, Kabeshov MA, Edgar M, Malkov AV. Adv. Synth. Catal. 2011; 353: 3347
• 14 Chaiyaveij D, Cleary L, Batsanov AS, Marder TB, Shea KJ, Whiting A. Org. Lett. 2011; 13: 3442
• 15 Frazier CP, Engelking JR, Read de Alaniz J. J. Am. Chem. Soc. 2011; 133: 10430
• 16 For oxidation of tertiary amines, see: Catino AJ, Nichols JM, Nettles BJ, Doyle MP. J. Am. Chem. Soc. 2006; 128: 5648
• 17 For oxidation of secondary amines, see: Choi H, Doyle MP. Chem. Commun. 2007; 745
• 18 For benzylic oxidation, see: Catino AJ, Nichols JM, Choi H, Gottipamula S, Doyle MP. Org. Lett. 2005; 7: 5167
• 19 For allylic oxidation, see: Catino AJ, Forslund RE, Doyle MP. J. Am. Chem. Soc. 2004; 126: 13622 ; and ref. 21 and 22 below
• 20 Choi H, Doyle MP. Org. Lett. 2007; 9: 5349
• 21 McLaughlin EC, Choi H, Wang K, Chiou G, Doyle MP. J. Org. Chem. 2009; 74: 730
• 22 For propargylic oxidation, see: McLaughlin EC, Doyle MP. J. Org. Chem. 2008; 73: 4317
• 23 For oxidation of phenol and aniline, see: Ratnikov MO, Farkas LE, McLaughlin EC, Chiou G, Choi H, El-Khalafy SH, Doyle MP. J. Org. Chem. 2011; 76: 2585
• 24 General Procedure for the Oxidative Acylnitroso Hetero-Diels–Alder Reaction Catalyzed by Dirhodium CaprolactamateA 0.0020 M solution of Rh₂(cap)₄·2MeCN in CH₂Cl₂ (0.25 mL, 0.0005 mmol, 0.1 mol%) and diene 3 (0.6 mmol, 1.2 equiv) were sequentially added to a solution of BocNHOH (66.6 mg, 0.5 mmol) in CH₂Cl₂ (2.5 mL). Then TBHP (5–6 M solution in decane; 2 mmol, 4 equiv) was added dropwise to the resulting mixture. The reaction mixture was stirred at r.t. and monitored by TLC. Reaction completion was confirmed by the disappearance of the starting material. The solvent was removed by evaporation to give the crude product, which was purified by silica gel chromatography to afford the desired products. Analysis of the cycloadducts 4a–e and 4g–i gave results identical to those previously reported.^6,28–33
• 25 tert-Butyl 3,6-diphenyl-3,6-dihydro-2H-1,2-oxazine-2-carboxylate (4f) The general procedure described above was followed using BocNHOH (66.6 mg, 0.5 mmol), 1,4-diphenyl-1,3-butadiene (123.8 mg, 0.6 mmol), Rh₂(cap)₄·2MeCN (0.0005 mmol), and TBHP (5–6 M solution in decane, 2 mmol). The reaction mixture was stirred for 12 h and purified by silica gel chromatography using PE–EtOAc (5:1) as eluent to give cycloadduct 4f (114 mg, 68%) as a colorless oil. ¹H NMR (400 MHz, CDCl₃): δ = 7.30–7.55 (m, 10 H), 6.11–6.17 (m, 2 H), 5.59 (br, 2 H), 1.52 (s, 9 H). ¹³C NMR (400 MHz, CDCl₃): δ = 154.4, 139.4, 137.3, 129.1, 128.8, 128.6, 128.4, 127.94, 127.88, 127.86, 126.6, 81.6, 79.2, 52.3, 28.5. ESI-HRMS: m/z calcd for C₂₁H₂₃NO₃ [M + H]⁺: 338.1756; found: 338.1756.
• 26 3-tert-Butyl-4-ethyl-5-(tert-butyldimethylsilyloxy)-8-methyl-2-oxa-3-azabicyclo[2.2.2]oct-5-ene-3,4-dicarboxylate (4j) To a solution of BocNHOH (146.5 mg, 1.1 mmol) in CH₂Cl₂ (2.5 mL) were sequentially added Rh₂(cap)₄·2MeCN (0.8 mg, 0.0011 mmol), followed by NaHCO₃ (184.4 mg, 2.2 mmol) and then diene 3j ³⁴ (390.7 mg, 1.32 mmol). The resulting solution was stirred for 10 min, after which TBHP (5–6 M solution in decane, 4.4 mmol) was added dropwise. The reaction mixture was stirred at r.t. for 14 h, solvent was removed by evaporation, and the residue was purified by silica gel chromatography using PE–EtOAc (10:1) as eluent to give cycloadduct 4j (221 mg, 47%) as a pale yellow oil. ¹H NMR (400 MHz, CDCl₃): δ = 5.38 (d, J = 6.8 Hz, 1 H), 4.69–4.72 (m, 1 H), 4.19–4.28 (m, 2 H), 2.55–2.58 (m, 1 H), 2.26–2.28 (m, 1 H), 1.47 (s, 9 H), 1.33 (t, J = 6.8 Hz, 3 H), 1.07 (d, J = 6.8 Hz, 3 H), 1.01–1.05 (m, 1 H), 0.91 (s, 9 H), 0.20 (s, 3 H), 0.18 (s, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 167.4, 158.7, 150.2, 101.8, 84.4, 81.9, 61.6, 51.8, 34.3, 32.2, 28.4, 25.5, 20.4, 18.1, 14.2, –4.6, –4.8. ESI-HRMS: m/z calcd for C₂₁H₃₇NO₆SiNa [M + Na]⁺: 450.2288; found: 450.2284.
• 27 Desilylation–β-Elimination Product 5 To a solution of cycloadduct 4j (51.0 mg, 0.12 mmol) in THF (2.0 mL) was added aq HF (40 wt%) (20 μL), and the resulting mixture was vigorously stirred for 90 min at r.t. The reaction was quenched with sat. aq NaHCO₃ and treated by usual workup. Purification by silica gel chromatography using PE–EtOAc (5:1) as eluent to give the product 5 as a colorless oil (29.7 mg, 79%). ¹H NMR (400 MHz, CDCl₃): δ = 7.64 (s, 1 H), 6.99–7.03 (m, 1 H), 6.13 (dd, J = 1.6, 10.0 Hz, 1 H), 4.22–4.30 (m, 2 H), 2.54–2.69 (m, 2 H), 2.37–2.45 (m, 1 H), 1.46 (s, 9 H), 1.28 (t, J = 6.8 Hz, 3 H), 1.28 (d, J = 6.8 Hz, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 193.8, 166.0, 156.3, 151.2, 129.2, 91.2, 82.2, 62.1, 35.8, 33.2, 28.3, 15.7, 14.3. ESI-HRMS: m/z calcd for C₁₅H₂₃NO₆Na [M + Na]⁺: 336.1423; found: 336.1415
• 28 Jekins NE, Ware RW. Jr, Atkinson RN, King SB. Synth. Commun. 2000; 30: 947
• 29 Zhang D, Sueling C, Miller MJ. J. Org. Chem. 1998; 63: 885
• 30 Hall A, Bailey PD, Rees DC, Rosair GM, Wightman RH. J. Chem. Soc., Perkin Trans. 1 2000; 329
• 31 Tolman V, Hanus J, Sedmera P. Collect. Czech. Chem. Commun. 1999; 64: 696
• 32 Defoin A, Joubert M, Heuchel J.-M, Strehler C, Streich J. Synthesis 2000; 1719
• 33 Cowart M, Bennett MJ, Kervin JF. Jr. J. Org. Chem. 1999; 64: 2240
• 34 Yamomoto K, Hentemann MF, Allen JG, Danishefsky SJ. Chem.–Eur. J. 2003; 9: 3242
• 35 Lub J, de Boer ThJ. Recl. Trav. Chim. Pays-Bas 1984; 103: 328
• 36 Samuni A, Goldstein S. J. Phys. Chem. A 2011; 115: 3022 ; and references cited therein