18 These starting materials were prepared in two steps, by transformation of commercially available cycloalkanones into the enol acetates and subsequent treatment of the latter compounds with acetyl nitrate.
Representative Procedure: To a solution of cyclo-heptanone (10 g, 90 mmol) in isopropenyl acetate (85 mL) was added p-toluenesulfonic acid (2.9 g, 15 mmol). The reacting mixture was refluxed for 24 h in an oil bath at 100 °C, and then it was cooled and diluted with Et2O
(20 mL). The solution was washed with sat. aq NaHCO3 (2 × 30 mL) and brine (2 × 30 mL). The organic layer was dried (Na2SO4) and evaporated, yielding 1-cycloheptenyl acetate (14.08 g, 100%), as a dark brown oil. To a solution of this compound in CH2Cl2 (30 mL) at 0 °C was successively added acetic anhydride (28.26 mL, 30.55 g, 295.7 mmol) and 96% sulfuric acid (0.5 mL). A mixture of glacial acetic acid (2.25 mL, 2.39 g, 40.8 mmol) and 65% nitric acid (6.75 mL) was then added dropwise. After stirring for an additional time of 3 h, the reacting mixture was diluted with CH2Cl2 (30 mL) and washed with brine (2 × 20 mL), and sat. aq NaHCO3 (3 × 20 mL, until no effervescence was observed). The organic layer was dried (Na2SO4) and evaporated and the residue was chromato-graphed on silica gel, eluting with 10:1 petroleum ether-ethyl acetate, yielding 7.482 g (54%) of compound 2a, as a pale yellow viscous oil. IR (NaCl): 1721 (C=O), 1158 and 1375 (NO2) cm-1. 1H NMR (250 MHz, CDCl3): δ = 5.34 (dd, 1 H, J = 9.5 and 3.9 Hz, H-2), 2.80-2.50 (m, 2 H, H-7), 2.40-2.20 (m,
1 H, H-3), 2.20-2.00 (m, 2 H, H-5,3), 2.00-1.75 (m, 2 H,
H-6,4), 1.75-1.50 (m, 2 H, H-6,4), 1.50-1.25 (m, 1 H, H-5). 13C NMR (63 MHz, CDCl3): δ = 201.7 (C-1), 94.1 (C-2), 41.7 (C-7), 29.1 (C-5), 29.0 (C-3), 26.6 (C-4), 24.2 (C-6). Anal. Calcd. for C7H11NO3 (M = 157): C, 53.50; H, 7.00; N, 8.92. Found: C, 53.37; H, 7.06; N, 8.85.
23
Representative Procedure: To a vigorously stirred dispersion of α-nitrocycloheptanone 2a (150 mg, 0.96 mmol) in H2O (5 mL) was added acrolein (2.4 mmol, 2.5 equiv). The mixture was stirred at r.t. for 8 h, and the aqueous phase was then extracted with Et2O (3 × 10 mL), which was dried (Na2SO4) and evaporated, yielding 172 mg (85%) of 3-(1′-nitro-2′-oxocycloheptyl)-propanal (3a), as a pale yellow, viscous liquid. IR (NaCl): 1721 (C=O), 1542 and 1347 (NO2) cm-1. 1H NMR (250 MHz, CDCl3): δ = 9.77 (s, 1 H, CHO), 2.80-1.40 (m, 14 H). 13C NMR (63 MHz, CDCl3): δ = 202.5 (C-2′), 199.7 (C-1), 98.4 (C-1′), 41.2 (C-3′), 38.3 (C-2), 35.1 (C-5′), 29.3 (C-7′), 28.6 (C-6′), 25.5 (C-4′), 24.4 (C-2). Anal. Calcd for C10H15NO4: C, 56.33; H, 7.09; N, 6.57. Found: C, 56.59; H, 7.29; N, 6.49.
26 For a similar effect of K2CO3 in the Michael reactions of 1,3-diones, see ref.
[21]
