4-Methyl-N-(5-methyl-3-oxo-8-oxabicyclo[3.2.1.]oct-6-en-1-ylmethyl)-benzenesulfonamide

Zinc powder (10.6 g, 160 mmol) was given to an ice-cold solution of methanol (40 mL) saturated with ammonium chloride. With vigorous magnetic stirring in an ice-bath, tetrachloroketone 1 [1] (4.59 g, 10 mmol) was added in small portions (exothermic reaction, the mixture should not be allowed to boil!). Then the ice-bath was removed, and the mixture was allowed to come up to room temperature with continuous stirring. Finally, the mixture was refluxed. A TLC showed that after 1 h the starting material 1 had disappeared. Unreacted zinc powder and inorganic salts were removed by suction and washed with methanol (50 mL). To the combined filtrates, 100 mL of a 0.6 molar solution of EDTA disodium salt (110 g in 500 mL water with 10 g NaOH) was added. The mixture was stirred for 1 h, and extracted with tert-butylmethyl ether (9 × 20 mL). The combined extracts were washed with saturated brine (50 mL) and dried overnight with magnesium sulfate. After filtration the solvent was evaporated. The remaining white solid was recrystallized from a mixture of ethanol and tert-butylmethyl ether (2:1 v/v, 30 mL). The slight pink-coloured crystals were filtrated and finally washed with a small amount of n-pentane to yield 2.74 g (85%) product.

Melting Point: 126–127 °C.

TLC (silica, hexane/tert-butylmethyl ether (1:1 v/v): A lemon-coloured spot emerged after spraying the sheet with vanillin/sulfuric acid reagent followed by heating with a hot-air gun; R_f = 0.07. The starting material (1) showed a pale yellow spot at R_f = 0.27.

¹H-NMR (250 MHz, CDCl₃): δ= 1.43 (s, 3 H, 5-CH₃); 2.43 (s, 3 H, CH₃C₆H₄SO₂); two AB sub-spectra with δ_A= 2.43, δ_B= 2.36, J_AB= 16.1 Hz = J_gem, and δ_A= 2.45, δ_B= 2.26, J_AB= 16.5 Hz= J_gem (4 H, H-2 and H-4); ABX sub-spectrum (8 + 4 lines) with δ_A= 3.30, δ_B= 3.14, δ_X= 5.13, J_AB= (-)13.0 Hz, J_AX= 7.8 Hz, J_BX= 4.6 Hz (3 H, diastereotopic CH₂-NH); AB sub-spectrum with δ_A= 6.00, δ_B= 5.92, J_AB= 5.8 Hz (2 H, H-6 and H-7); AA’BB’ sub-spectrum (4 lines) with δ_A= 7.75, δ_B= 7.32, J_AB= 8.2 Hz (4 H, H-2/6 and H-3/5 from CH₃C₆H₄SO₂).

¹³C-NMR (62.9 MHz, CDCl₃): δ = 21.5 (CH₃C₆H₄SO₂); 22.9 (5-CH₃); 46.9 (C-2); 47.2 (C-4); 51.1 (CH₂-N); 84.3 (C-5); 85.5 (C-1); 127.05 ( Tos-C-2/6); 129.8 (Tos-C-3/5); 133.2 (C-6); 136.65 (Tos-C-4); 137.9 (C-7); 143.6 (Tos-C-1); 205.2 (C-3).

IR (CDCl₃ film, cm^-1): 3380, 3280 (N-H); 2980, 2960, 2930, 2900, 2880 (CH); 1712 (C=O); 1600 (C=C); 1495, 1450, 1410, 1382, 1335, 1175.

Elemental Analysis: Calculated for C₁₆H₁₉NO₄S (321.4): C, 59.79%; H, 5.96%; N, 4.36%; S, 9.98%. Found: C, 59.70%; H, 5.99%; N, 4.19%; S, 9.95%.