4-Methyl-N-(2,2,4,4-tetrachloro-3-oxo-8-oxabicyclo[3.2.1.]oct-6-en-1-ylmethyl)-benzenesulfonamide

A mixture of N-furfuryl-p-toluenesulfonamide (1) (2.51 g, 10 mmol) [1] and pentachloroacetone [2] (3.23 g, 14 mmol) was cooled in an ice bath. With magnetic stirring, a 2-molar solution of sodium 2,2,2-trifluoroethoxide in 2,2,2-trifluoroethanol[3] (7 mL, 14 mmol) was added dropwise, over 15 min. Stirring was continued for 15 min at 0 °C and then at room temperature for 2–3 hours[4]. The mixture was allowed to stir for a further 2 hours. Then, the heterogeneous mixture was poured on saturated brine (20 mL). The precipitate was dissolved by adding a little of dichloromethane and water, and the organic layer was separated. The aqueous layer was acidified with hydrochlorid acid to pH 4–5 and then extracted with dichloromethane (4 ‘ 20 mL). The combined dichloromethane solutions were washed with saturated brine (20 mL) and dried overnight with magnesium sulfate. After filtration, the solution was concentrated in a rotary evaporator. The remaining yellow mass was recrystallized from dry ethanol (10 mL) to yield 3.60 g (81%) of 2 as a colourless crystalline solid.

Melting Point: 162–163 °C.

TLC (silica, hexane/tert-butylmethyl ether (1:1 v/v): A pale yellow spot emerged after spraying the sheet with vanillin/sulfuric acid reagent followed by heating with a hot-air gun; R_f = 0.27. The starting material (1) showed a brownish violet spot at R_f = 0.37.

¹H-NMR (250 MHz, CDCl₃): δ= 2.45 (s, 3 H, CH₃C₆H₄SO₂); ABX sub-spectrum (14 lines) with δ _A = 3.89, δ _B = 3.65, δ _X = 5.10, J_AB = (-)14 Hz, J_AX = 9.6 Hz, J_BX = 3.6 Hz, 3 H, diastereotopic CH₂-NH); 5.16 (d, J = 1.7 Hz, 1 H, H-5), AB sub-spectrum with δ _A = 6.48 (H-6), δ _B = 6.46 (H-7), J_AB = 5.5 Hz, the lines of the A part are split into doublets with J = 1.7 Hz; AA’BB’ sub-spectrum with δ _A = 7.76, δ _B = 7.35, J_AB = 8.2 Hz (H-2/6 and H-3/5 from CH₃C₆H₄SO₂).

¹³C-NMR/DEPT (62.9 MHz, CDCl₃): δ= 21.6 (+, CH₃C₆H₄SO₂); 42.2 (-, CH₂-N); 81.9 (C_q, C-4); 85.05 (C_q, C-2); 87.9 (+, C-5); 93.3 (C_q, C-1); 127.0 (+, C-2/6 of the tosyl group); 130.0 (+, C-3/5 of the tosyl group); 134.4 (+, C-6); 135.7 (+, C-7); 136.7 (C_q, C-4 of the tosyl group); 144.1 (C_q, C-1 of the tosyl group); 183.9 (C_q, C-3).

IR (CHCl₃ film, cm^-1): 3395, 3280 (N-H); 3110 (=C-H); 1768 with shoulder at 1750 (C=O); 1600 (C=C); 1495 (NH); 1430, 1340 (SO₂); 1163 cm^-1 (SO₂).

Elemental Analysis: Calculated for C₁₅H₁₃Cl₄NO₄S (445.15): C, 40.47%; H, 2.94%; Cl, 31.86%; N: 3.15%; S, 7.20%. Found: C, 40.24%; H, 3.02%; Cl, 31.63%; N, 3.15%; S, 7.15%.