4-Methyl-N-(2,2,4,4-tetrachloro-5-methyl-3-oxo-8-oxabicyclo[3.2.1.]oct-6-en-1-ylmethyl)-benzenesulfonamide

A mixture of 1 [1] (2.65 g, 10 mmol) 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.

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 satured 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 (60 mL) to yield 4.01 g (87%) of 2 as a colourless crystalline solid.

Melting Point: 177–178 °C.

TLC (silica, hexane/tert-butylmethyl ether (1:1 v/v): A light-blue spot emerged after spraying the sheet with vanillin/sulfuric acid reagent followed by heating with a hot-air gun; R_f = 0.31. The starting material (1) showed a red-brown spot at R_f = 0.38.

¹H-NMR (250 MHz, CDCl₃): δ= 1.75 (s, 3 H, 5-CH₃); 2.45 (s, 3 H, CH₃C₆H₄SO₂); ABX sub-spectrum (8 AB-lines, X part as a broad m) with δ _A = 3.89, δ _B = 3.58, δ _X = 4.88, J_AB = (-) 13.9 Hz, J_AX =10.1 Hz, J_BX = 3.3 Hz, 3 H, diastereotopic CH₂-NH); 6.34 (s, 2 H, H-7 + H-6); 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).

¹H-NMR (250 MHz, DMSO-d6): δ= 1.65 (s, 3 H, 5-CH₃); 2.39 (s, 3 H, CH₃C₆H₄SO₂); ABX sub-spectrum (8 AB-lines, 4 lines of the X part) with δ _A = 3.63, δ _B = 3.44, δ _X = 8.06, J_AB = (-)14.4 Hz, J_AX = 7.5 Hz, J_BX = 5.7 Hz, 3 H, diastereotopic CH₂-NH); 6.46 (d, J = 5.8 Hz, 1 H, H-7); 6.66 (d, J = 5.8 Hz, 1 H, H-6); AA’BB’ sub-spectrum with δ _A = 7.76, δ _B = 7.36, J_AB = 8.0 Hz (H-2/6 and H-3/5 from CH₃C₆H₄SO₂).

¹³C-NMR/DEPT (62.9 MHz, DMSO-d6): δ=16.2 (+, 5-CH₃); 20.9 (+, CH₃C₆H₄SO₂); 41.9 (-, CH₂-N); 84.7 (C_q, C-4); 87.1 (C_q, C-2); 91.2 (C_q, C-5); 92.7 (C_q, C-1); 126.35 (+, C-2/6 from CH₃C₆H₄SO₂-); 129.65 (+, C-3/5 from CH₃C₆H₄SO₂); 134.6 (+, C-6); 137.6 (C_q, C-4 from CH₃C₆H₄SO₂); 138.0 (+, C-7); 142.85 (C_q, C-1 from CH₃C₆H₄SO₂); 185.3 (C_q, C-3).

IR (CHCl₃ film, cm^-1): 3400 (N-H); 3110, 2960 (C-H); 1773, 1745 (C=O); 1600 (C=C); 1495 (NH); 1340, 1165 cm^-1 (SO₂).

Elemental Analysis: Calculated for C₁₆H₁₅C_l4NO₄S (459.2): C, 41.85%; H, 3.29%; Cl, 30.88%; N, 3.05%; S, 6.98%. Found: C, 41.59%; H, 3.23%; Cl, 30.75%; N, 2.91%; S: 7.03%.