Regioselective Synthesis of 2-(Arylthio)benzoates by the First Catalytic [3+3] Cyclocondensations of 3-(Arylthio)-1-(trimethylsilyloxy)-1,3-butadienes with 1,1,3,3-Tetramethoxypropane

Abstract

2-(Arylthio)benzoates were regioselectively prepared by the first catalytic [3+3] cyclizations of 3-(arylthio)-1-(trimethylsilyloxy)-1,3-butadienes with 1,1,3,3-tetramethoxypropane.

Key Words

arenes - cyclizations - diaryl sulfides - regioselectivity - silyl enol ethers

References and Notes

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17

Typical Experimental Procedure
To a CH₂Cl₂ solution (2 mL/mmol of 3) of 3 (1.5 mmol) and of 1,1,3,3-tetramethoxypropane (1.0 mmol) was added TMSOTf (0.1 mmol) at -78 ˚C. The solution was allowed to warm to 20 ˚C within 20 h. To the solution was added a diluted aq solution of HCl (15 mL). The organic and the aqueous layer were separated, and the latter was extracted with CH₂Cl₂ (3 × 15 mL). The combined organic layers were dried (Na₂SO₄), filtered, and the filtrate was concentrated in vacuo. The residue was purified by chromatography.
Methyl 2-(Phenylthio)benzoate (5a) Starting with 1,1,3,3-tetramethoxypropane (0.33 mL,
2.0 mmol), 3a (843 mg, 3.0 mmol), TMSOTf (0.036 mL,
0.2 mmol), and CH₂Cl₂ (4 mL), 5a was isolated as a highly viscous colourless oil (275 mg, 53%). ^¹H NMR (250 MHz, CDCl₃): δ = 3.66 (s, 3 H, OCH₃), 6.75 (dd, 1 H, ^³ J = 7.20, ⁴ J = 1.87 Hz, ArH), 7.06 (ddd, 1 H, ^³ J = 7.20, ⁴ J = 1.87, ⁵ J = 0.92 Hz, ArH), 7.16 (m, 2 H, ArH), 7.36 (m, 3 H, ArH), 7.48 (m, 2 H, ArH). ^¹³C NMR (62 MHz, CDCl₃): δ = 52.1 (OCH₃), 124.2 (ArCH), 126.7 (C), 127.4, 129.0 (ArCH), 129.7 (2C, ArCH), 131.1, 132.2 (ArCH), 124.6 (C), 135.5 (2C, ArCH), 143.1, 166.8 (C). IR (neat): ν = 3056 (w), 2948 (w), 1711 (s), 1585 (m), 1562 (m), 1433 (s), 1246 (s), 1189 (m), 1056 (s), 738 (s), 688 (s)530 (m) cm^-¹. GC-MS (EI,
70 eV): m/z (%) = 244 (100), 213 (76), 184 (55), 152 (16), 139 (10), 108 (8). HRMS (EI): m/z calcd for C₁₄H₁₂O₂S [M⁺]: 244.05525; found: 244.05570.