Remarkably Mild and Efficient Cetrimonium Bromide Catalyzed Friedel-Crafts Amidoalkylation of Sesamols with N-Boc Imines Generated In Situ in Aqueous Medium

Abstract

A remarkably mild and efficient cetrimonium bromide (CTAB) catalyzed Friedel-Crafts amidoalkylation of sesamol or its 2-substituted derivatives with N-Boc imines generated in situ was developed. A wide range of 6-amidoalkyl sesamols were synthesized in high yields. This methodology was also applicable to 2-naphthols.

Key words

sesamol - Friedel-Crafts amidoalkylation - α-amido sulfones - CTAB - 6-amidoalkyl sesamols

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8

Friedel-Crafts Amidoalkylation; General Procedure: N-Boc α-amido sulfone (0.2 mmol, 1.0 equiv), Na₂CO₃ (0.3 mmol, 1.5 equiv), CTAB (0.02 mmol, 10%) and H₂O (2 mL) were added to a 10-mL glass vial equipped with a small magnetic stirring bar. Sesamol (0.24 mmol, 1.2 equiv) was added and, after stirring for the stipulated time at 30 ˚C, the mixture was diluted with H₂O (3 mL) and extracted with Et₂O (3 × 25 mL). The organic layers were combined, dried over anhydrous sodium sulfate and concentrated under reduced pressure. The residue was subjected to silica gel flash chromatography (EtOAc-Hexanes, 1:10) to give the pure product.

9

Tert -butyl (6-Hydroxybenzo[d][1,3]dioxol-5-yl)(phenyl)-methylcarbamate (3a): Yield: 97%; white solid; mp 168.5-168.9 ˚C; ^¹H NMR (300 MHz, DMSO-d ₆): δ = 9.31 (s, 1 H), 7.61 (d, J = 9.6 Hz, 1 H), 7.29-7.22 (m, 4 H), 7.19-7.14 (m, 1 H), 6.92 (s, 1 H), 6.42 (s, 1 H), 6.11 (d, J = 9.6 Hz, 1 H), 5.88 (s, J = 0.6 Hz, 1 H), 5.84 (s, J = 0.6 Hz, 1 H), 1.39 (s, 9 H); ^¹³C NMR (75 MHz, DMSO-d ₆): δ = 154.99, 148.49, 146.09, 143.67, 139.83, 128.03, 126.63, 126.36, 121.09, 107.39, 100.60, 97.39, 77.99, 51.21, 28.28; HRMS (ESI):
m/z [M + Na]⁺ calcd for C₁₉H₂₁NNaO₅: 366.1317; found: 366.1312