A Facile Synthesis of Urushiol using 2, 3-Dimethoxybenzyl p-Tolyl Sulfone

Abstract

Urushiol, an important naturally occuring coating material, was synthesized from the readily available 2, 3-dimethoxybenzyl p-tolyl sulfone (1). The synthetic route is shown in Fig.-1. Compound (1) was easily synthesized from 2, 3-dimethoxybenzaldehyde in 3 steps in 73% overall yield as shown in Fig.-2. Treatment of (1) with sodium hydride in DMF followed by addition of organic halides (2) afforded alkylated products (3) in excellent to good yields (see Table-1). The reductive elimination of the sulforiyl group of (3) with 6% sodium amalgam gave 3-alkyl-veratrols (4) in excellent to good yields. Urushiol (5 a) and laccol (5 b) were obtained from the demethylation of 3-alkylveratrols (4 a-b) bearing methoxy groups as protective groups in good yields by treatment with boron tribromide in methylene dichloride. Further, urushiol (5 c-d) having a cis-olefin group in the side-chain was obtained from demethylation of 3-alkynyl-and 3-alkenylveratrols (4 e-f), respectively, by treatment with boron tribromide, followed by partial hydrogenation with Lindlar catalyst.