Benzo[b]thiophen derivatives. Part VI. The syntheses of 3-(2-amino-ethyl)-5-hydroxybenzo[b]thiophen and related compounds

Abstract

A synthesis of 3-(2-aminoethyl)-5-hydroxybenzo[b]thiophen (VII) by way of the key intermediate 3-chloromethyl-5-methanesulphonyloxybenzo[b]thiophen (Xa) is reported. The same intermediate has been used to synthesise N-substituted 3-aminomethyl-5-hydroxybenzo[b]thiophens. Rigorous proof is given that chloromethylation of sulphonate esters of 5-hydroxybenzo[b]thiophen occurs in the 3-position. Another route has been used to synthesise 3-(2-aminoethyl)-5-benzyloxybenzo[b]thiophen (VI) but the benzyl ether link could not be cleaved to give the free phenol. A synthetic route to N-substituted 2-aminomethyl-5-hydroxybenzo[b]thiophens (VIII; R = H) is established.