Condensed thiophen ring systems. Part XV. Preparation and some reactions of 2- and 3-(secondary amino)benzo[b]thiophens

Abstract

The 2-(secondary amino)benzo[b]thiophens (1)–(3) were obtained from 2,3-dibromobenzo[b]thiophen and the appropriate amine. They reacted with acetyl chloride in dry benzene to give the corresponding 3-acetyl derivatives (10)–(12). 2-Piperidinobenzo[b]thiophen was brominated in the 3-position and nitration with a mixture of acetic acid and fuming nitric acid gave the 3,6-dinitro-derivative (20) and tar. Successive treatment of 3-piperidinobenzo[b]thiophen with n-butyl-lithium and dimethylformamide gave 3-piperidinobenzo[b]thiophen-2-carbaldehyde, which was prepared also from 3-bromobenzo[b]thiophen-2-carbaldehyde and piperidine. Nitrosation of 3-piperidinobenzo[b]thiophen gave the 2-oxime of benzo[b]thiophen-2,3-dione via 3-hydroxy-2-nitrosobenzo[b]thiophen. 2-Nitro-3-piperidino-, 3-morpholino-2-nitro-, and 3,6-dinitro-2-piperidino-benzo[b]thiophen were treated with trialkyl phosphites and the tosylhydrazones of 2-morpholinobenzo[b]thiophen-3-carbaldehyde and 3-piperidinobenzo[b]thiophen-2-carbaldehyde were heated in bis-(2-methoxyethyl) ether in the presence of base (Bamford–Stevens reaction), but in no case did we observe cyclisation.