Studies on the syntheses of heterocyclic compounds. Part 681. A novel alkylation in the 4-position of isoquinoline derivatives

Abstract

Alkylations of 3,4-dihydro-6,7-dimethoxy-1-methylisoquinoline (1) with 2-methylcyclohex-2-enone (4) and with phenethyl bromide (19) in the presence of sodium hydride and dimethyl sulphoxide gave the 4-(2-methyl-3-oxo-cyclohexyl)(6) and 4-phenethyl (20) derivatives, respectively, of 6,7-dimethoxy-1-methylisoquinoline. The reaction of compound (1) with 1,4-naphthoquinone (7) under the same conditions afforded 7-methoxy-1 -methyl-6-methylsulphinylmethylisoquinoline (12) as a major product and several minor products. Compound (12) was converted into 7-methoxy-1,6-dimethylisoquinoline (13), synthesised alternatively from 4-methoxy-3-methyl-benzaldehyde (14).