Halohydrins of isoquinoline reissert compounds: base-induced rearrangement reactions providing isochromenes and new isoquinolines

Abstract

Various 3- or 4-methyl and unsubstituted 2-acyl-1-cyano-1,2-dihydroisoquinolines (Reissert compounds) have been converted into the corresponding chloro- or bromo-hydrins by treatment with aqueous hypochlorous acid or aqueous 1,3-dibromo-5,5-dimethylhydantoin, respectively. These 4-halo- 3-hydroxy-derivatives were generally convertible with base into the corresponding 1-acyliminoisochromenes and thence into the related isocoumarins. The chlorohydrin of 2-acetyl-1 -cyano-1,2-dihydroisoquinoline was transformed by sodium ethoxide into 1-ethoxy-4-formyl-3-methylisoquinoline, in the expected manner. However, the bromohydrin of 2-benzoyl-1-cyano-1,2dihydro-3-methylisoquinoline, which exists as the tautomeric bromoketone, gave, as the major product, 4-benzoyl-1-ethoxy-3-methylisoquinoline rather than 4-acetyl-1 -ethoxy-3-phenylisoquinoline. The mechanism of this new rearrangement is discussed.