In the"-coupled spectra of the 4-alkylisoquinolines, the resonances of C-6 and C-7 were predictably observed as clean doublets of doublets and that of C-8 appeared as a doublet of multiplets. It was thus possible to easily differentiate the C-7 and C-8 resonances, thereby completing the chemical shift assignments of the 4-substituted isoquinolines, which are catalogued in Table 111. Chemical shifts of the exocyclic carbons are shown in Chart I.
![2,3-Dimethoxy-6-methyl-5H-[1,3]dioxolo[4,5:5,6]indeno[1,2-c]isoquinoline-5,12(6H)-dione Structure](https://image.chemsrc.com/caspic/091/66358-49-4.png)
![3c-benzo[1,3]dioxol-5-yl-6,7-dimethoxy-2-methyl-1-oxo-1,2,3,4-tetrahydro-isoquinoline-4r-carboxylic acid methyl ester Structure](https://image.chemsrc.com/caspic/338/37039-63-7.png)