Effect of a bulky alicyclic substituent in position 3 on the structure and spectral characteristics of 1-(4',4'-dimethylcyclohexa-2',6'-dion-1'-ylidene)-1,2,3,4 -tetrahydroisoquinoline

The synthesis of spiro{cyclohexane-1'3-[1-(4',4'-dimethylcyclohexa-2',6'-dion-1'-ylidene)- 1,2,3,4-tetrahydroisoquinoline]} (I is performed. X-ray diffraction analysis and IR and electronic absorption spectroscopies have revealed that compound I, similar to 3,3-dimethyl (II) and 3,3-dimethyl-6,7-dimethoxy (III) derivatives of 1-(4',4'-dimethylcyclohexa-2',6'-dion-1'-ylidene)-1,2,3,4 -tetrahydroisoquinoline, exists as a enamine-diketone tautomer in both the crystal state and solutions. It is shown that substitution of cyclohexyl for two methyl groups in position 3 of molecule II weakly affects its three-dimensional and electronic structure