Unusual Condensation of 6,7-Dimethoxy-1,3,3-trimethyl-3,4-dihydroisoquinoline with 4-Antipyrylidenebarbituric Acid

Abstract

The reaction of arylidene barbituric acids with 1-methyl-3,4-dihydroisoquinolines, leading to the corresponding 8-azasteroid derivatives, has been described [Ref. 1, p. 208]. This reaction can be carried out both with the arylidene barbituric acid itself and in the three-component variant: by heating a mixture of the aldehyde, barbituric acid, and 1-methyl-3,4-dihydroisoquinoline in DMF [Ref. 1, p. 426]. Since 8-azasteroids with substituents in the 7 position have not yet been described, it was of interest to carry out the analogous reaction with 6,7-dimethoxy-1,3,3-trimethyl-3,4-dihydroisoquinoline. However, as we have established, the reaction of 6,7-dimethoxy-1,3,3-trimethyl-3,4-dihydroisoquinoline (1) with a mixture of 4-antipyrin aldehyde 2 and barbituric acid 3, or with the product 4 obtained by condensation of compounds 2 and 3, leads to formation of only 1-(6,7-dimethoxy-3,3-dimethyl-1,2,3,4tetrahydro-1-isoquinolylidene)-2-(3,5-diaza-2,4,6-trioxo-1-cyclohexylidene)ethane (5), which judging from the spin–spin coupling constant of the vicinal protons (~15 Hz), exists in the trans conformation.