Properties of 3,3-dialkyl-3,4-dihydro-isoquinoline cyclic azomethines

Abstract

The reactions of 3,3-dialkyl-3,4-dihydroisoquinoline cyclic azomethines with the methyl ester and p-toluidide of iodoacetic acid gave stable quaternary ammonium salts which were suitable dipoles for [3+2] cycloaddition reactions. Azomethines activated by iodomethylation react with potassium cyanide and malonodinitrile.Keywords: 3,3-dialkyl-3,4-dihydroisoquinolines, methyl ester and p-toluidide of iodoacetic acid, quaternary ammonium salts, dipolar [3+2] cycloaddition, reaction with potassium cyanide and malonodinitrile.Amongst cyclic azomethines isoquinoline derivatives [1] have greatest value in organic synthesis. We have previously prepared 3,3-dialkyl-3,4-dihydroisoquinoline cyclic azomethines [2,3]. The chemical properties of these compounds have been little studied up to this time. The aim of our work was to study their reaction with nucleophiles. The goal of the work was also to clarify the use of the named cyclic imine salts as potential dipoles in [3+2] cycloaddition reactions.Studies have shown that compounds 1a-c react with methyl iodoacetate to form the stable iodides 2a-c. The base 1c forms salt 2d similarly with iodoacetic acid p-toluidide. A study of the properties of compounds 1a-c has shown that bases of these cyclic azomethines do not react with C-nucleophiles like KCN or malonodinitrile without activation. The desired result can be achieved by activation of the imino group via iodomethylation. Hence reaction of the iodomethylate of imine 1c with potassium cyanide in alcohol gives the tetrahydroisoquinoline 3 which was characterized as the hydroiodide. The reaction of this compound with malonodinitrile occurs in the presence of sodium methylate in methanol to give the dinitrile 4. In the absence of the MeONa the reaction mixture yielded only the starting material. R 1 R 1 N R R N O OMe ICH 2 C(O)OMe 1a-c 2a-c + I -1,2 a,b R = H, c R = MeO; 1a,c, 2a R 1 = Me; 1, 2 b R = (CH 2 ) 5 , 2c R 1 = Me