Azocoupling reactions of enaminocarbonyl derivatives of 1,2,3,4-tetrahydroisoquinoline with diazonium salts

Abstract

It has been shown that enamino amide and enamino ketone derivatives of 1,2,3,4-tetrahydroisoquinoline react with diazonium salts to form azo compounds. Depending on the enamine structure they can exist just as azo dyes or as azohydrazone tautomers.Up to this time the reactions of heterocyclic enamines with diazonium salts have been little studied. It has previously been shown [1] that the conjugation of an excess of a diazonium salt with 1,3,3-trimethyl-3,4-isoquinoline leads to the formation of formazans. Evidently the reaction products can also be an azo dye depending on the structural features of the enamine. The formation of dyes can also be expected from enaminocarbonyl compounds having only one hydrogen atom on the β-carbon atom of the enamine group in their structure (enamino amides and enamino ketones).The aim of this work is a study of the structure of the azocoupling reaction products and the dependence on the structure of the starting 1,2,3,4-tetrahydroisoquinoline enaminocarbonyl derivatives.This study has shown that the azocoupling of enamino amide 1 [2] with diazonium salts gives the azo dyes 2a-d which exist in solution as a tautomeric equilibrium with the hydrazo form (compounds 3a-d). The tertiary amide 4 [3] reacts similarly to give the azo dyes 5a,b which show a similar solution equilibrium (hydrazones 6a,b).It is known [4] that amides of type 7 exist in the imino form. However, in the azocoupling of the named amide with p-nitrophenyldiazonium chloride it reacts as an enamine to give the azo dye 8. It should be noted that the azo dye reaction product could only be separated for the p-nitro substituent. Attempts to use less active electrophiles as diazo component (such as the phenyl and p-tolyldiazonium chlorides) in the reaction did not give an azo conjugation product.Coupling of diazonium salts with the enamino ketone 9 [5] gave the azo dyes 10a,b and hydrazo formation was not seen in this case. The stability of the azo form can be explained by the greater electronacceptor effect of a ketone group when compared with an amide. In the case where the azo component is a tertiary enamino ketone the azo dyes 11a,b are also formed and exist in solution as a mixture of the two π-diastereomers (Z and E).

Azocoupling reaction of 1-benzyl-3,4-dihydroisoquinolines with diazonium salts and the properties of its products

“…The azocoupling of 1,2,3,4-tetrahydroisoquinoline enamines with diazonium salts has been studied previously [1,2]. In chemistry and pharmacology 1-benzyl-3,4-dihydroisoquinolines are widely known and also show enamine properties [3], in particular drotaverine base (nospa) [4].…”