Aromatic nucleophilic substitution as a side process in the synthesis of alkoxy- and crown-substituted (Na)phthalocyanines

Abstract

This work reports on systematic survey for cyclotetramerization of crown-and butoxy-substituted phthalo-and naphtha-lonitriles in pentanol induced by DBU and PentOLi. It was demonstrated that these substrates undergo undesired side process of nucleophilic aromatic substitution of RO-groups with PentO-anions in dinitrile molecules. It results in cleavage of crown ether rings and leads to formation of inseparable mixture of (na)phthalocyanines with different ratios of intact and cleaved macrocyclic substituents. Butoxy-substituted substrates are notably less sensitive to nucleophilic attack. Application of magnesium pentoxide both as a base and templating agent does not result in crown ether ring opening reactions and affords target compounds in high yields. The results of work can be used as guidelines for the choice of bases and template agents in the synthesis of (na)phthalocyanines functionalized with macrocyclic substituents.