Synthesis of Mono- and Diphenyl Substituted Salicylic Aldehydes, Important Building Blocks for the Synthesis of Fluorescent Dyes and Dyes-Sensitizers for DSSC

Salicylic aldehydes are of interest for the synthesis of many biologically active compounds, ligands, fluorescent probes and functional dyes-sensitizers for DSSCs, etc. In this work, we have developed a method for the synthesis of mono- and diphenyl substituted salicylic aldehydes by the Suzuki-Miyaura cross-coupling reaction of the corresponding bromosalicylaldehydes with phenylboronic acid, in order to study the possibilities of modifying the structure of functional dyes. A series of experiments were performed on the variation of synthesis conditions, replacement of solvents and catalysts both under conditions of convection heating at atmospheric pressure and using a conductive heating reactor with a sealed vessel Anton Paar Monowave 50. In the process of searching for optimal reaction conditions, great attention was paid to the modern requirements of "green chemistry". The best result was obtained by carrying out the Suzuki-Miyaura cross-coupling reaction of bromosalicylaldehydes with phenylboronic acid in water using the Pd(PPh3)4 catalyst. This method was improved by using 10% Pd/C as a catalyst, which has a number of advantages, namely: greater availability, ease of storage and use, lower cost and environmental safety. Also, the 10% Pd/C catalyst is more resistant to environmental influences, which allowed the reactions to be carried out without the use of an inert atmosphere in a conductive heating reactor with a sealed tank Anton Paar Monowave 50.