Study of the reaction of iodoarylation of phenylacetylene by benzenediazonium tetrafluoroborate

Abstract

Anion-arylation reaction, as well as its partial case – Meerwein arylation reaction, is a valuable tool for construction of practically important compounds. Such reactions are mainly catalyzed by transition metals. In the same time, iodo-arylation is self-catalyzed reaction and does not require utilization of eco-unfriendly heavy-metal containing catalysts. However, there are only several reports concerning to this topic. In order to shed more light on the nature and distributions of products of this reaction, herein we thoroughly investigated iodoarylation reaction of phenylacetylene by benezenediazonium tetrafluoroborate in the presence of lithium iodide. Reaction has been performed at 0‑5°C in DMF. For analysis of reaction products and its ratio GC‑MS analysis have been applied. Seven main products of this reaction have been found. In the reaction mixture typical product of Sandmeyer reaction – iodobenzene (33.9 %) has been identified. Although in course of the reaction formation of dimethylaminobenzene (6.5 %) take place. Probably, formation of last is a result of benzene radical attack on the solvent (DMF). In the same time, formation of diiodostyrene (10.2 %) in reaction mixture was predictable, because it is well known that iodine anion easily can be oxidized by arenediazonium salts to elemental iodine, which further reacts with starting phenylacetylene. Further, orto- and para-iodobiphenyls (8.7 and 4.1 %, respectively) have been identified in the reaction mixture. Formation of such products was unexpected, however can be explained as subsequent arylation by Gomberg-Bachmann-Hey type reaction of formed iodobenzene. Finally, desired E- and Z-iodostilbenes have been formed in 36.6 % total yield with E/Z ratio close to 3:1. In conclusion, products of iodo-mediated reaction of benzenediazonium tetrafluoroborate with phenylacetylene in presence of lithium iodide have been investigated by GC‑MS analysis. Possible ways of formation of all identified compounds have been suggested. Key words : iodo-arylation, iodostilbenes, arenenediazonium salts, phenylacetylene, chromato-mass spectrometry.