Unexpected detection of 3-aroylbenzofuran side products in the synthesis of 2-arylbenzofurans: identification, characterization and comparison with chalcone’s fragmentation patterns using EI/MSn

A gas chromatography-mass spectrometry study of the intramolecular Wittig reaction revealed, together with the expected 2-phenylbenzofuran, the formation of an unexpected side product that has not been reported until now. This study reports the identification of the by-product, i.e. the 3- benzoyl-2-phenylbenzofuran, on the base of its mass spectrometric behaviour using a combination of electron ionization (EI), exact mass measurement, multiple stage mass spectrometry and labelled compounds. This study reports the common fragmentation pathways and discusses possible fragment structures of characteristic ions from a series of 3-aroyl-2-arylbenzofuran derivatives obtained as by-product under Wittig conditions. Emphasis is laid on the formation and structure investigation of the [M-H]+ and [M-OH]+ ions. Our results showed interesting analogies with the mass spectrometric behavior of chalcones.