Fragmentation of protonated 2-(2-phenylethyl)chromones from agarwood: the diagnostic role of ion/neutral complexes as reactive intermediates.

摘要: A positive-ion electrospray ionisation collision-induced dissociation mass spectrometric study on the fragmentation of [M + H](+) ions 2-(2-phenylethyl)chromone and a set nine hydroxyl- and/or methoxy-substituted derivatives has revealed highly prominent channel, loss benzoquinomethanes or benzaldehyde, respectively, as diagnostic feature for 2-(2-phenylethyl)chromones that bear hydroxyl group at para- (4'-), ortho- (2'-) benzylic (α-) position phenylethyl residue. Derivatives only meta- (3'-) do not undergo this elimination. The intermediacy ion/neutral complexes (INCs) is invoked to explain fragmentation, which involves remarkable intra-complex proton hydrogen atom transfer from remote 4'-OH (or 2'- α-OH) functionalities. Density functional theory (B3LYP/6-31G(d)) calculations confirm energetic preference these elimination channels agree with limited thermochemical data known benzoquinomethanes. INC-mediated losses benzaldehydes α-hydroxy-substituted correspond particularly facile (vinylogous) Grob fragmentation. may be viewed telling example role intermediates structural assignment constitutional isomers by spectrometry.