Nazarov Cyclization of 1,5-Bis-(2-methoxyphenyl)-1,4-pentadien-3-one in the Gas and Condensed Phases: An Experimental and Theoretical Study

摘要

Motivation: One method of choice for synthesis of cyclopentenones is acid-catalyzed electrocyclic ring closure of divinyl ketones (Nazarov cyclization) via conrotatory ring closure of the protonated ketone followed by 1,3-type H~(+)-shifts [1,2], which are solvent-assisted but forbidden in gas-phase. Recently, we demonstrated by MS/MS and DFT that proximal methoxy and hydroxyl groups are catalysts for proton transfers in gas-phase rearrangement and fragmentation of protonated 2-methoxychalcone [3]. The gas-phase cyclization reaction becomes analogous to its solution rearrangement.