Preparation of 1-Ethoxyisobenzofuran. Mechanistic Aspects of the Meerwein Ortho Ester Reaction

Article abstract of DOI:10.1021/jo00183a001

The reaction of O-ethylphthalidium tetrafluoroborate (1) with excess NaOCH3 in CH3OH gives ortho ester 4 as the major product.The mechanism of formation of this solvent-derived material is explored.A plausible intermediate, 1-ethoxyisobenzofuran (8), has been prepared and isolated in solution; 8 reacts readily with, e.g., CH3OD to give the mixed ortho ester 5 contaning ca. one deuterium/mole.This indicates that 8 reacts by rate-determining proton transfer, followed by collapse of the ion pair to give 5.On these and other grounds, 8 is ruled out as an intermediate in the reaction of 1 leading to 4.A mechanism for the latter process consistent with all observations is presented, involving rapid consumption of local alkoxide ion concentration followed by rapid exchange with solvent and eventual neutralization by diffusion of alkoxide from the bulk medium.