Neighboring assistance of a hydroxyl group on manganese dioxide oxidation of benzyl alcohols to lactones

Article abstract of DOI:10.3987/COM-95-S48

o-Hydroxymethylbenzyl alcohol and o-hydroxyethylbenzyl alcohols have been converted to phthalide and dihydroisocoumarins, very easily and in high yields, by oxidation with non-activated manganese dioxide. In contrast, the reaction of o-hydroxypropylbenzyl alcohol stopped at the aldehyde level, and afforded only a small amount of the corresponding lactone under the same condition. This implies that the first oxidation product, a benzaldehyde, could be oxidized further via a hemiacetal, but the second oxidation to lactone is very much dependent on the ability of stable intramolecular hemiacetal formation, and not on the intermolecular mode at all.