Methacryloyl chloride dimers: from structure elucidation to a manifold of chemical transformations

Abstract We report the isolation and elucidation of structure, formation mechanisms, and reactivity of elusive methacryloyl chloride dimers. Upon standing of a sample of methacryloyl chloride ( 1 ) for prolonged periods of time dimer 3 forms via oxa-Diels–Alder reaction even at low temperatures. If traces of a Lewis acid are present, dimer 3 isomerizes into a mixture of 2-oxo-cyclopentanecarbonyl chlorides 4 , 14 , and traces of 5 , with a relative ratio that depends on the nature of the Lewis acid and reaction time. Dimer 3 can also be separated and isolated by vacuum distillation and selectively converted into derivatives of 2,5-dimethyl-2-hydroxyadipic acid, as well as into the compound 14 by treating with a catalytic amount of titanium tetrachloride. Additionally, based on the study, suggestions on purification and handling of methacryloyl chloride are proposed.