Stereochemie und Mechanismus derPrins-Reaktion bei ausgeprägter Ladungsdelokalisierung im intermediären Carbeniumion

A detailed investigation of the reaction of 2.6-dimethyl-4-propenylphenol with formaldehyde showed thatPrins reactions of hydroxystyrenes in alkaline medium in most cases are kinetically controlled. By attack of formaldehyde, the same intermediate is generated from eithercis ortrans olefin. On further reaction by two independent pathways a 1.3-diol is formed by attack of a hydroxyl ion, or a 1.3-dioxane by reaction with additional formaldehyde via a hemiacetal. The steric course of the reaction is deduced from a discussion of the conformations of transition states.Prins reactions of arylolefins carrying strong +M-substituents proceed analogously under acylating conditions (e.g. in acetic acid) in weak acidic medium.

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