Influence of the Gas Atmosphere on the Deprotection of (Z)-γ -Hydroxy- α , β-Unsaturated Esters

The deprotection of O-protected (Z)-α-methyl-γ-hydroxy-α,β-unsaturated ester 1 furnishes dimer 2 when the reaction is performed under a nitrogen atmosphere, while compound 3 forms when the reaction is performed under an oxygen atmosphere.