2-Pyridyldimethylsilyl Group as a Removable Hydrophilic Group in Aqueous Organic Reactions: Formation of Molecular Aggregates and Dramatic Rate Enhancement in Diels-Alder Reactions

摘要

A novel methodology for aqueous organic reactions utilizing a 2-pyridyldimethylsilyl (2-PyMe_2Si) group as a removable hydrophilic group has been developed. It was found that 1,3-dienes bearing the 2-PyMe_2Si group form molecular aggregates in water when 1.0 equivalent of HCl was added, as evidenced by dynamic light-scattering experiments. The Diels-Alder reaction of 2-PyMe_2Si-substituted 1,3-dienes with various dienophiles took place in water at room temperature. The Diels-Alder reaction in organic solvents (Et_2O/toluene) under the same reaction temperature and time gave the cycloadduct in much lower yield, indicating the dramatic rate acceleration in water. The removel of the 2-PyMe_2Si group was accomplished by desilylation, oxidation, and electrophilic substitution.