Microwave Irradiation and Phase Transfer Catalysis in C-, O- and N-Alkylation Reactions.
György Keglevich, Alajos Grün and Erika Bálint
Affiliation: Department of Organic Chemistry and Technology, Budapest University of Technology and Economics, 1521 Budapest, Hungary.
Keywords: Microwave, phase transfer catalysis, C-alkylation, O-alkylation, N-alkylation.
In this review, the relevance of the combined use of the microwave (MW) and phase transfer catalytic (PTC) techniques is
studied within alkylations. In the solid–liquid phase C-alkylation of a series of simple CH-acidic compounds including P=O containing
derivatives, in most cases there is no need to use a phase transfer catalyst, as MW promotes the reaction in itself. In the MW-assisted
solid–liquid phase alkylation of phenol derivatives, the presence of an onium salt as a phase transfer catalyst ensures the predominance of
the O-alkylation. In the absence of base and catalyst, the alkylation of phenol derivatives proved to be C-selective. As regards the MWpromoted
solid–liquid phase alkylating esterification of phosphinic acids, the use of a phase transfer catalyst was beneficial in case of alkylating
agents of normal reactivity. In MW-assisted N-alkylations there is no general rule for the relevance of a phase transfer catalyst.
In the alkylation of phenotiazine, the presence of an onium salt promotes the formation of the N-alkylated product, while in the absence
of catalyst, the C-alkylation is predominant. Most of the C- and O-alkylations was performed under solvent-free conditions.
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