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.
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.
Keywords: Microwave, phase transfer catalysis, C-alkylation, O-alkylation, N-alkylation.
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