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Biginelli Reaction

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The Biginelli reaction involves an one-pot reaction between aldehyde and urea or thiourea in the presence of an acidic catalyst to afford 3,4-dihydropyrimidin-one. This reaction is also referred to as the Biginelli condensation and Biginelli dihydropyrimidine synthesis. It belongs to a class of transformations called multi-component reactions.

Biginelli Reaction

Biginelli reaction is an excellent promoter for the one pot synthesis of dihydroppyrimidinones via the Biginelli reaction, which involves the condensation of an aldehyde, a $\beta$-keto esterand urea. The traditional Biginelli reaction commonly proceeds under strongly acidic conditions and this protocol often suffers from low yields particularly in case of substituted aromatic or aliphatic aldehydes.

Biginelli Reaction Mechanism

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The mechanism of the Biginelli reaction has been the subject of the past decades. The accepted mechanism for the Biginelli multicomponent reaction involves intermediate imine formation between the aldehyde and urea components, followed by a Mannich type reaction with the enol derivative of the 1,3-dicarbonyl derivative.

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The mechanism suggested in this process presumes a thermal tautomerization to an enamine, followed by ring opening and electrocyclic ring closure with loss of hydrogen sulfide.

The Biginelli reaction was studied with 6 different benzaldehydes. To test the applicability of the microwave assisted synthesis reactor for heterogeneous reaction mixtures, the aldehyde component was changed.