Synthesis of Dihydropyrimidones and Thiazines by a Multicomponent Reaction

Significance

A four-component reaction for the synthesis of dihydropyrimidones (DHPMs) and thia­zines is presented. The reaction proceeds by a Horner-Wadsworth-Emmons reaction followed by an in situ aza-Diels-Alder reaction. The scope of this reaction was extensively studied. A broad range of nitriles and aldehydes can be used in this multicomponent reaction (MCR), whereas the variation of the phosphonate is limited. For a direct formation of the DHPMs, isocyanates with strong electron-withdrawing groups are necessary. Isocyanates with less electron-withdrawing groups need further heating under microwave conditions. By changing the isocyanates with isothiocyanates, the scope of this reaction was widened towards the synthesis of thiazines in moderate yields.