Recebido em 5/10/04; aceito em 30/3/05; publicado na web em 10/8/05 SYNTHESIS OF MONASTROL AND OF NEW BIGINELLI COMPOUNDS PROMOTED BY In(OTf) 3 . In this paper, we describe a practical route for the synthesis of Biginelli compounds using In(OTf) 3 . To study the generality of this catalyst, several examples using aromatic aldehydes, 1,3-dicarbonyl compounds, urea, and thiourea were investigated. The present procedure provides an efficient modification of the classical Biginelli reaction, namely short reaction times and simple work-up, that not only preserves the simplicity of the original protocol but also produces excellent yields of 3,4-dihydropyridin-2(1H)-ones. Thiourea was used with similar success to provide the corresponding 3,4-dihydropyridin-2(1H)-thiones. In this case, the (+/-)-monastrol, antimitotic agent, was obtained in 92% yield and new thio analogues were synthesized.