Diels-Alder reactions pyrazole synthesis

Radi M, Bernardo V, Bechi B, Castagnolo D, Pagano M, Botta M (2009) Microwave-assisted organocatalytic multicomponent Knoevenagel/hetero Diels-Alder reaction for the synthesis of 2,3-dihydropyran 2,3-c pyrazoles. Tetrahedron Lett 50 6572-6575... 

Another rapid protocol for the multicomponent microwave assisted organo-catalyst Knoevenagel/hetero Diels-Alder reaction (DKHDA) for the synthesis of substituted 2,3-dihydropyran [2,3-c] pyrazoles (xix) has been developed by Radi et al. [21]. 

Formycin has been prepared by constructing the pyrimidine ring from a 4-nitro-pyrazole-C-nucleoside precursor. Diels-Alder reactions have been used in a synthesis of DL-showdomycin (21) via the adduct (22) outlined in Scheme... 

Novel steroidal pyridazines are readily prepared from ADC compounds and steroidal A2,4-dienes,163 A14,1 -dienes,164 and A16,20-dienes.165 ADC compounds are also commonly used in the protection of the steroid 5,7-diene system (see Section V,A). These Diels-Alder adducts of steroidal dienes and azo dienophiles should not be confused with the so-called azasteroids, which are also prepared from ADC compounds. Cyclic ADC compounds such as the pyrazole-3,5-diones (7), and the diazaquinones 12 and 13 readily add to dienes to give bicyclic pyridazine derivatives,166168 and these reactions have been adapted to the synthesis of 5,10-diazasteroids (106).42 Similarly, the 13,14-diaza- (107) and 13,14,16-triazasteroid (108) ring systems have been prepared.169... 

---