Table 1. Microwave/PPE-Mediated Synthesis of DHPMs
 
DHPM X  Z R1  R2 R3      yield (%) 

a            b 
4a H O  H Me Et 85 79
4b 3-NO2 O H Me Et  93 51
4c 2-Cl O  H Me Et 95 51
4d 2-CF3 O H Me Et  76 15
4e 2,3-(Cl)2  O H Me Et 91 59
4f 3,4-(F)2  O H Me Et 87 66
4g 2-Me O  H Me Me 86 68
4h 4-NO2 O H Me Me  86 41
4i 3-NO2 O H Me i-Pr  94 -
4j H O  H Me t-Bu  81 55
4k 3,4-(F)2  O H Et Me 65c 55 
4l H O  Me Me Et 89 60
4m H S  H Me Et 82 42
4n 3-NO2 S H Me Et  71c 24
4o H S  Me Me Et 78 48
a Microwave/PPE-mediated reaction conditions, for details see ref. 10.
b Literature yields based on classical Biginelli conditions (cat. H+/EtOH).
c After chromatographic work-up.