nano-silica phosphoric acid: an efficient catalyst for one-pot synthesis of 3,4-dihydropyrimidin-2(1h)-ones (thiones) under solvent-free or sonication conditions

[ ' b i g i n e l l i r e a c t i o n ' , 3 , 4 , ' d i h y d r o p y r i m i d i n ' , ' 2 ( 1 h ) ' , ' o n e s ' , 4 , ' d i h y d r o p y r i m i d i n ' , ' 2 ( 1 h ) ' , ' t h i o n e s ' , ' h e t e r o g e n e o u s c a t a l y s t ' , ' m u l t i ' , ' c o m p o n e n t r e a c t i o n s ' , ' n a n o s i l i c a p h o s p h o r i c a c i d ' , ' s o n i c a t i o n c o n d i t i o n ' ]