INTRODUCTION Variations of building blocks in the classic version of Biginelli reaction: The great biological importance of DHPM nucleus has over the years prompted the development of various strategies for the synthesis of diversely functionalized dihydropyrimidine derivatives 1 . Making the variations in the original three reacting components can modify the classical Biginelli reaction 2 . The following building blocks have so far been documented as the variations of original Biginelli reaction. Oriental Journal of Chemistry Vol. 26(1), 307-317 (2010) Three component solvent-free synthesis and fungicidal activity of substituted pyrimido [4,5-d] pyrimidine-2-(1h)-one SANDEEP V. SHINDE¹*, WAMANRAO N. JADHAV¹ and NANDKISOHR N. KARADE² ¹Post Graduate Research Centre, Dnyanopasak College, Parbhani, 431 401 (India). ²School of Chemical Sciences, S.R.T.M. University, Nanded, 431 606 (India). (Received: February 03, 2010; Accepted: March 08, 2010) ABSTRACT A novel three component condensation of aromatic aldehyde, urea or thiourea and barbituric acid or N,N-1,3-dimethylbarbituric acid was carried out using L-proline as an organo-catalyst under solvent-free microwave conditions. The resulting product, pyrimido [4,5-d] pyrimidine-2-(1H)-one was checked for the fungicide activity. Keywords: Fungicidal acitivity, aromatic aldehyde.