An efficient catalyst free synthesis of nitrogen containing spiro heterocycles via [5+1] double Michael addition reaction

2,4-Diazaspiro[5.5]undecane-1,3,5,9-tetraones and 3-thioxo-2,4-diazaspiro[5.5]undecane-1,5,9-triones have been synthesized via double Michael addition of 1,5-diaryl-1,4-pentadien-3-one with active methylene compounds such as N,N-dimethyl barbituric acid, barbituric acid, thio-barbituric acid and N,N-diphenyl thiobarbituric acid in ethylene glycol at 100 degrees C in the absence of any catalyst to give high yields within a short reaction time. The structure has been confirmed by X-ray analysis. The single-crystal structure of the diazaspiro compound revealed that the C-Ar-H center dot center dot center dot pi, pi-pi stacking and intermolecular hydrogen bonding interactions act as major driving forces for crystal packing.