A Novel One Pot Synthesis of 1,3,7-Triaryl-1,2,3,4-tetrahydro-4-oxo-5-phenyl-2-thioxo-5H-pyrano[2,3-d]pyrimidines

Abstract

A novel one pot synthesis of 1,3,7-triaryl-1,2,3,4-tetrabydro-4-oxo-5-phenyl-Z-thio~0-5~-pyran0[2,3-~]pyrimidines has been described.It utilizes the reaction of different tbiobarbituric acids with chalcones.Pyrans and pyrimidines individually or in combination possess significant biological properties.A variety of routes have been described in literature for the synthesis of p y r a n o [ 2 , 3 -d ] p y r i m i d i n e ~. ~~~~~ The 2-0x0 analogues of the title compounds have been prepared earlier13 by a two step method which consists in the Michael addition of barbituric acids to chalcones and cyclisation of the formed diketo intermediate compounds.In continuation of our workz6 on p y r a n o [ Z , 3 -d l p y r i m i d i n e s , we herein report a new and one step synthesis of 1,3,7-triaryl-1,2,3,4-tetrahydr0-4-0~0-5-phenyl-Z- t11ioxo-5H-pyrano[Z,3-d]pyrimidines in good yields (85-95%).Thus, the reaction of 1 , 3 -( d i a r y 1 ) t h i o b a r b i t u r i c acids (1-7) with chalcone (1,3-diphenyl-2-propen-1--.one)(8a) or p-methoxychalcone (8b) in acetic acid in the presence of phosphorous -pentoxide at reflux temperature results in cyclocondensation to give the required 1,3,7-triaryl-1.Z,3,4-tet1~ahydro-4-0~o-5-pheny1-Z-thioxo-5H-pyrano[Z,3-d]pyrimi-1 dines ( z -Z Z a , 16b-ZZb).The structures were confirmed on the basis of H-nmr ---spectral data which showed, besides usual signals, two doublets at around 6 4.52 (d.J=5 Hz, 1H.H-5) and around 5.99 (d, J=5 Hz, lH, H-6).In this case, the reaction is believed to take place through the carbonium ion formation as shown below (Scheme 1).Alternatively, the title compounds have also been obtained in a two step In this case, the reaction of thiobarbituric acids (1-7) with (8) in methanol in the presence of triethylamine at reflux temperature -