Pergamon Terrahedron Vol. 51, No. 46, pp. 12775-12780, 1995 Elsevier Science Ltd Printed in Great Britain 0040.4020/95 $9.50+0.00 0040-4020(95)0083 l-4 Acid Catalysed Enamine Induced Transformations of 1,3-Dimethyl- 5-formyluracil. A Unique Annulation Reaction with Enaminones. Harjit Singh’, Dolly, Swapandeep Singh Chimni and Suhodh Kumar* Department of Chemistry Guru Nanak Dev UhiVerSlty. Amntsar - 143 005. India Abstract. 1,3-Dimethyl-5-formyluracil (1) with enaminones. 3-amino-5,5dimethylcyclohex-2- enone and 3-atninocycldhex-2enone in CH$ZN - TFA (10 : 0.1) gives annulation products - pyrimido[4,5-blquinolin-2,4,6(IH. 3H, 7’H)-trione derivatives along with Hantzsch type I .4- dibydropyridine derivatives However, I with ethyl p-aminocrotonate and 6-amino-1.3. dimetbyluracil. enamine ester and amide respectively. provides subsequent transformation products Uracil derivatisation at each of its reactive sites has attained paramount significance in evolving medicinally potential target compounds’ The nucleophile induced modifications of uracil and its derivatives emanating from their reactions at C-5 and / or C-62” or at an electrophilic appendage at C-S, make use of relatively strong nucleophiles viz. amines, hydrazines, cyanide ion etc. or of strongly basic reaction conditions (NaOH, NaOEt, BuLi etc ) Recently. we have reported” that under mild PTC conditions. 5-fat-myl-l.3- dimethyluracil (1) reacts with potential bisnucleophilic reagents - acetamides and acetones possessing Q- electronwithdrawing group to provide novel pyridopyrimidines and quinazoiines. Now, we report that under acidic conditions, biselectrophilic chromophore -C6H=C5-CHO of 1, reacts with binucleophilic unit -(‘H=CH- N< of enamine derivatives to undergo an unprecedented reaction to provide annulation or subsequent transformation products along with Hantzsch type 1,4-dihydropyridine derivatives. 1 and 3-amino-S.Sdimethylcyclohex-2-enone (2a) in refluxing acetonitrile -TFA gave two products The higher Rr component, (37%), m.p 155°C. M’ m/z 287, in its ‘H nmr spectrum shows gem dimethyl, methylene and N-methyl signals in 1: I ratio along with a lowfield 1H signal at 6 8 95 and could be assigned any of two isomeric structures 3a or 9 The proximity of two N-Me signals in its ‘H nmr and the formation of S-ketovinyluracil’ derivative in case of the reaction of 1 with I-morpholinocyclohexene favour the assignment of structure 3a for this compound The lower Rf component has been found to be a Hantzsch type product 4a (43%), m.p 145°C. Me m/z 411 Therefore, 2a which normally should react with formyl 12775