A general synthetic approach to pyrazolo [4,3-d]pyrimidines is reported. Aldehydes, arylideneanilines, carboxylic acids and orthoesters are used as one-carbon units for bridging the two amino functions of 4-amino-1-alkyl-3-propylpyrazole-5-carboxamides.J. Heterocyclic Chem., 42, 751 (2005).Pyrazolo [4,3-d]pyrimidine derivatives [1][2][3][4][5][6][7][8][9][10] are the structural analogues of purines. Their excellent adenosine receptor antagonist activity [9] and other useful pharmacological properties such as vasodilator [10,11] and antibacterial [12] activities made them interesting targets for synthesis.Herein, we report a facile general approach for the synthesis of pyrazolo [4,3-d]pyrimidin-7-one derivatives (6a-l) from 4-amino-1-methyl (or ethyl)-3-propylpyrazole-5-carboxamide 1a [13] or 11 using one-carbon electrophilic sources. Pyrazolo[4,3-d]pyrimidin-7-ones (6a-h) were obtained by refluxing 1a with appropriate aldehydes 2a-h in acetic acid containing a catalytic amount of p-toluenesulfonic acid. Tetrahydropyrazolo [4,3-d]pyrimidin-7-one derivative 7 was obtained when 1a was reacted with 4-N,N-dimethylamino benzaldehyde in acetic acid at ambient temperature. The intermediacy of 7 in the formation of 6a was proved by the independent conversion of 7 into 6a in refluxing acetic acid in the presence of p-toluenesulfonic acid.The versatility of arylideneanilines as aldehyde sourcecum-dehydrogenating agents in heterocyclisation reactions was earlier demonstrated in benzimidazole [14,15] and quinazolinone [16,17] chemistry. Therefore, we surmised Jul-Aug 2005 751Scheme 1

A facile approach to pyrazolo [4,3-e][1,4]diazepin-5,8-diones and pyrazolo[4,3-e]pyrrolo[1,2-a][1,4]diazepin-5,10-diones is reported. Strategy involved the utility of α-amino acid as a three-atom segment in the construction of diazepine skeleton on the preformed pyrazole ring.

Fused pyrimidine derivatives R 0515A Facile One Step Synthesis of 1,6-Dihydro-7H-pyrazolo[4,3-d]pyrimidin-7-ones.-Aldehydes (II), arylideneanilines (IV), carboxylic acids (V), and orthoesters (VII) are utilized as one-carbon electrophilic sources for bridging the two amino functions of pyrazole derivative (I) in a general approach to pyrazolopyrimidines. The insertion of a one-carbon unit using readily accessible starting materials and simple reaction conditions render this procedure attractive. -(REDDY, N. R.; REDDY, G. M.; REDDY, B. S.; REDDY*, P. P.; J. Heterocycl. Chem. 42 (2005) 5, 751-754; Dep. Chem., Osmania Univ., Hyderabad 500 007, India; Eng.) -H. Hoennerscheid 47-153

Fused pyrimidine derivativesFused pyrimidine derivatives R 0515 A Facile Synthesis of 6-Aryl-1-methyl-3-n-propyl-6,7-dihydro-1H-pyrazolo[4,3-d]pyrimidin-7-ones. -A facile one-pot method for the synthesis of biologically important pyrazolopyrimidinone derivatives (IV) (8 examples) is given. -(REDDY, N. R.; REDDY, G. M.; REDDY*, P. P.; Org. Prep. Proced. Int. 36 (2004) 1, 92-96; Dep. Chem., Osmania Univ., Hyderabad 500 007, India; Eng.) -R. Langenstrassen 25-166

2005 Multi-membered N-heterocycles R 0690 A new Entry to Pyrazolo[4,3-e][1,4]diazeoines. Facile Synthesis of Pyrazolo[4,3-e][1,4]diazepin-5,8-diones, 5,6,7-Triones and Pyrazolo[4,3-e]pyrrolo-[1,2-a][1,4]diazepin-5,10-diones. -A facile approach to various new pyrazolodiazepinone derivatives utilizing α-amino acids as a three atom segment in the construction of the diazepine skeleton is described. -(REDDY, N. R.; REDDY, G. M.; REDDY*, P. P.; J. Heterocycl. Chem. 42 (2005) 4, 675-678; Chem. Discovery Res.,