ISSN:
0021-8383
Schlagwort(e):
Chemistry
;
Organic Chemistry
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
Notizen:
General Syntheses and Rational Parameters for Structural Assignment of Isomeric Derivatives of [3,4]-fused Pyrazoles4 isomeric 1- or 2-methyl-, and 1- or 2-benzyl-pyrazolo[3,4-b]pyridones, i.e. the 4-oxo-types 17a, b or 11a, b and the 6-oxo-types 16a, b or 10a, b, are synthesized unambiguously. Cyclisation of 1-substituted 3- or 5-(1-methyl-2-ethoxycarbonyl-vinylamino)-pyrazoles 9a, b or. 15a, b, which were synthesized from 1-substituted 3- or 5-amino-pyrazoles and ethyl acetoacetate yields 11a, b or 17a, b in downtherm, but 10a, b or 16a, b in presence of acidic catalysts. The acidic cyclisation is preceded by a new rearrangement of 9 or 15 into 1- substituted 3- 27 or 5-amino-4-(1-methyl-2-ethoxycarbonyl-vinyl)-pyrazoles 30; mechanism and concurring reactions are explained. Because of their higher electron densities at C-4 it is easier to cyclise derivatives of 5-amino-pyrazoles compared to 3-amino-pyrazoles. All isomeric 1- or 2-substituted 4(6)-chloro-6(4)-methyl-pyrazolo-[3,4-b]pyridines are formed with POCl3 from the corresponding oxo-compounds.The position of a substituent at N-1 or N-2 of [3,4]-fused pyrazoles can be assigned using the significant 1H-n.m.r.-parameter ΔHMPTCDCL3 = δCDCl3 - - δHMPT (conc. HC - 3). If solvent influences are considered, δ(C = O) is a useful 13C-n.m.r.-parameter to distinguish the 4-oxo-types (11a, b; 17a, b) from the 6-oxo-types (10a, b; 16a, b) of pyrazolo[3,4-b]pyridones. Further own and lit. dates conc. structural assignment (n.m.r., i.r., u.v.) are discussed critically.
Zusätzliches Material:
3 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/prac.19793210602
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