Chemistry of diazocarbonyl compounds: XXX. Development of a synthetic approach to pyridazine structure via wittig reaction of fluoroalkyl-containing diazo keto esters

diaza-Wittig reactions of diketoesters phosphazines: Synthesis of tetrasubstituted fluoroalkyl-containing pyridazines

“…Therefore the development of new methods of preparation of this class compounds is an urgent problem of the synthetic organic chemistry.In keeping with published reports 3,4,6-trisubstituted pyridazines can be synthesized in good yields from 2-vinyl derivatives of 2-diazoketones by the intramolecular diaza-Wittig reaction [4][5][6][7][8][9]. The only example of the synthesis of the tetrasubstituted pyridazine with the use of analogous procedure was described in [10], where by the diaza-Wittig reaction of the posphazine of 4-diazopyrrolidinetrione with ethyl acetoacetate bicyclic pyrrolo[3,4-c]pyridazine was obtained.…”

“…The reaction progress was monitored and R f was measured by TLC on Silufol UV-254 pates (Kavalier, Czechia). Diazodicarbonyl compounds Ia, Ib were obtained from commercial ethyl or methyl 4,4,4-trifl uorooxobutanoates by the diazotransfer reaction [5], fl uoro-containing 1,3-dicarbonyl compounds IIа-IIc were obtained by Claisen condensation [16].…”

“…The signals of atoms С 3 at 152.8, 153.1 and of С 6 at 148.7 and 148.6 q ( 2 J C-F 35.9 Hz) in the spectra of pyridazines Vа, Vb, and also 152.8, 153.1 (C 3 ), 148.1 q (C 6 , 2 J C-F 35.9 Hz) in the spectra of VIа, VIb are located in the region of the 13 С NMR spectra characteristic of unsubstituted [15] and trisubstituted pyridazines [5,7,9].…”

“…The monitoring of the reaction progress by 1 Н NMR spectroscopy showed that under these conditions a fairly complex mixture of products formed containing alongside the target compounds also a diazoacetic ester phosphazine and the other reaction products, and according to the data of 1 Н NMR spectrum of the reaction mixture the yield of pyridazines V did not exceed 30-32%. The relatively low yield of pyridazines V and the occurrence of the side processes in the reaction with the use of the triphenylphosphine is apparently due to the ready dissociation of the triphenylphosphazines IV formed in the fi rst stage into the initial components, PPh 3 and diazoketoesters I [5,12,13]. This decreases the effi ciency of the subsequent diaza-Wittig reaction, and in the presence in the reaction mixture of a little water formed in the stage of condensation it makes possible the diaza-WITTIG REACTIONS OF DIKETOESTERS PHOSPHAZINES parallel proceses: the hydrolysis of fl uoroalkyl-containing diazoketoesters I [5] and/or of phosphazines IVа, IVb [13,14].…”

“…The relatively low yield of pyridazines V and the occurrence of the side processes in the reaction with the use of the triphenylphosphine is apparently due to the ready dissociation of the triphenylphosphazines IV formed in the fi rst stage into the initial components, PPh 3 and diazoketoesters I [5,12,13]. This decreases the effi ciency of the subsequent diaza-Wittig reaction, and in the presence in the reaction mixture of a little water formed in the stage of condensation it makes possible the diaza-WITTIG REACTIONS OF DIKETOESTERS PHOSPHAZINES parallel proceses: the hydrolysis of fl uoroalkyl-containing diazoketoesters I [5] and/or of phosphazines IVа, IVb [13,14]. In this connection in further experiments phosphine IIIb was used since it provided phosphazines more stable against thermolysis and hydrolysis [9].…”