Stereochemistry and reactivity of F- and H-vinyldiazocarbonyl compounds and their phosphazines: synthesis of pyrazoles and pyridazines

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 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].…”

“…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].…”

N-vinylation and N-allylation of 3,5-disubstituted pyrazoles by N–H insertion of vinylcarbenoids

“…The majority of known vinyldiazo compounds are characterized by their facile isomerization to 1H-pyrazoles through a thermally induced electrocyclic 1,5-cyclization leading to a 3H-pyrazole, followed by a sigmatropic shift to yield the aromatic 1H-pyrazole. While this long known transformation [4][5][6] constitutes a convenient pyrazole synthesis from diversely substituted vinyldiazoacetates [7][8][9][10][11], it is often an unwanted side reaction in syntheses based on transition-metal catalyzed carbene transfer reactions from such vinyldiazo compounds to a broad range of substrates (cyclopropanation, insertion into N-H, O-H and C-H bonds and more [12]). Diazo compounds 1 and 3 are two examples which have recently been employed frequently for carbenoid transformations, and their isomerization to pyrazoles 2 and 4 (Scheme 1), respectively, has been noticed on several occasions (for examples, see refs.…”

Towards the total synthesis of (-)-phorbol for novel anti-cancer studies

“…101 Thus, the complex nature of the mixture in combination with low conversion and the unexpected spontaneous cyclisation of the diazo compound proved fatal to this approach and as such it was abandoned.…”