Diazo Strategy for the Synthesis of Pyridazines: Pivotal Impact of the Configuration of the Diazo Precursor on the Process

Abstract

Phosphazenes of vinyldiazocarbonyl compounds having cis stereochemistry of the functional groups on the vinyl bond readily produce pyridazines by a diaza-Wittig process, whereas their counterparts with trans configuration remain intact under similar reaction conditions. Upon UV irradiation trans-phosphazenes furnish pyridazines through a tandem trans-to-cis isomerization followed by intramolecular cyclization. At elevated temperatures trans-(triphenyl)phosphazenes dissociate to give the initial vinyldiazo compounds, which produce pyrazoles in high yields. The first theoretical study on the mechanism of the diaza-Wittig process by DFT calculations at the M06-2X/6-31G(d) level of theory suggest that for the cis-phosphazenes a rapid tandem [2+2] cycloaddition/cycloelimination process with low energy barriers is preferred over trans isomers.

Lewis and Brønsted basicity of phosphine-diazomethane derivatives

“…Since the original report by Staudinger and Meyer, 41 literature studies [42][43][44][45][46][47][48] have probed the reactions of diazomethanes with phosphine donors. In a similar fashion, we have probed the addition of Ph3P to a solution of EtOC(=O)CH(N2) to afford a pale yellow solution from which crystals were isolated of the product 1 in 86% yield.…”

“…These metric parameters are similar to those found in the previously reported structures of EtCO2CH=CMe(EtOC=O)C(NNPPh3) and MeCO2CH=C(CF3)(MeC=O)C(NNPPh3). 46 The corresponding reactions of Cy3P and tBu3P with EtOC(=O)CH(N2) also afforded pale yellow solutions. These solutions exhibited 31 P{ 1 H}, NMR signals at 41.7 and 53.1 ppm, respectively while the 1 H and 13 C{ 1 H} NMR were consistent with the formulation these products as EtOC(=O)CH(NNPR3) (R = Cy 2 and tBu 3) (Scheme 2).…”

Crystal structures of [IrCl2(NHCHPh)((dppm)(C(N2dppm))-κ3 P,C,P′)]Cl·5.5MeCN and [IrI(NHCHPh)(((dppm)C(N2))-κ2 P,C)(dppm-κ2 P,P′)]I(I3)·0.5I2·MeOH·0.5CH2Cl2: triazene fragmentation in a PCN pincer iridium complex

“…The P3-N2 bond length [1.586 (4) Å ] is in the range of P N double bonds observed for iminophosphoranes (Ireland et al, 2010;Peng et al, 2011;Sun et al, 2011). Corresponding bond lengths in other phosphazene systems exhibit values of 1.62-1.64 Å for P-N, 1.36-1.39 Å for N-N and 1.31 Å for C-N. (Bethell et al, 1992;Supurgibekov et al, 2011;Galina et al, 2013;Nikolaev et al, 2016). The P2-C1 bond length [1.836 (4) Å ] indicates a single bond.…”

Synthesis of a Novel 1,4-Dicarbonyl Scaffold – Ethyl 3-Formyl-4,5-dihydrofuran-2-carboxylate – and Its Application to the Synthesis of Pyridazines

“…materials. 30 This diversity of applications has led to the development of new methods for the synthesis of compounds containing heterocyclic pyridazines, such as intramolecular diaza-Wittig cyclization, 31 cascade electrocyclic processes, 32 cyclization reaction of a piperidone derivative, glyoxylic acid and hydrazine, 33 and cross-coupling reactions and cyclization reactions of 1,4-dicarbonyl compounds with hydrazines. 30,34 The present study that we describe here is a method for obtaining a novel 1,4-dicarbonyl compound 2 through the rearrangement of ethyl 2-(4,5-dihydrofuran-3-yl)-2-oxoacetate (1), as well as its applications as a precursor for the synthesis of a series of dihydrofuropyridazines 6a-l (Scheme 1).…”