Reaction of Phosphines with 1-Azido-(2-halogenomethyl)benzene Giving Aminophosphonium-Substituted Indazoles

Abstract

The reaction between a 1-azido-(2-halogenomethyl)benzene and a phosphine gives different products depending on the nature of the halogen, the phosphine itself and the solvent employed. While PPh3 (2 equiv.) reacts with the chloro reagent in toluene to give the expected iminophosphorane-phosphonium adduct, trialkylphosphines (PCy3 and PEt3) surprisingly furnish an aminophosphonium substituted by a zwitterionic indazole. The bicyclic product can also form from PPh3 using the bromo reagent in acetonitrile. A mechanism is proposed for this cyclization based on DFT calculations.

An Ionic Liquid Medium Enables Development of a Phosphine-Mediated Amine–Azide Bioconjugation Method

“…The ionic-liquid-based tetrazene-forming amine–azide coupling reaction provides an efficient and selective bioconjugation strategy, and this study implies the presence of untapped opportunities for further development of click-chemistry-like reactions in untraditional media. Beyond the bioconjugation field, the present report also highlights the breadth of the reactivity of azide groups behaving as electrophiles (i.e., umpolung reactivity): while phosphine-mediated azide reactions (i.e., phosphazide − and iminophosphorane , ) are known to cause nucleophilic attack toward various electrophiles, − covalent bond formation with nucleophiles (amine groups) is unprecedented. Perhaps ionic-liquid-mediated reactivity enhancement plays a key role in the activation of the reaction intermediates (Figure S35), − promoting the electrophilic nature of the phosphine azide species to cause the N–N bond formation reaction. , Interestingly, although nitrogen-rich functional groups such as diazirine, azide, and tetrazine have been extensively studied and utilized in a wide variety of chemistry fields, ,, tetrazene is extremely understudied to date, presumably because of the dearth of mild and selective synthetic methodologies. , Given the excellent chemoselectivity as well as the abundance of amine- or azide-containing molecules, the present method provides new opportunities for the investigation of the tetrazene group.…”

Electronic Effects in Phosphino‐Iminophosphorane PdII Complexes upon Varying the N Substituent

“…In each case, the formation of a single compound identified by the presence of two doublets in 31 For 1 d, the reaction with AgOTf was not satisfying and the 31 P{ 1 H} NMR spectrum of the crude mixture showed various resonances among which some corresponding to Ag I coordinated PPh 2 units, recognizable thanks to their characteristic coupling pattern due to the two Ag I isotopes ( 107 Ag and 109 Ag). The chloride abstraction was alternatively conducted with thallium triflate, which we previously successfully used for Fe II iminophosphorane complexes, [21] this allowed to isolate [Pd(L H )-Cl(CN t Bu)](OTf) 2 d in 68 % yield. Within this series, 2 c and 2 d appeared as the most fragile, they decomposed after some hours in dichloromethane, and exchange reactions occurred in acetonitrile rendering their 13 C{ 1 H} NMR characterization difficult.…”