Synthesis of functionalized pyridazin-3(2H)-ones via nucleophilic substitution of hydrogen (SNH)

Three-Component cine,ipso-Disubstitution of Nitrocoumarins

The development of a three-component cine,ipso-disubstitution of nitrocoumarins is reported. The reaction leverages the electrophilicity of nitrocoumarins, the nucleophilicity of nitronates, and the leaving group ability of nitrite (NO2-) to yield complex polyfunctionalized biaryls that often display stable axial chirality.

Reliable Functionalization of 5,6-Fused Bicyclic N-Heterocycles Pyrazolopyrimidines and Imidazopyridazines via Zinc and Magnesium Organometallics

DFT-calculations allow prediction of the reactivity of uncommon N-heterocyclic scaffolds of pyrazolo[1,5-a]pyrimidines and imidazo[1,2-b]pyridazines and considerably facilitate their functionalization. The derivatization of these N-heterocycles was realized using Grignard reagents for nucleophilic additions to 5-chloropyrazolo[1,5-a]pyrimidines and TMP2 Zn ⋅ 2 MgCl2  ⋅ 2 LiCl allowed regioselective zincations. In the case of 6-chloroimidazo[1,2-b]pyridazine, bases such as TMP2 Zn ⋅ MgCl2  ⋅ 2 LiCl, in the presence or absence of BF3  ⋅ OEt2 , led to regioselective metalations at positions 3 or 8. Subsequent functionalizations were achieved with TMPMgCl ⋅ LiCl, producing various polysubstituted derivatives (up to penta-substitution). X-ray analysis confirmed the regioselectivity for key functional heterocycles.

Synthesis of Functionalized Pyrazin-2(1 H)-ones via Tele-Nucleophilic Substitution of Hydrogen Involving Grignard Reactants and Electrophiles

The reaction of 6-chloro-1-methylpyrazin-2(1 H)-one with Grignard reactants followed by quenching with different electrophiles gave access to a variety of 3,6-difunctionalized 1-methylpyrazin-2(1 H)-ones. This regioselective three-component reaction represents the first example of a tele-nucleophilic substitution of hydrogen (S_N^H) in which the anionic σ^H adduct is quenched by electrophiles (other than a proton) before elimination takes place. Quenching the reaction with iodine (I₂) or bromine (Br₂) provides an alternative reaction pathway, yielding a 3-functionalized 6-chloro-1-methylpyrazin-2(1 H)-one or 5-bromo-6-chloro-1-methylpyrazin-2(1 H)-one, respectively. The halogens present offer opportunities for further selective transformations.

Specific N-Alkylation of Hydroxypyridines Achieved by a Catalyst- and Base-Free Reaction with Organohalides

A specific N-alkylation of 2-hydroxypyridines is achieved by reacting with organohalides under catalyst- and base-free conditions. The observed HX-facilitated conversion of pyridyl ether intermediates to 2-pyridone products may account for the success and specific N-alkylation of the reaction under the unexpectedly simple conditions. This new reaction may provide a useful alternative for the synthesis of 2-pyridones and analogous structures because of its >99% N-selectivity, relatively broad scopes of both substrates, and no mandatory use of catalysts and bases.

A Novel Method for the Synthesis of Haloisoquinolines Involving an Electrophile-exchange Process

A synthesis of haloisoquinolines through electrophilic cyclisation involving an electrophilic-exchange process has been developed. A variety of 2-alkynyl benzyl azides are cyclised in the presence of KX (X = I, Br, Cl) and electrophilic fluoride reagents, to afford the corresponding haloisoquinolines in moderate to good yields. Reagents for electrophilic halogenation have been generated from their inorganic salts (M+X-) by oxidation with a Selectfluor reagent and reacted in situ with the substrates.

Synthesis of functionalized pyridazin-3(2H)-ones via selective bromine-magnesium exchange and lactam directed ortho C-H magnesiation

Selective bromine-magnesium exchange on 2-benzyl-5-bromo-4-methoxypyridazin-3(2H)-one could be achieved when MesMgBr was used as reagent. With more nucleophilic RMgCl species (R = Bu, i-Pr, Ph) both nucleophilic addition-elimination at C-4 and bromine-magnesium exchange at C-5 occurred. In 2-benzyl-5-bromopyridazin-3(2H)-one, which does not contain a substituent at C-4, addition could not be suppressed. Less nucleophilic Mg amides (TMPMgCl·LiCl) allowed regioselective C-H magnesiation at the C-4 position in such substrates, as exemplified for 2-benzyl-5-chloro- and 2-benzyl-6-chloropyridazin-3(2H)-one. Quenching of the magnesiated pyridazinones with electrophiles gives access to a variety of hitherto unknown pyridazin-3(2H)-one derivatives.