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8.2.4.1.1.2 Variation 2: Reactions of Carbanions with Aromatic Nitro Compounds

DOI: 10.1055/sos-SD-008-00826

Jonczyk, A.; Kowalkowska, A.Science of Synthesis, (200681021.

Carbanions bearing a leaving group (halogen, arylsulfanyl, aryloxy, dialkyl dithiocarbonate), generated from the corresponding CH acids by bases, undergo reaction with carbocyclic[‌154‌‌156‌] and heterocyclic[‌157‌] nitroarenes according to the vicarious nucleophilic substitution (VNS) pathway. The process consists of the formation of a σH complex which then undergoes a base-mediated elimination. Acidification of the product thus formed affords nitroarenes substituted at the 2- or 4-position with respect to the nitro group. Products of the vicarious nucleophilic substitution (VNS) reaction, i.e. compounds ortho substituted to the nitro group, are useful substrates for the synthesis of heterocyclic compounds.[‌157‌] This process is often realized using powdered sodium hydroxide in dimethyl sulfoxide[‌61‌,‌158‌‌171‌] or liquid ammonia;[‌158‌,‌161‌] typical phase-transfer catalysis conditions are not suitable but an ion-pair extraction technique has been applied in some cases.[‌158‌] The vicarious nucleophilic substitution (VNS) reaction allows the functionalization of nitrobenzene[‌161‌,‌163‌] and of nitronaphthalene,[‌161‌] as well as of nitroquinoline[‌164‌] derivatives with α-(cyanoalkyl)[‌161‌,‌163‌,‌164‌] or α-[(alkoxycarbonyl)alkyl][‌161‌] groups, nitrobenzene,[‌162‌,‌163‌,‌169‌] nitronaphthalene,[‌165‌] nitroquinoline,[‌164‌] nitroindole,[‌166‌] and nitrobenzofuroxan[‌167‌] derivatives with an α-(sulfonylalkyl) group; and nitrobenzene and nitronaphthalene derivatives with a (phenylsulfinyl)methyl group;[‌158‌] as well as nitro aromatic compounds with other functional groups, e.g. to give 19 (Schemes 19 and 20).[‌61‌,‌159‌,‌160‌] Quaternary ammonium salts are particularly useful reagents for the introduction of N,N-disubstituted carbamoylmethyl groups into aromatic nitro compounds.[‌170‌] An intramolecular variant of the VNS reaction leads to the formation of five-, six-, and seven-membered benzosultam derivatives.[‌168‌]

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