Oxidative addition reactions of ω-alkenyl nitronate anions

Abstract

Anions are oxidatively added to nitronate anions to yield a-substituted nitroalkanes when potassium hexacyanoferrate( 111) is used as oxidant. Oxidation of nitronate anions yields intermediate anitroalkyl radicals, which undergo addition by anions to give intermediate a-substituted nitroalkane radical anions, which are further oxidised to yield the a-substituted nitroalkanes. The nitronate anions used are derived from 5-nitrohex-1 -ene, 6-nitrohept-1 -ene, endo-5-nitro-exo-6-phenylbicyclo[2.2.1]hept-2-ene, and 1 -(bicyclo[2.2.1] hept-5-en-endo-2-yl) -2-nitropropane. The intermediate a-nitroalkyl radicals underwent addition of anions to form radical anions faster than intramolecular cyclisation onto the a-alkenes. The a-nitroalkyl radical derived from 1 -(bicyclo[2.2.1] hept-5-en-endo-2yl)-2-nitropropane underwent cyclisation when the oxidation was carried out in the absence of an added anion. The addition of anions (thiocyanate, benzenesulfinate, 4-~hlorobenzenethiolate, and nitrite) to the a-nitroalkyl radicals derived from endo-5-nitro-exo-6-phenylbicyclo[2.2.1] hept-2-ene occurred stereoselectively from the less hindered exo face. Oxidative addition of 4-chlorobenzenethiolate to the nitronate from endo-5-nitro-exo-6-phenylbicyclo[2.2.1] hept-2-ene gave an unusual cyclisation via addition of a thiyl radical to the alkene.Iowa State University, Ames, for helpful discussions, and The Boots Company, Nottingham, for running high-field NMR spectra.

Nucleophilic Substitution Reactions by Electron Transfer

“…Bowman et al proposed that the lack of cyclization of the 2-nitrohex-5-enyl radical is due to a faster rate for - CMe 2 NO 2 addition than for cyclization. Nitroalkyl radicals are also intermediates in the oxidative addition to nitronate anions, a reaction in which no cyclization was detected . Nevertheless, they add readily when the alkene is strongly nucleophilic as in the alkylation of enamines .…”

“…Nitroalkyl radicals are also intermediates in the oxidative addition to nitronate anions, a reaction in which no cyclization was detected. 155 Nevertheless, they add readily when the alkene is strongly nucleophilic as in the alkylation of enamines. 156 According to these results, cyclization of R-nitroalkyl radicals is possible whenever the unsaturated bond is more nucleophilic than that of a simple alkene.…”

Intramolecular cyclization of 1-nitroalkenyl radicals generated by one-electron oxidation of aci-nitro anions with CAN: stereoselective formation of 3,4-functionalized tetrahydrofurans

“…In conclusion, although it has been previously believed that cyclization of a-nitroalkenyl radicals for synthetic purposes could only be useful if groups more nucleophilic than unactivated alkenes are present, 14 our results show that, in turn, a-nitroalkenyl radicals generated by one-electron oxidation of aci-nitro anions with CAN lead stereoselectively to bifunctionalized tetrahydrofurans bearing three contiguous stereogenic centers. Moreover, the scope of subsequent conversions of the nitro and nitrate ester groups 15 should expand the utility of this new strategy in organic synthesis.…”

The Last Fortress of Tin's Tyranny – Protodenitration of Nitroalkanes

“…Subsequently, the reaction proceeds as a free‐radical chain reaction (Scheme 10). [69] Further investigation into the mechanism was undertaken by Bowman [225] …”