Nitroethylene: a stable, clean, and reactive agent for organic synthesis

Abstract

Contrary to current belief, nitroethylene is a stable reagent and holds promise as a useful and reactive synthon.Nitroethylene can be prepared in 20-25-g lots, and standard, refrigerated solutions in common solvents providea good and ready source of the reagent. The reagent purity can be easily monitored by titration againsttetraphenylcyclopentadienone (tetracyclone) coupled with the isolation of the colorless crystalline adduct. Withreactive substrates, nitroethylene reacts with greatest ease at low temperatures, leading to functionalized systemshaving potential for further elaboration. With systems that require heating, the limited stability of nitroethyleneitself complicates the course of the reaction. Cyclopentadiene, 5-[ (benzyloxy)methyl]cyclopentadiene,5 -(methoxymethyl)cyclopentadiene, 5-(1,3-dithianyl)cyclopentadiene, 5-(trimethylsilyl)cyclopentadiene, andspiroheptadiene readily gave (4 + 2) adducts with nitroethylene, each possessing attraction as a syntheticintermediate. Adducts from furan and acetoxyfulvene undergo rearrangement via u cleavage. The (4 + 2) adductfrom 9-diazofluorene spontaneously extrudes nitrogen, leading to spironitrocyclopropane. Indole readily undergoesMichael addition to give 80% 3-(nitroethy1)indole and 15% of novel bis adduct. The 2,6 Michael adduct ariseswith 1-morpholinocyclohexene, and @-pinene undergoes an ene reaction with nitroethylene. Novel 2-nitroethylphosphonates, useful in Wittig-Hornerreactions, arise from nitroethylene and phosphites in tert-butyl alcohol.