An Electron-Catalyzed Cope Cyclization. The Structure of the 2,5-Dicyano-1,5-hexadiene Radical Anion in the Gas Phase

Abstract

The radical anion of 2,5-dicyano-1,5-hexadiene is shown to undergo Cope cyclization in a flowing afterglow-triple quadrupole apparatus. The cyclic structure of the 2,5-dicyano-1,5-hexadiene radical anion was established by using chemical reactivity. The ion reacts with CO2 and CS2 by addition, whereas the radical anions of closed-shell molecules such as fumaronitrile do not react with these reagents. The ion exhibits reactivity characteristic of a distonic ion in that it sequentially adds CO2 and NO or NO2. It reacts with NO by forming a product at m/z 135 corresponding to addition followed by loss of HCN. The reactivity and CID spectrum of the product ion at m/z 135 agrees with that of oximate ion, which requires a cyclic precursor ion. Attempts to generate radical anions of acrylonitrile and 2,6-dicyano-1,6-heptadiene were unsuccessful, providing additional evidence against a linear structure as a stable structure for 2,5-dicyano-1,5-hexadiene radical anion. The cyclization of the radical anion of the 2,5-dicyano-1,5-hexadiene is the first example of an electron-catalyzed Cope cyclization.

Functionalization of N-tert-butoxycarbonyl-7-and N-tert-butoxycarbonyl-8-bromo-10-azabicyclo[4.3.1]deca-3,7-dienes. A route to a ferruginine homolog

“…The use of other reagents (dimethylacetamide, ethyl acetate, Ac 2 O, or acetonitrile) led only to trace amounts of ketone 4b. In the series of the tropane bicycles, a transformation of compounds of the type 4b into ferruginine homologs (4c) is a well devel oped process 5 involving selective reduction of the inacti vated C=C bond in the presence of RhCl(Ph 3 P) 3 , re moval of the protecting group, and reductive N methy lation.…”

Antiaromaticity-promoted radical anion stability in α-vinyl heterocyclics

“…44 Through DFT calculations, Alabugin and coworkers demonstrated in 2003 that remote substituent effects and benzannelation of enediyne lead to the dynamic interplay between antiaromaticity (reactant radical anions) and aromaticity (transition and product), promoting radical anionic cyclorearomatization reactions with much higher efficiency than the thermal mode. 45 Similarly, both theoreticians 46 and experimentalists 47 confirmed the formation of cyclohexane-1,4-diyl radical anions during the electron-catalyzed Cope cyclization reaction.…”

14 Organic gas-phase ion chemistry

“…The hydride adduct, formed by reaction of fluoride with difluorophenylsilane [eqn. (3)], is proposed as an active reducing reagent.…”