Protonated nitro group as a gas-phase electrophile: experimental and theoretical study of the cyclization of o-nitrodiphenyl ethers, amines, and sulfides.
A novel gas-phase electrophilic cyclization, initiated by the protonation of a nitro group, occurs for 2-nitrophenyl phenyl ether and for the analogous sulfide and amine, leading to heterocyclic intermediates in each case. Subsequently, the cyclic intermediates dissociate via two pathways: (1) unusual step-wise eliminations of two OH radicals to afford heterocyclic cations, [phenoxazine - H](+), [phenothiazine - H](+), and [phenazine + H](+), and (2) expulsion of H(2)O, to yield a heterocyclic ketone, followed by loss of CO. The proposed structures of the gas-phase product ions and reaction mechanisms are supported by chemical substitution, deuterium labeling, accurate mass measurements at high mass resolving power, product-ion mass spectra obtained by tandem mass spectrometry, mass spectra of reference compounds, and molecular orbital calculations. Using a mass spectrometer as a reaction vessel, we demonstrate that, upon protonation, a nitro group becomes an electrophile and participates in cyclization reactions in the gas phase.
Moolayil
Joseph T
JT
Department of Chemistry, Sacred Heart College Thevara, Cochin, Kerala, India.
George
Mathai
M
Srinivas
R
R
Giblin
Daryl
D
Russell
Amber
A
Gross
Michael L
ML
D000588:Amines / Q000737:chemistry*; D003500:Cyclization; D005740:Gases / Q000737:chemistry*; D008956:Models, Chemical; D008970:Molecular Weight; D010647:Phenyl Ethers / Q000737:chemistry*; D011522:Protons; D021241:Spectrometry, Mass, Electrospray Ionization; D013440:Sulfides / Q000737:chemistry*
D000588:Amines; D005740:Gases; D010647:Phenyl Ethers; D011522:Protons; D013440:Sulfides