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Exploring the intrinsic polar [4 + 2 + ] cycloaddition reactivity of gaseous carbosulfonium and carboxonium ions
Author(s) -
Basher Muftah M.,
Corilo Yuri E.,
Sparrapan Regina,
Benassi Mario,
Augusti Rodinei,
Eberlin Marcos N.,
Riveros José M.
Publication year - 2012
Publication title -
journal of mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 1076-5174
DOI - 10.1002/jms.3109
Subject(s) - chemistry , isoprene , isomerization , adduct , reactivity (psychology) , protonation , methyl vinyl ketone , cycloaddition , dissociation (chemistry) , medicinal chemistry , furan , ketone , thiophene , photochemistry , ion , organic chemistry , catalysis , medicine , polymer , alternative medicine , pathology , copolymer
Gas‐phase reactions of model carbosulfonium ions (CH 3 ‐S + = CH 2; CH 3 CH 2 ‐S + = CH 2 and Ph‐S + = CH 2 ) and an O‐analogue carboxonium ion (CH 3 ‐O + = CH 2 ) with acyclic (isoprene, 1,3‐butadiene, methyl vinyl ketone) and cyclic (1,3‐cyclohexadiene, thiophene, furan) conjugated dienes were systematically investigated by pentaquadrupole mass spectrometry. As corroborated by B3LYP/6‐311 G(d,p) calculations, the carbosulfonium ions first react at large extents with the dienes forming adducts via simple addition. The nascent adducts, depending on their stability and internal energy, react further via two competitive channels: (1) in reactions with acyclic dienes via cyclization that yields formally [4 + 2 + ] cycloadducts, or (2) in reactions with the cyclic dienes via dissociation by HSR loss that yields methylenation (net CH + transfer) products. In great contrast to its S‐analogues, CH 3 ‐O + = CH 2 (as well as C 2 H 5 ‐O + = CH 2 and Ph‐O + = CH 2 in reactions with isoprene) forms little or no adduct and proton transfer is the dominant reaction channel. Isomerization to more acidic protonated aldehydes in the course of reaction seems to be the most plausible cause of the contrasting reactivity of carboxonium ions. The CH 2 = CH‐O + = CH 2 ion forms an abundant [4 + 2 + ] cycloadduct with isoprene, but similar to the behavior of such α,β‐unsaturated carboxonium ions in solution, seems to occur across the C = C bond. Copyright © 2012 John Wiley & Sons, Ltd.