10.1021/acs.joc.6b00561.s002
Andreas Schmidt
Andreas
Schmidt
Sviatoslav Batsyts
Sviatoslav
Batsyts
Alexey Smeyanov
Alexey
Smeyanov
Tyll Freese
Tyll
Freese
Eike G. Hübner
Eike G.
Hübner
Martin Nieger
Martin
Nieger
Dipolar Bent and Linear
Acetylenes Substituted by
Cationic Quinolinium and Anionic Benzoates. Formation of Mesomeric
Betaines
American Chemical Society
2016
methylquinolinium
bond
Linear Acetylenes Substituted
CC
DFT
carboxylate group
2016-04-18 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Dipolar_Bent_and_Linear_Acetylenes_Substituted_by_Cationic_Quinolinium_and_Anionic_Benzoates_Formation_of_Mesomeric_Betaines/3204916
3-Ethynylquinoline
was subjected to a Sonogashira–Hagihara
reaction with methyl 2-, 3-, and 4-bromobenzoates, respectively, and
then <i>N</i>-methylated to give 3-[((methoxycarbonyl)phenyl)ethynyl]-1-methylquinolinium
salts (two X-ray analyses). On saponification of the 3- and 4-substituted
benzoates, the mesomeric betaines 3- and 4-[(1-methylquinolinium-3-yl)ethynyl]benzoates
were formed. By contrast, the 2-benzoate derivative gave either the
corresponding (1-oxo-1<i>H</i>-isochromen-3-yl)quinolinium
derivative or the mesomeric betaine 2-(1-methylquinolinium-3-yl)-1,3-dioxo-2,3-dihydro-1<i>H</i>-inden-2-ide depending on the reaction conditions. A DFT
calculation predicts a <i>transoid</i> conformation of the
acetylene bond in the intermediate 2-[(1-methylquinolinium-3-yl)ethynyl]benzoate
which is due to a strong hydrogen bond between the carboxylate group
and 2<i>H</i> of the quinolinium ring, in addition to a
1,5-interaction between the carboxylate group and the CC triple bond.
The bond angles of the <i>transoid</i> CC triple bond were
calculated to be 211.6° and −175.1° in vacuo. The
corresponding linear triple bond is 50.4 kJ/mol less stable in vacuo
according to the calculation, and the N-heterocyclic carbene quinoline-2-ylidene
is not formed as a tautomer.