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Bending Enamine Patterns of Stabilized Pentalenes into "Polymethine Ylides"
Valentin Thery1, Cyriac Barra1, Alexandra Simeoni1
1Univ. Grenoble-Alpes, UMR CNRS-UGA 5250, CS 40700, 38058 Grenoble, France.
Abstract:
We report the synthesis and structural study of 2-substituted 1,3-bis(dimethylamino)pentalenes. The two electrons donating substituents shift the formally anti-aromatic pattern toward more suitable polarized structures. A subtle steric trade-off can result either in planar cyclopentadienyl vinamidiniums or in distorted structures featuring a pyramidalized ylidic carbon adjacent to a stabilized π-conjugated iminium (polymethine). This latter pattern mimics a postulated activated distorted geometry for key Breslow intermediates in the active site of thiamine-dependent enzymes. It highlights how the energetic drive to avoid anti-aromaticity can be used to access models for unconventional distorted conformations of organic molecules.
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