Bending Enamine Patterns of Stabilized Pentalenes into "Polymethine Ylides".

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).