Push–pull and pull–push effects in isatylidenes

✍ Scribed by Martha S. Morales-Ríos; Manuel García-Velgara; Humberto Cervantes-Cuevas; Celina Alvarez-Cisneros; Pedro Joseph-Nathan

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 122 KB
• Volume: 38
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/(sici)1097-458x(200003)38:3<172::aid-mrc618>3.0.co;2-d

✦ Synopsis

A series of C-8 mono-and disubstituted isatylidenes were prepared in order to examine the influence of the substituent on the polarization of the ethylenic carbons C-3 C-8. Donor-acceptor C-8 substitution resulted in an inversion of the polarization of the ethylenic carbons, as evidenced by the 13 C NMR spectra, and because these compounds can exist in solution as equilibrium mixtures of the E-and Z-isomers. The dual donor-acceptor character of the heterocycle is controlled by the cross-conjugated C-3 C-8 double bond, in which the C-3 carbon atom has the possibility of conjugating with either the donor or the attracting portion of the heterocyclic system, consistent with contributions from isatylidene resonance forms which induce the C-8 carbon atom to be charged either positively or negatively, thus allowing an opposite sense of the push-pull effect.