Redox-Associated Variation of Hückel Aromaticity from Lactam-Embedded Smallest Antiaromatic trans -Doubly N-Confused Porphyrins: Synthesis and Characterization

• Published in: Journal of organic chemistry 2020-02, Vol.85 (4), p.2059-2067
• Main Authors: Halder, Nyancy, Sangeetha, Mohandas, Usharani, Dandamudi, Rath, Harapriya
• Format: Article
• Language: English
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/acs.joc.9b02788

High-yield synthesis, spectroscopic and solid-state structural proof of the lactam-embedded smallest ever metal-free stable Hückel antiaromatic -doubly N-confused [16] porphyrins are reported. These new facets of -doubly N-confused porphyrins have been anticipated to exhibit the redox-associated variation of Hückel aromaticity as a mere consequence of the amido-like structures of the N-confused N-methyl pyrrole rings of the macrocycles. Strong aromaticity upon NaBH reduction leading to a resonance dipolar structure of the [18]π-conjugated system as the reduced congener with concomitant Hückel topology are the important highlights. Excellent agreement between experimental spectroscopic measurements and the theoretically determined properties elucidate aromaticity switching upon chemical reduction. Recent years have witnessed an upsurge of demand for the experimental realization of stable antiaromatic systems because of their versatile applications in material science. The conformational rigidity and the enriched stability of these novel 16π antiaromatic doubly N-confused porphyrins might entitle these macrocycles toward such applications.