Spectrometry and Reactivity of the 1-Hydropyrenyl Anion

A study of the charge distribution in the 1-hydropyrenyl anion (2⁻), and of its regioselectivity toward electrophilic attack was undertaken. In order to obtain reliable information on the reactive positions in 2⁻, a model with the same conjugated system was prepared, which has its 1-position fixed with a spirocyclopentane ring. Highly resolved ¹H and ¹³C NMR spectra of this spirotcyclopentane-1,1′-[1H]pyrenyl] anion (1⁻) and of 2⁻ were obtained. These spectra could be completely assigned by means of COSY, NOESY, and 2D ¹H-¹³C COSY techniques. According to the ¹³C NMR measurements, 5-C of 1⁻ and 2⁻ bears the highest negative charge. The results of PM3 semiempirical calculations support this finding and, furthermore, a large HOMO coefficient was calculated at the quaternary 3a-C of 2⁻, suggesting that this position is susceptible toward attack by soft electrophiles. In full agreement with the ¹³C NMR and PM3 results, 5-C of 1⁻ and 2⁻ show the highest reactivity toward electrophilic attack, while the quaternary 3a-C of 1⁻ and 2⁻ is attacked by soft electrophiles. These new results contradict earlier findings because until now, carbon atom 9-C of the 1-hydropyrenyl anion (2⁻) was assumed to be the most reactive position, and soft electrophiles were thought to attack 10a-C of 2⁻.