Stable ion NMR and GIAO-DFT study of novel cations from 8,16-dicyano[2.2]metacyclophanedienes and from strategically substituted/benzannelated dihydropyrenes: charge-induced tropicity modulation and pi-switching.

Kenneth K Laali, Takao Okazaki, Reginald H Mitchell, Khurshid Ayub, Rui Zhang, Stephen G Robinson

Index: J. Org. Chem. 73(2) , 457-66, (2008)

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Abstract

The dicyanometacyclophanediene 1 is diprotonated at the cyano groups (1H2 2+) in various superacid media. Upon quenching, intact 1 and the ring-closed CPD 2 were obtained in a 3:2 or 3:1 ratio, depending on the superacid system. Compound 2 undergoes ring opening in the superacid to give the ipso-monoprotonated 2H+, which on quenching furnishes 1-cyanopyrene as a major product together with 2 and 1. The dication 3 2+, with strongly deshielded internal methyls, was generated from the epoxyannulene 3. Ketones 4-6 and ester 7 are O/C diprotonated to give paratropic carboxonium-annulenium dications (4H2 2+, 5H2 2+, 6H2 2+, and 7H2 2+, respectively). Ester 8 gives a trication by two-electron oxidation and O-protonation. Conjugated carboxylic acid 9 gives a mixture of two dications by CO and ring protonation. The dibromo derivatives 10 and 11 form carboxonium ions, whereas the monobromo derivative 12 is O/C diprotonated to give an oxonium-annulenium dication. Charge delocalization modes and tropicity in the resulting species are evaluated by NMR and GIAO-DFT. Facile formation of 2 from 1 in quenching experiments indicates that thermal closing can be achieved with the diprotonated dinitrile, without imposing skeletal rearrangement.