We found that phenethylcarbamates that bear ortho-salicylate as an ether group (carbamoyl salicylates) dramatically accelerate OC bond dissociation in strong acid to facilitate generation of isocyanate cation (N-protonated isocyanates), which undergo subsequent intramolecular aromatic electrophilic cyclization to give dihydroisoquinolones. To generate isocyanate cations from carbamates in acidic media as electrophiles for aromatic substitution, protonation at the ether oxygen, the least basic heteroatom, is essential to promote CO bond cleavage. However, the carbonyl oxygen of carbamates, the most basic site, is protonated exclusively in strong acids. We found that the protonation site can be shifted to an alternative basic atom by linking methyl salicylate to the ether oxygen of carbamate. The methyl ester oxygen ortho to the phenolic (ether) oxygen of salicylate is as basic as the carbamate carbonyl oxygen, and we found that monoprotonation at the methyl ester oxygen in strong acid resulted in the formation of an intramolecular cationic hydrogen bond (>CO(+) H⋅⋅⋅O<) with the phenolic ether oxygen. This facilitates OC bond dissociation of phenethylcarbamates, thereby promoting isocyanate cation formation. In contrast, superacid-mediated diprotonation at the methyl ester oxygen of the salicylate and the carbonyl oxygen of the carbamate afforded a rather stable dication, which did not readily undergo CO bond dissociation. This is an unprecedented and unknown case in which the monocation has greater reactivity than the dication.

A series of 9-fluorenyl cations has been studied and it is shown that increasing charge on a heterocyclic substituent group enhances the anti-aromatic character of the carbocation system. Similarly, a series of dibenzosuberenyl cations has been studied and increasing charge on a substituent group is shown to enhance aromatic character in the carbocation system. These studies include the direct observations of dicationic and tricationic species using stable-ion conditions and low temperature NMR. The structures of these ions were further characterized using DFT calculations, confirming that highly charged organic ions may exhibit unusual distributions of π-electrons and delocalization of electrons in 4n or 4n+2 π-systems.

A superacid-promoted method for the synthesis of 9,9-diarylfluorenes is described. The chemistry involves cyclizations and arylations with biphenyl-substituted heterocyclic ketones and a mechanism is proposed involving superelectrophilic intermediates. The key reactive intermediates-dicationic and trication fluorenyl cations have been observed by low-temperature NMR and the mechanism has been further studied using DFT calculations.

Functionalized angular cycloalkane-fused naphthalenes were prepared using a two-step process involving a Pdcatalyzed Suzuki−Miyaura coupling of aryl pinacol boronates and vinyl triflates followed by a boron trifluoride etherate-catalyzed cycloaromatization.