Cyclodehydrations Leading to Indene Products Having N‑Heterocyclic Substituents

In this Note, we describe superacid-promoted cyclodehydrations leading to functionalized indenes. The product indenes are synthesized having N-heterocyclic substituents, including pyridyl, imidazolyl, pyrimdyl, and other groups. A mechanism is proposed involving dicationic, superelectrophilic intermediates. The protonated N-heterocyclic rings are shown to dramatically lower the LUMO energy level of the carboxonium electrophile (compared to that of a similar uncharged system)

Intramolecular Conjugate Additions with Heterocyclic Olefins

The intramolecular reactions of olefinic <i>N</i>-heterocycles have been studied. In triflic acid-promoted reactions, conjugate addition is observed with pyrazine-, 2-pyrimidine-, and 2-quinoxaline-based olefins and a phenyl group nucleophile. Markovnikov addition is observed with pyridine and 5-quinoxaline-based olefins. These results are in accordance with previous observations relating the type of additionconjugate or Markovnikovto the positions of olefinic substituents of the <i>N</i>-heterocycle

Synthesis of Heterocycle-Containing 9,9-Diarylfluorenes Using Superelectrophiles

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