Dearomative Ring Expansion of Polycyclic Arenes

Abstract

Benzocycloheptenes constitute a common structural motif embedded in many natural products and biologically active compounds. Herein, we report their concise preparation from non‐activated polycyclic arenes using a two‐step sequence involving dearomative [4+2]‐cycloaddition with arenophile in combination with palladium‐catalyzed cyclopropanation, followed by cycloreversion‐initiated ring expansion. The described strategy provides a working alternative to the Buchner reaction, which is limited to monocyclic arenes. Overall, this methylene‐insertion molecular editing approach enables rapid and direct conversion of simple (hetero)arenes into a range of substituted (aza)benzocycloheptatrienes, which can undergo a myriad of downstream functionalizations.

π-Extended Rubrenes via Dearomative Annulative π-Extension Reaction

“…The DAPEX method consists of three fundamental steps: (i) a dearomative [4 + 2] cycloaddition of 4-methyl-1,2,4-triazoline-3,5-dione (MTAD) with aromatic compound; (ii) an iron-catalyzed annulative diarylation, which was originally developed by Nakamura and co-workers; (iii) aromatization by the removal of MTAD . Hence, the DAPEX of rubrene was initiated by the dearomatization of the tetracene core (Figure a).…”

Recent advances in the dearomative functionalisation of heteroarenes

“…In addition to further developments in the area as discussed above new modes of dearomatisation still remain to be thoroughly explored, such as dearomative atom-insertions and dearomative atom-mutations, concepts introduced and recently published by Sarlah. 4 c ,48 Both of these offer many opportunities for new disconnections and would present a leap in the way we use dearomatisation reactions in general. So far, these approaches have focused on adding and building onto the existing heterocyclic frameworks rather than the possibility of completely rearranging them.…”

Skeletal Editing: Interconversion of Arenes and Heteroarenes

“…In the initial incarnation of the methodology, cyclopropana-tion was achieved through thermal or photolytic activation of the diazoester and typically exhibited poor regioselectivity. However, in 1980 Noels and co- [26,27] workers reported a rhodium-catalyzed Buchner reaction which improved regioselectivity. [30,31] Subsequent advances have led to further improvements in both regioselectivity and reaction scope, [32 -35] and in 2017, a regio-and enantioselective variant was demonstrated in flow.…”