Intramolecular Aromatic Carbenoid Insertion of Biaryldiazoacetates for the Regioselective Synthesis of Fluorenes

Abstract

The rhodium- or copper-catalyzed intramolecular aromatic carbenoid insertion of biaryldiazoacetates offers a convenient route to fluorene carboxylates with high yields. Whereas, thermal conditions provided a mixture of two regioisomeric products when substituted biaryldiazoacetates were employed as substrates. The developed catalytic conditions displayed an excellent level of regioselectivity, presumably owing to steric effects. The insertion mechanism was assumed to be an electrophilic aromatic substitution, which was supported by preliminary mechanistic studies. A chloro-substituted fluorene derivative was efficiently synthesized and utilized as a base-sensitive protecting group of amines.

Gold(I) Carbenes by Retro-Buchner Reaction: Generation and Fate

“…35−37 Interestingly, related rhodium- or copper-catalyzed annulation of biaryl diazoacetates leads to fluorene carboxylates, 38 which emphasizes the similar reactivity of rhodium, copper, and gold carbenes.…”

Recent Progress towards Transition‐Metal‐Catalyzed Synthesis of Fluorenes

“…Rhodium catalysts have also been explored for the construction of fluorenes. In 2011, a new synthetic method for the synthesis of fluorene carboxylates via Rh‐ or Cu‐catalyzed intramolecular carbenoid insertion into aryl C(sp 2 )H bonds was described by Chang and co‐workers (Scheme ) 25. Through this strategy, biaryldiazoacetates 25 could be converted to fluorene carboxylates 26 in moderate to excellent yields (62–97 %).…”

Transition‐Metal‐Free Intramolecular Carbene Aromatic Substitution/Büchner Reaction: Synthesis of Fluorenes and [6,5,7]Benzo‐fused Rings

“…As shown in Equation (2), the metal‐free reaction afforded the intramolecular aromatic substitution product 7 in 51 % yield (conditions A). However, the Rh 2 (OAc) 4 ‐catalyzed reaction afforded the same product in 95 % yield (conditions B) 12f. In contrast, both transition‐metal‐free and Rh 2 (OAc) 4 ‐catalzyed reaction of N ‐tosylhydrazone 1 b afforded the corresponding intramolecular aromatic substitution product 2 b in similarly high yields (Table 1, entries 2 and 3).…”