Synthesis of Fluorenes via Tandem Copper-Catalyzed [3 + 2] Cycloaddition and Rhodium-Catalyzed Denitrogenative Cyclization in a 5-Exo Mode from 2-Ethynylbiaryls and N-Sulfonyl Azides in One Pot

Abstract

An efficient synthetic method of fluorenes having an enamine moiety at C-9 methylene bridge is developed from N-sulfonyl-4-biaryl-1,2,3-triazole derivatives via Rh-catalyzed denitrogenative cyclization in a 5-exo mode. Rh-catalyzed denitrogenative cyclization followed by catalytic hydrogenation produces N-tosylaminomethyl-substituted fluorenes in one pot. Moreover, fluorenes are synthesized via tandem Cu-catalyzed [3 + 2] cycloaddition and Rh-catalyzed denitrogenative cyclization in a 5-exo mode starting from 2-ethynylbiaryls and N-sulfonyl azides in one pot.

Recent Progress towards Transition‐Metal‐Catalyzed Synthesis of Fluorenes

“…As a precursor of α‐imino Rh carbenoid, N ‐sulfonyl‐1,2,3‐triazoles have also been evaluated in the synthesis of fluorene. Most recently, Lee and co‐workers reported an efficient synthetic method for the preparation of fluorenes 36 bearing an enamine moiety at the C9 methylene bridge from N ‐sulfonyl‐4‐biaryl‐1,2,3‐triazole derivatives by Rh‐catalyzed denitrogenative cyclization in a 5‐ exo mode 29. The one‐pot Cu‐catalyzed [3+2] cycloaddition followed by Rh‐catalyzed denitrogenative cyclization produced substituted fluorenes 36 in 60–73 % yields (Scheme ).…”

CuO-Nanoparticles Catalyzed Synthesis of 1,4-Disubstituted-1,2,3-Triazoles from Bromoalkenes

“…When other aromatic substitutions such as naphthyl and thiophenyl were investigated, thiophenyl sored up to a great margin while naphthyl slipped to poor yield ( Table 2, entries 8-9). On the other part of this study, fixing the olefin (1a), various azides were subjected to this condition and examined the outcome ( Table 2, entries [10][11][12][13][14][15]. Excellent yields of triazoles were registered with methyl and methoxy benzyl azides ( Table 2, entries 10-11).…”

“…Even though 1,2,3-triazoles have not been isolated from natural sources, 5 they have unveiled new horizons in various areas such as drug discovery, 6,7 materials, 8,9 polymers 10 and supramolecules. 11,12 Besides their usage as synthetic intermediates, [13][14][15] they have also enormously contributed to the industry as photo stabilizers, corrosion inhibitor, dyes, fluorescent whiteners and optical brightening agents. 16,17 Subsequently, Ruthenium-catalyzed azide-alkyne cycloaddition (RuAAC) was developed to prepare the complementary 1,5-disubstituted 1,2,3-triazoles.…”

Divergent Reactions between α‐Imino Rhodium Carbenoids and 1,3‐Diketones: Substrate‐Controlled O–H versus C–H Insertion

“…The characteristic imine functionality adjacent to the rhodium carbenoid center renders these carbene species especially useful in the synthesis of various nitrogen‐based building blocks and heterocycles . Carbene insertion into a C–H bond is generally the initial step for many tandem annulations . This has led to the formation of diverse heterocycle frameworks such as indoles, fused indolines, azepines, pyrrolizidines, and dihydrobenzofurans .…”