Synthesis of Furo[2,3‐f]dibenzotropones via Intramolecular Wittig Reaction of Alkylidene Dibenzo‐β‐tropolones

Abstract

A strategy was developed for synthesizing furan‐fused dibenzotropones via intramolecular Wittig reactions of alkylidene dibenzo‐β‐tropolones and acylating reactants in catalytic or stoichiometric conditions. With these protocols, a series of furo[2,3‐f]dibenzotropones were obtained in 49–99% yields within 1–10 hours. Mechanistic studies of the base‐free phenomena revealed that the organophosphane acts both as a mediator and a regenerable Brønsted base under heating.

Novel Metal-Free Synthesis of 3-Substituted Isocoumarins and Evaluation of Their Fluorescence Properties for Potential Applications

“…Since its discovery more than half a century ago, the Wittig reaction has been widely utilized in organic synthesis due to its simple synthesis, excellent functional group tolerance, and environmental friendliness. Moreover, intramolecular Wittig reactions have been recognized as a valuable strategy for the synthesis of a variety of heterocycles [ 27 , 28 ], although a Wittig reaction involving a variety of carbonyl reagents (e.g., aldehydes, ketones, esters, and amides) has found widespread application in the synthesis of structurally diverse compounds [ 29 , 30 , 31 , 32 ]. Intermolecular Wittig reactions incorporating acid anhydrides as carbonyl components have been less commonly reported [ 33 , 34 ].…”

Synthesis of Trisubstituted Furans from Activated Alkenes by P(III)/P(V) Redox Cycling Catalysis

“…20,30 Recently, Lin and co-workers also revised their method toward the synthesis of furo[2,3-f ]dibenzotropones. 31 In the field of activated alkenes, neither the use of 1,2diacylethenes nor 3-acyl acrylates has been explored for the metal-free, catalytic synthesis of substituted furans, and only few examples can be found in the literature under stoichiometric conditions. 32 Thus, our aim was to explore these activated alkenes in a Michael-addition/acylation/Wittig sequence under phosphine redox cycling catalysis and develop methods for the synthesis of new products in the valuable field of substituted furans (Scheme 1c).…”

“…This methodology was adapted for different reactions, including reductive C–N coupling reactions, Morita–Baylis–Hilman/Wittig cascade, Vilsmeier–Haack reaction, Staudinger/Aza-Wittig reaction, base-free Wittig reaction, and the reduction of activated alkenes. − P­(III)/P­(V) redox cycling catalysis has also been employed for the formation of substituted furans. Lin and co-workers reworked their method for the synthesis of tetrasubstituted furans from trisubstituted activated alkenes using stoichiometric amounts of tributylphosphine toward the use of catalytic amounts of a phospholane catalyst with silyl chlorides as promoters and phenylsilane as a terminal reductant (Scheme a). , He and co-workers updated their synthesis of tetrasubstituted furans starting from acrylates toward the use of catalytic amounts of tributylphosphine at elevated temperatures with the same terminal reductant (Scheme b). , Recently, Lin and co-workers also revised their method toward the synthesis of furo­[2,3- f ]­dibenzotropones …”