Silver‐Catalyzed Sequential Cascade Reaction of Isocyanides with 1‐(2‐Ethynyl‐phenyl)‐prop‐2‐yn‐1‐ol: Access to Benzo[b]fluorenes and Benzofuran‐Pyrroles

Abstract

A silver-catalyzed cycloaromatization of 1-(2-ethynyl-phenyl)-prop-2-yn-1-ol with isocyanides efficiently provides benzo[b]fluorene and benzofuran-pyrrole derivatives through a modular cascade reaction that includes a nucleophilic attack on the diyne substrate. A CÀC cross-coupling/oxygen transportation/Diels-Alder/hydrogen shift/isomerization cascade mechanistic pathway is proposed.

Silver-Mediated [3 + 2] Cycloaddition of Alkynes and N-Isocyanoiminotriphenylphosphorane: Access to Monosubstituted Pyrazoles

“…Among these reported protocols, [3 + 2] cycloadditions of alkynes and isocyanides have attracted much attention due to their high efficiency and atom-economy. In the past, substantial advances have been achieved in the use of this strategy for the synthesis of pyrroles and their derivatives (Figure A) . However, these processes often rely on isocyanides with an α-acidic hydrogen, as these species efficiently provide the “CNC” building block.…”

Silver‐Catalyzed and Silver‐Promoted Reactions of Isocyanides

“…Wang's group cooperated with Bi's group developed an AgF-catalyzed cascade reaction of methylene isocyanides 11 with 1-(2-ethynyl-phenyl)-prop-2-yn-1-ol 10 for the synthesis of 2,4-disubstituted benzofuran-pyrroles 12, although only 3 examples were provided (Scheme 2a). [7] A plausible reaction mechanism was proposed as shown in Scheme 2a. Initially, silver complex 13 was formed owing to the coordinating effect of the hydroxyl and alkynyl units.…”

“…A silver-catalyzed sequential cascade cycloaromatization of 1-(2-ethynyl-phenyl)-prop-2-yn-1-ol 194 with isocyanides 195 to provide benzo[b]fluorene 196 was reported by Wang and Bi's group (Scheme 24a). [7] Mechanistic pathway was proposed for this benzo[b]fluorene synthesis, as shown in Scheme 24b. In the first step, the Ag complex 197 was generated from the reaction of 194 with silver catalyst.…”

Recent advances in the cascade reactions of enynols/diynols for the synthesis of carbo- and heterocycles

“…In 2019, the groups of Bi and Wang reported a silver-catalyzed sequential cascade reaction of diynols 173 or 176 with isocyanides 174 in the presence of DBU, which allowed the preparation of various benzo[ b ]fluorenes 175 or benzofuran-pyrroles 178 in good yields (Scheme 62). 73 The products depended on the presence of a hydroxy group on the aromatic ring of diynols 173 . In the presence of 10 mol% of AgF, various diynols with electron-rich and deficient substituents on the aromatic rings could react with isocyanides 174 to afford the corresponding products 175 under mild conditions.…”