Cascade Cyclization of 1,5-Diynols and (RO)2P(O)SH to Construct Benzo[b]fluorenyl S-Alkyl Phosphorothioates under Catalyst-Free Conditions

An efficient and practical cascade cyclization of 1,5-diynols with (RO)2P(O)SH as the acid promoter and nucleophile under mild conditions was developed. A variety of highly substituted benzo[b]fluorenyl-containing S-alkyl phosphorothioates were successfully constructed in moderate to excellent yields. Furthermore, this protocol exhibited good functional group tolerance, a broad substrate scope, and potential practical applications, with water as the only byproduct. The reaction proceeded with allenyl thiophosphate as a key intermediate, followed by a Schmittel-type cyclization process to produce the target product.

Direct Synthesis of Benzo[b]fluorenyl Thiophosphates via Tandem Cyclization of Diynols with (RO)2P(O)SH

A general and metal-free protocol for the construction of benzo[b]fluorenyl thiophosphates was developed through the cascade cyclization of easily prepared diynols and (RO)₂P(O)SH, with water as the only byproduct. The novel transformation involved the allenyl thiophosphate as the key intermediate, followed by Schmittel-type cyclization to achieve the desired products. Notably, (RO)₂P(O)SH acted not only as a nucleophile but also as an acid-promoter to initiate the reaction.

Gold-catalyzed multicomponent reactions

Multicomponent reactions (MCRs) have emerged as an important branch in organic synthesis for the creation of complex molecular structures. This review is focused on gold-catalyzed MCRs with a special emphasis on the recent developments.

Synthesis of 1H-isoindoliums by electrophile-mediated cascade cyclization/iodination of propargylamine-based 1,6-diynes

A highly regio- and chemoselective synthesis of 1H-isoindoliums through a facile and novel cascade cyclization reaction of propargylamine-based 1,6-diynes under mild conditions has been developed. Different functional groups were compatible under the optimized reaction conditions, giving the corresponding products in up to 94% yields. Upon treatment with a base, the alkyne moiety of 1H-isoindoliums could be further transformed to allenes in excellent yields.

Gold-Catalyzed Tandem Annulations of Pyridylhomopropargylic Alcohols with Propargyl Alcohols

A gold-catalyzed tandem annulation of propargylic alcohols and pyridylhomopropargylic alcohols is achieved, providing an atom-economical approach to a diverse set of polycyclic dihydrobenzofurans in good yields. The reaction proceeds via the 5-endo-dig cyclization/Meyer-Schuster rearrangement/Friedel-Crafts-type pathway. In this way, three C-C bonds and one C-O bond form to give a polycyclic skeleton in a one-pot process. Moreover, the products exhibit unique optical properties, which reveal their potential application value.

Gold nanoparticles stabilized by PEG-tagged imidazolium salts as recyclable catalysts for the synthesis of propargylamines and the cycloisomerization of γ-alkynoic acids

Water-soluble gold nanoparticles prepared in the presence of PEG-tagged tris-imidazolium bromide, containing Au(0) and Au(i) species, are reusable catalysts.