Cascade Cyclization of 1,5-Diynols and (RO) 2 P(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) 2 P(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.