Syntheses and Stability of Alkynyl S,N-Acetals Derived from 2-Propynals

Abstract

Two types of synthetic methods for S,N-acetals derived from 2-propynals were described. Thioformamides, lithium acetylides, and alkylating agents were the key substrates. In the first method, methylation of thioformamides with MeOTf followed by reacting with lithium acetylides led to the title compounds. As an alternative method, the direct addition of lithium acetylides to thioformamides gave lithium thiolates, which was then alkylated. With these two methods, a wide range of derivatives including bis-S,N-acetals were provided, and their stability was influenced by the substituents at the alkynyl carbon atom. The introduction of silyl group enhanced the stability effectively.