Ferrocenium salts with different counterions can act as mild, one-electron oxidants for organic reactions, and can also be served as catalyst. Some ferrocenium salts are readily available (FcPF₆, Fc = ferrocenium cation), and some are air and moisture tolerant, such as ([FcB(OH)₂]SbF₆), where the cyclopentadienyl ring bears a boronic acid substituent. Previously, we reported the efficacy of FcPF₆as a catalyst for etherification reactions of tertiary propargylic alcohols with one or two aromatic substituents. To date, we developed reactions with different cyclopropyl-substituted propargylic alcohols utilizing CH₂Cl₂ as the solvent and FcPF₆ (5 mol%) as the catalyst at 40 ^oC for 2 hours. This resulted in the successful formation of ene-yne or cyclopropyl substituted products, which highlights the importance of substituents present on the propargylic substrates. More electron-rich substituents like thiophene presumably form a carbocation intermediate and reacted much faster than the phenyl substituent.
Different substituents on the propargylic alcohol seem to influence the speed of the reaction. Mechanistic studies point toward an ionic-, S_N1 mechanism. We have compared the reactivity of [FcB(OH)₂]SbF₆ as a catalyst (5 mol%) for the etherification of propargylic alcohols with other ferrocenium catalysts under identical reaction conditions. The catalyst [FcB(OH)₂]SbF₆shows better reactivity than FcPF₆. Relying on our previous knowledge, we developed a new system with ferrocenium salts as a promoter to activate glycosyl halide donors. We performed glycosylation between glycosyl halide donors (Cl and F substituents) and glycosyl acceptors (1⁰ and 2⁰). We were able to obtain disaccharides in 10 – 95% isolated yields with α/β ratios from 1/1 to β-only.

Deva Saroja Talasila

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