Propargylation of arabinogalactan with propargyl halides—a facile route to new functionalized biopolymers

•An efficient method to propargylation of arabinogalactan was developed.•Etherification of polysaccharide was carried out in aqueous alkaline/toluene system.•Degree of substitution of arabinogalactan propargyl ethers attains 2.8.•The structure of ethers was confirmed by IR and 13C NMR.•Allenyl ethers and silver acetylides of arabinogalactan were prepared.

New arabinogalactan propargyl ethers with degree of substitution (DS) up to 2.8 have been obtained by propargylation of arabino-3,6-galactan (AG) with propargyl bromide (PB) in the two-phase system 30–60% КОН aqueous solution/toluene in the presence of triethylbenzylammonium chloride (TEBAС) or without catalyst (ambient temperature, 1–24 h) in 20–87% yields. The highest yields have been reached using TEBAС as phase-transfer catalyst, though the non-catalytic version proves to be also efficient (DS 2.8, 70% yield). The propargylation of AG is less effective in the systems MОН (M = Na, K)/DMSO. DS of propargyl AG reaches 1.8 (70% yield) when propargyl chloride is used as propargylating agent, while with PB under the same conditions DS value does not exceed 0.4–0.6, the yields being 44–65%. Under the action of t-BuOK/DMSO system, the AG propargyl ethers have been isomerized to the corresponding unstable allenyl ethers. AG propargyl ethers with DS 2.0 have been almost exhaustively metallated with Ag2O/NH3 system to give AG–Ag acetylides derivatives with Ag/CC ratio equaling 0.95.

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