Reactions with and in Anydrous Hydrogen Fluoride, 13. A Convenient One‐Pot Synthesis of Glucofurano[2,1‐d]oxazolines with an Additional 3,5,6‐Orthoester Function
The reactions of dioxolanylium and oxazolinium ions, formed in anhydrous HF from N-acylated 2-amino-2-deoxy-D-glucoses and one equivalent of carboxylic acid anhydride or chloride, were investigated by treatment of their HF solutions with triethylamine/alkane or triethylamine/ether systems. Thus, the 2-acylamido-2-deoxy-D-glucoses 1 and 2 react with acetic anhydride, dodecanoic anhydride or pivaloyl chloride in anhydrous HF at −30°C to give 5,6-dioxolanylium ions. On treatment with formic acid at room temperature they undergo further reaction to yield the thermodynamically favored 3,6-anhydro derivatives. The glucofurano-oxazolines 3–5, containing an orthoester substructure, as well as the 3,6-anhydro-D-glucofuranose derivatives 6 and 7 can be isolated after treatment of the HF solutions with triethylamine. The oxazoline derivative 4 was used as glycosyl donor for methanol giving the methyl glycoside 8 without cleavage of the orthoester moiety.