Hydrozirconation/bromination, followed by a Michaelis-Arbuzov reaction, as a convenient approach towards polyfunctional glycosylphosphonates

Preparation of propargyl 1,2-orthoesters of carbohydrates: From side reactions in dichloromethane to optimized reaction conditions in acetonitrile

In this note, supercritical fluid chromatography coupled to high-resolution mass spectrometry (SFC-HRMS) has been used to identify a chloro glycoside formed during the preparation of propargyl 1,2-orthoesters in dichloromethane. Additional studies revealed that 20-40% of this side-product was obtained depending on the source of anhydrous solvent, and that tetrabutylammonium iodide amplifies this side-reaction. Finally, a reliable procedure was developed in acetonitrile to prepare these glycosyl donors from perbenzoylated bromo glycosides in manno, gluco and galacto series in 63-74% yield.

Access to 5-bromopentanal and 6-bromohexanal derivatives via the bromination/hydrolysis of C,O-bis-zirconocenes generated from unsaturated Weinreb amides

Access to 5-bromopentanal and 6-bromohexanal derivatives from Weinreb amides is described. The method relies on the sequential C-bromination/zircona-aminal hydrolysis of bis-C,O-zirconocenes, which are generated in situ from unsaturated Weinreb amides using Schwartz's reagent. Synthetic illustrations of such bromo-aldehydes, which can act as carbocycle and heterocycle precursors, are also presented.