Synthesis of a (β-acetamido-α-acetoxyethyl)boronic ester via azido boronic esters
(Azidomethyl)boronic esters of 1,2-dicyclohexyl-1,2-ethanediol ( DICHED ) and pinanediol have been prepared from the corresponding (bromomethyl)boronic esters. Conversion to (2-azido-1-chloro- or bromoethyl)boronic esters by reaction with a (dihalomethyl)lithium followed. Attempted displacement of halide from DICHED (2-azido-1-haloethyl)boronates with alkoxides failed. Reaction of either pinanediol or DICHED (2-azido-1-chloromethyl)boronate with sodium acetate in acetic acid yielded the 1-acetoxy derivative as a ~1:1 mixture of diastereomers, indicating probable involvement of an α-boryl carbocation intermediate. Hydrogenation of the pinanediol azido boronic ester over platinum in a solution of hydrogen chloride in dioxane was accompanied by deacetylation to form the impure (2-amino-1-hydroxyethyl)boronic ester hydrochloride. Attempted purification of this material resulted in deboronation to ethanolamine. Acetylation yielded pinanediol (2-acetamido-1-acetoxyethyl)boronate.
Matteson, Donald S.,Maliakal, Davis,Fabry-Asztalos, Levente
p. 2258 - 2262
(2008/09/21)
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