کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
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1323155 | 977270 | 2008 | 5 صفحه PDF | دانلود رایگان |
![عکس صفحه اول مقاله: Synthesis of a (β-acetamido-α-acetoxyethyl)boronic ester via azido boronic esters Synthesis of a (β-acetamido-α-acetoxyethyl)boronic ester via azido boronic esters](/preview/png/1323155.png)
(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.
A (2-azido-1-chloroethyl)boronic ester resisted alkoxide substitution but yielded a mixture of epimeric acetates with sodium acetate via a carbocationic route. Azide hydrogenation in acid was accompanied by acetate cleavage to an α-hydroxy boronic ester that was unstable unless acylated promptly.Figure optionsDownload as PowerPoint slide
Journal: Journal of Organometallic Chemistry - Volume 693, Issue 13, 15 June 2008, Pages 2258–2262