Acetoxonium ions from acetoxyoxiranes and orthoesters: their conversion into ethylidene acetals, rearrangement, and solvolysis

J. Grant Buchanan, Alan R. Edgar

Research output: Contribution to journalArticle

Abstract

The acid-catalysed ethylidenation of some methyl pentopyranosides has been studied and the configuration at the acetal carbon atom assigned by p.m.r. spectroscopy. There is a strong preference for the isomer in which the methyl group has the endo configuration. Several cyclic alkyl orthoacetates derived from methyl pentopyranosides have been prepared by orthoester exchange and the endo C-methyl isomer shown to preponderate. Treatment of vicinal acetoxyoxiranes and orthoacetates with boron trifluoride followed by lithium borohydride, or with diborane, yields ethylidene acetals in which the C-methyl group is endo. Rearrangements of the hexachloroantimonate salts of acetoxonium ions derived from methyl lyxo- and arabino-pyranosides, possessing trans-vicinal acetoxyl groups, have been studied. The ions having the arabino configuration are preferred in both the a and ß series. The reaction of cyclic orthoacetates of methyl ß-L-arabinopyranoside and some derivatives with dry acetic acid proceeds via an acyclic acetoxonium ion to yield only products having the L-arabino configuration. © 1976.

Original languageEnglish
Pages (from-to)289-304
Number of pages16
JournalCarbohydrate Research
Volume49
Issue numberC
Publication statusPublished - Jul 1976

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