Oxidative ring expansion of furans

The aza-Achmatowicz oxidative ring expansion of furans and its synthetic application were reviewed <1998SL105>. An interesting example of performing the Achmatowicz oxidation of furfuryl alcohol and its aza variant simultaneously on the bisfuran-containing 1,3-amino alcohol 32 in the synthesis of aza-C-linked disaccharides is depicted in Scheme 19 <2005CC1646>. 

Oxidative ring expansion of furans. The transformation into pyranones effected in the presence of camphorsulfonic acid is similar to that involving r-BuOOH-VO(acac)2, but there must be also an oxidation at the benzylic position of the original skeleton. 

From 17, the remaining retrosynthetic disconnections to readily available starting materials are relatively easy to deduce. First, syntheses of pyranones such as 17 are known to be possible through oxidative ring expansion of furan intermediates such as 18 mediated by a range of electrophilic species like dimethyldioxirane (DMDO), mCBPA, and A-bromosuccinimide. In turn, the bond between the furan ring and the adjacent hydroxy-substituted carbon atom could then be retrosynthetically cleaved to lithiated species 19 and its... 

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