"Furan Endwise Peeling" of Celluloses: Mechanistic Studies and Application Perspectives of a Novel Reaction

The mechanism of a novel reaction type, the “furan endwise peeling” reaction, has been studied. Making extensive use of experiments on model compounds, the structural prerequisites to the reaction were found to be a 2‐hydroxpyran β‐glycosidically linked to a 2‐(2‐furyl)ethyl moiety. Proceeding from the reducing end of the celluloses, the reaction causes the one‐by‐one loss of anhydroglucose units (AGUs) which are concomitantly converted into 2‐(tetrahydroxybutyl)furans (4) by co‐reacting with 1,3‐dicarbonyl compounds such as ethyl acetoacetate (1). The key step of the reaction is the formation of a furan at the reducing end followed by the attack of the 2‐OH group of the last‐but‐one AGU at this terminal furan. The intermediate, unstable dioxepane fragments by cleavage of the glycosidic bond. The terminal AGU is released as a substituted furan, the “new” reducing end reacting immediately with the 1,3‐dicarbonyl component to form a new terminal furan which, in turn, undergoes the same cycle. The “furan endwise peeling” reaction represents an interesting way to convert cellulosic biomass by an easy procedure into substituted furans that are valuable fine chemicals with multiple uses.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)