Application of the triisobutylaluminum-promoted reductive rearrangement tosucrose-5-enes

Carbohydrate-based vinyl acetals (5-hex-enopyranosides) undergo reductive r earrangement with triisobutylaluminum (TIBAL) to afford highly functionaliz ed cyclohexanes in which both the aglycon and anomeric stereochemistry are retained. Here, we report the first application of this process to the rear rangement of hex-5-enopyranosides of sucrose in which the interglycosidic o xygen atom of the vinyl acetal system links the anomeric centers of both mo nosaccharide units. The sucrose-derived 5-hex-enopyranoside 1 undergoes smo oth reductive rearrangement with TIBAL to afford the (1 -->2 ') ether-linke d pseudo-disaccharide 2 in 34% yield. The rearrangement is accompanied by s ome loss of stereochemical integrity at C-2 ' due to a competitive exo-clea vage of the interglycosidic (O-C2 ') bond, hence diastereomers at C-2 ' are also obtained in 12% yield. The 4-O-allyl-protected sucrose-5-ene 3 is sim ilarly transformed into the corresponding (1 -->2 ') ether-linked pseudo-di saccharide 4, illustrating the compatibility of the allyl group with the TI BAL reaction conditions.