Organocatalyzed Knoevenagel-addition-simple access to carbon chain-elongated branched carbohydrates

Chain elongations of unprotected carbohydrates via a Knoevenagel-addition are described. The reactions were carried out in the presence of catalytic amounts of tertiary amines. The C-C bond formation processes yielded high syn-stereoselectivities. Additionally, through an asymmetric induction controlled by the configuration of the deployed carbohydrates pyranoid or furanoid products were formed. Yields were strongly increased by the use of 5-protected carbohydrates in these transformations.