Direct Aldolization of Unprotected Fructose to Bio-Based Surfactants

A new alkylation mode of fructose was developed by direct aldolization of unprotected fructose with fatty aldehydes as alkylating agents. The reaction occurs in the presence of a base in a mixture of water/EtOH at 60 °C under microwave irradiation. Trimethylamine was found the most effective base for the aldolization of fructose with short chain aldehydes (C4–C8) while better results were obtained with K2CO3 in association with tetrabutylphosphonium bromide (TBPB) for long chain aldehydes (C8–C12). The corresponding alkylated fructose were obtained as mixture of 3 main tautomers (the β-pyranoid form being the predominant isomer) and were isolated with 31–46% yield. These aldolization products were also reduced under hydrogen to give the corresponding alkylated heptaols with 84–96% isolated yields.