Furans and pyrans derivatives from the hydroformylation of ethyl ricinoleate and castor oil

The hydroformylation of ethyl ricinoleate and castor oil using HRh(CO)(PPh3)3 as catalyst precursor was performed under mild conditions to achieve complete conversion of double bonds in 6 h. Due to an intramolecular condensation between carbonyl and hydroxyl groups, 2-hydroxy-furans are obtained as major product being the aldehyde only a minor product. However, aldehydes can be selectively obtained if the hydroxyl group of ethyl ricinoleate or castor oil was silylated before the hydroformylation reaction. In order to understand the role of rhodium in these cyclization process, these hydroxy-silylated aldehydes were deprotected in the absence of the metal. It was observed that the free hydroxide readily reacts with the aldehyde group, producing the furans and pyrans, which indicates that rhodium is not required to the furanization reaction.