Facile Synthesis of 4-Hydroxycinnamaldehydes

4-Hydroxycinnamaldehydes are key intermediates in the biosynthesis and degradation of lignins, the class of aromatic polymers that are responsible for much of the recalcitrance in converting lignocellulosic biomass to liquid fuels. Access to these aldehydes is needed for investigation of biochemical pathways, a crucial step in manipulating lignin biosynthesis for cost-effective biofuels production. Here, p-coumaraldehyde, caffealdehyde, coniferaldehyde, and sinapaldehyde were efficiently prepared by coupling the corresponding 4-hydroxycinnamic acids with N,O-dimethylhydroxylamine, followed by selective reduction with diisobutylaluminum hydride. The protecting-group-free total synthesis of these aldehydes does not require the use of a controlled atmosphere, nor chromatographic purification; thus, although it remains in the realm of moderately well-trained synthetic chemists, the syntheses are particularly convenient.