(E)-4-coumaraldehyde + reduced [NADPH--hemoprotein reductase] + O2 = (E)-caffeyl aldehyde + oxidized [NADPH--hemoprotein reductase] + H2O + H(+)
(e)-4-coumaraldehyde + reduced [nadph--hemoprotein reductase] + o2 = (e)-caffeyl aldehyde + oxidized [nadph--hemoprotein reductase] + h2o + h(+)