Patent US2158518 (http://l2.espacenet.com/dips/viewer?PN=US2158518&CY=gb&LG=en&DB=EPD)
. It describes a one pot synthesis of cuminic aldehyde from benzene, aluminium chloride, CuCl, isopropyl chloride and bubbling in CO gas. The end product is not pure, but a raw purification should be possible by first isolating the bisulfite adduct, followed by a fractionated distillation to isolate fairly pure cuminic aldehyde.