I've done some more searching on Espacenet and again found two interesting patents about Piperonal synthesis. Here they are.
A process for preparing piperonal Patent US4157333 (http://l2.espacenet.com/dips/viewer?PN=US4157333&CY=gb&LG=en&DB=EPD)
Abstract
A process for preparing piperonal which compriss the steps of reacting 1,2-methylenedioxybenzene with an N-alkylformanilide and a condensing agent comprising one or more compounds selected from the groups consisting of phosgene, phosphorus oxychloride, phosphorus oxybromide, thionyl chloride, thionyl bromide, sulfuryl chloride, sulfuryl bromide, phosphorus trichloride and phosphorus pentachloride and then hydrolizing the resulting reaction product.
Preparation process for piperonal Patent US5095128 (http://l2.espacenet.com/dips/viewer?PN=US5095128&CY=gb&LG=en&DB=EPD)
Abstract
Preparation process for piperonal by decarboxylating oxidation of 3,4-methylenedioxymandelic acid by nitric acid in aqueous medium in the presence of HCl.
Life without chemistry would be a mistake.
Some more patents were found on Espacenet. But unfortunately no abstacts are available.
Process for preparing piperonal Patent GB1591268 (http://l2.espacenet.com/dips/viewer?PN=GB1591268&CY=gb&LG=en&DB=EPD)
Process for the Preparation of Methylenedioxybenzene, 1,3-benzoxathiole and derivatives thereof Patent GB1097270 (http://l2.espacenet.com/dips/viewer?PN=GB1097270&CY=gb&LG=en&DB=EPD)
Life without chemistry would be a mistake.