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In a study associated with a previous investigation1, a simplified synthesis of croweacinaldehyde, 2-methoxy-3,4-methylenedioxybenzaldehyde (IV), was desired. This aldehyde has been prepared2 from daphnetin (I) by methylenation, followed by treatment with sodium hydroxide and dimethyl sulfate and ozonization of the resulting cinnamic acid (II).
As an approach to the synthesis of IV, 1-methoxy-2,3-methylenedioxybenzene (III) was treated with phosphorus oxychloride and N-methylformanilide3. The aldehyde (IV) was obtained in a 46% yield. Since IIIis readily prepared from o-vanillin by the method of Baker and co-workers4, the present work offers a convenient synthesis of croweacin aldehyde (IV).
To 13.5 g. (0.1 mole) of N-methylformanilide there was added 15.3 g (0.1 mole) of phosphorus oxychloride. The solution was allowed to stand for 30 minutes and then 6g (0.04 mole) of 1-methoxy-2,3-methylenedioxybenzene4a (III) was added. The reaction mixture was heated at 100°C for two hours, cooled to room temperature and poured into ice-water. The solid product was collected by filtration and crystallized from dilute alcohol. The weight of material melting at 103°C (lit.2 104°C) was 3.3g (46%).
The 2,4-dinitrophenylhydrazone was prepared in the conventional manner and crystallized from ethyl acetate; mp 254-255°C (lit.2 254°C). A portion of the aldehyde was oxidized with potassium permanganate to give croweacic acid, 2-methoxy-3,4-methylenedioxybenzoic acid, melting at 155°C (lit.2 153°C).