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5H-[1,3]dioxolo[4,5-f]indole (5,6-Methylenedioxyindole) is an indole analogue commonly used in the preparation of other biologically active molecules, such as fungicides and anticancer agents.

The general procedure for the synthesis of 5,6-methylenedioxyindole from [2-(1,1-dimethylethoxy)-2-oxoethyl]triphenylphosphonium inner salt and 6-nitropiperonyl aldehyde was as follows: In a 50 mL round-bottomed flask equipped with a magnetic stirrer, 6-nitropiperonyl aldehyde (2 mmol), [2-(1,1-dimethylethoxy)-2-oxoethyl]triphenylphosphonium inner salt (2.2 mmol), triphenylphosphine (4.6 mmol), and diphenyl ether (10 mL) were added in sequence. mmol), triphenylphosphine (4.6 mmol) and diphenyl ether (10 mL). The reaction mixture was heated to 260 °C and kept for 1 hour. Upon completion of the reaction, the mixture was cooled to room temperature and the crude product was directly sampled onto a silica gel column. Separation was carried out by column chromatography using a gradient elution system of petroleum ether to 3:1 (v/v) petroleum ether/ethyl acetate to purify the target product 5,6-methylenedioxyindole.

[1] Tetrahedron Letters, 2018, vol. 59, # 19, p. 1851 - 1854