Benzene → Benzopyran

Participants

Reaction Steps

The compound 4 is refluxed under heating in a solvent such as benzene, chlorobenzene, toluene and xylene, in the presence of an acid catalyst such as p-toluenesulfonic acid and camphor sulfonic acid, using a Dean-Stark apparatus, while removing liberated water, or the hydroxyl group of compound 4 is activated into acetyl, trifluoroacetyl, methanesulfonyl, trifluoromethanesulfonyl or p-toluenesulfonyl using acetic anhydride, trifluoroacetic acid, methanesulfonyl chloride, trifluoromethanesulfonyl chloride or p-toluenesulfonyl chloride and removing the activated hydroxy using a base such as triethylamine, N-methylmorpholine and diazabicycloundecene, particularly preferably diazabicycloundecene, to give a chromene (compound 5 wherein R1, R2 and R3 are as defined above).

Provenance & Evidence