The prenyl group: a versatile hydroxy protecting group, removable chemoselectively under mild conditions

Iodine in dichloromethane (in the presence of 3 Å molecular sieves for acid-sensitive substrates) and 2,3-dichloro-5,6-dicyanoquinone (DDQ) in dichloromethane–water (9:1) are mild and efficient methods to cleave prenyl ethers. These reaction conditions are compatible with the presence of other protecting groups such as acetals, acetates, allyl, benzyl and TBDPS groups. Exposure of aryl prenyl ethers to iodine led to the formation of 3-iodo-2,2-dimethylchroman derivatives in acceptable yields via a tandem Friedel–Crafts/iodocyclization reactions. Facile one-step transformation of two iodinated dimethylchroman derivatives allowed the synthesis of natural flavanoids among them: zanthoxylol, an anti-sickling agent.