Tandem Claisen Rearrangement/6-endo Cyclization Approach to Allylated and Pren­ylated Chromones

Allyl, dimethylallyl and prenyl ethers derived from o‐acylphenols reacted upon microwave irradiation to form C‐allylated or ‐prenylated chromone derivatives, depending on the substitution pattern of the arene and the allyl substituent. The reaction proceeds through a tandem Claisen rearrangement and 6‐endo‐trig or 6‐endo‐dig cyclization sequence. For prenyl ethers, the tandem sequence can be extended by a Cope rearrangement to furnish 6‐prenylchromones. The method is potentially useful for the synthesis of natural products and drugs. Prenyl‐ and allylchromones are accessible from readily available aryl alkynyl or aryl alkenyl ketones through a microwave‐promoted tandem Claisen rearrangement and 6‐endo‐trig or 6‐endo‐dig cyclization sequence. Application of the method to the synthesis of the natural product pestaloficiol J is demonstrated.