Synthesis of 8-Prenylflavonoids Natural Products by Microwave Promoted Claisen Rearrangement

8-Prenylflavonoids are a class natural products with significant biological activities. The total synthesis of three prenylflavonoid natural products, 8-prenylquercetin-3-methylether (1), 8-prenylquerccetin-3,7,3', 4'-tetramethyl ether (2) and Artochamin C (3), was achieved through methoxymethyl protection, aldol condensation, iodine catalytic cyclization, dimethyl sulfoxide (DMSO) oxidation, O-prenylation, microwave promoted Claisen rearrangement, deprotection, O-methylation and prenyl group side chain cyclization, staring from commercially available 2,4,6-trihydroxyacetophenone and 3,4-dihydroxy benzaldehyde. The key step of microwave promoted Claisen rearrangement formed 8-C-prenylflavonoids from 5-O-prenylflavonoids was investigated. All the synthesized compounds were confirmed by H-1 NMR. C-13 NMR and MS techniques.