Gram-Scale Synthesis of Loganetin from S-(+)-Carvone

Loganetin is the aglycone moiety of loganin that has a 5,6-fused bicyclic framework and exhibits a wide range of interesting biological activities. A gram-scale synthesis of loganetin has been accomplished from the readily accessible S-(+)-carvone. The key reactions of the synthesis are a Favorskii rearrangement to introduce four stereocenters and a sulfuric acid-meditated deprotection/cyclization reaction to assemble the sensitive dihydropyran ring with complete stereoselectivity. This work also enables us to synthesize C1 methoxy loganetin and the enantiomer of loganetin successfully.