Diels-alder reactions with ethyl 1-benzofuran-3-carboxylates
摘要:
Substituted salicylaldehydes reacted with ethyl diazoacetate to give ethyl 1-benzofuran-3-carboxylates containing various substituents in the aromatic ring. The Diels-Alder reaction of these compounds with Danishefsky's diene was regioselective, and it provided an effective method for the construction of the heterocyclic skeleton of hexahydrodibenzo[b,d]furan-7-one or tetrahydrodibenzo[b,d]furan-7-one. The adducts were found to undergo rearrangement to substituted 4'-hydroxybiphenyl-2-yl methyl carbonates during column chromatography on silica gel.
A nine-step stereoselective formalsynthesis of (±)-morphine from readily available o-vanillin is presented. The carbocyclic structure of morphine was quickly assembled through an orchestration of the intermolecular Diels–Alder/Claisen/Friedel–Crafts sequential reaction. This approach involves many one-pot procedures and no protecting groups, and only a few chromatographic purifications are required