Model studies on the synthesis of milbemycin β3
Abstract
2,4-Di(lithio-oxy)penta-1,3-diene and 2,4-di(lithio-oxy)-3-methylpenta-1,3-diene condensed with tetrahydropyran-2-one to give 2-methyl- and 2,3-dimethyl-1,7-dioxaspiro [5.5] undec-2-en-4-one; subsequent reduction gave the derived alcohols (LiAlH4) and 2,3-dimethyl-1,7-dioxaspiro [5.5]undec-3-ene (LiAlH4– AlCl3); the milbemycin β3 unit ethyl 2-acetyl-4-hydroxy-5-methylbenzoate was prepared from ethyl 2-(4-chlorophenylthio)-4-oxopent-2-enoate and (E)-1-methoxy-2-methyl-3-trimethylsilyloxy-buta-1,3-diene via a Diels–Alder reaction.