Studies toward the total synthesis of 1-oxacephalosporins 2: synthesis and reactions of oxazolinoazetidinones bearing a γ,γ'-bis-oxygen-functionalized β-methylbutenoate side chain
The racemic title compounds 3 were prepared by chlorolysis of the appropriate 3-acylamino-4-methylthio-2-azetiainones 1. The cleavage of the 1,3-dioxane ring was accomplished by proton and Lewis acids to form the intermediate diols 8, which rapidly undergo lactonization with formation of hydroxymethyl substituted butenolides 10. Neither 8 nor 10 cyclizes to give the 1-oxacephems 9 or 12. A convenient