Peracid Oxidation of 4-Isoxazolines as a Method for the Preparation of α, β-Unsaturated Carbonyl Compounds

Article abstract of DOI:10.1021/jo00245a021

A study of the MCPBA peracid oxidation of a series of 4-isoxazolines has been carried out.A variety of isoxazolines were synthesized by treating nitrones with electron-deficient alkynes.An alternate approach involves dipolar cycloaddition of nitrones with activated allenes followed by a subsequent base-catalyzed isomerization of the initially formed cycloadduct.Treatment of the 5-exo-methyleneisoxazolidine derived from the reaction of N-benzylidenemethylamine N-oxide and (phenylsulfonyl)propadiene with LDA followed by γ-alkylation also produced substituted 4-isoxazolines.The peracid oxidation of the isoxazoline ring afforded α,β-unsaturated carbonyl compounds in excellent yield.Reductive cleavage of the sulfonyl group of some of the enones was achieved by initial protection of the carbonyl functionality by cyanosilylation using trimethylsilyl cyanide, and this was followed by aluminum-amalgam reduction.The cycloaddition-oxidation procedure provides an attractive route to synthesize α,β-unsaturated ketones since it avoids acidic or basic conditions.