Cycloaromatization of α-Oxoketene Dithioacetals with 5-Lithiomethyl-3-methylisoxazole: A New General Method for the Synthesis of Substituted and Annulated 1,2-Benzisoxazoles
作者:Dinah Pooranchand、J. Satyanarayana、H. Ila、H. Junjappa
DOI:10.1055/s-1993-25840
日期:——
A new route to 6-substituted 4a-e and 5,6-annulated 4f-l 1,2-benzisoxazoles has been developed through regioselective 1,2-nucleophilic addition of 5-lithiomethyl-3-methylisoxazole (2) to a variety of α-oxoketene dithioacetals 1a-l and subsequent cycloaromatization of the resulting hydroxyacetals in the presence of boron trifluoride -diethyl ether complex. The corresponding 4-dethiomethylated benzisoxazoles 6a-d were also synthesized by cyclocondensation of β- methylthio-α,β-unsaturated ketones with 2 under identical conditions. The reaction was further extended for the synthesis of (6-benzisoxazolyl)-substituted ethylenes 9a-e, butadienes 9f-g and hexatriene 9h by subjecting α-cinnamoyl ketene dithioacetals 7a-e and their higher enyl analogs 7f-h to similar transformations.
通过将 5-硫代甲基-3-甲基异噁唑(2)与多种δ-±-氧代酮二硫代乙醛 1a-l 进行 1,2-亲核加成,并随后在三氟化硼-二乙基醚络合物存在下对所生成的羟基乙醛进行环芳基化,开发出了一条制备 6-取代型 4a-e 和 5,6-annulated 4f-l 1,2-苯并异噁唑的新途径。在相同的条件下,δ-甲硫基-δ,δ-不饱和酮与 2 环缩合,也合成了相应的 4-二硫甲基化苯并异噁唑 6a-d。通过使δ-肉桂酰基酮二硫代乙醛 7a-e 及其高烯基类似物 7f-h 发生类似的转化,该反应进一步扩展到合成(6-苯并异噁唑基)取代的乙烯 9a-e、丁二烯 9f-g 和己三烯 9h。