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Organic Lab Reactions 162

Organic Lab Reactions 162 - THE HYDROGEN FLUORIDE METHOD...

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THE HYDROGEN FLUORIDE METHOD 157 » The Hydrogen Fluoride Method In 1939 it was observed 16 that anhydrous liquid hydrogen fluoride is an excellent agent for effecting intramolecular acylation of aryl sub- stituted aliphatic acids. Since that time a number of cyclizations have been performed with this reagent (Table VIII). The general procedure consists in allowing a solution of the acid in hydrogen fluoride to stand for a few hours in an open vessel at room temperature. The excellence of.the method lies in the simplicity of manipulation and in the consistently good yields. The examples in Table VIII include the cyclizations of a 'number of different types of arylbutyric and arylpropionic acids. Of the twenty-nine ring closures, nineteen were accomplished in yields of 87% or better. The unique cyclizing power of hydrogen fluoride is shown with 7-(4-methoxy-3- biphenyl)-butyric acid (formula XXXVII). Ring closure was realized, if only to the extent of 16%, whereas other methods, including the Friedel-Crafts, were unsuccessful.
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