Base-promoted interconversions between acetylenes and cumulenes

BASE-PROMOTED INTERCONVERSIONS BETWEEN ACETYLENES AND CUMULENES 1. ISOMERIZATIONS WITH CATALYTIC AMOUNTS OF BASE 

The composition of the products from the isomerization of an unsaturated compound under the influence of a catalytic amount of a base is governed by the relative thermodynamic stabilities of the starting compound and the product. Of particular synthetic interest are isomerizations in which there is an accumulation of an isomer in the isomerization sequence. Isolation of the desired intermediate in a reasonable state of purity is often a matter of careful selection of the base and the solvent. The following reactions are representative examples  

CH3O-CH2-CSC-CH2-OCH3 ----------------- - CH30-CH=C=CH-CH2-0CH3— -CH30(CH=CH)20CH3 

The last isomerization is remarkable in that the triple bond can shift through a long carbon chain to the terminus, where it is fixed as the (kinetically) stable acetylide. The reagent is a solution of potassium diami no-propyl amide in 1,3-di-aminopropane. In some cases alkali metal amides in liquid ammonia car also bring about contra-thermodynamic isomerizations the reactions are successful only if the triple bond is in the 2-position. 

The enyne system in the amines 828=88-8 8-882 can be reversed by potassium amide in liquid ammonia. Addition of the enyne amines to an equivalent amount of this reagent gives the potassium acetylides, K-8e8-88=88-8R2, from which the ynene amines can be obtained in excellent yields by addition of solid ammonium chloride. 

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Base-promoted interconversions between acetylenes and cumulenes... 

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