Stereochemistry of cyclic compounds Communication 4. Condensation of 1-vinylcyclohexene with citraconic anhydride

Abstract

1. A study has been made of the diene condensation of 1-vinylcyclohexene (I) with citraconic anhydride (II), and it has been shown that in this reaction the ortho and meta adducts (III) and (IV) are formed in the proportions of 5 : 1 and in an overall yield of 92%. Hydrolysis of the cis anhydrides (III) and (IV) yielded the corresponding cis-1,2,3,5,6,7,8,8a-octahydromethyl-1,2-naphthalenedicarboxylic acids (V) and (VI), and the structures and spartial configurations of these have been proved. 2. The unsaturated cis anhydrides (III) and (IV), and also the corresponding cis acids (V) and (VI), are readily hydrogenated in a sterically selective manner at a platinum catalyst into the corresponding saturated compounds (VII), (VIII), (XV), and (XVI), the direction of the reaction being determined by the screening effect of the cis substituents at (C-1)-(C-8a) on the double bond. 3. By the isomerization of the cis diesters (IX), (X), and (XVII) with the aid of sodium methoxide, the corresponding trans acids (XI), (XII), and (XIX) have been obtained in good yield, and this reaction may provide a convenient method for their synthesis. The hydrogenation of the unsaturated trans acid (XIX), unlike that of the isometric trans acid (XI), is not sterically selective. 4. By treatment with acetyl chloride in a mixture of acetic anhydride and acetic acid, the cis diesters (IX) and (XVII) have been caused to undergo isomerization with displacement of the double bond to give the cis diesters (XIII) and (XXI). Further isomerization of these in presence of sodium methoxide yields the trans acids (XIV) and (XXII), which have an inter-ring double bond. These acids, as also the esters (XIII) and (XXI), cannot be hydrogenated over a platinum catalyst under the usual conditions. 5. Irrespective of the temperature (within the range 100–230°), the condensation of 1-vinylcycohexene with citraconic anhydride proceeds by exo-addition.