Stereochemistry of cyclic compounds Communication 8. Condensation of cis-1,2,4a,5,8,8a-hexahydro-4a, 7-dimethyl-4-vinylnaphthalene with citraconic anhydride

Summary

• 1. The condensation of 1,2,4a,5,8,8a-hexahydro-4a, 7-dimethyl-4-vinylnaphtlalene (1) with citraconic anhydride was studied, and all four theoretically possible stereoisomeric cis anhydrides (II; a, b, c, and d) were isolated. The structures of these, as ortho-addition products, were proved by dehydrogenation of the corresponding cis acids (III; a, b, c, and d) into 1,7-dimethylphenanthrene. No diene-synthesis products formed by para addition were detected.

• 2. When the isomeric cis acids (IIIa, IIIb, and IIIc) and the derivatives (anhydrides, diesters, lactone acids, and lactone esters) were hydrogenated in presences of a platinum catalyst, only one molecular proportion of hydrogen was observed — by reaction at the double bond in the ring A. Under these conditions the second double bond (in the ring G) was not hydrogenated. A peculiar feature in all of these hydrogenation reactions was their steric selectivity, which resulted in the formation of individual hydrogenated derivatives in which the 3- and 10-methyl groups always have a cis arrangement.

• 3. Isomerization of the cis diester (VII) with sodium methoxide yielded the trans acid (IX), which was hydrogenated to the trans acid (XI).

• 4. The isomeric cis acids (IIIa) and (IIIb), which were obtained in predominating amount, differ in the disposition of the substituents at C-5 and C-10, for double-bond migration in the diesters (VIII) and (XXII) yields different cis diesters (XIV) and (XXII) having an inter-ring double bond. On the other hand, displacement of the double bond in the cis diester (VIII) and (XXV) gives, in each case, the same cis diester (XIV), so that the isomeric cis acids (IIIa) and (IIIc) differ only in the disposition of hydrogen at C-8.

• 5. The cis acids (IIIb) and (XVI), unlike the isomeric cis acids (IIIa) and (VI), are extremely prone to lactonization, and even when treated with diazomethane they give mainly the cis lactone esters (XVII) and (XX), instead of the corresponding diesters. This difference is in accord with their spatial structures; in the cis acid (IIIb), in which there is a trans arrangement of the 10-methyl and 13-carboxyl, the 10-methyl has no screening effect, and as a result lactonization is facilitated.