Reactions of cyclononatetraenyl dianion with electrophiles: geometry and conformation of 1,3,6-cyclononatrienes

Carbonation of the parent cyclononatetraene dianion gives a mixture of (a) the minor products, 1,3,6-cyclononatriene-5,9- and 5,8-dicarboxylic acids, and (b) the major product, bis(5-carboxy-1,3,6-cyclononatrien-9-yl). In contrast, the 9,9-dimethyl dianion affords almost entirely a mixture of the two monocyclic diacids. Similar results are obtained on trimethylsilylation. Conformations of the products are discussed.