ISOPIMARIC ACID

Evidence is presented for the epimeric character of the C-13 substituents in pimaric and isopimaric acids and for the nuclear double bond location in isopimaric acid. This work, coupled with recent synthetic work and rotatory dispersion evidence, permits assignment of the structure and stereochemistry IV to isopimaric acid. Hydroboration and selenium dioxide oxidation of the acid are described.

NITROGEN-FREE DERIVATIVES OF ATISINE: AN EXTREMELY HINDERED CARBOXYLIC ACID

The action of nitrous acid on azomethines derived from the alkaloid atisine gave a good yield of nitrogen-free hemiacetal, thus providing the first means of removing the nitrogen from the diterpenoid alkaloids. Transformation products of the hemiacetal, including the most hindered carboxylic acid hitherto known, are described. The internal oxidation–reduction reactions encountered in this and related work are discussed.

THE STEREOCHEMISTRY OF THE PIMARIC ACIDS

Isodextropimaric and dextropimaric acids have been shown to have the same stereochemistry at C1, C11, and C12, but to be epimeric at C7. A critical survey is made of the present evidence with regard to the stereochemistry at C13 in these acids. Preliminary experiments on the action of formic acid on isodextropimaric acid are reported.