Studies in terpene synthesis: a model investigation

Abstract

In an attempt to find a feasible synthetic route to the C/D ring system in the terpene kaurene and the terpene alkaloids veatchine and garryine a model synthesis was undertaken. The benzal derivative (1) of 1-hydrindanone on alkylation with methallyl iodide gave (2). The stereochemistry of the ring fusion of (2) was not established, but may be considered to be cis by analogy to similar alkylations. Ozonolysis of (2) gave (3) having carbonyl bands at 5.55, 5.70, and 5.83p. (methylene chloride). Compound (3) was considered to be the anhydride, rather than the expected triketone, on the basis of elemental analysis; and a concerted mechanism, involving the ozonide I, was proposed to account for its formation; and on basic hydrolysis of (3) compound (4), having infrared absorption not unlike that of a diacid, was obtained. Lithium aluminum hydride reduction of (2) gave (5), which formed the acetoxy derivative (6). Ozonolysis of (6) gave (7), which was converted to the diketo alcohol (8) by basic hydrolysis. Compound (8) was converted to the acetate (9), which was considered to be an isomer of (7) by mixed melting point depression, since the infrared spectra of (7) and (9) were identical. More work needs to be done to establish the configuration of (7) and (9). Yields in the reactions were not high enough to merit application of the method in the synthesis of the terpenes considered.