Abstract
Treatment of geranoyl chloride (20) with triethylamine in toluene at reflux gave the vinylketene 21 which underwent a [2 + 2] cycloaddition to give 7,7-dimethyl-2-methylenebicyclo[3.1.1]heptan-6-one (24) in 43% yield. Isomerization over Pd gave chrysanthenone (6) in quantitative yield. Wolff-Kishner reduction gave d-pinene (5) in 70% yield. A similar sequence of reactions starting from (ZJS)- and (F^E)-famesoyl chloride gave ketones 51 and 57, which were converted to d-cts-bergamotene (8) and ß-tnms-bergamotene (9), respectively. d-Copaene (10) and ß-ylangene (11) were prepared from 57 by a three-step sequence. Treatment of the imidazolide 59 with tri-n-butyltin hydride in toluene at reflux gave a 46% yield of a 1:1 mixture of 10 and 11. Selenium dioxide oxidation of 11 gave the antitumor agent lemnalol. The mechanisms of the regiospecific ketene generation and the [2 + 2] cycloaddition reaction have been explored, and the reactivity of the novel bicyclo[3.1.1 ]heptanones has been examined.