Campnosperma Exudates. The Optically Active Long Chain 5-Hydroxycyclohex-2-Enones and Long-Chain Bicyclo[3.3.1]Nonane-3,7-Diones

Abstract

Re-examination of the optically active long-chain 5-hydroxycyclohex-2-enones of Campnosperma species has confirmed the former structural assignments, except that in Tigaso oil both the 5- hydroxycyclohex-2-enones and the phenolic components contain a significant (35-40%) proportion of compounds with di-unsaturation in the C₁₉-chain. Further study has been made of the conversion of (-)-endo-4-hexadecyl-l-hydroxybicyclo[3.3.l]nonane-3,7-dione (10) into a mixture of an optically inactive and optically active β- diketones. The major product from this reaction is (±)-5-(1-acetylheptadecy1)cyclohexane-1,3-dione (1l), which on methylation with diazomethane gives a mixture of two diastereoisomeric Omethyl ethers. These undergo cyclization to give a mixture of two epimeric 4-hexadecyl-l-methoxybicyclo[3.3.l]nonane-3,7-diones, (16) and (17), but reduction of the enol ethers followed by cyclization leads to an epimeric mixture of 4 hexadecylbicyclo [3.3.l]nonane-3,7-dion, (21) and (22).

A detailed n.m.r. study of the bicyclo[3.3.l]nonane-3,7-diones, (10), (16), (17), (21), (22), (27) and (28), indicates that all have a chair-chair conformation, and also shows which of these compounds have an equatorial substituent, (10), (16), (21) and (27), and which an axial, (17), (22) and (28), at C4. Reduction of the bicyclo[3.3.1]nonane-3,7-diones with sodium borohydride gives oxaadamantane derivatives, and reduction of one diastereoisomeric β- diketone Omethyl ether gives a high yield of (±)-endo-4-hexadecyl-exo-3-methyl-2-oxabicyclo[3.3.l]nonane-7-one (25), the structure of which has been fully derived from n.m.r. study.