SELECTIVE REACTIONS OF TRANS-1,6-DIMETHYLBICYCLO[4.3.0]NONANE-2,7-DIONE, AN INTERMEDIATE FOR TRITERPENE SYNTHESIS

The six-membered carbonyl function of the title compound (1) is more reactive in nucleophilic addition reactions than the five-membered ketone. Reduction, ketalization, organolithium addition, and sulfur ylide condensation all proceed selectively at that site. If the six-membered ketone is blocked (e.g., 7), reactions at the five-membered carbonyl group are found to be very sluggish. In a study of more than a dozen strong nucleophiles only DIBAL and allylic Grignard reagents added to this function. Lithium ethoxyacetylide reacts with 7 in an anomolous fashion. The enolate anion formed by proton transfer from 7 to the acetylide base adds to the carbon-carbon triple bond, giving 19 in high yield. Trideuterio analogues of 1, 2, 7, 9, and 10 have been prepared so that the angular methyl resonance signals from these compounds can be assigned. Chemical shift increments derived from steroids can be applied to derivatives of 1. Both carbonyl functions in 1 generate enolate anions which may be trapped as silyl ether derivatives or condensed with benzaldehyde. One equivalent of strong base generates the six-membered ring enolate under equilibrating conditions, and this was trapped as silyl ether 23. Unexpectedly, condensation of 1 with 1 equiv of benzaldehyde gave the five-membered ring benzylidene product 27 under equilibrating conditions. © 1979, American Chemical Society. All rights reserved.