STEREOSELECTIVE CONVERSION OF KETO GROUPS INTO METHYL VINYL QUATERNARY CARBON CENTERS

In the presence of bis(triphenylphosphine)nickel dichloride both trans- (1b) and cis-4-tert-butyl-1-vinylcyclohexa-nol (1c) reacted with methylmagnesium bromide affording r-4-tert-butyl-t-1-methyl-1-vinylcyclohexane (4a), 1-n-propylidene-4-tert-butylcyclohexane (3b), and r-4-tert-butyl-c-1-methyl-1-vinylcyclohexane (5a) in a 19:5:1 ratio. This reaction was applied to vinylcarbinols prepared from four manool-derived 13-hydrophenanthrones (8, 9a, 10a, and 7-dehydro-10a) for di-terpene synthesis. In the cases leading to terminal olefins 8, 14-dihydropimaradiene (14b), 7, 8-dihydroisopimaradiene (15b), and Δ7(8)-pimaradiene (17b) were produced. The first olefin was transformed into the tetracarbocyclic diterpene hibaene (23) in five high-yielding steps. © 1978, American Chemical Society. All rights reserved.