Rearrangements in the Diterpenoid Series. I. The Solvolysis of Methyl 15β-tosyloxy-13-isopropyl-17-noratis-13-en-18-oate

Abstract

The synthesis o f methyl 15~-hydroxy-l3-isopropyl-17-noratis-13-en-18-oate (14b) is described. Compound

Biogenetic-Type Rearrangements of Terpenes

“…A cyclic transition state, in which the C14,ß-proton is transferred to the departing sulfonate group, was proposed for this pyrolytic elimination. In the enantiomeric series, A YER and DESHPANDE have achieved a similar rearrangement of an atisane-like diterpene tosylate in which the two carbon bridge (C13-C14) is unsaturated (368). The success of this rearrangement was attributed to charge delocalization by the d 13 double bond in the transition state.…”

“…Since the initial suggestion that the aconane skeleton is biogenetically derived from an atisane precursor (363)(364)(365), there have been a number of attempts to effect the proposed Cg-+Cts rearrangement (366)(367)(368). PELLETIER and ICHIHARA first reported that 15-hydroxy-17-noratisane derivatives undergo rearrangement ofthe ethanobridge (C13-Ct4), instead of the C9 -Cs bond (as in 292), regard1ess of the configuration of the hydroxyl group (366).…”

“…Under somewhat stronger acidic conditions, '1'-taraxasterol (354 -as benzoate) is epimerized at C19 to the more stable lupenol-l (368 as benzoate) (451). The latter reaction is considered to proceed through the ~1 9 -taraxasterene isomer which is unstable with respect to (368) owing to steric interference between the c19 methyl and c12 methylene groups. The successful isolation of the less stable '1'-taraxasterol (354) from formic acid-treatment is attributed to a combination ofthe moderate acidity and its insolubility in this medium .…”

Resin acids. XXVIII. Rearrangements in the photolevopimaric acid series. Paradigm of bicyclo[2.2.0]- and bicyclo[2.1.1]hexane chemistry

“…Acid-catalyzed cleavage, however, provided conclusive proof for the presence of a cyclopropane ring. Treatment with HC1 gave a substance C21H33O2CI (43) (mass spectrum) which displayed a one-proton peak in the vinyl region similar to that of 39 itself and a broadened one-proton singlet at 4.46 ppm (W1/2 = 6 Hz) assignable to H-14. This is the result of cyclopropane ring cleavage in such a manner so as to form the most stable carbonium ion, in this instance an allylic carbonium ion.…”