Ring C Functionalized Diterpenoids. Part II Cleavage of the Cyclopropane Ring in Methyl ent-Trachyloban-19-oate with Thallic Acetate

Abstract

Reaction of methyl ent-trachyloban-19-oate ( l a ) with thallic acetate gave four major products including the ent-atisane derivatives, 2-4. Since the substrate is readily obtainable from the common sunflower, this reaction provides a valuable route to these and related compounds. The fourth compound, 5, may derive from an ent-atisane intermediate by contraction of ring D.La reaction de I'ent-trachylobanoate-19 de methyle avec ]'acetate thallique a conduit a quatre produits majeurs dont les derives 2-4 de I'ent-atisane. Puisque le substrat est facile a isoler du tournesol commun, cette reaction permet donc d'obtenir aisement ces differents produits. Le quatrieme compost, 5, peut provenir d'un intermediaire ent-atisane par contraction du cycle D.[Traduit par le journal]Can. J. Chem., 51,4167 (1973) As indicated in the preceding paper, we have been interested in synthesizing ring C oxygenated / diterpenoids, among them 13-substituted ent-

The conformation of tetracyclic diterpenes. IV. The crystal and molecular structure of a minor product of oxidative cleavage of methyl ent-trachyloban-19-oate with thallic acetate

“…Formally, like all other oxidative cleavage products isolated (Campbell, Gunn, McAlees & McCrindle, 1973, (IIa) derives from electrophilic attack on C(13)-C(16) in methyl ent-trachyloban-19-oate. It presumably arises from intermediate (III) by heterolysis of the -TI(OAc)2 group, migration of the ~-hydride from C(1 I) to C(13), and capture of solvent at C(ll).…”

“…Structures have been assigned to all but one of the products isolated from the complex mixture obtained by reaction of methyl ent-trachyloban-19-oate (I) with thallic acetate (Campbell, Gunn, McAlees & McCrindle, 1973. A tentative structure (IIa) was advanced for this product on the basis of spectroscopic evidence and mechanistic considerations (Campbell et al, 1975); however, this structure was incon-Sistent with the resistance of the corresponding diol (IIb) to cleavage by periodate (McAlees, McCrindle & Murphy, 1975).…”

“…A tentative structure (IIa) was advanced for this product on the basis of spectroscopic evidence and mechanistic considerations (Campbell et al, 1975); however, this structure was incon-Sistent with the resistance of the corresponding diol (IIb) to cleavage by periodate (McAlees, McCrindle & Murphy, 1975). Only very small quantities of the compound were available, but fortunately crystals of the diol proved suitable for X-ray analysis, and the structure determination was undertaken to elucidate the structure and to examine the conformation of the molecule in general and the bicyclic ring system in particular.…”

Rearranged Diterpenoids from the Biotransformation of ent-Trachyloban-18-oic Acid by Rhizopus arrhizus

“…Thus, the structure of 8 is established as ent -1α-hydroxyrhizop-15-en-18-oic acid, representing a new family of natural pentacyclic diterpenes having a carbon backbone that we have named rhizopene. A compound having a cyclopropane ring at C-11, C-12, and C-13 was reported to have been obtained chemically by R. McCrindle, but no spectroscopic evidence supported this claim . A biogenetic hypothesis of compound 8 is provided in the Supporting Information (S18).…”

Skeletal Rearrangements of Rings C and D of the Kaurene and Beyerene Tetracyclic Diterpenoids

“…This was discharged by a backbone rearrangement of the C-10 methyl group to C-9. The oxidation of methyl trachylobanate with thallium (III) acetate afforded 45 a complex mixture of products.…”