X-Ray crystal and molecular structure of the acid-catalysed rearrangement product of a beyer-15(16)-en-12-one system

Abstract

Sumwary A double 1,2-rearrangement of a 12-oxo-beyer-15( 16)-ene system across the 12,13-single bond, reversible after reduction of the double bond, is confirmed by X-ray crystal structural analysis.THE isolation and identification of a new naturally occurring compound of the beyerane class1 was recently reported.2 Dissolution of ent-3P-hydroxybeyer-15( 16)-en-Z, 12-dione (Ia)? in acetic acid-acetic anhydride resulted in its ready acetylation to (Ib) : A , , (EtOH throughout) 296 nm ( E 233), r 9-26 (3H, s, 20-H). Addition of either conc. H,SO,, 70% HClO,, or BF,-Et,O to the ice cold solution of either (Ia) or (Ib) induced rearrangement in high yield to the ap-unsaturated ketone (IIa),

ent-(1aR)-1-α-(1a-Hydroxy-1a-phenyl)-3β-hydroxy-11α-bromo-12-oxo-2-norbeyeran-3β-carboxylic acid 2,1a-lactone

“…The absolute configuration was determined, and it confirmed previous assignments for this family of compounds (Laing, Pegel & Piacenza, 1973;Laing, Pegel, Piaeenza, Waight & Phillips, 1974;Laing, Sommerville, Hanouskova, Pegel, Piacenza, Phillips & Waight, 1972;Laing & Sommerville, 1975;Sommerville & Laing, 1976a,b,c). (Sommerville & Laing, 1976a,b,c).…”

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

“…ref. 5) and of three quaternary methyl groups respectively. The high-field position of the C-20 methyl resonance results from shielding by the A '~ olefinic bond (5,6).…”

“…5) and of three quaternary methyl groups respectively. The high-field position of the C-20 methyl resonance results from shielding by the A '~ olefinic bond (5,6). The hydroxyl group is placed at C-12 rather than at C-14 since a very large downfield shift of the C-17 methyl group resonance is observed upon addition of tris(dipivaloy1methanato)europium (Eu(dpm),), the normalized (7) ratio of the shifts induced in the methyl resonances being 10:2.7:1.4 for C-17, 3The numbering system used for formulae 5 and 7 is not systematic but rather a consequence of mechanistic considerations.…”