Stereospecific Syntheses from Podocarpic Acid
The triterpene precursor, 12-methoxypodocarpa-8,11,13-trien-3-one (46)*, has been prepared via the 3a-alcohol (48) formed by
opening of the 3a,4a-epoxide (13) with lithium diethylamide.
The total synthesis of the methyl ether of the natural
product, (+)-hinokione, has been achieved by a similar sequence
involving prior addition of an isopropyl group at C 13 of the methoxy
acid (4) ( Scheme 1 ) .
A study of the boron trifluoride rearrangements of the
three epoxides (12), (13), and (14), has been made using benzene and
dimethyl sulphoxide as solvents.
The stereochemistry of a series of 6-bromo-7-oxo
derivatives of diterpenoids possessing an aromatic ring-C is discussed
and the assignment of configuration of the 6-bromo substituents from
n.m.r. and n.0.e. data is examined.
A preliminary investigation into the possibility of
preparing a 9a-methyl steroidal analogue by addition of a
cyclopentatone ring across positions 3 and 4 of ring-A of the
podocarpic system is also reported.