by

The spectroscopie data led to the formulation of partial structures XII and XIII.
Xlla R = H
Xllb R = Ac
CH J
o
The HRMS of anhydroarthrosporone displays a base peak at ml z '22 (C,H100). This
peak may be accounted for via the proposed mechanism in Scheme VII on the assumption
that the partial structure XIV is present in the molecule.
The DC NMR speetrum of anhydroarthrosporone (21 l exhibits two quaternary
carbon signais, one of which bears the gem dimethyl group (XIII). Since one of the
substituents on the carbon {j to the carbonyl in XII is a methyl group (XIV), it follows that
the gem dimethyl group (XIII) can be incorporated in only two ways. Insertion of the gem
dimethyl group between C-' , and C-9 followed by bond formation between C-' and C-2
gives rise to structure 35, whereas insertion of the gem dimethyl group between C-' and
C-9 followed by bond formation between C-2 and C-' , gives rise to structure 36.
Ali the spectroscopie data presented for anhydroarthrosporone acetate (34) is
consistent with either a hirsutane skeleton (35) or with skeleton 36. In addition the lH NMR
spectrum of acetate 34 shows deshielding of three protons and one of the singlet methyls
with respect to the lH NMR spectrum of 21. For each of structures 35 or 36 the
deshielded protons would be those vicina/ and cis to the acetoxyl group. Thus the
XIII
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