Notes and references
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Scheme 5
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(S,S)-2 in 84% yield which exhibited [α]D +141.4 (c 0.7 in
MeOH) (lit.,8 [α]D +128 (c 0.21 in MeOH)).
Our attention then turned to structurally related β-methyl
enone (S,S)-3 (Fig. 1). This enone was also isolated from the
pathogenic fungus Lasiodiplodia theobromae and showed
growth inhibitory effects on seedlings of Nicotiana tabacum.8
Surprisingly, the enone was isolated from Lasiodiplodia theobro-
mae as a mixture of enantiomers (∼60 : 40 mixture of (S,S)-3
and (R,R)-3). The plan was to utilise enone (S,S)-1 in a synthesis
of the major enantiomer in the naturally occurring mixture.
Thus, Me3SiCl-promoted conjugate addition of lithium
dimethylcuprate to enone (S,S)-1 gave an intermediate silyl enol
ether. Subsequent Saegusa oxidation using catalytic Pd(OAc)2 in
the presence of oxygen16 delivered β-methyl enone 12 in 92%
yield (Scheme 5). Then, the BDA group was removed using
TFA–water to give (S,S)-3 in 74% yield. Our synthesised (S,S)-3
exhibited [α]D +107.0 (c 1.0 in MeOH) (lit.,9 [α]D +11.3 (c 0.01
in MeOH) for a ∼60 : 40 mixture of (S,S)-3 and (R,R)-3 isolated
from Lasiodiplodia theobromae).
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H. C. Steffens, T. D. Towers and M. Voith, Tetrahedron, 2000, 56, 9633;
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catalogue number 643742.
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In conclusion, a 6-step, catalytic asymmetric synthesis of
butane diacetal-protected (4S,5S)-dihydroxycyclohexen-1-one
(S,S)-1 has been developed and utilised in the synthesis of two
cyclohexenone natural products isolated from Lasiodiplodia
theobromae. Enone (S,S)-1 can now be considered a useful start-
ing material for future synthetic endeavours.
Acknowledgements
We thank Syngenta and The University of York for funding.
7668 | Org. Biomol. Chem., 2012, 10, 7666–7668
This journal is © The Royal Society of Chemistry 2012