over several hours established an equilibrium mixture of 2
and 18 with an approximate 1 : 1 ratio. Further attempts
to promote [4+2] Diels–Alder dimerisation of 2/18 using
Grieco’s conditions29 i.e. 5M LiClO4 solution, were also
unsuccessful, with only inter-conversion between isomeric
cyclooctatrienes 2 and 18 being observed.
8 M. F. Jacobsen, J. E. Moses, R. M. Adlington and J. E. Baldwin,
Tetrahedron, 2006, 62, 1675.
9 J. E. Banfield, D. St. C. Black, S. R. Johns and R. I. Willing, Aust.
J. Chem., 1982, 35, 2247.
10 K. C. Nicolaou, N. A. Petasis, R. E. Zipkin and J. Uenishi, J. Am.
Chem. Soc., 1982, 104, 5555.
11 K. C. Nicolaou, N. A. Petasis, J. Uenishi and R. E. Zipkin, J. Am.
Chem. Soc., 1982, 104, 5557.
In summary, although we have developed the first synthesis
of the bicyclo[4.2.0]octadiene pre-kingianin A (2) (and the
corresponding isomer 18), which is believed to be the penulti-
mate precursor to kingianin A (1), studies of the biomimetic
dimerisation of 2 into 1 have been inconclusive. It is clear
however that the process is not spontaneous, implying that 1 is
not a simple artefact of isolation. We believe therefore that the
process involved in the proposed dimerisation of pre-kingianin
A (2) into 1 in vivo may be subtler than hitherto expected . This
is consistent with the chemistry of cyclohexadienes, which do
not undergo Diels–Alder dimerisation readily. Further studies
to delineate the requirements of this intriguing dimerisation of
2/18 to kingianin A (1) are now in progress in our laboratory
and will be reported in due course.
12 K. C. Nicolaou, R. E. Zipkin and N. A. Petasis, J. Am. Chem. Soc.,
1982, 104, 5558.
13 K. C. Nicolaou, N. A. Petasis and R. E. Zipkin, J. Am. Chem. Soc.,
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15 S. J. Eade, M. W. Walter, C. Byrne, B. Odell, R. Rodriguez,
J. E. Baldwin, R. M. Adlington and J. E. Moses, J. Org. Chem.,
2008, 73, 4830.
16 (a) C. M. Beaudry and D. Trauner, Org. Lett., 2005, 7, 4475;
(b) K. A. Parker and Y. -H. Lim, J. Am. Chem. Soc., 2004,
126, 15968; (c) J. E. Moses, J. E. Baldwin, S. Bruckner,
¨
S. J. Eade and R. M. Adlington, Org. Biomol. Chem., 2003, 1, 3670.
17 B. Capuano, I. T. Crosby, E. J. Lloyd, A. Podloucka and
D. A. Taylor, Aust. J. Chem., 2003, 56, 875.
18 C. Jubert and P. Knochel, J. Org. Chem., 1992, 57, 5425.
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The authors thank the EPSRC (PS, DR) and The University
of Nottingham for financial support. Thanks to Professors
G. Pattenden and C. J. Hayes for helpful advice.
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c
This journal is The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 10605–10607 10607