alkenes were chosen to explore the general suitability of 5-PCP
for epoxidation. Thus, the reactivity of the alkenes towards
electrophilic oxygen ranged from the electron-rich 2,3-di-
methylbut-2-ene (containing a tetraalkyl-substituted double
bond) to the electron-deficient allyl phenyl ether (containing a
monosubstituted, oxygen-deactivated double bond). Other al-
kenes were chosen to demonstrate the stability of the resulting
epoxide under the reaction conditions (styrene, a-pinene,
means that the hydrogen ion concentration in solution is
extremely low. In turn, this means that acid-catalysed changes
in the epoxide, when formed, are reduced to a very low level,
enabling the isolation of even acid-sensitive epoxides in high
yield and purity. 5-PCP itself is partly soluble in the solvents
described here. This implies it has all of the kinetic advantages
of a homogeneous reaction but, being a very weak acid, does not
produce a significant hydrogen ion concentration in the reaction
medium. Thus, there is little or no effect from acid-catalysed
decomposition of the product epoxide. In the most sensitive
epoxides prepared in this work (e.g. styrene oxide), reaction
proceeded to virtually 100% yield with no evidence for acid-
catalysed rearrangement products (phenylacetaldehyde in the
case of styrene oxide). Until full hazard information is
available, 5-PCP should be treated with caution, as with any
peroxy compound.
1,2-diallyloxyethane), the stereo integrity of reaction (cis- and
trans-stilbene) or the selectivity of reaction (limonene, having
two different double bonds).
In each case, epoxidation proceeded to give virtually a 100%
yield of very pure product epoxide. Reaction rates were as
expected from the known mechanism of epoxidation with
peroxyacids.1 Thus, at room temperature, reaction of 2,3-di-
methylbut-2-ene, 1-methylcyclohexene, cyclohexene, cyclo-
,6
octene and a- and b-pinene with 5-PCP was fast in CH
the less reactive alkenes, such as oct-1-ene, allyl phenyl ether,
,2-diallyloxyethane and diallyl maleate, higher temperatures
were needed to achieve reaction in a reasonable time. Such
reactions could be carried out in CH Cl under reflux (35 °C),
,2-dichloroethane (at 50 °C), EtOAc (at 55 °C) and toluene (at
0 °C). When the epoxidation was carried out at higher
2 2
Cl . For
Notes and References
1
†
E-mail: rj05@liv.ac.uk
2
2
1
5
1 See for example, M. Hudlicky, Oxidations in Organic Chemistry, ACS
Monograph 186, American Chemical Society, Washington DC, 1990,
pp. 60–65; J. March, Advanced Organic Chemistry, Wiley, New York,
temperatures than these, reaction was faster and a clean product
was still obtained, but there was some small loss of active
oxygen over long periods of time. In these cases, somewhat
more than a 1 equiv. of peroxyacid to each double bond was
needed. Thus, after a period of about 100 h at 60 °C with 2
equiv. of 5-PCP, epoxidation of the two allylic bonds in
diallylmaleate ceased at about 60–70% because of depletion of
the peroxyacid; addition of a further 1 equiv. (0.5 equiv. for
each bond) caused the reaction to proceed to completion and to
give a very pure product.
1
985, pp. 733–735.
C. Venturello, M. Abneri and M. Ricci, J. Org. Chem., 1983, 48,
831.
2
3
3
4
R. Landau, G. Sullivan and D. Brown, Chem. Technol., 1979, 9, 602.
A. Tuel and Y. B. Taarit, J. Chem. Soc., Chem. Commun., 1994,
1
667.
5
A. M. d’A Rocha Gonsalves, R. A. W. Johnstone, M. M. Pereira and
J. Shaw, J. Chem. Soc., Perkin Trans. 1, 1991, 645.
6 D. Swern, in Organic Peroxides, ed. D. Swern, Wiley-Interscience,
New York, 1970, vol. 1, pp. 313–374 and see ref. 1 above.
7
M. Hirano, S. Yakabe, A. Satoh, J. H. Clark and T. Morimoto, Synth.
Commun., 1996, 26, 4591; T. Mino, S. Masuda, M. Nishio and
M. Yamashita, J. Org. Chem., 1997, 62, 2633.
In all of the reactions, the product acid (5-carboxyphthali-
mide 2) was almost totally insoluble in the solvent. This
behaviour is highly advantageous in two ways. First, the
product acid can be filtered off easily from the reaction medium
and re-used; this potentially low-cost acid can be recycled with
hydrogen peroxide to give little or no environmentally dis-
advantageous by-product. Second, the insolubility of the acid,
due to extensive strong intermolecular hydrogen-bonding,9
8
9
J. P. Sankey and A. P. James, (Interox Chemicals), PCT Int. Appl., WO
9
1 09,843, 11th July, 1991; Chem. Abstr., 1991, 115, 282510h.
N. Feeder and W. Jones, Acta Crystallogr., Sect. C, 1994, 50, 824.
1
0 W. H. Perkin and J. F. S. Stone, J. Chem. Soc., 1925, 127, 2295.
Received in Cambridge, UK, 13th November 1997; 7/08179K
430
Chem. Commun., 1998