Triphenylphosphine-catalysed conversion of maleic anhydride into acrylate esters

Article abstract of DOI:10.1016/S0040-4039(03)01272-3

Maleic anhydride has been converted into a range of acrylate esters on treatment with a suitable alcohol using triphenylphosphine as a catalyst.

Full text of DOI:10.1016/S0040-4039(03)01272-3

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 44 (2003) 5523–5525
Triphenylphosphine-catalysed conversion of maleic anhydride into
acrylate esters
Gareth R. A. Adair, Michael G. Edwards and Jonathan M. J. Williams*
Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK
Received 28 April 2003; revised 9 May 2003; accepted 16 May 2003
Abstract—Maleic anhydride has been converted into a range of acrylate esters on treatment with a suitable alcohol using
triphenylphosphine as a catalyst. © 2003 Elsevier Science Ltd. All rights reserved.
We have recently reported an indirect Wittig reaction
of alcohols with phosphonium ylides, proceeding via a
catalysed alcohol–aldehyde–alkene–alkane sequence.1
Whilst trying to expand the scope of this process, we
considered using phosphonium ylide 2,2 which is readily
prepared by the addition of triphenylphosphine to
maleic anhydride 1.3 However, we found that, even in
the absence of any catalyst, the phosphonium ylide 2
reacts with benzyl alcohol to afford benzyl acrylate 3,
along with triphenylphosphine as a by-product (Scheme
1).
for 24 hours. The reaction was readily accomplished
with primary and unhindered secondary alcohols. In
the case of more sterically hindered alcohols the reac-
tion was either slower or failed under the reaction
conditions employed.
Two possible mechanisms for acrylate formation are
presented in Scheme 3. Protonation of ylide 2 would
lead to the phosphonium salt 5, which could undergo
ring-opening to provide phosphonium carboxylates 6
and/or 7 via path A and/or path B. Decomposition of
these carboxylates would lead to the observed acrylate
product 4, liberating the phosphine catalyst.
Since triphenylphosphine is required for the conversion
of maleic anhydride 1 into ylide 2, and is then recov-
ered in the subsequent formation of acrylate ester 3, we
reasoned that it should be possible to use
triphenylphosphine as a catalyst for the direct conver-
sion of maleic anhydride 1 into acrylate ester 3. Indeed
this process was successfully achieved using 10 mol%
triphenylphosphine and a variety of alcohols to provide
a range of acrylate esters 4, as identified in Scheme 2
and Table 1.
Phosphines have previously been used as a nucleophilic
catalyst in Baylis–Hillman reactions,5 and other pro-
cesses.6,7 We were interested to see if other nucleophilic
catalysts could be employed in the maleic anhydride
transformation. Interestingly, whilst an alternative
phosphine
(BINAP-rac-2,2%-bis(diphenylphosphino)-
1,1%-binaphthyl) proved to be effective, other potential
nucleophilic catalysts were not suitable, as shown in
Scheme 4 and Table 2. Triethylamine and DABCO
(1,4-diazabicyclo[2.2.2]-octane) afforded no acrylate
products, although some ring-opened product was
formed. DMAP (4-(N,N-dimethylamino)pyridine) did
This simple procedure involves adding a small excess of
the alcohol to maleic anhydride in toluene, addition of
the phosphine catalyst and heating to reflux in toluene
Scheme 1. Two-step conversion of maleic anhydride into benzyl acrylate.
* Corresponding author.
0040-4039/03/$ - see front matter © 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0040-4039(03)01272-3

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G. R. A. Adair et al. / Tetrahedron Letters 44 (2003) 5523–5525
Scheme 2. Phosphine-catalysed conversion of maleic anhy-
dride into acrylates.
Scheme 4. Alternatives to PPh3 as catalysts for acrylate for-
mation.
Table 1. Conversion of maleic anhydride into acrylate
esters
Table 2. Use of alternative catalysts
Catalyst
Conversion (%)a
Alcohol
Isolated yield (%)
PPh3 (25 mol%)
100
100
0
0
21
0
PhCH2OH
MeOH
79
75a
87
79
60
51
0
BINAP (25 mol%)
Et3N (100 mol%)
DABCO (100 mol%)
DMAP (100 mol%)
Bu4NI (100 mol%)
PhCHꢀCHCH2OH
C11H23OH
Ph(CH3)CHOH
(−)-Menthol
(+)-Fenchyl alcohol
t-BuOH
a Conversion of maleic anhydride into benzyl acrylate—determined
0
0
by analysis of the 1H NMR spectrum.
Ph(CH3)2COH
a Due to the volatility of the product in this example, the yield was
calculated from analysis of the 1H NMR spectrum, using dimethyl-
furan as an internal standard.4
In these examples, one equivalent of phosphine was
employed as these reactions were found to be slower
than for the unsubstituted case. Dimethylmaleic anhy-
dride 8 was found to be inert under these reaction
conditions. The monomethylmaleic anhydride (citra-
conic anhydride) 9, afforded a-methyl substituted acryl-
ate 11 as the only observed product. The regio-
chemistry observed in this process is consistent with
intermediate 12—the methyl substituted analogue of
intermediate 7 in Scheme 3, again suggesting that path
B is preferred.
provide a small amount of acrylate product, but was
clearly less efficient than the phosphine catalysts.
Since non-phosphine based nucleophiles would be less
able to support the formation of an ylide, this suggests
that the formation of an intermediate ylide may be
involved in the phosphine-catalysed reaction. This is
therefore consistent with path B.
In summary, we have discovered an unusual phosphine-
catalysed process for the conversion of maleic anhy-
dride into acrylate esters.
The formation of substituted acrylates was attempted
using substituted maleic anhydrides 8 and 9 (Scheme 5).
Scheme 3. Possible mechanistic pathways for the phosphine-catalysed formation of acrylates.

G. R. A. Adair et al. / Tetrahedron Letters 44 (2003) 5523–5525
5525
Acknowledgements
We wish to thank the EPSRC for a QUOTA studentship
(to M.G.E.) and the University of Bath for funding for
an undergraduate research project (to G.R.A.A.).
References
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2002, 41, 4740.
2. Phosphonium ylide 2 is commercially available from
Aldrich Chemical Company.
3. (a) Hudson, R. F.; Chopard, P. A. Helv. Chim. Acta 1963,
245, 2178; (b) Hedaya, E.; Theodoropulos, S. Tetrahedron
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4. Gerritz, S. W.; Sefler, A. M. J. Comb. Chem. 2000, 2, 39.
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6. For a recent review on the use of phosphines as reagents
and catalysts, see: Valentine, D. H.; Hillhouse, J. H.
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7. Du, Y.; Lu, X.; Zhang, C. Angew. Chem., Int. Ed. 2003,
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Scheme 5. Formation of substituted acrylates.