In situ oxidative diol cleavage - Wittig processes

Article abstract of DOI:10.1016/S0040-4039(02)01331-X

1,2-Diol cleavage followed by in situ trapping of the resulting aldehyde with a stabilised phosphorane is described; both manganese dioxide and silica-supported sodium periodate can be used as the heterogeneous oxidant, but the latter reagent is generally the most efficient.

Full text of DOI:10.1016/S0040-4039(02)01331-X

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 6185–6187
In situ oxidative diol cleavage–Wittig processes
Helen S. Outram, Steven A. Raw and Richard J. K. Taylor*
Department of Chemistry, University of York, Heslington, York YO10 5DD, UK
Received 5 June 2002; accepted 28 June 2002
Abstract—1,2-Diol cleavage followed by in situ trapping of the resulting aldehyde with a stabilised phosphorane is described; both
manganese dioxide and silica-supported sodium periodate can be used as the heterogeneous oxidant, but the latter reagent is
generally the most efficient. © 2002 Elsevier Science Ltd. All rights reserved.
We have recently described an in situ manganese diox-
ide-mediated alcohol oxidation-stabilised Wittig
sequence which can be applied to both activated1 and
non-activated2 primary alcohols (Eq. (1)). We subse-
quently extended the oxidation–Wittig methodology to
allow the use of phosphonates and non-stabilised phos-
phonium salts.3 This one-pot methodology avoids the
need to isolate the intermediate aldehydes, which is
beneficial in terms of time and particularly useful if the
aldehydes are toxic or unpleasant to handle.
In the preliminary investigation, a range of 1,2-diols
in dichloromethane were treated with MnO2/
Ph3PꢀCHCO2Et. The cleavage of 1,2-diols to give the
corresponding carbonyl compounds using manganese
dioxide is documented.7 We were delighted to observe
the successful conversion of most of the diols into the
corresponding a,b-unsaturated esters, as summarised in
Table 1.8
Initial studies were carried out using acyclic 1,2-diols
(entries i–iv). 1,2-Dihydroxyhexane underwent cleav-
age–Wittig trapping to give adduct 1 in 33% yield
(entry i). Ethyl 4-oxo-oct-2E-enoate (16%) was also
isolated from this reaction, possibly as a result of
keto-aldehyde formation.7,11 In a similar manner, 1,2,6-
trihydroxyhexane was transformed into enoate 2, albeit
in lower yield (entry ii). meso-Hydrobenzoin underwent
this transformation much more efficiently giving 3 in
high yield (97%, entry iii). A mannitol-derived diol was
also studied (entry iv), but the expected product 4 was
not observed using the manganese dioxide conditions.
(1)
We now report that similar conditions can be employed
for an in situ diol oxidative cleavage–Wittig sequence
(Eq. (2)).4 This procedure can be effected using com-
mercial activated manganese dioxide, but we have
found that silica-supported sodium periodate5 often
gives even better yields. A recent report6 from Dunlap
et al. on the use of the periodate-mediated sequence
prompts us to publish our own results in this area.
Cyclic diols were also investigated (entries v–vii). Thus,
trans-1,2-cyclohexanediol produced diester 5 in low
yield (entry v). However, cis-1,2-cyclododecanediol12
underwent the in situ cleavage–elaboration to give
product 6 in 64% yield (entry vi), although the corre-
sponding cyclododecadienediol12 gave tetraene 7 rather
less efficiently (entry vii).
We also found that silica-supported sodium periodate is
useful for the same one-pot transformation (Table 1,
entries i–vii). It is noteworthy that the periodate proce-
dure gave higher yields than manganese dioxide in most
examples, with hydroxybenzoin the only exception
(entry iii), and that the periodate procedure worked
with the protected mannitol derivative whereas the
(2)
* Corresponding author. E-mail: rjkt1@york.ac.uk
0040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)01331-X

6186
H. S. Outram et al. / Tetrahedron Letters 43 (2002) 6185–6187
Table 1. In situ diol oxidative cleavage–Wittig processesa
manganese dioxide procedure was unsuccessful (entry
iv). The periodate reactions were carried out using
diethyl ether as solvent, and in all but one of the cases
the reactions were complete after 3 h. This compares to
reaction times of 20 h when dichloromethane is
employed as solvent.6
propane-1,2-diol 8 gave the expected product 10 with
silica-supported periodate but gave product 9, result-
ing from further oxidative degradation13–Wittig trap-
ping, under the manganese dioxide conditions (Scheme
1). In all cases, apart from the protected mannitol
example with periodate (entry iv), the E-alkenes pre-
dominated, as expected. In the mannitol example, a
predominance of the Z-alkene was seen; this is in
contrast to the published6 report (using dichloro-
methane as solvent) in which the E-isomer apparently
predominates.
It should be noted that 3,3-dimethylbutane-1,2-diol did
not undergo the cleavage–Wittig process with either
oxidant, presumably for steric reasons. Another inter-
esting observation was that 3-(4-methoxyphenyl)-

H. S. Outram et al. / Tetrahedron Letters 43 (2002) 6185–6187
6187
Scheme 1.
The above procedure allows aliphatic aldehydes to be
generated and trapped under extremely mild conditions
and so complements the in situ oxidation–Wittig route
using manganese dioxide with non-activated alcohols,
which requires extensive periods in refluxing toluene.2
In addition, these reactions are extremely easy to per-
form, the work-up consisting simply of filtration fol-
lowed by solvent evaporation and chromatography. We
are currently optimising these procedures and applying
them in natural product synthesis.
6. Dunlap, N. K.; Wosenu, M.; Jones, J. M.; Carrick, J. D.
Tetrahedron Lett. 2002, 43, 3923–3925.
7. Ohloff, G.; Giersch, W. Angew. Chem., Int. Ed. Engl.
1973, 12, 402–402.
8. Novel products were fully characterised; known products
gave consistent spectroscopic data.
9. General procedure for manganese dioxide process: To a
solution of the diol in CH2Cl2 (10 ml/mmol) was added
(carboethoxymethylene)triphenylphosphorane (2.2 equiv-
alents) followed by activated MnO2 (Aldrich, 21764-6; 20
equiv.) and the reaction was stirred at rt. A further two
portions of MnO2 (20 equiv. each) were added at 4 h
intervals. After a total of 24 h, the mixture was filtered
through Celite® and the volatiles removed in vacuo. The
products were then purified by column chromatography.
10. General procedure for sodium periodate process: A 0.65
M solution of NaIO4 in warm H2O (1.3 equiv.) was
added dropwise to a suspension of silica (1.5 g/mL of
NaIO4 solution) in diethyl ether (10 mL/mmol of diol)
with vigorous stirring. To this mixture was added the diol
and (carboethoxymethylene)triphenylphosphorane (2.2
equiv.) and the resulting mixture was stirred at rt for 1–3
h. After the reaction was complete, the mixture was
filtered through a sinter and the volatiles were removed in
vacuo. The products were then purified by column chro-
matography.
Acknowledgements
We thank the BBSRC for a quota studentship (S.A.R.).
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