Scheme 5 Synthesis and thermal transformation of 2-acetoxy-1,3-
dioxolane 24.
patterns. Both reactions were stereospecific as observed by
NMR analysis of the crude distillates, in which no signals
(o1%) due to the alkene with the opposite stereochemistry
were detected in the spectra.
Scheme 6 Synthesis of 2,5-dihydrofuran (27) from erythritol (25) and
possible intermediates 26 and 28 (pathways a and b, respectively).
The transformation of erythritol (25) to 2,5-dihydrofuran (27)
is a good example of how this reaction could offer an
efficient approach to the conversion of biomass to value-added
chemicals.
In order to demonstrate the capability of thermal transfor-
mation of the cyclic orthoesters of type b (Scheme 3) to
generate a double bond, the synthesis of a 2-acyloxy-1,3-
dioxolane from a 2-alkyloxy-1,3-dioxolane was carried out.
1,2-Decanediol (6) was used as a model system for this study.
The 2-ethoxy-1,3-dioxolane derivative 23 was prepared and
subsequently converted12 to the 2-acetoxy-1,3-dioxolane 24
(Scheme 5). When a mixture of dioxolanes 23 and 24 was
carefully heated, the 2-acetoxy-1,3-dioxolane 24 was trans-
formed into the olefin 13 at 40–48 1C, while compound 23 was
unaffected.
In conclusion, we have uncovered an improved selective
one-pot, one-reagent deoxygenation technique for converting
vicinal diols to unsaturated systems in high yields, and provide
evidence for an unexpected concerted mechanism for the
critical bond-changing processes in this transformation. Our
preliminary results with inexpensive biomass-derived polyols
suggest that the reaction of polyhydroxy compounds with
formic acid will be a valuable alternative for the manufacture
of reduced oxygen content products.
The above results suggest that the formic acid-mediated
didehydroxylation might be extendable to carbohydrates,
an economically and environmentally important target.
Preliminary results with sugar polyols are very promising.
Erythritol (25) is a four-carbon sugar alcohol that is accessible
through yeast or fungal fermentation of glucose from corn
starch (Fig. 1). The reaction of 25 with formic acid
at 210–220 1C, following the procedure described above for
glycerol (1), gave a distillate that contained 2,5-dihydrofuran
(27) along with water and formic acid. A 39% yield of the pure
dihydrofuran 27 was isolated after purification by fractional
distillation (Scheme 6).
The authors gratefully acknowledge Dow Chemical Co. and
Director, Office of Science, of the U.S. Department of Energy
under Contract No. DE-AC02-05CH11231 (to R.G.B.
and J.A.E.) for support of this work and the postdoctoral
scholarship support of the Fulbright Program and the
Ministry of Science and Innovation (Spain) (to E.A.).
Notes and references
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To investigate the course of this reaction, cis-1,4-anhydro-
erythritol (26) was prepared by acid-catalyzed cyclo-
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conversion of erythritol to 2,5-dihydrofuran. If deoxygenation
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dehydration (Scheme 6, path b). However, as shown in
Scheme 6, 28 did not yield 2,5-dihydrofuran when submitted
to our standard formic acid-mediated didehydroxylation
conditions, pointing to path a as the most plausible reaction
pathway.
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metathesis or by catalytic rearrangement of vinyl oxirane.
ꢀc
This journal is The Royal Society of Chemistry 2009
Chem. Commun., 2009, 3357–3359 | 3359