Mendeleev Commun., 2008, 18, 309–311
insignificantly (entries 3 and 4). Primary alcohols are cleanly
the corresponding carbonyl compounds with IBX because of the
possibility to simplify the isolation procedure. Moreover, the
great similarity of the reaction results obtained in DMF and
DMSO allows us to suppose that DMF could also serve as a
convenient solvent in other reactions with IBX as the reagent.
oxidized to corresponding aldehydes without overoxidation
(entries 6 and 9), α-glycol is equally well oxidized to corre-
sponding α-diketone (entry 8). The oxidation is entirely chemo-
selective for the primary and secondary hydroxyl groups, i.e.,
the sensitive functional groupings (tert-α-ketol, dienone, anisole)
remain intact. 1.1–1.2 equiv. of IBX for each hydroxyl group of
a substrate are enough for a quantitative oxidation as oxidation
of DMF practically does not proceed during the reaction period.
The course of oxidation could be observed visually: the heavy
sediment of IBX, which occupies at first a small part of the
reaction volume, gradually diminished and disappeared, but
instead a fine white precipitate of IBA appears in the whole
reaction volume at 20–40% conversion of an alcohol. This
precipitate of IBA thickens significantly the reaction mixture
in the end of reaction but does not hamper stirring.
Being similar to DMSO in the characteristics mentioned
above on the application as a solvent in reactions with IBX,
DMF possesses significant advantage due to much greater
volatility (bp 153 °C/760 Torr, 50 °C/18 Torr, 25 °C/3.7 Torr).
Therefore, the isolation of high-boiling products of the oxida-
tions in DMF can be performed without aqueous treatment,
extraction and chromatography, merely by the filtration (to remove
IBA) and filtrate evaporation at < 50 °C in a laboratory vacuum.
This simple isolation procedure provides nearly quantitative
yields of analytically pure products. At the same time, without
additional manipulations, one isolates > 90% of formed IBA,
which could be used in economic synthesis of IBX,28 and
regenerates DMF.
This study was supported in part by the Presidium of the
Russian Academy of Sciences (2007–2008).
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†† General procedure. Solid IBX (1.1–1.5 equiv. for each oxidized
hydroxyl group of a substrate) was added as a single portion to the
solution of alcohol in absolute DMF (3.5–5.0 ml per mmol of IBX)
and the suspension was vigorously stirred with teflon magnet at room
temperature (23–25 °C), until total conversion of the alcohol (and inter-
mediate products in the case of α-glycols) according to TLC analysis. In
the course of the reactions the starting white suspension pales gradually,
sometimes until transparency, then again becomes milk-white and thickens.
The mixture was diluted with 5–6 volumes of CH2Cl2 (or Et2O, or
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the case of acidic compounds) (2 g mmol–1 of alcohol). The filtrate was
rotoevaporated to dryness at < 50 °C, finally in vacuum < 5 Torr. If
evaporation residue is not completely soluble in CH2Cl2 (due to traces
of IBX-derived products), the residue was filtered once more through the
already used column and evaporated. The obtained residue is an oxidation
product pure by TLC and NMR analyses. The top of the column contains
IBA, pure by NMR, which can be collected with a > 90% yield.
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‡‡ We found in some separate experiments that the addition of a small
quantity of ButOH (2 equiv. to IBX) accelerates by a factor of 2–3 the
oxidation of alcohols with IBX in THF, and an increase in ButOH
quantity (up to 8 equiv.) does not enhance further the catalytical effect.
The interaction between ButOH and IBX with the equilibrium formation
of the covalent adduct But–IBX is known.30 ButOH itself is not suitable
as a solvent for oxidations with IBX (entry 9 in Table 1).
Received: 29th July 2008; Com. 08/3192
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