Several methods for the oxidation of aldehydes to the corresponding carboxylic acids are known.1,2 However, no one seems to be completely satisfactory, the major drawbacks being high costs, low selectivities, and complex operating conditions. Their application to large-scale preparations is therefore difficult.We thus addressed our attention to the use of the inexpensive sodium chlorite,1 23 which reacts with aldehydes under very mild conditions to give carboxylic acids (eq 1).RCHO + HC102 -RCOOH + HOC1(1)However, hypochlorite ion must be removed in order to avoid side reactions, since the redox pair HOC1/CT is a more powerful oxidant than C102"/H0C1.4 5Another drawback is the oxidation of C102™ to C102 according to eq 2.38,5 HOC1 + 2C1CV -2C102 + Cl" + OH*(2) 2-Methyl-2-butene,78,8 resorcinol,38•7 and sulfamic acid38•9 have been tested as HOC1 scavengers. 2-Methyl-2-butene must be used in a very large excess. Resorcinol is converted into 4-chloro-1,3-dihydroxybenzene, which must be removed from the reaction mixture. Sulfamic acid works well in the oxidation of hydroxylated aromatic aldehydes, but it gave poor results in the case of ,/3-unsaturated aldehydes (see below).

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A General synthetic method for the oxidation of primary alcohols to aldehydes: ( S )‐(+)‐2‐methylbutanal reactant: 44.05 g (0.50 mol) of (S)‐(−)‐2‐methyl‐1‐butanol product: (S)‐(+)‐2‐methylbutanal byproduct: (S)‐(+)‐2‐Methylbutanoic acid product: butanal

300 mg, 7.9 mmol), (OEP)RhmCl (4.0 mg, 6 µ ;[Rh] = 0.6 mM), and an internal standard (p-xylene, mesitylene, or durene, appropriate amount) in dry THF (10 mL) exposed to dry air was stirred at 20-25 °C. The oxygenation of 1-methylcyclohexene was carried out by using the rhodium catalyst in an amount 2 or 20 times as much as that used above ([Rh] = 1.2 or 12 mM). The electronic spectra of the reaction mixture underwent no significant change even after 100 h. The formation of oxygenation products was monitored by gas chromatography. Similarly was carried out the oxygenation of 1,5-cyclooctadiene and acetylenes (1-heptyne and 3-heptyne) by using substrate (300 mg), NaBH4 (300 mg), and (OEP)RhraCl or (TPP)RhmCl (4.0 mg) in THF (20 mL). Reaction products, after conversion if necessary to silylated derivatives, were identified by gas chromatography on the basis of coinjection with authentic samples, and their yields determined also by gas chromatography. 2-Methylcyclohexanol as a mixture of stereoisomers arising from the oxygenation of 1 -methylcyclohexene was purified by preparative gas chromatography. The stereoisomer distribution was determined by XH NMR spectroscopy by taking advantage of the characteristic signals for hydroxymethine protons at 3.1 (for E isomer) and 3.75 (for Z isomer).The following control runs were carried out by using cyclohexene as substrate: (1) without rhodium porphyrin catalyst, (2) without 02, (3) without NaBH4, and (4) with NaBH(OCH3)3 in place of NaBH4. In neither case was detected oxygenation of substrate to any significant extent. Another control run using cyclohexene oxide in place of cyclohexene under otherwise identical oxygenation conditions did not give cyclohexanol.Borane Transfer. A mixture of (OEP)RhmCl (40 mg, 0.06 mmol), NaBH4 (100 mg, 2.64 mmol), and 1-pentene (70 mg, 1.0 mmol) in THF (2 mL) in a vessel sealed with a rubber septum was degassed by freeze-pump-thaw cycles and was stirred at room temperature for 19 h. The electronic spectrum of the mixture showed Xmu at 395, 514, and 545 nm, indicating the formation of (OEP)RhH.3 Following the standard procedure for the analysis of organoboranes,28 the mixture was then subjected to gas chromatography at 170 °C on a column of silicone SE-30 (2 m), which had been treated with Silyl-8 (Pierce Chemical Co.) to mask protic sites with trimethylsilyl groups. The product was readily identified as tripentylborane on the basis of coinjection with the authentic sample prepared by hydroboration of olefin with diborane under standard conditions. The mixture was exposed to air, stirred for 20 min, and then analyzed by gas chromatography to show the formation of 1-pentanol and 2-pentanol (94:6, in a total yield of 45% based on mol of Rh complex used).Oxidation of Alkylborane. A THF solution of (E)-bis(2methylcyclohexy 1)borane11 was prepared by the hydroboration of 1-methylcyclohexene (96 mg, 1.0 mmol) with borane-THF ( 1) (0.5 mL, 0.5 mmol) in THF (1 mL) under nitrogen. To this was added 1 N aqueous NaOH (0.5 mL), and the mixture was stirred ...

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Keywords: Biaryls / Biphasic catalysis / Epoxidations / Fluorinated ligands / ManganeseThe synthesis of sterically hindered chiral (salen)manganese complexes bearing perfluoroalkyl ponytails and their use in asymmetric epoxidation reactions are described. For better understanding of the relative influences of steric and electronic effects on the enantioselectivity of the fluorous catalysts, the epoxidation of 1,2-dihydronaphthalene and benzosuberene was first studied under homogeneous conditions. It was shown that the presence of sterically demanding tertbutyl groups and, to a lesser degree, the displacement of the electron-withdrawing perfluoroalkyl substituents from the ligand core provide ees higher than those attainable with first generation fluorous chiral (salen)manganese complexes featuring perfluoroalkyl substituents in the key positions (3,3Ј

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