The conversion of amino diols to aminohydroxy acids by oxidation of the primary hydroxy group mediated by homogeneous and heterogeneous TEMPO (2,2,6,6-tetramethylpiperidine 1-oxyl radical) is reported. The synthesis uses NaOCl as primary oxidant and TEMPO, either dissolved in the homogeneous phase or entrapped in a sol-gel matrix, as catalytic mediator. Homogeneous TEMPO is suitable for the oxidation of aliphatic methylamino diols, while the hybrid organic-inorganic silica sol-gel catalysts are more selective mediators for the oxidation of benzylic amino diols like the potent antibiotic chloramphenicol which, under homogeneous conditions, are unselectively oxidized to benzoic acids.

solution was concentrated and distilled in a Kugelrohr apparatus (100 °C pot temperature, 30 mm) to provide 0.342 g (50%) of 2-methylcyclohexanol. Analysis by VPC (10% TCEP, 6 ft x l/a in., 110 °C) revealed no observable amounts of the cis isomer. The cis and trans isomers may also be distinguished by the NMR signal of the proton on the carbon adjacent to the oxygen. The cis isomer exhibits a multiple! at 3.7 ppm while the trans isomer exhibits a multiplet at 2.9 ppm. Again, none of the cis isomer could be detected.Acknowledgment is made to the donors of the Petroleum Research Fund, administered by the American Chemical Society, for support of this research.

Steric interaction between the N-substituent and the vinyl substituent of 1 -substituted 1 -(1 -substituted pyrrol-2-y1)ethenes destabilises the cisoid conformation (1 b), thereby inhibiting (,4 + =2) cycloaddition reactions leading to dihydroindoles. Bulky N-substituents also sterically inhibit the Michael addition of dimethyl acetylenedicarboxylate at the 5-position of the pyrrole ring.

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