Selective TEMPO‐Oxidation of Alcohols to Aldehydes in Alternative Organic Solvents

Abstract

The TEMPO-catalyzed oxidation of alcohols to aldehydes has emerged to one of the most widely applied methodologies for such transformations. Advantages are the utilization of sodium hypochlorite, a component of household bleach, as an oxidation agent and the use of water as a co-solvent. However, a major drawback of this method is the often occurring strict limitation to use dichloromethane as an organic solvent in a biphasic reaction medium with water. Previous studies show that dichloromethane cannot easily be substituted because a decrease of selectivity or inhibition of the reaction is observed by using alternative organic solvents. Thus, up to now, only a few examples are known in which after a tedious optimi- [a]

Synthetic Processes toward Nitriles without the Use of Cyanide: A Biocatalytic Concept Based on Dehydration of Aldoximes in Water

“…These examples underline that Oxds also accept bis‐aldoximes as substrates very well, as exemplified for linear aliphatic representatives of this compound class [13] . Recently, not only the oxidation of monoalcohols to aldehydes, but also the oxidation of diols to dialdehydes, was successfully performed by means of a (2,2,6,6‐tetramethylpiperidin‐1‐yl)oxyl‐catalyzed oxidation in nitriles as a solvent [11] …”

“…[13] Recently,n ot only the oxidation of monoalcohols to aldehydes, but also the oxidation of diols to dialdehydes, was successfully performed by means of a( 2,2,6,6-tetramethylpiperidin-1-yl)oxyl-catalyzed oxidation in nitriles as asolvent. [11] Summary and Outlook…”

“…In many cases, aldehydes are commercially available or easily accessible from cheap raw materials. For example, aldehydes can be prepared in an elegant fashion through the hydroformylation of alkenes or oxidation of alcohols [10, 11] . A comparison of the chemoenzymatic synthesis of nitriles from aldehydes by using Oxds for the dehydration of aldoximes and hydrocyanation, as a selected well‐known example of “classical” nitrile synthesis, is shown in Scheme 3.…”

“…The required aldehydes are themselves broadly accessible by homogeneous catalyzed hydroformylation of alkenes with syngaso rb yo xidation of alcohols by meanso f, for example, a( piperidin-1-yl)oxylr adical as ac atalyst ands odium hypochlorite as an oxidation agent. [10,11] The enzymesu tilized for this biotransformation are the aldoxime dehydratases (Oxds). Oxds, belonging to the enzyme class of lyases (EC 4.99.1.5-4.99.1.7), were first described in 1998 by Asano et al,a nd their high potential for organic synthesis has just recently been intensively explored.…”

“…The required aldoximes are easily accessible by condensation of the bulk chemical hydroxylamine with aldehydes (Scheme 1). The required aldehydes are themselves broadly accessible by homogeneous catalyzed hydroformylation of alkenes with syngas or by oxidation of alcohols by means of, for example, a (piperidin‐1‐yl)oxyl radical as a catalyst and sodium hypochlorite as an oxidation agent [10, 11] . The enzymes utilized for this biotransformation are the aldoxime dehydratases (Oxds).…”