Magtrieve^TM (CrO₂): A Versatile Oxidant in Organic Synthesis

Introduction

Magtrieve is a magnetically retrievable oxidant based on tetravalent chromium dioxide (CrO₂). [1] It is a selective, heterogeneous form of CrO₂, whose reduced form stays on the crystal surface. It is insoluble in most common organic solvents. Reactions with Magtrieve^TM are typically performed in chlorinated solvents or toluene. Magtrieve has found wide application in organic synthesis, such as in the oxidation of allylic alcohols to allylic aldehydes, [2] the formation of benzyl from benzoin, [3] the aromatization of imidazolines, [4] the conversion of 2-hydroxymethyl-6,7- bis(pentylsulfanyl)tetrathiafulvalene into 2-formyl-6,7- bis(pentylsulfanyl) tetrathiafulvalene, [5] oxidation of 2-methoxyphenols to 1,4-benzoquinones, [6] etc. This reagent is still ferromagenetic and can be conveniently removed after the reaction by a simple magnetic separation, because only the surface of the CrO₂ is reduced. This has significant environmental and cost advantages over traditional chromium reagents that require aqueous work-up and consequent appropriate disposal of the chromium waste. In addition, the reduced chromium surface can be simply reconverted into CrO₂ by heating in air, thus adding to its recyclability and cost-effectiveness. Magtrieve as an oxidant is a very well-suited reagent for microwave synthesis because it carries the benefit of efficient conversion of electromagnetic energy into heat according to the dielectric heating mechanism. [7]

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