Development of environmentally benign oxidations using hypervalent iodine (III) reagents

We have synthesized a novel, nonpolymer-supported recyclable hypervalent iodine (III) reagent, 1,3,5,7-tetrakis [4-(diacetoxyiodo) phenyl] adamantane 3a and its derivatives 3b, c and utilized them in environmentally benign oxidations. The new reagents 3a-c mediate a wide range of oxidative transformations with efficiencies similar to those of conventional reagents, phenyliodine (III) diacetate (PIDA), pheyliodine (III) bis (trifluoroacetate) (PIFA), and (hydroxyl (tosyloxy) iodo). benzene (HTIB), and have higher reactivity compared with polymer-supported recyclable reagents such as poly (diacetoxyiodo) styrene (PDAIS) and poly {bis (trifluoroacetoxy) iodo} styrene (PBTIS). In all cases, tetraiodide 4 was recovered nearly quantitatively in a pure form after simple workup, i.e., filtration. Reoxidation of 4 to 3a with m-chloroperbenzoic acid also proceeded quantitatively, without loss of oxidative activity. Recyclable 3a-c are used in various organic solvents as well as water, and thus mild and clean oxidation of alcohols in water has been achieved using 3a. A facile synthesis of aldehydes from primary alcohols has also been demonstrated using a dual recycling strategy, with 3a and recyclable 2,2,6,6-tetramethyl-1-piperidinyloxy free radical (TEMPO).