A USEFUL 12-I-5 TRIACETOXYPERIODINANE (THE DESS-MARTIN PERIODINANE) FOR THE SELECTIVE OXIDATION OF PRIMARY OR SECONDARY ALCOHOLS AND A VARIETY OF RELATED 12-I-5 SPECIES

The stable 10-I-4 species 1-hydroxy-1,3-dihydro-3,3-bis(trifluoromethyl)-1,2-benziodoxole 1-oxide ((fluoroalkoxy)iodinane oxide 7) is the ring-closed form of omicron-iodoxyhexafluorocumyl alcohol. It is prepared by the oxidation of chloroiodinane 6 with potassium bromate in aqueous sulfuric acid. The X-ray crystal structure of the tetrabutylammonium salt of 7 (10-I-4 anion 10) showed the unusual feature of an apical, negatively charged oxide ligand. Iodinane oxides 1 and 7 are readily converted to stable 12-I-5 periodinanes by treatment with carboxylic acid anhydrides or sulfur tetrafluoride. Tris(acyloxy)periodinanes 13 and 14 (derived from the ring-closed form of omicron-iodoxybenzoic acid), 1-hydroxy-1,2-benziodoxol-3(1H)-one 1-oxide (1), and 17 and 18 (derived from 7) are extraordinarily stable. 1,1,1-Triacetoxy-1,1-dihydro-1,2-benziodoxol-3(1H)-one (13), the ''Dess-Martin Periodinane'', is an extremely useful reagent for the conversion of primary and secondary alcohols to aldehydes and ketones at 25-degrees-C. It does not oxidize aldehydes to carboxylic acids under these conditions. It selectively oxidizes alcohols in the presence of furan rings or sulfides and does not react with vinyl ethers. Geraniol is oxidized to geranial by 13 without isomerization to nerol. Benzylic or allylic alcohols are selectively oxidized in the presence of saturated alkanols. The alcohol oxidation mechanism involves intermediates with alkoxy ligands replacing acetoxy ligands at the 12-I-5 iodine. It also oxidizes N-benzylbenzamide to benzaldehyde. Four other 12-I-5 species, 1,1,1-tris(trifluoroacetoxy)-1,1-dihydro-1,2-benziodoxol-3(1H)-one (14), 1,1,1,-trifluoro-1,1-dihydro-1,2-benziodoxol-3(1H)-one (15), 1,1,1-tris(acetoxy)-1,1,1,3-tetrahydro-3,3-bis(trifluoromethyl)-1,2-benziodoxole (17), and 1,1,1-tris(trifluoroacetoxy)-1,1,1,3-tetrahydro-3,3-bis(trifluoromethyl)-1,2-benziodoxole (18), also oxidize alcohols to aldehydes and ketones. All of the tris(acyloxy)periodinanes undergo facile ligand exchange with alcohols. The reaction between triacetoxyperiodinane 13 and pinacol gives an isolable, crystalline, spirobicyclic periodinane, 25. The acetoxy group of periodinane 25 undergoes degenerate ligand exchange with acetic acid rapidly on the NMR time scale.