The direct oxidative coupling reaction has been an attractive tool for environmentally benign chemistry. Reported herein is that the hypervalent iodine catalyzed oxidative metal-free cross-coupling reaction of phenols can be achieved using Oxone as a terminal oxidant in 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP). This method features a high efficiency and regioselectivity, as well as functional-group tolerance under very mild reaction conditions without using metal catalysts.

The direct oxidative coupling reaction has been an attractive tool for environmentally benign chemistry. Reported herein is that the hypervalent iodine catalyzed oxidative metal-free cross-coupling reaction of phenols can be achieved using Oxone as a terminal oxidant in 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP). This method features a high efficiency and regioselectivity, as well as functional-group tolerance under very mild reaction conditions without using metal catalysts.

A combination of phenyliodine bis(trifluoroacetate) (PIFA) and trifluoromethanesulfonic acid was found to be an effective activator for the glycosylation reaction, of which the glycosyl donor was p-(octyloxy)phenyl 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-1-thio-D-glucopyranoside or p-(octyloxy)phenyl 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-1-thio-D-galactopyranoside. The reaction proceeded with good yields when naturally occurring and derived alkanols, such as cholestanol, (–)-menthol, 1- and 2-adamantanols and nor-kauranol, were employed as acceptor substrates. Interestingly, the glycosylation reaction of sterically hindered terpenoid alcohols, such as (–)- and (+)-borneols and (+)-fenchyl alcohol, with p-(octyloxy)phenyl 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-1-thio-D-glucopyranoside afforded the desired β-glycoside in quantitative yield. Moreover, the present reaction was useful to synthesize disaccharides of which the non-reducing end was composed of a D-glucosamine or D-galactosamine unit.

We started our hypervalent iodine research about 30 years ago in the mid-1980s. We soon successfully developed the single-electron-transfer oxidation ability of a hypervalent iodine reagent, specifically, phenyliodine(III) bis(trifluoroacetate) (PIFA), toward aromatic rings of phenyl ethers for forming aromatic cation radicals. This was one of the exciting and unexpected events in our research studies so far, and the discovery was reported in 1991. It also led to the next challenge, developing the metal-free oxidative couplings for C–H functionalizations and direct couplings between the C–H bonds of valuable aromatic compounds in organic synthesis. In order to realize the effective oxidative coupling, pioneering new aromatic ring activations was essential and several useful methodologies have been found for oxidizable arenes. The achievements regarding this objective obtained in our continuous research are herein summarized with classification of the aromatic ring activation strategies.

A method for coupling azoles with pyrroles and related compounds using a hypervalent iodine reagent has been developed. The oxidative coupling to produce the CN bond directly from CH and NH bonds is attractive in view of sustainable chemistry by avoiding prefunctionalization of the substrates. Notably, the reactions are found to be N¹-selective at the azoles and tolerant of a broad range of substrates and functional groups.

Direct oxidative coupling is an attractive tool for environmentally benign green chemistry. We report the novel oxidative synthesis of hexahydroxytriphenylene by using a hypervalent iodine reagent. The reaction proceeds under very mild conditions for reducing acid waste and in a very short time at room temperature.

Metal-free oxidative CC coupling by using polyalkoxybenzene-derived diaryliodonium(III) salts as both the oxidant and aryl source has been developed. These salts can induce single-electron-transfer (SET) oxidation to yield electron-rich arenes and subsequently transfer the polyalkoxyphenyl group into in situ generated aromatic radical cations to produce biaryl products. The reaction is promoted by a Lewis acid that activates the iodonium salts. It has been revealed that the reactivity of the salts under acidic conditions is quite different to their known behavior under basic conditions. The reactivity preference of a series of iodonium salts in the SET oxidation and their ligand transfer abilities have been systematically investigated and the results are summarized in this report.

We have successfully established an efficient route to the core structure of donor–acceptor head-to-tail (H–T)-linked regioregular oligothiophenes, which includes the following key synthetic steps, that is, hypervalent iodine induced direct and regioselective coupling of thiophenes and the use of the obtained bithiophenes as excellent coupling substrates for the Suzuki and Stille couplings. The versatility of this new approach is highlighted in the dramatic improvement of the yield (ca. 59 % overall yield) of MK-2, a high-performance organic dye, for photovoltaic applications.

The direct oxidative biaryl coupling reaction is an attractive tool for environmentally benign green chemistry. A novel direct method for the synthesis of bithiophene using a hypervalent iodine reagent has been developed. The reaction mechanism has also been investigated, casting light on the reaction intermediate and revealing the reactivity with iodonium salts.