Misc

Iminoiodanes serve as excellent nitrenoid progenitors in the aziridination of olefins and in the C-H amidation of alkanes under transition metal-catalyzed conditions. The methodology for synthesis of the iminoiodanes is, however, very limited and all of the methods reported rely on ligand exchange on iodine of aryliodanes. We report the first example of transimidations yielding sulfonyliminoiodanes, which involves an imido transfer from iminobromane to the iodine atom of iodobenzenes at room temperature under metal-free conditions. Rate dependence on the concentration of iodobenzene suggests a bimolecular nitrenoid transition state, involving a rate-limiting nucleophilic attack of iodobenzene on the negatively charged nitrogen of sulfonyliminobromane. Hammett plot indicates large buildup of positive charge on the iodine of iodobenzenes in the transition state.

Ethynyl(phenyl)(tetrafluoroborato)-λ3-iodane (1) serves as an efficient Michael acceptor, but its synthetic application is limited due to the low thermal stability. We found that the λ3-iodane (1) forms the supramolecular 1:1 complex (2) with 18-crown-6 in a high yield and the complexation dramatically increased the stability of the labile λ3-iodane (1). Solid state structure with pentacoordinated iodine(III) was determined by X-ray analysis and solution structure was examined by 1H NMR and CSI–MS, and binding constant was measured. The complex (2) holds for the high reactivity toward attack of nucleophiles and serves as a direct ethynylation agent for enolate anions, sulfinates, and phosphites. The 18-crown-6 ligand in (2) makes it possible to synthesize the highly labile (Z)-(β-alkoxyvinyl)phenyl-λ3-iodanes, which have never been synthesized, as a crown ether complex.

Reported here for the first time are the stereoselective synthesis and reaction of simple silver (Z)-enethiolates, which serve as a stabilized (Z)-enethiol storage. In contrast to labile enethiols, silver (Z)-enethiolates are stable even in solutions, and their isolation and purification are very simple. The method for synthesis of silver (Z)-enethiolates involves an unusual vinylic SN2 reaction of (E)-vinyliodane(III) with thiobenzamides yielding the inverted (Z)-S-vinylthioimidonium salts, followed by their regioselective C-S bond cleavage with silver acetate. Alkylation, arylation, and Michael addition of silver (Z)-enethiolates yielding (Z)-vinyl sulfides was dramatically accelerated by the addition of Bu4NI (LiI), which probably generates reactive ammonium (Z)-enethiolates with an increased nucleophilicity.

Report here for the first time is generation of labile cyclopentenyl cation from 1-cyclopentenylbromanes(III) 3 by thermal solvolysis, which relies on the hyperleaving group ability of hypervalent arylbromanyl(III) groups. Thermal solvolysis of 1-cyclopentenylbromanes(III) 3a,b at 20-50 C affords cyclopentanone, 1-chlorocyclopentene, (1-cyclopentenyl)halobenzenes, and 1-cyclopentenylhalogans(III) depending on the conditions, being the trapping products of 1-cyclopentenyl cation by the solvents and by the leaving group bromoarenes. Both deuterium labeling experiments and reaction kinetics strongly suggest an SN1 mechanism involving generation of cyclopentenyl cation.

Stable bromonium ylides have been synthesized and structurally characterized for the first time. The bromonium ylides selectively undergo transfer of the aryl group to nitrogen heterocycles. This is in a marked contrast to the reaction of the iodonium ylides, which produces pyridinium ylides through transylidations. Intermolecular transylidation between halonium ylides under thermal and catalytic conditions, which makes it possible to synthesize a hitherto unknown kind of chloronium ylides as well as a variety of bromonium and iodonium ylides, was developed. The thermal transylidations of bromonium to iodonium ylides probably involve generation of a reactive carbene. Compared to the bromonium and iodonium ylides, the chloronium ylide serves as a much better progenitor for generation of carbenes. A greater leaving group ability of the chroranyl(III) and bromanyl(III) groups compared to that of the iodanyl(III) group seems to be responsible for the observed differences in reactivity.