総説・解説等

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.

エチニル-l3-ヨーダン（１）はエノラートアニオンなどの求核種に直接エチニル基を導入できる合成上特異な反応剤である。[1] 東京化成工業より既に市販されているが、問題となるのはその安定性である。室温で保存すると分解してしまうため、幅広く利用するためにはその安定性を向上させる必要がある。我々は（１）に18-クラウン-6(18C6)を作用させたところ、室温で保存できる安定な結晶として1:1錯体（２）を得ることに成功した(Scheme 1)。[2] ２つの酸素原子とσ*(I–C)軌道との間の超原子価相互作用により安定化されていることがX線結晶解析図(Figure 1)からわかる。CSI–MSやJobプロットを用いて溶液中での構造も決定した。安定性の向上が原因であると思われるが、1:1錯体（２）はエチニル化剤として極めて有用である。代表例をScheme 2に示す。いずれの場合も反応は高収率で進行し、（１）の反応性が大幅に改良された。（１）を用いると不安定なZ-ビニル-l3-ヨーダンも合成可能である。

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.

超脱離基である三価の超原子価ヨウ素置換基を有するビニル-λ3-ヨーダンは、SN1機構で種々のビニルカチオンを発生することが知られているが、シクロペンテニル-λ3-ヨーダンの加溶媒分解反応では、シクロペンテニルカチオンは発生しない。我々はこれを遥かに凌ぐ脱離能を有する三価の超原子価臭素置換基を導入したシクロペンテニル-λ3-ブロマンを設計・合成し、その加溶媒分解反応を実施した。興味深いことに、本反応は緩和な条件下にSN1機構で進行し、シクロペンテニルカチオンが生成している。

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.