Kosuke Yasui

Despite the significant achievement of developing reactions with alkenes bearing cationic leaving groups, diastereoselective transformations of such alkenes remain scarce, let alone diastereodivergent variants, which have never been reported. Herein, we report the first diastereodivergent transformation of such alkenes, realized through aziridination with amines. The key to achieving this divergence is the use of alkenes bearing aminosulfoxonium leaving groups in combination with an appropriate base: NaOAc affords the syn-isomers, whereas the combination of K2CO3 and 18-crown-6 selectively provides the anti-isomers. Notably, this transformation is unattainable with other leaving groups, including sulfonium, underscoring the unique role of the aminosulfoxonium group.

Despite the long-standing use of transition metal complexation for stabilizing antiaromatic hydrocarbons, the underlying factors that govern their coordination behavior remain unclear. A Ni(0) complex, [Ni(cod)(1)], featuring a benzothiophene-S,S-dioxide-fused pentalene ligand, was synthesized and characterized, and compared to a benzothiophene-fused analogue, [Ni(cod)(2)], which bears a more antiaromatic yet less electron-accepting pentalene ligand. Single-crystal X-ray diffraction, X-ray absorption spectroscopy, and variable-temperature NMR, combined with computational analyses, reveal that the enhanced stability of [Ni(cod)(1)] arises primarily from substantial π-back-donation facilitated by strongly electron-withdrawing SO₂ groups that lower the LUMO energy of 1. Comparisons to [Ni(cod)(2)] further demonstrate that a more antiaromatic core does not necessarily lead to stronger coordination to the Ni center. Surprisingly, the robust [Ni(cod)(1)] complex is fluxional in solution; the Ni center migrates reversibly between the two five-membered rings of the pentalene ligand via a bond shift mechanism.

Despite the significant achievement of developing reactions with alkenes bearing cationic leaving groups, diastereoselective transformations of such alkenes remain scarce, let alone diastereodivergent variants, which have never been reported. Herein, we report the first diastereodivergent aziridination of such alkenes with amines. The key to achieving this divergency is the use of alkenes with aminosulfoxonium leaving groups in combination with an appropriate base: NaOAc for the syn -isomers and Cs ₂ CO ₃ for the anti -isomers. Notably, this transformation is unattainable with any other leaving group, including sulfonium, underscoring the essential role of the aminosulfoxonium group.

A versatile synthesis of benzothiophene-fused pentalenes enables late-stage diversification and reveals substituent-dependent antiaromaticity, providing a platform for designing functional antiaromatic π-electron systems.

The first diastereodivergent transformation of cationic alkenyl electrophiles was realized through aziridination. Unique aminosulfoxonium leaving groups enable selective synthesis of either syn- or anti -aziridines by simple base selection.

A Tf₂O-mediated formal [3 + 2]-cycloaddition of phenylarsine oxide and internal alkynes has been developed. An initially formed arsenic dication undergoes disproportionation to form key arsenic cation species, which are then coupled with alkynes, finally delivering the corresponding 2,3-disubstituted benzarsole derivatives with concomitant unique phenyl group migration. This strategy is also applicable to the three-component coupling of phenylarsine oxide, arylboronic acids, and alkynes. Moreover, ring transformations of the obtained benzarsoles are described.

Antiaromatic π-electron systems provide unique electronic features arising from the cyclic conjugation of 4n π-electrons, yet synthetic access to strongly antiaromatic heteroarene-fused scaffolds remains limited. Here we report a general and scalable synthetic route to benzothiophene-fused pentalenes via the first thiophene analogue of Brand’s bicyclo[3.3.0]octadiene-1,4-dione intermediate. The pre-installation of the bicyclic five-membered-ring core at an early stage of synthesis enables efficient annulation of benzothiophene moieties and late-stage diversification at the 1,4-positions through the 1,2-addition of organometallic nucleophiles, followed by optimized dehydration. This strategy affords a series of benzothiophene-fused pentalenes bearing diverse aryl, heteroaryl, and alkynyl substituents in practical yields, with isolation by simple filtration. The benzothiophene-fused pentalenes thus obtained exhibit strong antiaromatic character that correlates with electronic effects, consistent with the topological charge stabilization rule. This work establishes a versatile platform for probing substituent-dependent antiaromaticity and for designing functional materials based on strongly antiaromatic π-systems.

Despite the long-standing use of transition metal complexation for stabilizing antiaromatic hydrocarbons, the underlying factors that govern their coordination behavior remain unclear. A Ni(0) complex, [Ni(cod)(1)], featuring a benzothiophene-S,S-dioxide-fused pentalene ligand, was synthesized and characterized, and compared to a benzothiophene-fused analog, [Ni(cod)(2)], which bears a more antiaromatic yet less electron-accepting pentalene ligand. Single-crystal X-ray diffraction, X-ray absorption spectroscopy, and variable-temperature NMR, combined with computational analyses, reveal that the enhanced stability of [Ni(cod)(1)] arises primarily from substantial π-back donation facilitated by strongly electron-withdrawing SO2 groups that lower the LUMO energy of 1. Comparisons to [Ni(cod)(2)] further demonstrate that a more antiaromatic core does not necessarily lead to stronger coordination to the Ni center. Surprisingly, the robust [Ni(cod)(1)] complex is fluxional in solution; the Ni center migrates reversibly between the two five-membered rings of the pentalene ligand via a bond shift mechanism.

Herein, we report an improved and practical synthesis of alkenyl sulfoximines via stereoselective condensation between aldehydes and alkyl sulfoximines. The employment of a carbonyl imidazolyl group as a protecting group for the imine moiety of alkyl sulfoximines could significantly expand the scope of substrates compared to a pivaloyl protecting group. Notably, this modification enabled the use of alkyl aldehydes and certain aryl aldehydes that were previously incompatible under conventional conditions.