A lithium amide-promoted halogen dance of 2,5-dibromothiophene led to the formation of thermodynamically stable thienyllithium, which underwent Negishi coupling to provide the corresponding 2-arylated 3,5-dibromothiophenes in one pot. The resultant β-bromo group was much less reactive than the remaining α-bromo group, enabling facile synthesis of multiply arylated thiophenes. In addition to the scope of this reaction, its synthetic utility of the one-pot halogen dance/Negishi coupling is demonstrated by the syntheses of thiophene-fused indoles and other pyrrole alkaloids.

A catalytic system for asymmetric intramolecular dehydrative allylation was established, which was developed from a dehydrative-alcohol-allylation catalyst, CpRu-2-quinolinecarboxylic acid. A CpRu complex of Cl-Naph-PyCOOH, a chiral pyridine-2-carboxylic acid bearing a 2-chloronaphthalen-1-yl group at the C(6) position and a methyl group at the C(5) position, was designed by investigating the ligand structure-reactivity relationship in the intramolecular dehydrative allylation of alcohols. The catalyst showed high reactivity and enantioselectivity toward allylic cyclization from allylic alcohols with nucleophilic moieties, such as protic hydroxy, acylamino, and carboxyl groups, affording a variety of corresponding chiral cyclic ethers, amines, and lactones. Aprotic pyrroles were also utilized as C-nucleophiles. Furthermore, unstable hemiacetal, hemiaminal, or aminal formed in situ were transformed to the corresponding protected chiral 1,2- or 1,3-O,O, O,N, N,O, or N,N bifunctional compounds by the catalyst. The catalytic activity toward allylic alcohol is based on the soft ruthenium/hard Brønsted acid synergetic effect in which a double bond interacts with ruthenium and a hydrogen bond forms between protons and the hydroxy group. Additionally, the chloro group at naphthalene plays a key role in forming a halogen bond with nucleophilic moieties. This interaction allows easier formation of the transition state of oxidative addition, resulting in high enantioselectivity caused by performing only one major catalytic cycle. This account summarizes these results and provides insight into the reaction mechanisms.

Terpenoids including more than 80,000 species are ubiquitous in nature. The biosynthetic reaction mechanism to produce diverse range of terpene skeleton from simple biosynthetic precursors, dimethylallylpyrophosphate (3) and isopentenylpyrophosphate (4) has attracted much attention. In this article, biosynthetic reaction mechanisms of terpene synthases by using deuterium labelled acyclic terpene probes are described. Five different kinds of deuterium labeled geranylgeranyl pyrophosphates are selectively synthesized by Z-selective formation of a vinyl tosylate followed by the Negishi coupling reaction as well as Pd catalyzed reductive desulfonylation reaction. The deuterium-labelled geranylgeranyl pyrophosphates are treated with a diterpene cyclase, CotB₂ to provide the cyclization products. Structure analysis of the cyclization products was performed by nuclear magnetic resonance spectroscopy to trace the deuterium in the products. Based on the analysis, a unique biosynthetic reaction mechanism of CotB₂ via cyclopropylcarbinyl cation rearrangement with the methylene chain exchanging at C8 and C9 was proposed. The stereoselectivity of the characteristic cyclopropane rearrangement was discussed from the comparative viewpoints of the previous studies on the acid catalyzed transformation of thujopsenes, biosynthetic studies of verrucosane-2β-ol, and tsukubadiene in which the cyclopropane rearrangement mechanism is involved in the transformation.

π-Conjugated molecules have attracted much attention over recent years and have applications in various organic devices. The crystals of these molecules are attractive materials for developing unique and/or high-performance devices due to anisotropic densely packed supramolecular 3D self-assembled structures. However, these are not flexible and therefore not suitable for flexible/wearable devices. In this article, the author’s recent work on elastic crystals based on supramolecular synthon of targeted crystal structure (fibril lamella of slip-stacked molecular wires from rigid and planar π-conjugated molecules) and their unique applications are summarized. Unlike common organic crystals, designed thiophene-fluoroarene π-conjugated molecules exhibits elastic bending flexibility with π-functionality. This supramolecular design concept offers top-down synthesis of crystalline fibers and films. Moreover, the functionality and flexibility of such a crystal realized both high-performance flexible fluorescent waveguide and reversible mechnofluorochromic behaviors.

The synthesis of a multiboron heterocycle and its application to a direct amidation catalyst are described. The heterocycle comprised of B₃NO₂ is called DATB. The DATB-catalyzed direct amide formation is well suited for the synthesis of a wide range of amides, including previously intractable ones. The catalysis can also be applied to peptide synthesis and N-acylation of sulfoximines. The most active DATB contains four boron atoms in its structure, and the detailed mechanistic study revealed their distinctive roles in the catalytic cycle, depending on the given chemical environment. A pyrimidine containing analog was also developed and evaluated as a more readily accessible amidation catalyst than the original one. The Pym-DATB is now available from a commercial vendor. Current trends and future perspective in the boron-catalyzed direct amidation are also discussed.

Sulfur (VI) fluoride exchenge (SuFEx) is a family of click chemistry which allows conversion of phenols or amines to their respective fluorosulfates. Although SuFEx is a powerful tool for functionalization of phenols, this reaction has several problems. This review focused on recent improvements and advances in SuFEx chemistry.