Lundurines A-D were isolated in 1995 from the Malayan plant Kopsia tenuis, which has been used in folk medicine and is a rich source of biologically active alkaloids. Their intriguing hexacyclic framework includes an unprecedented cyclopropa [b] indole that has only ever been identified in lundurines. While these structural features have been attractive as synthetic targets, the first total synthesis was not reported until 2014. While lundurine B and D exhibit appreciable toxicity toward B16 melanoma cells and also reverse multidrug resistance in vincristine-resistant KB cells, their limited availability has prevented further studies for drug development. Therefore, the synthetic studies for these alkaloids and clarify the mechanism of their biological activity should contribute to medicinal chemistry. This review summarizes recent synthetic efforts in the total synthesis of lundurines and related alkaloids.

A sulfonium species generated from sulfoxide and acid anhydride is a useful reagent for organic synthesis owing to its powerful electrophilicity. Among the various sulfonium-mediated reactions, interrupted Pummerer reaction has been well-investigated recently, which progresses the nucleophilic attack of substrate on sulfur atom of sulfonium such as Swern-type oxidation. Although interrupted Pummerer reactions are reported with various substrate such as alcohols, alkenes, enol ethers, the application to aromatics is limited because of the stability of initially generated arylthionium salts. In contrast, we previously developed intramolecular reaction via arylthionium intermediate for installing nucleophile to indole 2α-position in a one-pot procedure. This reaction was proceeded with special substrate by intramolecular reaction, therefore, it was unexplored as a general synthetic method.

This article describes the details of the development of sulfonium species mediated reactions to functionalize indoles by intermolecular interrupted Pummerer reaction.

Extension of the π-system of porphyrins has attracted the interest of many chemists for applications such as light-emitting displays, organic thin-film electronics, and photosensitizers as a near-infrared dye. Herein we report our recent works on synthesis of aromatic ring-fused porphyrins and ring-expanded porphyrins with no meso-bridges. Porphyrins linked with aromatic ring through bicyclo[2.2.2]octadiene were prepared via the tetramerization and [3+1] porphyrin synthesis methods. The subsequent thermal conversion afforded ring-annelated porphyrins. Core-modified benzoporphyrins and π-extended BODIPYs were also obtained by the similar retro Diels-Alder strategy.

Ring-expanded porphyrins with no meso-bridges, cyclo[n]pyrroles(n=8 and 10), were selectively synthesized by using an oxidative coupling of the corresponding 2,2’-bipyrrole in the presence of appropriate template dianions. These octaphyrins and decaphyrin exhibited a markedly red-shifted strong L band at ca. 1,000-2,000 nm.

N-Alkynylamide (ynamide) is recognized as a polarized alkyne, due to the delocalization of lone-pair electrons on the nitrogen atom to the carbon-carbon triple bond, and it is widely used in recent organic synthesis. We conducted the studies on the efficient and useful molecular transformation of ynamides with transition metal catalysis, and several new methods of ynamide transformation were developed. First, we demonstrated new synthetic protocol of enamide from ynamide. Thus, γ-siloxyenmides were efficiently prepared by the nickel(0)-catalyzed regio- and stereoselective coupling of ynamide, aldehyde and silane. Moreover, regioselective synthesis of tri- and tetra-substituted enamides was achieved by palladium-catalyzed silaboration of ynamide. On the other hand, 2-amino-1,3-dinenes were synthesized by ruthenium-catalyzed formal hydrovinylation of ynamide with ethylene. Carboxylation of ynamide with CO₂ mediated by nickel(0) complex gave α-substituted-β-aminoacrylate, which was transformed into β²-amino acid derivative in a enantioselective manner by rhodium-catalyzed asymmetric hydrogenation. Finally, the first total synthesis of (−)-herbindoles A, B and C was achieved by [2+2+2] cyclization of dialkynylynamide.

The introduction of fluorine(s) into organic compounds can change physical, chemical, and biological properties of their original molecules. In the context, the trifluoromethyl group (CF₃) is probably the most popular; it is also most applied in the design and development of drugs, agrochemicals, and material science. The development of effective and efficient synthetic approaches to access such trifluoromethylated molecules has gained great attention. Although the direct trifluoromethylation method using various trifluoromethylating reagents appears to be the latest trends, such reagents are ordinarily expensive. On the other hand, the use of trifluoromethylated building blocks represents an alternative approach provided that the trifluoromethylated building blocks are satisfied the following conditions: 1) easy to prepare from commercially available reagents 2) easy to handle 3) wide application ability. Our group has been interested in the preparation of fluorinated building blocks containing vinyl sulfonium group as a key functional group. On the basis of the above concept, so far, β-(trifluoromethyl)vinyl sulfonium salt, β-(difluoromethyl)vinyl sulfonium salt, and α-fluorovinyl sulfonium salt have already synthesized from readily available starting materials in high overall yields in short steps. These salts have functioned as a two-carbon homologation reagent containing trifluoromethyl, difluoromethyl, and monofluoro moiety. In this article, we will discuss synthesis and application of the fluorinated vinyl sulfonium salts and related compounds.

Pyranonaphthoquinone natural products are widely distributed in plants and microorganisms, and they have diverse biological activities. Angular benzochromenes are a small class of natural products isolated from Conospermum and Pentas plants. Conocurvone, a trimeric benzochromene isolated from Conospermum plants, has potent anti-HIV activity. We have focused compounds which exhibit biological activity, or in which the activity is further enhanced by having oligomeric structure as a target of total synthesis. In this paper, the discovery and biological activity of trimeric benzochromene conocurvone and its related compounds were outlined and synthetic studies toward monomeric chromenoquinones was described including our research, in which the benzochromene framework was constructed by Diels-Alder reaction of oxygenated furans and chromene-derived benzynes.

Acid chlorides are among the most versatile building blocks in organic synthesis. Traditional approaches to prepare these compounds involve the reaction of carboxylic acids with halogenating reagents. The present review focused on the recent advances for the synthesis of acid chlorides using palladium catalyst as alternative strategies.

Synthesis of multi-substituted arenes is one of the most important areas of research in organic synthesis. This review discusses new methodologies to introduce various nucleophiles to electron-rich arenes by photoredox catalysis. These methodologies can be considered as complementary to the traditional nucleophilic aromatic substitution, which uses electron-deficient arenes as substrates.