π-Conjugated molecules and polymers are expected to have a variety of applications in organic electronics. Control over how these π-conjugated systems stack in the solid state is crucial for utilization of their desirable photophysical and electrical properties. Some molecules need to be designed with enhanced π-stacking abilities, whereas others might display novel properties as a result of restricting their π-stacking abilities. Furthermore, π-conjugated molecules or polymers that display partial π-stacking are of interest for potential new applications because of the synergy of the contrasting properties of stacked and isolated π-conjugated systems. Here, we highlight recent progress in molecular design to control π-stacking, with a particularly focus on the redox properties of these unique molecular systems.

α-Chloro-substituted organomagnesiums, referred to as magnesium carbenoids, are reactive intermediates that can be generated from α-chloro-substituted sulfoxides and Grignard reagents via the sulfoxide/magnesium exchange reaction. The simultaneous existence of magnesium and chlorine atoms on the carbon atom bestows intriguing reactivity on the magnesium carbenoids. The magnesium carbenoids show three different types of reactivity, namely, nucleophilic, electrophilic, and carbene-like reactivity. The diverse reactivity of magnesium carbenoids enables a variety of organic transformations. This account summarizes our recent study on the development of reactions using magnesium carbenoids and mechanistic study on the magnesium carbenoid reactions using DFT calculations.

This paper describes racemic syntheses of naturally occurring lactams, epolactaene, berkeleyamide D, rubrobramide, flavipucine, and isoflavipucine. The key step is a regioselective Darzens reaction between glyoxals and α-bromo-β-ketoamides. (±)-Epolactaene was synthesized by a Darzens reaction between methylglyoxal and α-bromo-β-ketoamide. The synthesis of (±)-berkeleyamide D was accomplished in only four steps from the reported starting material. The key features of this synthesis include the construction of a spirocyclic ring system by a C-acylation reaction followed by an intramolecular spirocyclization via an epoxide-opening reaction. Following optical resolution by chiral HPLC, the absolute configurations of both enantiomers of berkeleyamide D were determined by the vibrational circular dichroism exciton chirality method. The construction of the core tricyclic ring system of (±)-rubrobramide was achieved by a cascade reaction in a single step from an α,β-epoxy-γ-lactam. The α,β-epoxy-γ-lactam was prepared by the Darzens reaction. The absolute configuration of naturally occurring (＋)-rubrobramide was determined by vibrational circular dichroism exciton chirality method. (±)-Flavipucine and isoflavipucine were synthesized from an epoxyketone, which was prepared by reaction of isobutylglyoxal with a protected α-bromo-β-ketoamide. Removal of the protective groups in the epoxyketone, and formation of the pyridone ring gave (±)-flavipucine, which was converted into isoflavipucine by thermal isomerization.

Direct catalytic enantioselective alkynylation of carbonyl compounds and imines is one of the most efficient approaches for the synthesis of propargylic alcohols and propargylamines, which are potent building blocks for synthesizing functionalized molecules. While a variety of methods for the reactions with aldehydes and aldimines have been established, the reactions with ketones and ketimines remain underdeveloped due to their reduced reactivity and difficulty in stereocontrol. In this account, we summarized our studies on direct enantioselective alkynylation reaction of α-ketoester and α-ketiminoesters catalyzed by phenylbis(oxazoline)(phebox)-rhodium(III) complexes, affording enantioenriched propargyl alcohols and propargylamines with a tetrasubstituted carbon stereocenter under proton-transfer conditions. The catalytic system was compatible to a wide range of functional groups, including electrophilic formyl groups, and allowed for the development of an efficient method to access enantioenriched α-CF₃-substituted thalidomide analogs. Mechanistic studies revealed that generation of the (alkynyl)(phebox)Rh(III) complex from the (diacetato)(phebox)Rh(III) complex determined the overall reaction rate in the initial stages of the reaction. These results, along with the observed facile exchange of the alkynyl ligand on the (alkynyl)(phebox)Rh(III) complexes, led us to use (trimethylsilylethynyl)(phebox)Rh(III) complexes as a new pre-catalyst. The new catalytic system with (trimethylsilylethynyl)(phebox)Rh(III) precatalysts exhibited enhanced catalytic performance, reduced catalyst loading to as low as 0.5 mol%, and expanded the substrate scope of the reaction with less reactive α-ketiminophosphonate and cyclic N-sulfonyl α-ketiminoesters.

Synthesis of polycyclic compounds by using inter- and intramolecular photocycloaddition reactions of aromatic rings with unsaturated components was investigated. Intramolecular [3+2] photocycloaddition of alkenylnaphthalenes gave triquinane compounds in high yields. Photospirocyclization also took place from alkenylnaphthalenes. Photocycloaddition of alkynylnaphthalenes gave other kinds of triquinane compounds. Novel eight-membered ring compounds were formed in intramolecular photocycloaddition of alkenylphenanthrenes. Inter- and intramolecular photocycloaddition reactions of alkenes to pyrene and chrysene were also developed. When cyclopropane derivatives were used, processes of [3+2] photocycloaddition and photoalkylation were observed. Hydrogen bonding interactions can be used for development of regio- and stereoselective photocycloaddition reactions. Singlet exciplexes are served as reactive intermediates in these photocycloaddition reactions.

Protected hydroxyl malononitriles, known as masked acyl cyanide (MAC) reagents are one of the most useful umpolung synthons to function as carbon monoxide equivalents with both nucleophilic and electorophilic reactivity. This dual reactivity, only characteristic in a few acyl anion equivalents, enables MAC reagents to afford a series of structurally diverse products by a one-carbon homologation under mild conditions. This review highlights the utility of MAC reagents in catalytic enantioselective carbon-carbon bond forming reactions that have been reported recently.

Pleuromutilin is an antibiotic having protein synthesis inhibitory activity isolated from Pleurotus mutilus by Kavanagh and co-workers in 1951. Due to its unique pharmacological action mechanism, it is expected to be used as a medicine. Indeed, some of the semi-synthesized derivatives have already been approved as medicines and widely used. Two examples of asymmetric total synthesis reported in recent years are described focusing on the construction method of its framework.