Communesins are a class of heptacyclic indole alkaloids that contain two aminal moieties and two contiguous quaternary carbon centers. We have investigated the construction of the pentacyclic skeleton of the communesins by employing the oxidative rearrangement of aurantioclavine derivatives, which are believed to be biosynthetic intermediates of the polycyclic communesin alkaloids. The quaternary C-7 carbon center was constructed in a stereoselective manner, whereas the installation of the C-11 stereocenter requires an epimerization process. The isolation of a 2-ethoxyindolenine prior to the reduction of the nitro group and cyclization steps was critical to the success of this strategy.

A new method has been developed for the synthesis of tetrahydro-2H-fluorenes based on a Pd(0)-catalyzed benzylic C(sp³)−H functionalization. Importantly, the success of the cyclization step was dependent on there being substituents at the two positions ortho to the benzylic group to avoid an undesired C(sp²)−H functionalization. This method was subsequently used to prepare the right-hand fragment of the hexacyclic triterpenoid benzohopanes, and therefore represents a powerful tool for the construction of the related compounds.

Caprazamycin A has significant antibacterial activity against Mycobacterium tuberculosis (TB). The first total synthesis is herein reported and features a) the scalable preparation of the syn-β-hydroxy amino acid with a thiourea-catalyzed diastereoselective aldol reaction, b) construction of a diazepanone with an unstable fatty-acid side chain, and c) global deprotection with hydrogenation. This report provides a route for the synthesis of related liponucleoside antibiotics with fatty-acid side chains.

Caprazamycin A has significant antibacterial activity against Mycobacterium tuberculosis (TB). The first total synthesis is herein reported and features a) the scalable preparation of the syn-β-hydroxy amino acid with a thiourea-catalyzed diastereoselective aldol reaction, b) construction of a diazepanone with an unstable fatty-acid side chain, and c) global deprotection with hydrogenation. This report provides a route for the synthesis of related liponucleoside antibiotics with fatty-acid side chains.

Bifunctional benzothiadiazine-catalyzed epoxidation of α,β-unsaturated amides proceeds efficiently to give chiral 2-oxiranecarboxamides in excellent yields of 89–99 % and with good enantioselectivity of up to 84 % ee. A synthetic application of the oxiranecarboxamides is also described.

Assoanine, pratosine, hippadine, and dehydroanhydrolycorine belong to the pyrrolophenanthridine family of alkaloids, which are isolated from plants of the Amaryllidaceae species. Structurally, these alkaloids are characterized by a tetracyclic skeleton that contains a biaryl moiety and an indole core, and compounds belonging to this class have received considerable interest from researchers in a number of fields because of their biological properties and the challenges associated with their synthesis. Herein, a strategy for the total synthesis of these alkaloids by using CH activation chemistry is described. The tetracyclic skeleton was constructed in a stepwise manner by C(sp³)H functionalization followed by a Catellani reaction, including C(sp²)H functionalization. A one-pot reaction involving both C(sp³)H and C(sp²)H functionalization was also attempted. This newly developed strategy is suitable for the facile preparation of various analogues because it uses simple starting materials and does not require protecting groups.

The formal synthesis of hemiterpene spirooxindole alkaloids elacomine (1) and isoelacomine (2) is described. Heck reaction of protected iodoanilines with 5,6-dihydro-2H-pyran-2-one or six-membered unsaturated lactams was investigated. The coupling product was readily converted to a carbamoyl chloride with an incorporated diene unit. The spiro(pyrrolidine-3,3′-oxindole) skeleton, which corresponds to the carbon skeleton of 1 and 2, was efficiently constructed from this intermediate by using a domino palladium-catalyzed Heck reaction and bismuth-catalyzed hydroamination. An isolated byproduct of the reaction could also be converted to the spirooxindole skeleton.

Hydrogen-bond (HB)-donor catalysts that bear a 2-aminoquinazolin-4-(1H)-one or a 3-aminobenzothiadiazine-1,1-dioxide skeleton have been developed, and it has been shown that these catalyst motifs act similarly to other HB-donor catalysts such as thioureas. The highly enantioselective hydrazination of 1,3-dicarbonyl compounds was realized even at room temperature with up to 96 % ee for 2-aminoquinazolin-4-(1H)-one-type catalysts, which were more effective than the corresponding urea and thiourea catalysts. In addition, benzothiadiazine-1,1-dioxide-type catalysts were shown to promote the isomerization of alkynoates to allenoates with high enantioselectivity. To overcome the problem that the products were obtained as mixtures with the starting alkynoates, we developed the tandem isomerization and cycloaddition of alkynoates for the synthesis of advanced chiral compounds such as bicyclo[2.2.1]heptenes and 3-alkylidene pyrrolidine without a significant loss of enantioselectivity.

An unusual ring-contraction rearrangement to give spirocyclopropanes from fused cyclobutanols (see scheme) has been developed. It is found that the strain energy of the substrates derived from an additional fused ring and the stereoelectronic effect of the migrating σ bond are important factors. It is noteworthy that the rearrangement proceeds in a stereospecific manner. Moreover, the method provides a spiro(cyclopropane–indane) framework from tricyclo[6.3.0.02,5]undecane, which corresponds to illudane and the protoilludane skeleton.

Domino reactions have received great attention as efficient synthetic methodologies for the construction of structurally complex molecules from simple materials in a single operation. Catalysts in domino reactions have also been well studied. In these reactions, a catalyst activates the substrate(s) only once, and the structure of the product is delineated at that time. Recently, the new concept of “tandem catalysis” in domino reactions, in which catalyst(s) sequentially activate more than two mechanistically distinct reactions, has been proposed. Tandem catalysis is categorized into three subclasses: orthogonal-, auto-, and assisted-tandem catalyses. Auto-tandem catalysis is defined as a process in which one catalyst promotes more than two fundamentally different reactions in a single reactor. An overview of recent and significant achievements in auto-tandem catalysis is presented in this paper.

Toward concise access to functionalized amides and lactams, palladium-catalyzed amidations of alkynes and alkenes with formamide derivatives were developed. Cyanoformamides having an alkynyl group were found to undergo intermolecular cyanoamidation in the presence of palladium catalyst to afford α-alkylidene lactams. Whereas, when cyanoformamides that possess a 1,1-disubstituted alkenyl group were used as starting materials, α,α-disubstituted lactams were obtained. The latter reaction was extended to enantioselective transformation by utilizing optically active phosphoramidites as ligand. Furthermore, chloroformamides having a 1,1,2-trisubsituted alkenyl group were found to give α-vinyl-lactams in the presence of palladium catalyst, base and silver salt. Additionally, formal intermolecular hydroamidation of alkenes was performed through one-pot hydroboration-carbamoylation sequence. © 2008 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 8: 386–394; 2008: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.20159