Kiyosei Takasu

The azulene moiety, composed of contiguous pentagonal and heptagonal rings, is a structural defect that alters the electronic, magnetic, and structural properties of graphenes and graphene nanoribbons. However, nanographenes embedded with an azulene cluster have not been widely investigated because these compounds are difficult to synthesize in their pure form. Herein, azulene-embedded nanographenes bearing a unique cove-type edge were synthesized by a novel synthetic protocol. Experimental and

The rhodacyanine dye MKT-077 (1), a potent antitumor agent, was found to possess strong in vitro activity against Plasmodium falciparum and a low cytotoxicity. Several new rhodacyanine dyes related to 1, containing a variety of linked heterocyclic moieties, were synthesized, and their antimalarial potencies were evaluated. The synthetic rhodacyanines were found to have EC(50) values against P. falciparum in vitro in the range of 4-300 nM. Several compounds in this series have remarkable selectiv

An efficient catalytic (2 + 2)-cycloaddition reaction leading to the formation of cyclobutane rings has been devised. The process transforms silyl enol ethers and alpha,beta-unsaturated esters into polysubstituted cyclobutanes with a high degree of trans-stereoselectivity. Both the rate and stereoselectivity of the process can be controlled by the choice of the ester group and silyl substituents. The results of stereochemical studies show that the cycloaddition step in this reaction proceeds in

Acid instead of base: Kinetic resolution of secondary alcohols is realized using chiral Brønsted acid catalyzed acylation instead of the conventional basic conditions. A broad range of functional groups are tolerated, such as aldehydes, carboxylic acids, and enoates. The selectivity factor (s) reaches up to 215 at ambient temperature.

[reaction: see text] An intermolecular aza-double Michael reaction leading to functionalized piperidin-2-ones from simple starting materials has been developed. The method allows alpha,beta-unsaturated amides to be used as a synthon of the piperidine nucleus. In addition, the utility of this methodology is demonstrated by its application to a formal synthesis of the indolo[2,3-a]quinolizidine alkaloids, (+/-)-deplancheine, (+/-)-tacamonine, and the antidepressant paroxetine.

Abstract [3+2] Cycloadditions of silyl enol ethers with donor‐acceptor (D‐A) cyclopropanes, such as 2‐alkoxycyclopropanecarboxylates and 2‐( p ‐methoxyphenyl)cyclopropyl phenyl ketone, proceed in the presence of a catalytic amount of triflic imide (Tf 2 NH) to give functionalized cyclopentanes in high yield. The catalytic process allows promotion of the cycloaddition of substrates incorporating Lewis basic functions, such as ether and carbamate moieties. Moreover, multicomponent [4+2]‐[3+2] casc

This Account summarizes our recent development of triflic imide (Tf2NH)-catalyzed cycloaddition and cascade reactions. Reactions of electron-rich olefins, possessing a silyl group, with α,β-unsaturated carbonyl compounds afforded highly substituted cyclobutanes, cyclopentanes, and bicyclo[4.2.0]octanes in good to excellent yields. In the reactions, Tf2NH acts as a precatalyst to produce a strong Lewis acid, silyl triflic imide, which activates the cycloaddition reactions. Reactions of electron-r

Several beta-carbolines including naturally occurring substances and their corresponding cationic derivatives were synthesized and evaluated for antimalarial (antiplasmodial) activity in vitro and in vivo. A tetracyclic carbolinium salt was elucidated for antileishmanial and antitrypanosomal activities in vitro as well as antiplasmodial activity. Quarternary carbolinium cations showed much higher potencies in vitro than electronically neutral beta-carbolines and a good correlation was observed b

The treatment of 4-[(5E)-6-methoxycarbonyl-5-hexenyl]-3, 4-dimethyl-2-cyclopenten-1-one (5) with LHMDS, TMSI-HMDS, Bu(2)OTf-HMDS, or TMSCl-NEt(3)-ZnCl(2) caused the intramolecular double Michael addition to afford tricyclo[6.3.0.0(3, 9)]undecan-10-one 12 in high yields with perfect stereoselectivity. The methodology was further elaborated to achieve efficient total syntheses of (+/-)-culmorin (1) and (+/-)-longiborneol (2). The common precursor 13 of them was obtained from 14 in 94% yield as a s

[reaction: see text] A stereoselective approach to the spirocyclic nucleus of halichlorine and pinnaic acids has been developed starting from a piperidine derivative. A key transformation in this sequence involves a cascade radical translocation/cyclization process.