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Volume 59, Issue 11
Displaying 1-10 of 10 articles from this issue
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Jun Terao, Nobuaki Kambe2001 Volume 59 Issue 11 Pages 1044-1051
Published: November 01, 2001
Released on J-STAGE: November 13, 2009
JOURNAL FREE ACCESSNew catalytic reactions for regioselective introduction of alkyl and/or silyl functionalities to alkenes and dienes are described. These reactions proceed efficiently under mild conditions by the use of Cp2TiCl2 as a catalyst in the presence of Grignard reagents. The present study would provide a prototype for the practical use of alkyl halides and chlorosilanes in transition metal-catalyzed reactions. In these reactions, ate complexes of titanocene play important roles as the active species. The scope and limitations, as well as reaction pathways, are discussed.View full abstractDownload PDF (1399K) -
Chengguo Jia, Tsugio Kitamura, Yuzo Fujiwara2001 Volume 59 Issue 11 Pages 1052-1061
Published: November 01, 2001
Released on J-STAGE: November 13, 2009
JOURNAL FREE ACCESSEfficient inter- and intramolecular hydroarylations of C-C triple bonds by simple electron-rich arenes have been realized in the presence of Pd (II) or Pt (II) catalysts and an acid such as trifluoroacetic acid and acetic acid. The reaction of heteroarenes such as pyrroles and indoles occurs under very mild conditions (e.g. at room temperature in neutral solvents such as CH2Cl2). The reaction provides a very good strategy for functionalization of arenes as well as heteroarenes, affording arylalkenes. The intramolecular reaction offers a concise and straightforward route to biologically interesting heterocycles such as coumarins, quinolinones and thiocoumarins. The possible mechanism involving electrophilic metalation of aromatic C-H bonds by a cationic metallic species such as [Pd (O2CCF3)] + and the formation of a vinyl cationic species is discussed.View full abstractDownload PDF (1417K) -
Masaki Shimizu, Takuya Kurahashi, Tamejiro Hiyama2001 Volume 59 Issue 11 Pages 1062-1069
Published: November 01, 2001
Released on J-STAGE: November 13, 2009
JOURNAL FREE ACCESSNovel synthetic reagents with gem-silylboryl and gem-diboryls have been prepared through formation of an ate complex from a lithium carbenoid and an interelement compound such as (dimethylphenylsilyl) (pinacolato) borane or bis (pinacolato) diboron, followed by 1, 2-migration of the silyl or boryl group from a negatively charged boron to the carbenoid carbon. Alkenylidene-type carbenoids afforded 1-boryl-1-silyl-1-alkenes and 1, 1-diboryl-1-alkenes, applicable to boron-mediated coupling reactions. Reaction of α-chloroallyllithiums with the silylborane gave 1-boryl-1-silyl-2-alkenes, which were shown to serve as a versatile reagent for stereodivergent allylation leading to 4-oxy-(E)-alkenylboronates and 4-oxy-(Z)- alkenylsilanes. 1-Boryl-1-silylallenes were synthesized from 3-acyloxy- or 3-chloroalkynyllithium and the silylborane. Furthermore, novel synthesis and application of 2, 3-diboryl-1, 3-dienes are presented.View full abstractDownload PDF (1275K) -
Interdependence among Geometry, Spin Multiplicity, and ReactivityYasutake Takahashi, Athanassios Nicolaides, Hideo Tomioka2001 Volume 59 Issue 11 Pages 1070-1077
Published: November 01, 2001
Released on J-STAGE: November 13, 2009
JOURNAL FREE ACCESSThe singlet and triplet states of cyclobutenylidene 1 and benzocyclobutenylidene 2 have been studied computationally (using ab initio and DFT methods) in order to assess the effect of angle strain on the S-T gap of vinyl- and phenylcarbenes. It is found that both carbenes have a singlet ground state. Cyclobutenylidene 1 hasa more significant singlet-triplet gap (-25 kcal mol-1) than benzocyclobutenylidene 2 (-14.5 kcal mol-1). The strong preference of 1 for a singlet ground state may be understood if it is viewed as bicyclobut-1-ene with a considerably puckered ring. Singlet benzocyclobutenylidene (12) is computed to have also a puckered cyclobutene ring albeit less pronounced. The lowest isomerization path available for singlet cyclobutenylidene (11) is the formation of vinylacetylene, which is predicted to have a barrier of around 9 kcal mol-1. Our calculations suggest that singlet benzocyclobutenylidene (12) lies in a rather deep potential well and should be observable under suitable experimental conditions. However, under low-temperature Ar matrix conditions no evidence for the formation of carbene 2 was obtained from the photolysis of precursor 15. On the other hand, laser flash photolysis (LFP) of precursor 16 enables us to observe benzocyclobutenylidene at room temperature. The lifetime of carbene 12 is determined to be 0.6-0.7, us in cyclohexane. The mCXY value for carbene 12 is determined to be 0.43, revealing a strong electrophilic nature and ranking 12 second among the electrophilic carbenes listed in the carbene philicity spectrum.View full abstractDownload PDF (1760K) -
Ken Kamikawa, Takashi Watanabe, Motokazu Uemura2001 Volume 59 Issue 11 Pages 1078-1085
Published: November 01, 2001
Released on J-STAGE: November 13, 2009
JOURNAL FREE ACCESSAxially chiral biaryls are stereoselectively prepared by utilizing planar chiral arene chromium complexes. Both enantiomers of an axial biaryl could be synthesized starting from a single enantiopure arene chromium complex, and this method is applied to the synthesis of the vancomycin A-B ring system and korupensamines.View full abstractDownload PDF (1628K) -
Jun-ichi Yoshida, Kenichiro Itami2001 Volume 59 Issue 11 Pages 1086-1094
Published: November 01, 2001
Released on J-STAGE: November 13, 2009
JOURNAL FREE ACCESSA novel phase tag strategy for the solution-phase synthesis, in which a 2-pyridyldimethylsilyl group functions as an efficient tag for acid/base extraction, is described. Various tagging and detagging protocols, and transformations using building blocks bearing the 2-pyridyldimethylsilyl group have been developed.View full abstractDownload PDF (1591K) -
A ocused Library ApproachMikiko Sodeoka, Yoshiyasu Baba2001 Volume 59 Issue 11 Pages 1095-1102
Published: November 01, 2001
Released on J-STAGE: November 13, 2009
JOURNAL FREE ACCESSSelective inhibitors of protein phosphatases are expected to be useful tools for clarifying the biological functions of the phosphatases themselves, and also candidates for novel therapeutics. In terms of the catalytic site structure, protein phosphatases can be divided into two large groups: one is the protein serine/threonine phosphatases (PPs) group, and the other is the protein phosphatases (PTPs)/dual-specificity phosphatases (DSPs) group. We planned a library approach to the identification of PP- or PTP/DSP-selective inhibitors, in which unique structures derived from natural products are used as “core” phosphate mimics. In this paper we describe a synthesis and evaluation of a PTP/DSP inhibitor-oriented library. A series of novel tetronic acid derivatives were synthesized and evaluated as inhibitors of the dual-specificity protein phosphatases VHR and cdc25B, and tyrosine phosphatase PTP-S2. Several compounds were found to be potent inhibitors of cdc25B which is a key enzyme for cell-cycle progression.View full abstractDownload PDF (1672K) -
Seijiro Hosokawa, Susumu Kobayashi2001 Volume 59 Issue 11 Pages 1103-1108
Published: November 01, 2001
Released on J-STAGE: November 13, 2009
JOURNAL FREE ACCESSThe total synthesis of madindolin A was achieved. Stereoselective construction of the quaternary carbon in the cyclopentenedione moiety was accomplished by alkylation of dienolate bearing a chiral auxiliary. The coupling of sterically hindered aldehyde 17 and acid-sensitive amine 30 was achieved by developing a new reductive amination method using Sn (OTf)2 and NaBH(OAc)3. After the reductive coupling, the cyclopentenedione skeleton of madindoline was constructed by intramolecular condensation of triketone 5.View full abstractDownload PDF (794K) -
Mitsuo Sekine, Tomohisa Moriguchi, Takeshi Wada, Kohji Seio2001 Volume 59 Issue 11 Pages 1109-1120
Published: November 01, 2001
Released on J-STAGE: November 13, 2009
JOURNAL FREE ACCESSThis review deals with our recent studies of the synthesis of naturally occurring nucleic acid derivatives having P-N linkages. The total synthesis of a nucleotidic antibiotic, agrocin 84 (1), having two different types of unique phosphoramidate bonds is described in detail. Synthesis of this natural product remained unrealized for a long time after its discovery in 1974, but development of a new method for the construction of the P-N bond led us to our final goal. Phosmidosine (2) is an antibiotic that has an antifungal activity and has a rare O-methylated phosphoramidate structure. This compound was also successfully synthesized by use of 5-(3, 5-dinitrophenyl)-1H-tetrazole (DNPT) as the powerful activator of an N-prolyl phosphorodiamidite derivative that was condensed with an 8-oxoadenosine derivative. Several related compounds were also synthesized. These phosmidosine derivatives were found to exhibit significant antitumor activities. In connection with these studies, the synthesis and biological properties of aminoacylamido-AMP derivatives having N-P bonds as stable analogues of aminoacyl-AMP are also described.View full abstractDownload PDF (1830K) -
Hiroaki Toshima2001 Volume 59 Issue 11 Pages 1121-1129
Published: November 01, 2001
Released on J-STAGE: November 13, 2009
JOURNAL FREE ACCESSTotal synthesis of biologically active compounds related to plant disease and the physiological function has been accomplished. Coronatine, its related compounds, β-resorcylic acid derivatives, decumbic acid, aliphatic δ-lactones, cepaciamides, and piscidic acids, were selected as the synthetic targets. In these syntheses, the chiral pool method and catalytic asymmetric synthesis were also applied to introduce the requisite stereogenic centers. Combination of the two methods made it possible to synthesize a sufficient amount of the required enantiomers and diastereomers for biological studies.View full abstractDownload PDF (1713K)
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