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Volume 65, Issue 8
Displaying 1-8 of 8 articles from this issue
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Toward Structural Elucidation of Catalytically Active SpeciesMasahiro Terada2007 Volume 65 Issue 8 Pages 748-760
Published: August 01, 2007
Released on J-STAGE: October 20, 2010
JOURNAL FREE ACCESSWe have developed highly enantioselective carbonyl-ene reactions catalyzed by a chiral titanium complex prepared from optically pure binaphthol (BINOL) and (i-PrO)2TiCl2 in the presence of molecular sieves (MS) 4 A. During the course of the structural elucidation of catalytically active “BINOL-Ti”, MS 4 A employed in the catalyst preparation step was found to function not only as a base to trap HCl but also as H2O donor eventually providing the active “BINOL-Ti”. The effect of counter cations of zeolites was also investigated in the catalyst preparation step. A sufficient content of Na cation in the zeolites is the key for efficient formation of the active “BINOL-Ti”. Direct transformation of BINOL-Ti (Oi-Pr)2 under the influence of the hydrated MS 4 A into the active catalyst was examined, where BINOL-Ti (Oi-Pr) 2 was assembled into the active “BINOL-Ti” primarily composed of μ3-oxo (Ti3O) species via the di-μ3-oxo bridging tetranuclear titanium complex. Although the exact structure of the active “BINOL-Ti” has not yet been determined, we proposed a plausible pathway to the formation of active “BINOL-Ti” from BINOL and (i-PrO)2TiCl2 under the influence of hydrated MS 4 A.View full abstractDownload PDF (2138K) -
Yoshiaki Nishibayashi, Yoshihiro Miyake, Sakae Uemura2007 Volume 65 Issue 8 Pages 761-771
Published: August 01, 2007
Released on J-STAGE: October 20, 2010
JOURNAL FREE ACCESSRecent development of optically active chiral ligands, ferrocenyloxazolinylphosphines (FOXAP), and their application to catalytic asymmetric reactions are reviewed. FOXAP have been prepared in high yields from the corresponding chiral oxazolinylferrocenes via diastereoselective lithiation followed by quenching with chlorodiphenylphosphine. They work as chiral ligands quite effectively for a variety of transition metal-catalyzed asymmetric reactions such as hydrosilylation and transfer hydrogenation of ketones and imines, kinetic resolution of alcohols, carbon-carbon bond forming reactions and ring-opening reactions.View full abstractDownload PDF (1743K) -
Shuji Akai, Yasuyuki Kita2007 Volume 65 Issue 8 Pages 772-782
Published: August 01, 2007
Released on J-STAGE: October 20, 2010
JOURNAL FREE ACCESSThe lipase-catalyzed transesterification of alcohols with acyl donors in organic media has gained increased attention as a powerful method for the preparation of optically enriched compounds under very mild conditions, in which the vinyl esters 2 have been most frequently employed as the acyl donors; however, they are not always satisfactory.
We applied the ethoxyvinyl esters 6 to the lipase-catalyzed transesterification reactions for the first time and discovered their advantages, viz., (i) the efficient reactivity and enantiotopic selectivity similar to or higher than those of 2 and (ii) the ready availability of the esters 6 having a suitably functionalized acyl moiety from the corresponding carboxylic acids and their applicability to the enzymatic reactions. These findings have opened a new possibility of the lipase-catalyzed reactions. In this review, several examples are introduced along with some related recent progress on the lipase-catalyzed asymmetric syntheses. The topics include (i) the enantioselective desymmetrization of prochiral 2, 2-disubstituted 1, 3-propanediols using 1-ethoxyvinyl 2-furoate 6b, (ii) the lipase-catalyzed domino reactions using suitably functionalized acyl donors 6e-i for the direct preparation of optically enriched cyclic compounds having multi stereogenic carbon centers, (iii) the dynamic kinetic resolution (DKR) of racemic secondary alcohols by the combined use of lipases and the ruthenium complexes 36a-g, and (iv) the DKR of racemic allylic alcohols (44, 45) by the combination of lipases and the vanadium compound 43. Application of these reactions to the asymmetric total synthesis of natural products is also described.View full abstractDownload PDF (1613K) -
Hiroyuki Akita2007 Volume 65 Issue 8 Pages 783-794
Published: August 01, 2007
Released on J-STAGE: October 20, 2010
JOURNAL FREE ACCESSThis review summarizes the chemoenzymatic syntheses of biologically active natural products based on a combination of chemical diastereoselectivity and enzymatic enantioselectivity using lipase. Both primary alcohols possessing a chiral center at β-position of hydroxyl group and secondary alcohols were subjected to the lipase-assisted acylation in the presence of acyl donor to afford the optically active esters and the optically active alcohols corresponding to the starting material. These optically active compounds were converted to the biologically active natural products such as bisabolane type sesquiterpenes, oudemansins, nikkomycins B and Z, chuangxinmycin, cystothiazoles and melithiazols possessing antifungal and cytotoxicic activities, inhibition of NADH oxidation, etc.View full abstractDownload PDF (1712K) -
Takayuki Doi, Hiroshi Tanaka, Takashi Takahashi2007 Volume 65 Issue 8 Pages 795-804
Published: August 01, 2007
Released on J-STAGE: October 20, 2010
JOURNAL FREE ACCESSSolid-phase syntheses of combinatorial libraries based on natural products, such as, (i) vitamin D3, (ii) macrosphelide A, (iii) aurilide, (iv) aeruginosin 298-A, (v) trisaccharides, (vi) clavulone, (vii) 15-deoxyPGJ2, (viii) phlorizin, (ix) naltrindole, and (x) norbinaltorphimine are described. The highly convergent synthetic strategies that enable the high-throughput syntheses of their derivatives are also outlined.View full abstractDownload PDF (1447K) -
Chihiro Kibayashi, Sakae Aoyagi, Hideki Abe2007 Volume 65 Issue 8 Pages 805-819
Published: August 01, 2007
Released on J-STAGE: October 20, 2010
JOURNAL FREE ACCESSThe purpose of this review is to describe some of our achievements in the total synthesis of the tricyclic marine alkaloids isolated from the ascidians such as fasicularin, lepadiformine, and cylindricine C. The first total synthesis of (±) -fasicularin and (±) -lepadiformine was accomplished employing a stereocontrolled intramolecular hetero-Diels-Alder reaction of an N-acylnitroso moiety to an exocyclic diene. The synthesis of natural (-) -enantiomer of lepadiformine was then undertaken using a highly efficient protocol involving a new variant of an N-acyliminium ion-initiated intramolecular spirocyclization. These syntheses of lepadiformine led to revision of the published structure of the natural product, formerly assigned incorrectly, and established its absolute stereochemistry to be 2R, 5S, 10S, 13S. The developed strategy based on the spirocyclization was also applied to the total synthesis of (+) -cylindricine C and (-) -fasicularin. The ability of fasicularin to damage DNA by acting as an alkylating agent was investigated.View full abstractDownload PDF (2236K) -
Mamoru Tobisu2007 Volume 65 Issue 8 Pages 820-821
Published: August 01, 2007
Released on J-STAGE: October 20, 2010
JOURNAL FREE ACCESSThe oxidation of C-H bonds adjacent to heteroatoms has been known as an efficient method to generate iminium and oxocarbenium ions. However, the method has rarely been applied to the subsequent C-C bond formation reactions. In this short review, recent examples of such C-H oxidation/C-C bond formation reactions are described.View full abstractDownload PDF (324K) -
[in Japanese], [in Japanese], [in Japanese], [in Japanese], [in Japane ...2007 Volume 65 Issue 8 Pages 822
Published: August 01, 2007
Released on J-STAGE: October 20, 2010
JOURNAL FREE ACCESSDownload PDF (188K)
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