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Volume 53, Issue 2
Displaying 1-9 of 9 articles from this issue
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Hiroyuki ISHIBASHI, Tatsunori SATO, Masuzumi IKEDA1995 Volume 53 Issue 2 Pages 85-94
Published: February 01, 1995
Released on J-STAGE: November 16, 2009
JOURNAL FREE ACCESSFree radical cyclization is rapidly becoming an important method for the synthesis of cyclic compounds. This review summarizes our recent studies on the synthesis of nitrogen-containing heterocycles by means of cyclization of N-alkenic carbamoylmethyl radicals which are generated from the corresponding α-haloamides by treatment with tributyltin hydride in the presence of azobis (isobutyronitrile) (AIBN) Ruthenium-catalyzed chlorine atom transfer cyclizations of α-chloro-α-thioacetamides have also been examined. These reactions are classified into several types of ring closures including relatively difficult 4-exo-trig and 5-endo-trig cyclizations which provide β- and γ-lactams, respectively. Applications of the method to the synthesis of natural products are also presented.View full abstractDownload PDF (1028K) -
Tadao ISHIZUKA, Takehisa KUNIEDA1995 Volume 53 Issue 2 Pages 95-103
Published: February 01, 1995
Released on J-STAGE: November 16, 2009
JOURNAL FREE ACCESSBoth enantiomers of cis-4, 5-disubstituted 2-oxazolidinones, DHAOx, DMAOx, CPAOx and HMC0x, which are sterically congested and conformationally fixed by bicyclo [2.2.1] and [2.2.2] ring systems are newly prepared by the Diels-Alder reactions of 2-oxazolone with the cyclic dienes such as anthracenes and cyclopentadienes followed by optical resolution with MAC acid. These compounds, particularly DMAOx and HMCOx, serve well as the most powerful 2-oxazolidinones chiral auxiliaries reported so far for the asymmetric reactions such as alkylations, the Diels-Alder reactions, the Michael-type additions and aldol reactions.
Sterically congested 2-aminoalcohol derivatives derived from the ring-opening of DHAOx and DMAOx are shown to be highly useful auxiliaries for enantioselective additions of diethylzinc to aldehydes and enantiodivergence of meso-dicarboxylic anhydrides.View full abstractDownload PDF (967K) -
Shuji KANEMASA1995 Volume 53 Issue 2 Pages 104-115
Published: February 01, 1995
Released on J-STAGE: November 16, 2009
JOURNAL FREE ACCESSThis review focuses on our own attempts of metal ion-assisted stereo- and regiocontrol of 1, 3-dipolar cycloaddition reactions : N-Metalated azomethine ylides, or metal enolates, of alkylideneamino nitriles and esters undergo endo-selective cycloadditions to α, β-unsaturated carbonyl acceptors to give 1-pyrrolines and pyrrolidines. Magnesium allylic alkoxides are highly reactive in nitrile oxide cycloadditions which are exclusively syn-selective and regioselective. Equally fruitful are nitrone cycloadditions to allylic alkoxides and Lewis acidcatalyzed nitrone reactions with allylic alcohols and enones.View full abstractDownload PDF (1411K) -
Yukihiko HASHIMOTO, Kazuaki KUDO, Kazuhiko SAIGO1995 Volume 53 Issue 2 Pages 116-121
Published: February 01, 1995
Released on J-STAGE: November 16, 2009
JOURNAL FREE ACCESSWe focused on neighboring group participation as a key step for controlling the structures of cationic intermediates, and developed a valuable cation precursor, 2, 2-dimethoxyethyl ester, as well as selective reactions directed by a sulfenyl group. It was found that 2, 2-dimethoxyethyl esters generate cyclic cationic intermediates on the action of a Lewis acid via neighboring group participation of the ester function toward the acetal carbon. The cationic intermediates thus generated were useful for the stereoselective Michael reaction as well as the Diels-Alder reaction. The reactions applying neighboring effect of a sulfenyl group were also examined. As a result, stereoselective aldol reactions of the substrates containing a sulfenyl group were developed. Moreover, regioselective pinacol rearrangement and allylation reaction, and stereoselective cationic cyclization could be effectively carried out under the control of a sulfenyl group.View full abstractDownload PDF (679K) -
Masahisa NAKADA1995 Volume 53 Issue 2 Pages 122-137
Published: February 01, 1995
Released on J-STAGE: January 28, 2010
JOURNAL FREE ACCESSThe first total synthesis of the antitumor macrolide rhizoxin in a highly stereocontrolled manner has been achieved. The efficient construction of optically pure key building fragments designed based on rational retrosynthetic analysis was accomplished in a concise manner. Synthesis of the Right-Wing started from the chiral half-ester generated by asymmetric hydrolysis of the corresponding meso-diester using pig liver esterase. The remaining chiral centers of the fragment were constructed by cyclic hydroboration. Synthesis of the LeftWing was accomplished starting from methyl (S) -3-hydroxy-2-methylpropionate which in turn had been prepared again by enzyme mediated transformation.
Coupling of Right-Wing and Left-Wing was carried out by Julia condensation, and the macrocyclic lactone was constructed by intramolecular Horner-Emmons reaction. Finally, the stereoselective epoxidation was achieved cleanly after formation of unsaturated 16-membered macrocyclic lactone. Chromophore-side-chain moiety was constructed at final stage by reaction of the phosphineoxide in 80% yield with high selectivity (E/Z= >20/1).
The present methodology will be useful for the synthesis of the homologues or man-made rhizoxins.View full abstractDownload PDF (1592K) -
Kenso SOAI, Tadakatsu HAYASE1995 Volume 53 Issue 2 Pages 138-150
Published: February 01, 1995
Released on J-STAGE: November 16, 2009
JOURNAL FREE ACCESSA series of N, N-dialkylnorephedrines and pyrrolidinylmethanol derivatives are synthesized as chiral catalysts and as chiral ligands for the highly enantioselective 1, 2- and conjugate additions of organozinc reagents to aldehydes, ketones, phosphinylimines and α, β-unsaturated ketones. N, N-Dibutylnorephedrine (DBNE) and diphenyl (1-methylpyrrolidin-2-yl) methanol (DPMPM) are used as chiral catalysts in the enantioselective addition of dialkylzincs to aldehydes (up to 100% ee). Chiral thiophosphoramidate and N-benzyl-N-methylephedrinium halides are also enantioselective catalysts. Polystyrene and silica gel (and alumina) supported N-alkylnorephedrines with or without a spacer are used as heterogeneous chiral catalysts. Chiral compounds prepared include sec- alcohols, furylalcohols, alkynylalcohols, allylalcohols, β-hydroxynitrile, fluorine- containing alcohols, deuterated alcohols, γ-hydroxyketones, pyridylalkylalcohols, diols, hydroxyaldehyde, γ- and δ-hydroxyesters, butyro-and δ- valerolactones. Enantioselective Reformatsky reaction with aldehydes and ketones using DPMPM and N, N-diallylnorephedrine affords chiral β-sec-, and β-t-hydroxyesters, respectively. Enantioselective alkylation of aldehydes using DBNE is applied to the synthesis of chiral alkylphthalides, (+) -Iepicidin A, and a precursor of tacalcitol. Diastereodivergent alkylations of α or β-chiral aldehydes are achieved by using the appropriate enantiomer of DBNE or DPMPM. Self-replication and auto-multiplication of chiral zinc alkoxides of pyridylalkylalcohols and diols as asymmetric autocatalysts is described. Enantioselective and/or diastereoselective alkylation of diphenylphosphinylimine affords chiral amine. Chiral nickel complex with DBNE catalyzes the enantioselective conjugate addition of dialkylzincs to α, β-unsaturated ketones.View full abstractDownload PDF (1457K) -
Eiichi KIMURA1995 Volume 53 Issue 2 Pages 151-153
Published: February 01, 1995
Released on J-STAGE: November 16, 2009
JOURNAL FREE ACCESSDownload PDF (463K) -
Takaaki MIYAZAWA, Shinichi MATSUMOTO1995 Volume 53 Issue 2 Pages 154-155
Published: February 01, 1995
Released on J-STAGE: November 16, 2009
JOURNAL FREE ACCESSDownload PDF (120K) -
[in Japanese], [in Japanese], [in Japanese], [in Japanese]1995 Volume 53 Issue 2 Pages 156
Published: February 01, 1995
Released on J-STAGE: November 16, 2009
JOURNAL FREE ACCESSDownload PDF (153K)
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