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Volume 53, Issue 8
Displaying 1-8 of 8 articles from this issue
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Kaoru NAKAMURA, Yoshihiko HIROSE1995 Volume 53 Issue 8 Pages 668-677
Published: August 01, 1995
Released on J-STAGE: November 16, 2009
JOURNAL FREE ACCESSRecently, lipases are used widely as reagents for syntheses of chiral compounds, although organic chemists have only a little knowledge about characteristics of individual lipases. Reactivities and selectivities of lipase-catalyzed reactions are reviewed from a viewpoint of organic syntheses in the present article, which will be usefull for a guide to the proper selection of a lipase for kinetic resolutions of racemic compounds.View full abstractDownload PDF (1306K) -
Masahito SEGI, Tadashi NAKAJIMA1995 Volume 53 Issue 8 Pages 678-686
Published: August 01, 1995
Released on J-STAGE: November 16, 2009
JOURNAL FREE ACCESSNovel chalcogenating reagents, bis (dimethylaluminum) chalcogenides (Me2AlEAlMe2, E=Se (6), S (7), Te (8)), were prepared in situ by the transmetalation of bis (tributyltin) chalcogenides with trimethylaluminum in toluene at 80°C. Aldehydes and ketones were directly converted by the reaction with 6 to the corresponding selenoaldehydes and selenoketones, respectively, which were effectively trapped by 1, 3-dienes to afford their Diels-Alder adducts. Similarly, the reaction of N, N-disubstituted formamides and isocyanates with 6 gave selenoformamides and isoselenocyanates in good yields, respectively. α, β-Unsaturated selenoaldehydes and ketones underwent a regioselective [4+2] dimerization to yield cyclic diselenide derivatives. These reactive species also underwent intermolecular Diels-Alder cycloadditions in two different modes depending on the trapping agents. Furthermore, a variety of selenocarbonyl compounds were efficiently synthesized by the reaction of acetal derivatives with 6. The Wittig-type reaction of selenoaldehydes with any type of phosphorus ylides gave E-olefins predominantly. Similar reaction of aldehydes or ketones with 8 afforded cycloadducts of the corresponding telluroaldehydes or telluroketones and dienes. On the other hand, the reaction of isocyanates with 8 gave isocyanides in good yields, in which 8 acted as a deoxygenating reagent.View full abstractDownload PDF (1078K) -
Katsuo OHKATA, Kin-ya AKIBA1995 Volume 53 Issue 8 Pages 687-699
Published: August 01, 1995
Released on J-STAGE: November 16, 2009
JOURNAL FREE ACCESSA series of 10-S-3 type sulfuranes, tetraazathiapentalenes (10a-i, 11a-f, 12, and 17) fused with pyrimidine ring and/or pyridine ring, were prepared by oxidation of the corresponding thioureas. The restricted internal rotation of the pyrimidine ring was observed by temperature dependent 1H NMR spectrum which gave the kinetic parameters of ΔG298_??_=16.6kcal/mol, ΔH=15.9kcal/mol, and ΔS_??_=-2.4 eu at 25°C for the rotational barrier in 10a. The substituent effect to the kinetic data can be reasonably explained in terms of electronic balance of the N-S-N hypervalent bond or the different degree of contribution of resonance canonical structures. Comparison of the rotational barrier of 10a with that of model compounds (18 and 24) suggests that hypervalent N-S-N stabilization in 10a is more than 6kcal/mol. Methylation of these 10-S-3 type sulfuranes (10a, 10d, and 11a) was investigated to clarify the electronic effect in these molecules. The crystal structure of the neutral symmetric sulfurane 10a reveals to be a planar molecule in which the sulfur atom was found to be in the same plane of the two pyrimidine rings. The S-N bond lengths 1.948(3) and 1.938(3) Å are longer than the sum of the covalent bond radii, consistent with a bond order less than unity. The crystal structures of the dicationic symmetric sulfurane 17 and the unsymmetrical sulfurane 11a also show to be planar molecules. The S-N distances in 11a were different each other due to the electronic imbalance between the apical ligands. Semi-empirical calculation (AM 1) of these systems (10a and 17) indicate the expected electronic features of the hypervalent molecules (10-S-3 sulfuranes) and the small contribution of π-overlapping in the N-S-N bonds.View full abstractDownload PDF (1559K) -
Chihiro KIBAYASHI1995 Volume 53 Issue 8 Pages 700-711
Published: August 01, 1995
Released on J-STAGE: November 16, 2009
JOURNAL FREE ACCESSIn this review our own work on the development of chiral approaches to nitrogenous natural products based on a methodology involving conformational control in the transition states under nonchelation conditions has been presented. On 1, 2-asymmetric induction in the reaction of achiral reagents at the diastereotopic faces of a prochiral C=X (X=C, N, O etc.) group adjacent to an asymmetric carbon atom, the increased π-facial selectivity is brought about by conformational fixation of the single bond between the asymmetric center and the prochiral reaction center. Apart from cyclic chelation control, the useful ways to achieve this is to utilize the conformational restraints imposed by Cram-Felkin-Anh mode of nucleophilic addition, inside alkoxy effect, and allylic 1, 3-strain. Employing these nonchelation methodologies for controlling the stereochemistry of acyclic systems, we have succeeded in the enantiopure preparation of nitrogenous natural products including alkaloids, azasugars, and antibiotics.View full abstractDownload PDF (1487K) -
Shinya HARUSAWA, Takushi KURIHARA1995 Volume 53 Issue 8 Pages 712-723
Published: August 01, 1995
Released on J-STAGE: November 16, 2009
JOURNAL FREE ACCESSA highly stereoselective synthesis of (Z) - or (E) -double bonds in 10-membered thiolcarbonates is achieved by the [3, 3] sigmatropic rearrangement of 8-membered thionocarbonates which proceeds through the chairlike vs. boatlike transition states. The formation of the 8-membered intermediates followed by their [3, 3] sigmatropic rearrangements were investigated by experiments and theoretical calculations. Their utilities of this methodology have been demonstrated by the unique and stereoselective synthesis of (-)-yellow scale pheromone. Moreover, medium-membered heterocyclic allenes were synthesized by this method. The structure and reactivity of a new type of strained 8-membered allene were also examined. Using this method combined with a novel application of the newly developed SmI2-HMPA reduction of the cyclic allene, the antifungal constituent of a Sapium japonicum was synthesized.View full abstractDownload PDF (1340K) -
Hisao TAKAYANAGI1995 Volume 53 Issue 8 Pages 724-736
Published: August 01, 1995
Released on J-STAGE: November 16, 2009
JOURNAL FREE ACCESSThe first total synthesis of sarcophytol A, an anticarcinogenic marine cembranoid, was achieved in a highly stereo- and enantioselective manner starting with (E, E)-farnesol ; it includes : 1) a newly developed Z-selective (Z : E=>35 : 1) Horner-Emmons reaction using a phosphonate nitrile, 2) a modified cyanohydrin macrocyclization, and 3) an enantioselective (93% ee) reduction of macrocyclic ketone as its key steps. Enantiomerically pure sarcophytol A was obtained by a single recrystallization. An improved synthetic process appropriate for a large-scale preparation using geraniol as the starting material was also developed. It included a new ketal Claisen rearrangement using 2, 2-dimethoxy-2, 3-dimethylbutan-2-ol for α-ketol isoprene elongation, which was applied to sequences for highly stereoselective (E>99%) synthesis of trisubstituted γ, δ-unsaturated aldehydes and acids. Enantiomers of macrocyclic ethers, (2Z, 4E) and (2E, 4Z), were obtained from a product of the ketal Claisen rearrangement via baker's yeast reduction. [2, 3]-Wittig rearrangement of these compounds afforded enantiomers of both sarcophytol A and T with high enantioselectivity (91-98% ee) in high yields. Surprisingly, almost perfect reverse chirality transfer was observed between these geometrical isomers, i.e. (R)-ether gave (S)-alcohol in (2Z, 4E) isomer, while (R)-alcohol in (2E, 4Z) isomer.View full abstractDownload PDF (1599K) -
Osamu MIYANO1995 Volume 53 Issue 8 Pages 737-738
Published: August 01, 1995
Released on J-STAGE: November 16, 2009
JOURNAL FREE ACCESSDownload PDF (174K) -
[in Japanese], [in Japanese]1995 Volume 53 Issue 8 Pages 739
Published: August 01, 1995
Released on J-STAGE: November 16, 2009
JOURNAL FREE ACCESSDownload PDF (160K)
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