In 2018, it is expected that there will be a major revision of the International System Units (SI) which result in all seven base units being defined by fixing values certain atomic or fundamental constants. As part this revision, kelvin, unit thermodynamic temperature, redefined assigning value to Boltzmann constant k. This explicit-constant definition define kelvin terms SI derived energy, joule. It sufficiently wide encompass any form thermometry. The planned redefinition has motivated...

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAsymmetric .alpha.-amination of ketone enolates by chiral .alpha.-chloro-.alpha.-nitroso reagents: a new approach to optically pure erythro-.beta.-amino alcoholsWolfgang Oppolzer, Osamu Tamura, Gajendran Sundarababu, and Marcel SignerCite this: J. Am. Chem. Soc. 1992, 114, 14, 5900–5902Publication Date (Print):July 1, 1992Publication History Published online1 May 2002Published inissue 1 July...

A concise synthesis of maremycins and D1 has been accomplished via cycloaddition a chiral cyclic nitrone with (E)-3-ethylidene-1-methylindolin-2-one as key step. This clarifies the stereochemistry is suitable for large-scale biological screening.

Abstract Successive treatment of N ‐acylsultams 3 with sodium hexamethyldisilazide, 1‐chloro‐1‐nitrosocyclohexane ( 1 ), and aq. HCl gave diastereoisomerically pure, crystalline ‐hydroxyamino‐acid derivatives 5 . These were converted into various amino acids 7 , ‐hydroxyamino 8 an ‐Boc‐amino acid 9 S )‐Isoleucine 17 ) )‐2‐acetamido‐3‐phenylbutyric 23 obtained from ‐crotonoylsultam 15 via 1,4‐addition organomagnesium or organocopper reagent followed by enolate ‘amination’

The total syntheses of tetrapeptides tubulysins D (1 b), U c), and V d), which are potent tubulin polymerization inhibitors, described. synthesis Tuv (2), an unusual amino acid constituent tubulysins, includes 1,3-dipolar cycloaddition reaction chiral nitrone D-6 derived from D-gulose with N-acryloyl camphor sultam (-)-9 employing the double asymmetric induction, whereas Tup (20), another acid, involves a stereoselective Evans aldol (Z)-boron enolate generated...

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThe chemistry of O-silylated ketene acetals. Stereocontrolled synthesis 2-deoxy- and 2-deoxy-2-C-alkyl-erythro-pentosesYasuyuki Kita, Osamu Tamura, Fumio Itoh, Hitoshi Yasuda, Hiroko Kishino, Ya Yuan Ke, Yasumitsu TamuraCite this: J. Org. Chem. 1988, 53, 3, 554–561Publication Date (Print):February 1, 1988Publication History Published online1 May 2002Published inissue 1 February...

The structural features and conformational conversion of the N-methyl pyridyl amide oligomer bearing 2,6-disubstituted pyridines were investigated. 1H NMR X-ray crystallography revealed that environment-responsive type control can be performed. bond switching together with intramolecular hydrogen-bonding effects caused dynamic protonation-associated from layered to spiral then flat.

Strategic use of oxophilic (hard) gold(III) and π-philic (soft) gold(I) catalysts provides access to two types cyclic ethers from propargylic alcohols. Thus, heating alcohols with an catalyst (AuBr3) results in cyclization afford bearing acetylenic moiety, due coordination the oxygen hydroxyl group. On other hand, a (Ph3PAuNTf2) induces Meyer–Schuster rearrangement α,β-unsaturated ketones, which undergo gold(III)-catalyzed intramolecular oxa-Michael addition carbonyl group,

An efficient synthetic method for multisubstituted pyridines from β-aryl-substituted α,β-unsaturated oxime ethers and alkenes via Pd-catalyzed C–H activation has been developed. Systematic optimization of catalyst ligands revealed that sterically hindered increased the reactivity. Mechanistic studies suggested products are formed by β-alkenylation followed aza-6π-electrocyclization. Various oximes could be utilized to afford with complete regioselectivity. The usefulness this methodology was...

A novel binucleating ligand, N,N'-bis[(2-diphenylphosphino)phenyl]formamidine (Hdpfam), has been prepared and utilized for the synthesis of homo- heterobimetallic palladium/platinum complexes M2R2(μ-X)(μ-dpfam) (M = Pd, Pt; R Me, p-Tol, Cl; X Cl, Br, I; dpfam N,N'-bis[(2-diphenylphosphino)phenyl]formamidinate). Treatment Hdpfam with 2 equiv MRX(tmeda) or MRX(cod) in presence tmeda produced homobimetallic complexes. The complex PdPtMe2(μ-Cl)(μ-dpfam) was obtained by reaction PdMeCl(cod)...

Optically pure (5R)- [and (5S)]-5,6-dihydro-5-phenyl-2H-1, 4-oxazin-2-one N-oxides [(5R)- and (5S)-2] were designed as chiral (E)-geometry-fixed alpha-alkoxycarbonylnitrones 1. The nitrones (5S)-2 synthesized by three-step oxidation of (R)- (S)-phenylglycinols [(R)- (S)-3], condensation the resulting (S)-2-hydroxylamino-2-phenylethanols (S)-5] with glyoxylic acid, cyclization intermediary (S)-6b. nitrone (5R)-2reacted olefins 7-14 under mild conditions to afford corresponding cycloadducts...

Chiral and cyclic nitrones were synthesized by TBAT-mediated desilylative cyclization of ω-mesyloxy-O-tert-butyldiphenylsilyloximes, readily prepared from sugar derivatives a consecutive treatment with O-tert-butyldiphenylsilylhydroxyl­amine mesyl chloride. The method was applied to sequential nitrone formation intramolecular cycloaddition.

A simple synthesis of 3,3,3-trifluoropropenyl compounds by means the TBAF-mediated Horner reaction is described. The reagent, 2,2,2-trifluoroethyldiphenylphosphine oxide, was readily prepared either Arbuzov ethyl diphenylphosphinite with 2,2,2-trifluoroethyl iodide or treating chlorodiphenylphosphine trifluoroacetic acid and water. Treatment phosphine oxide aromatic aldehydes in presence TBAF at room temperature afforded corresponding good yields. present method very convenient for preparing...

Bu3SnH-mediated radical cyclizations of 2-(2-bromophenyl)-N-ethenylacetamide gave 6-exo cyclization product 15 as the major product, whereas N-[2-(2-bromophenyl)ethyl]-N-ethenylamides almost exclusively 7-endo products. These results indicated that position carbonyl group on enamide played an important role in deciding course cyclization. The selective was applied to concise construction a cephalotaxine skeleton.

Total synthesis of grandisine D (5) was achieved by a Brønsted acid mediated Morita−Baylis−Hillman (MBH) ring-closure reaction and stereoselective aldol condensation with (S)-5-methylcyclohexenone (9) as key steps. The MBH approach also applicable for the construction aza-fused bicyclic systems pyrrolizidine stemona alkaloids.

A C-amide-substituted O-silylated oxime, (E)-(tert-butyldimethylsiloxyimino)acetic acid N,N-dimethylamide (8b), on treatment with 2.2 equiv of BF3·OEt2, in situ generated boracyclic nitrone-type intermediate BF3·14, which underwent cycloaddition alkenes to give 3,5-cis-isoxazolidines as the major products. The mechanism was strongly supported by isolation reaction 14 that characterized X-ray diffraction and its further reaction. This successfully applied synthesis syn-HPA-12 known an...

The 4-hydroxy 4-substituted glutamic acid moiety is a common substructure of biologically important natural products such as monatin [(2S,4S)-2], lycoperdic (3), and dysiherbaine (4). To develop methodology for syntheses these products, cycloadditions nitrone 5 with 2-substituted 2-propen-1-ols 6 acrylates 8 were investigated. Reactions alcohols in the presence MgBr2OEt2 gave cycloadducts 7 highly stereoselective manner, whereas noncatalyzed reactions afforded adducts 9. Using former...

ADVERTISEMENT RETURN TO ISSUEPREVLetterNEXTA Short Synthesis of Lennoxamine Using a Radical CascadeTsuyoshi Taniguchi, Keiko Iwasaki, Masahiko Uchiyama, Osamu Tamura, and Hiroyuki IshibashiView Author Information Division Pharmaceutical Sciences, Graduate School Natural Science Technology, Kanazawa University, Kakuma-machi, 920-1192, Japan Cite this: Org. Lett. 2005, 7, 20, 4389–4390Publication Date (Web):September 3, 2005Publication History Received4 July 2005Published online3 September...

The first syntheses of (−)-funebrine [(−)-1] and (−)-funebral [(−)-2] are described. feature sequential formation nitrone VI from methyl glyoxylate (5) with oxime 6, transesterification (E)-crotyl alcohol (4), intramolecular cycloaddition the resulting VII bearing crotyl ester to afford cycloadduct 7 as a major product. adduct was readily elaborated amino lactone (−)-3, key synthetic intermediate (−)-1 (−)-2.