Showing papers on "Total synthesis published in 1986"

Selective Synthesis by Use of Lewis Acids in the Presence of Organocopper and Related Reagents. New Synthetic Methods (61)

Abstract: Organometallic compounds with pronounced nucleophilicity such as organocopper and organolithium compounds, and powerful electrophiles, such as BF3 and AlCl3, are generally thought to be incompatible under normal, homogeneous reaction conditions. As a matter of course, it is anticipated that the two species cannot coexist and undergo transmetalation reactions. To our surprise, however, RCu and BF3 are compatible at low temperature. RCu·BF3 and related organocopper-Lewis acid reagents exhibit new and unique reactivities and selectivities: in conjugate additions, e.g., not only activation but also high regio-, stereo-, and chemo-selectivity as well as very high asymmetric induction is observed; allylic derivatives are alkylated regioselectively, and reaction towards carbonyl groups, imines, epoxides, aziridines, ethers, acetals, orthoformates, and pyridinium salts is in each case found to be selective. RLi·BF3 and related organolithium-Lewis acid reagents also exhibit noteworthy selectivities and reactivities. These complex reagents are utilized in the key steps of the total synthesis of many important natural products, such as certain terpenes, steroids, and alkaloids.

Enzymes as Catalysts in Organic Synthesis

Abstract: Lectures.- Baker's yeast mediated preparation of carbohydrate-like chiral synthons.- Alcohol dehydrogenase catalysed oxidoreduction reactions in organic chemistry.- On the use of viologen dyes for stereospecific bioreduction.- Approaches to chiral building blocks for natural product synthesis.- Use of microorganisms for the resolution of synthetically useful bicyclo[ 3.2.0] hept-2-en-6-ones.- The scope of biocatalysts in organic chemical processing.- Enantioselective synthesis of biologically active cyclopentanoids via enzyme catalysed asymmetric reactions.- Creation of novel chiral synthons with pig liver esterase: application to natural product synthesis and the substrate recognition.- Application of microbial transformations in the total synthesis of natural products.- Approaches to chiral building blocks for natural products synthesis.- Synthesis of enantiomerically pure unnatural compounds via non-biomimetic homoaldol reactions.- Aldolases as catalysts in organic synthesis.- Immobilised redox enzymes and their use as catalysts for fine chemical synthesis.- Applications of microbes and microbial enzymes in environmental control and organic synthesis.- Synthesis of chirally labelled substrates using enzymes.- Synthesis of L-amino acids by isolated enzymes and microorganisms.- Development of an enzyme reactor for food chemistry.- Preparation and properties of semisynthetic flavoenzymes.- The study and redesign of enzymes by protein engineering.- Evolutionary guidance and the engineering of enzymes.- Posters.- Baker's yeast mediated synthesis of protected ?-hydroxyaldehydes.- Enantioselective PLE-catalyzed hydrolysis of meso-dimethyl tetrahydrophthalate on a 100 mole scale - protection of the enzyme by addition of bovine serum albumin.- Enantio- and diastereoselectivity of microsomal epoxide hydrolase: potential applications to the preparation of non-racemic epoxides and diols.- Efficient enzymic production of enantiomerically pure amino acids.- Biohydroxylation of non activated carbon atoms. A model for the hydroxylation site of the fungus beauveria sulfurescens.- "Sterols Bioconversions in systems with an organic phase".- Second-generation biocatalysis.- Round-table discussions.- I. Nicotinamide recycling.- II. Enzymatic hydrolysis of nitriles, amides, urethanes and carbonates.- III. Enzymes in organic solvents. Enzymatic esterification.- IV. General discussion "Where do we go?". Conclusions and suggestions.- - Chiral building blocks.- - Role of enzymes in protection and deprotection.- - Regioselective reactions using enzymes.- - New areas for enzyme applications.- - Artificial coenzymes, genetic - and proteinengineering.- - Requests from synthetic organic chemists.- - Final remarks.- List of contributors.

Total synthesis of mycophenolic acid

Abstract: Synthese a partir de t-butyldimethylsiloxy-8 (=R-8) methoxy-1 methyl-5 octene-4yne-1 et de methoxymethoxymethyl-3 (=R'-3) methyl-2 cyclobutene-2one-1 via la cyclisation de l'acide R-3 R'-6 hydroxy-2 methoxy-4 methyl-5 benzoique

Approach to the total synthesis of chlorothricolide: synthesis of (.+-.)-19,20-dihydro-24-O-methylchlorothricolide methyl ester ethyl carbonate

Abstract: An approach to the total synthesis of the 14-membered macrolide antibiotic aglycon chlorothricolide is presented. Key steps from the two halves to (±)-19,20-Dihydro-24-O methylchlorothricolide, methyl ester, ethyl carbonate include initial esterification across the C1 and C25 carbons followed by macrodilactonization across the C17 and C14 carbons. Ester enolate Claisen rearrangement and subsequent decarboxylation afforded the intact lactone. Functionalization of the top half is explored. The ester enolate Claisen rearrangement of propionate derivatives of resolved 1-(t-butyldimethylsilyl)-trans-2-butene-1-ol is reported. Subsequent protiodesilation of the reduced and protected Claisen products resulted in the formation of 2,3-dimethyl-4-pentenyl ethers. Thus, the secondary α-silyl alcohol has functioned as a chiral primary alcohol equivalent. The Claisen rearrangement of vinyl ethyl derivatives of 5-tert-butyl-1-(hydroxymethyl)-1-cyclohexene is reported. The standard allyl vinyl ether conditions as well as the triethyl orthoacetate and ester enolate variants of the Claisen rearrangement all resulted in the formation of cis(axial)-4-tert-butylcyclohexyl-substituted systems. Thus, in sterically unbiased cases, this [3.3] sigmatropic process results in the axial attachment of the side chain in a cyclohexyl system.

DNA-mediated photoelectron transfer reactions

Abstract: The first enantioselective total synthesis of (-)-asperdiol has been accomplished in 15 steps from epoxygeranyl bromide. It is noteworthy that the trisubstituted epoxide was robust enough to survive the conditions for the nucleophilic displacement reactions which were used to form the C-12, C-13 and the '2-3, C-4 bonds. The epoxide also survived the reductive desulfonylation and the intramolecular Horner-Emmons reaction. Our assumption that the cyclization to the 14-membered ring in the desepoxy series would be more straightfoward than in the epoxy series, which provided the impetus for the synthesis of (+)-desepoxyasperdiol, was shown to be false. A number of the optically pure fragments which were used for the total synthesis of 1, particularly 4 and 7, will be useful for the synthesis of other cembranoids.

Total synthesis of echinocandins. I. Stereocontrolled syntheses of the constituent amino acids.

Abstract: Figure 1. (a) UV-visible absorption spectrum of pyrimido[5,4-g]pteridine N-oxide 1 (5 X M ) in MeCN. (b) Difference spectrum of the mixture of 1 (5 m M ) and D M A (250 m M ) vs. 1 (5 m M ) in MeCN. (c) Wavelength dependence (presented by the yield of M M A ) in the photochemical demethylation of D M A by 1. A solution of 1 (5 m M ) and D M A (50 m M ) in MeCN was irradiated by using a grating monochromator (JASCO Model CRM-FA) with 2-kW Xe lamp and 4-nm band width under argon atmosphere for 2 h.

Cobalt-catalyzed one-step assembly of B-ring aromatic steroids from acyclic precursors

Abstract: Because of their varied physiological activity, steroids are important testing grounds on which to explore the utility of novel synthetic methodology In this study cobalt, in the form of CpCo(CO)/sub 2/ is used as a matrix around which to assemble natural and unnatural polycyclic products, including the steroid nucleus In this way, the total synthesis of A-ring aromatic systems of the estrone type was achieved via the D --> ABCD and A --> ABCD strategies An approach is reported here in which all four rings are assembled (0 --> ABCD) in one step to give B-ring aromatic derivatives with complete control of the crucial stereochemistry of the C,D-ring juncture This strategy has been accomplished previously only by employing biomimetic cyclizations and not en route to the rate target class of compounds which has never been constructed by total synthesis 13 references, 1 table

Naked Sugars as Synthetic Intermediates - Total Synthesis of L-Daunosamine

Abstract: Note: Univ lausanne,inst chim organ,ch-1005 lausanne,switzerland. Reference LGSA-ARTICLE-1986-017doi:10.1021/jo00376a055 Record created on 2005-11-09, modified on 2017-05-12

Highly stereocontrolled synthesis of some trioxygenated cyclohexenes: an asymmetric total synthesis of (-)-methyl triacetyl-4-epishikimate

Abstract: The title compound (XI) is prepared in 23.4% overall yield and ≥ 98% enantiomeric purity from the known polyfunctional bicyclic lactone (I).

Total synthesis of (-)-coriolin

Abstract: Synthese en 14 etapes a partir de la bicyclo [2.2.2] octene-7 dione-2,5(±) avec comme etape cle un rearrangement photochimique oxadi-π-methane