Showing papers in "Synthesis in 1988"

The Design and Application of Free Radical Chain Reactions in Organic Synthesis. Part 1

Abstract: The successful application of free radical transformations in organic synthesis requires a basic knowledge of elementary radical reactions and an understanding of the principles of free radical chain reactions. Using illustrative examples from the recent literature as a framework, this review provides an introduction to the design and application of free radical reactions for use in organic synthesis. While a few nonchain reactions are discussed, the primary focus is on four of the most important and versatile methods to conduct radical chain reactions. These are: the tin hydride method, the fragmentation method, the thiohydroxamate ester method (the Barton method), and the atom-transfer method. Particular emphasis is placed on the selectivity requirements which must be met for the design of sequences of radical reactions. The review appears in two parts in consecutive issues. Part 1 contains Sections 1 (Introduction) and 2 (The Tin Hydride Method), and Part 2 contains Sections 3 (The Fragmentation Method), 4 (The Thiohydroxamate Ester Method), 5 (The Atom-Transfer Method), and 6 (Non-Chain Methods). Part 1 1.Introduction 1.1.Chain Reactions and Synthetic Planning 2.The Tin Hydride Method 2.1.Intramolecular Cyclizations 2.2.Intermolecular Additions 2.3.Combination Sequences Part 2 3.The Fragmentation Method 4.The Thiohydroxamate Ester Method 5.The Atom-Transfer Method 5.1.Hydrogen Atom Transfer Addition and Cyclization 5.2.Halogen Atom Transfer 5.2.1. Halogen Atom Transfer Addition 5.2.2. Halogen Atom Transfer Cyclization 5.3.3. Halogen Atom Transfer Annulation 5.3.Heteroatom-Halogen Donors 5.4.Organocobalt Group Transfer 6. Non-Chain Methods 7.Summary and Conclusions

Didehydroamino acids (DDAA) and didehydropeptides (DDP)

Abstract: Syntheses, reactions, and spectroscopic investigations in the field of didehydroamino acids published between 1982 and October 1987 are reviewed. A survey of natural compounds containing this subunit is also given. 1. Introduction 2. Syntheses of Didehydroamino Acids and Didehydropeptides 2.1. Syntheses via Elimination Reactions 2.2. Syntheses via C-C Bond Formation 3. Syntheses of Didehydropeptides by Amide Formation 3.1. Merrifield Peptide Synthesis 4. Isolation, Structure Elucidation, and Syntheses of Natural Products Containing Didehydroamino Acids 4.1. Syntheses of Peptide Hormones Containing Didehydroamino Acids 4.2. Didehydropeptides from Bacteria 4.3. Didehydropeptides from Fungi 4.4. Didehydropeptides from Marine Organisms 5. Reactions of Didehydroamino Acids 5.1. Reactions at the α,β-Double Bond 5.2. Reactions at the Carboxyl Function 5.3. Reactions at Nitrogen 6. Spectroscopic and Physical-Chemical Investigations of Didehydroamino Acids and Didehydropeptides

Intramolecular Addition Reactions of Allylic and Propargylic Silanes

Abstract: Revue sur la regio- et la stereoselectivite de l'addition intramoleculaire de divers silanes allyliques ou propargyliques a des molecules comportant un groupe accepteur (cetones, enones et dienones). Applications a la synthese totale de produits naturels

Improved Procedures for the Preparation of Cycloalkyl-, Arylalkyl-, and Arylthioureas

Abstract: Deux voies d'acces aux composes du titre: reaction de derives d'aniline avec l'isothiocyanate de l'acide benzoique suivie d'hydrolyse basique ou reaction d'ammoniac avec des isothiocyanates

Titanium Induced Coupling of Imines to Symmetrical Vicinal (R*,R*)-Diamines

Abstract: Symmetrical vicinal (R*,R*)-d,l-diamines were prepared from the corresponding imines and low valent titanium species generated by the action of titanium tetrachloride on amalgamated magnesium

Reduction of Some Functional Groups with Zirconium Tetrachloride/Sodium Borohydride

Abstract: Reduction des doubles liaisons C=O, C=N et des triples liaisons C≡N; obtention d'alcools et d'amines

Convenient synthesis of methyl 1-methyl-2,4-dibromo-5-imidazolecarboxylate

Abstract: Description de trois methodes de synthese a partir de sarcosine, de methyl-1 imidazole ou de diaminomaleonitrile

A Convenient Synthesis of 2-Deoxy-β-D-glucopyranosides

Abstract: The O-(2-deoxy-2-phenylthio-α-D-glucopyranosyl) trichloroacetimidate α-3 was obtained from 3,4,6-tri-O-benzyl-D-glucal (1) in a two-step procedure. This compound is a powerful glycopyranosyl donor, which with typical alcohol acceptors provided mainly the corresponding 2-phenylthio-substituted 2-deoxy-β-D-glucopyranosides β-5a to β-5d. These were converted by Raney nickel treatment to the desired 2-deoxy-β-D-glucopyranosides 6 in high yields

New and Efficient Lewis Acid Catalysts in Intramolecular Ene Reactions

Abstract: Differents acides de Lewis sont testes dans la reaction du citronellal sur le malonate de dimethyle pour determiner quel est le plus efficace pour l'obtention d'un des stereoisomeres d'isopropenyl-2 methyl-5 cyclohexanemalonate de dimethyle

Convenient One-Pot Conversion of Alcohols into Esters via Hemiacetal Intermediates

Abstract: A simple and efficient one-pot oxidative procedure, adaptable to a large scale, is described for the preparation of methyl esters from either primary alcohols or vic-diols. The aldehyde is generated by Swern or periodate oxidation, followed by bromine oxidation of the methyl hemiacetal formed in aqueous methanolic solution.