The synthesis of 4-dialkylaminopyridines can be accomplished in two steps starting from pyridine. Compared to pyridine, these derivatives are approximately 104 times more active when used as acylation catalysts. Dialkylaminopyridines are being used with ever-increasing frequency for acylation reactions which proceed either incompletely or not at all in pyridine. This article reviews the various possible applications of 4-dialkylaminopyridines in terpene, steroid, carbohydrate and nucleoside chemistry as well as in the transformation of amino acids into α-acyl aminoketones and polymerization of isocyanates. In addition, N-substituted 4-dialkylaminopyridinium salts can be used for the transfer of sensitive groups to nucleophiles in aqueous medium. The exceptional catalytic effect of these derivatives, even in non-polar solvents, is due, in part, to the formation of high concentrations of N-acylpyridinium salts which are present in solution as loosely-bound, highly reactive ion pairs.

4-Dialkylaminopyridines as Highly Active Acylation Catalysts. [New synthetic method (25)]

4‐Dialkylaminopyridine als hochwirksame Acylierungskatalysatoren

Aminopyridines as acylation catalysts for tertiary alcohols

Publisher Summary The chapter focuses tautomerism and electronic Structure of biological pyrimidines. The understanding of the tautomeric properties of the purine and pyrimidine bases of the nucleic acids and the determination of the electronic properties of the principal tautomers are of fundamental importance in molecular biology, in particular, in connection with the theory of mutations. The principal tautomeric properties of the fundamental biological pyrimidines-cytosine, uracil, and thymine-are due to the presence in these N-heteroaromatic compounds of electron-donor substituents, such as NH and OH, and of SH in some important analogs. The chapter discusses tautomerism of cytosine and presents the essential physicochemical properties of cytosine and some of its derivatives and to the theoretical interpretation of these properties. The chapter also discusses tautomerism and physicochemical properties of uracil and thymines and to give a theoretical interpretation of these properties. The study of the optical properties of naturally occurring pyrimidines and purines is a problem of great interest in molecular biology. The knowledge of these properties provide information important for understanding energy transfer, hypochromism, photochemistry, optical rotatory dispersion, circular dichroism, magnetic optical rotator dispersion, and magnetic circular dichroism of DNA, RNA, and related model systems. Tautomerism, electronic structures, and spectra of rare pyrimidine bases of the nucleic acids have also been discussed.

Taulomerism and Electronic Structure of Biological Pyrimidines

Publisher Summary The chapter focuses on the recent advances in the chemistry of benzo[b]furan and its derivatives. The chemistry of benzofuran derivatives has developed in a spectacular fashion: research in this field has reached such a scale that the period covered by this review has given rise to a larger number of papers than that between 1870 and 1950. It has proceeded along the following three main lines: (1) Extraction, determination of structures, partial or total synthesis of the simple or complex heterocyclic derivatives constituting the natural benzofuran derivatives of vegetable origin. (2) Synthesis of benzofuran derivatives with physiological, pharmacological, therapeutic, or toxic properties. (3) Studies on the reactivity of benzofuran and its derivatives from the chemical and physical point of view. Many substances with physiological, pharmacological, therapeutic, or toxic properties are to be found among natural products with a benzofuran ring. As to synthetic benzofuran derivatives prepared for the study of their physiological properties, their number is large. Benzofuran is prepared in semicommercial amounts. The chapter discusses the presence of benzofurans in coal tar and in petroleum. Natural benzofuran derivatives have also been discussed. The numerous syntheses of the benzofuran ring may be classified under four headings: (1) Formation of the heterocyclic ring from an aromatic substrate (2) formation of the heterocyclic ring from a nonaromatic substrate (3) fusion of the benzene ring to a furan substrate (4) formation of the heterocyclic ring from other heterocyclic compounds.

Recent Advances in the Chemistry of Benzo[b]furan and Its Derivatives. Part I: Occurrence and Synthesis

Die Wurzeln mehrerer Gerbera-Arten enthalten die bekannten Polyine 1 und 2. Aus Gerbera crocea wurden zusatzlich das Acetophenon-Derivat 3 und zwei neue Cumarine (4 und 7) isoliert, deren Strukturen durch spektroskopische Daten sowie durch Synthese geklart werden.



Naturally Occuring Coumarin Derivatives, IX1) On the Constituents of the Genus Gerbera



The roots of several Gerbera species contain the known polyynes 1 and 2. In addition from Gerbera crocea the acetophenon derivative 3 and two new coumarins (4 and 7) were isolated, the structures being elucidated by spectroscopic data as well as by synthesis.

Natürlich vorkommende Cumarin‐Derivate, IX1) Über die Inhaltsstoffe der Gattung Gerbera

Ausgehend von Osthenol (1) werden die Cumarine 3, 4 und 7 auf eindeutige Weise dargestellt. Weiterhin wird eine Synthese des Samidins (12) beschrieben.



Naturally Occuring Coumarin Derivatives, VII Synthesis of Racemic Lomatin, Columbianetin, Angenomalin and Samidin



Starting with osthenol (1) the coumarins 3, 4 and 7 have been prepared in an unequivocal manner. Furtheron a synthesis of samidin (12) is described.

Heinrich Franke

Papers

Natürlich vorkommende Cumarin‐Derivate, IX1) Über die Inhaltsstoffe der Gattung Gerbera

Natürlich vorkommende Cumarin‐Derivate, VII Synthese von racemischen Lomatin, Columbianetin, Angenomalin und Samidin

Natuerlich vorkommende cumarin-derivate 7. mitt. synthese von racemischem lomatin, columbianetin, angenomalin und samidin

Natuerlich vorkommende cumarin-derivate 9. mitt. inhaltsstoffe der gattung gerbera