This Review provides an in-depth account of the synthesis of spirocyclic indolenines. Over the last 77 years, a wide array of diverse synthetic methods has been developed in order to generate these synthetically useful and biologically important spirocyclic scaffolds. The main synthetic strategies discussed are grouped into three main categories, namely interrupted Fischer indolisations, dearomatisation reactions of indoles and condensation reactions. The historical background, common synthetic challenges, current state-of-the-art and future perspectives of this field are examined.

Synthesis of Spirocyclic Indolenines

6 – Bile Pigments: Bilatrienes and 5,15-Biladienes

Publisher Summary This chapter discusses the properties and preparation methods of furoxans and benzofuroxans. The history of its structure is briefly outlined. Many furoxan structures are determined by crystallographic methods, and as a result the dimensions of the heterocyclic ring are known in a wide variety of fused and substituted examples. Dynamic resonance effects (DNMR)—signal-broadening and coalescence phenomena at medium and fast exchange rates—are characteristic of furoxans fused to aromatic rings. The spectrum of benzotrifuroxan is analyzed and compared with that of the trifurazan. The methods of benzofuroxans preparation are: (1) dimerization of nitrile oxides, (2) dehydrogenataion of dioximes, (3) preparations from olefins and nitrogen oxides, (4) miscellaneous furoxan synthesis, and (5) benzofuroxans and other aromatic-ring-fused systems. The simple deoxygenation of furoxans to furazans is provided. Furoxans can be reduced in a variety of ways, depending upon the conditions used. It includes: (1) catalytic hydrogenation, (2) reduction with complex hydrides, (3) reduction with phosphorus compounds, (4) reduction with dissolving metals and metal ions, (5) electrochemical and other reducing methods. The chapter considers the principal substituent groups on the furoxan ring and the reactions they undergo.

Furoxans and Benzofuroxans

This review deals with general and significant developments in the area of building block chemistry of lightly-fluorinated aliphatic compounds, that is, those that contain one, two, or three, fluorine atoms. For the purposes of the review, building blocks are small readily-available materials that already contain fluorine atoms. They are classified according to the number of carbon atoms supplied to the target molecule, rather than according to the number of fluorine atoms. Finally, certain fluorinated motifs which may be generated easily, and are then transformable in useful ways, are discussed.

Building Block Approaches to Aliphatic Organofluorine Compounds

The transient hot-strip (THS) method has been used for thermal conductivity and thermal diffusivity studies of electrically conducting materials by introducing a thin electrically insulating layer between the hot strip and the metallic material under study. The insulating layer introduces a certain thermal contact resistance between the hot strip (heat source cum temperature sensor) and the surface of the sample to be studied. To account for this thermal resistance a theory has been developed which indicates how measurements on these kind of materials should be performed and how the reduction of data from transient recordings should be carried out to give reliable results. The new experimental approach, which should be applied whenever a thermal contact resistance is suspected, has been demonstrated by two series of measurements on a stainless steel at room temperature.

http://iopscience.iop.org/article/10.1088/0022-3727/19/5/007/pdf

Thermal transport studies of electrically conducting materials using the transient hot-strip technique

Publisher Summary This chapter deals with the chemistry of five-membered ring fluorinated heterocycles. Fluorine and perfluoroalkyl groups positioned strategically in target molecules can considerably modify the chemical properties, biological activity, and selectivity. Fluoro-containing compounds play a significant role in medicinal and agricultural chemistry, as well as in material science. A number of fluoro and perfluoroalkyl-substituted pharmaceuticals, agrochemicals, dyes, and polymers are largely commercialized. Important differences in chemical reactivity of fluorinated compounds are based on the difference in: (1) carbon–fluorine, (2) carbon–hydrogen bond energy, and (3) electronegativity between fluorine and hydrogen. It is observed that fluorine introduced into biologically active molecules can block metabolism. There are two fundamentally different strategies, by which fluorine and perfluoroalkyl groups can be introduced into target molecules: (1) direct introduction that occurs by direct substitution of hydrogen by fluorine and perfluoroalkyl groups in a late step of the reaction sequence, and (2) introduction of fluorine and perfluoroalkyl groups by the application of fluorine-containing building blocks, derived from the readily available starting materials.

Enno Brunner

Papers

Fluoro Heterocycles with Five-Membered Rings

Stokvis-Reaktion, XIX. Klassifizierung der Tripyrrene; Additionen an die Methylenpyrrolinon-Doppelbindung

Über eine Ordnung der Dipyrromethene und über die Betainstruktur des Bilirubins. XI. Mitteilung zur Stokvis-Reaktion

Reaktionen von Halogen‐aminomethylen‐2H‐pyrrolen und Halogen‐pyrrolaldehyden

Pyrrolinone, IV Pyrrolin‐2‐one mit β‐ständigen elektronenziehenden Substituenten