Methodology In Organic Synthesis Research Articles

ChemInform Abstract: Stereoselective Isomerization of Acetylenic Derivatives as a New Methodology in Organic Synthesis

The transition metal catalyzed isdmerization reac- tions of acetylenic derivatives were studied. (E,E)-Conju- gated dienones, dienoic esters and dienoic amides were syn- thesized from corresponding a,b-ynones, 2-ynoic esters and 2-ynoic amides, respectively. 2-Ynols were first isomerized to the corresponding 2-enones or 2-enals. The reactions can be accomplished simply, in high yield, and stereoselectively. It is proposed that allenic compounds are initially formed as the main intermediates and then isomerized further to the products. A convenient and potential useful methodology is provided for the preparation of important intermediates in the synthesis of natural products.

Stereoselective isomerization of acetylenic derivatives as a new methodology in organic synthesis

Abstract

Concluding remarks

Organometallic chemistry is now firmly entrenched in the methodology of organic synthesis. That this is so has been clearly demonstrated during the course of this meeting. Two themes have emerged. First, the power of organometallic reagents to provide enhanced selectivity in stoichiometric processes. In this area the use of carbene complexes, transition metal acyls, 7t-allyIs and arenes are already offering powerful new methods for the synthesis of a wide range of functionalized compounds with very high diastereo- and enantioselectivities. Many of the methods described are already efficient and routine. Intramolecular cycloadditions of eneynes, catalysed by palladium, now represent short routes to polycyclic systems of some complexity. Even in the held of selective protection organometallics offer advantages, for example in the case of reactive acetylenes.

The introduction of elemental fluorine into organic synthesis methodology using acetyl hypofluorite as a carrier

Acetyl Hypofluorite CH 3COOF ( 1 ) which is synthesized in situ using elemental fluorine, is the first hypofluorite without perfluoroalkyl group. Obviously its oxygen bound fluorine is less reactive in electrophylic fluorinations than the fluorine in CF 3COOF, CF 3OF and alike. This makes 1 a better candidate for cleaner reactions with many organic substrates. Acetyl hypofluorite adds itself across various double bonds in Markovnikoff mode proving the electrophilicity of the oxygen bound fluorine. Unlike most of the other electrophilic fluorinating reagents it reacts well with various anionic centers present in organo-metallic compounds. This reaction opens a new route for synthesis of numerous fluorine containing derivatives. Of special importance is the electrophilic fluorination of activated aromatic rings. Phenol and aniline derivatives usually react smoothly with 1 to give mainly the ortho fluoro derivative. We found that the reaction proceeds via addition elimination mechanism and indeed, when working in very mild conditions some of the corresponding adducts can be isolated. This reaction opens a new and effective route for rapid specific aromatic fluorinations a route which can substitute the old Balz-Schiemann reaction in many cases. Since acetyl hypofluorite can be prepared in a short time from F 2 and then react in situ very rapidly with the organic substrate it is an excellent candidate to serve as a carrier for 18F radioisotop from the radio active elemental fluorine to biological interesting compounds for use in the positron emitting transaxial tomography (PETT).

Applications recentes de la reaction de retro-diels-alder en synthese organique

During the past few years a number of reports have appeared, dealing with applications of the retro-Diels-Alder reaction, which now takes a place in the methodology of organic synthesis. An attempt is made here to summarize all the important work which has been done in this field from 1970 until the end of 1976. The accent will be the simplicity and broad variety of synthetic applications.