Carbonyl compounds heterocyclic synthesis, intramolecular

REVIEWS - Useful reviews have appeared entitled "As5nranetric Syntheses" "New applications of Malononltrlle in Organic Synthesis," s "Intramolecular Ene Reaction in Organic Synthesis," and "a-Sulfenylated Carbonyl Compounds in Organic Synthesis." Additional articles summarize stereospecific olefin syntheses, heterocyclic syntheses by benzyne cycllza-tlons, and ring transformations of pyrimidines. ... 

Carbonyls. Several papers have appeared this year from Issleib s group describing the synthesis of heterocyclic phosphorus compounds by acid-catalysed condensations of phosphines with carbonyl compounds. (Mercapto-alkyl)phenylphosphines (31) react with aldehydes or ketones to form 1,3-thiaphospholans or 1,3-thiaphosphorinans. The intermediate compound (32) can be isolated from a similar reaction with phenylisothiocyanate and is converted into a thiaphospholan by intramolecular loss of hydrogen sulphide. 

Heterocycles.—The phosphonium salt (59) is an effective three-carbon synthon, as demonstrated by its reaction with enolates of /9-keto-esters (Scheme 20) to give cyclopentenyl sulphides via an intramolecular Wittig reaction.63 Ylides are also intermediates in the synthesis of dihydrofurans (60) from the cyclopropylphos-phonium salt (61) and sodium carboxylates (Scheme 21).64 Cumulated ylides are very useful for the synthesis of heterocyclic compounds, e.g. (62), from molecules which contain both an acidic Y—H bond and a carbonyl or nitroso-function, as shown in Scheme 22.65... 

The Nef reaction often represents the key transformation in a reaction sequence in which it is involved. The synthesis of simple aliphatic ketones or aldehydes is probably not the most useful application of the Nef reaction. More important is the access to dicarbonyl compounds for intramolecular cyclization reactions leading to a large variety of carbocycles or heterocycles. However, the method can be capricious and success depends on the structure of the substrate. In order to overcome synthetic drawbacks, several roundabout methods have been devised for application to peculiar polyfunctionalized molecules. The number of modifications of the Nef reaction which can be carried out under a wide variety of conditions clearly reveals that no procedure is of general application. The scope and limitations of the different modifications will be discussed considering the structure of desired carbonyl derivative. 

An extensive review of the synthesis of a wide variety of five-membered heterocyclic compounds, via the formal 3-1-2-cycloaddition reactions of aziridines with alkenes, alkynes, nitriles, carbonyl groups, and heterocumulenes, has been presented." Supercritical CO2 has been used as the solvent in the formal 3-1-2-cycloaddition reactions of A-benzyl- and A-cyclohexyl-2-benzoyl-3-phenylaziridines with allenoates to yield pyrrole derivatives." The Lewis acid-catalysed intramolecular formal 3-1-2-cycloaddition reactions of 2-methyleneaziridines with tethered alkenes or alkynes (23) yielded cw-octahydrocyclopenta[c]pyrroles (24) after reductive workup. The reaction mechanism proceeds in a stepwise manner via a 2-aminoallyl cation (Scheme The Cu(I)/DTBM-Segphos-catalysed 1,3-dipolar cycloaddition reactions of a-silylimines and activated alkenes yielded highly enriched 5-unsubstituted a-quaternary proline cycloadducts with excellent diastereo- and enantio-selectivities (73-99% The... 

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