Die durch Lewis-Säuren katalysierte Cyclisierung von Geranylaceton

Geranylacetone ( 1a , 1b ) in the presence of a Lewis acid, undergoes a novel cyclization reaction to yield the two diastereomers 9-oxabicyclo[3·3·1]nonene 2 and 3 as main products. The formation of 2 and 3 is not stereospecific, i.e. both isomers 1a and 1b produce the same product mixture ( 2 / 3 ～ 2:1 ratio). This is in contrast to the known Brønsted-acid catalyzed cyclization of 1 , leading exclusively to the chromenes 4 and 5 in a stereospecific reaction. The reaction mechanisms and the structural assignments are discussed.     

Synthesen von Phosphonocarbonsäuren durch Michael-Addition

Syntheses of Phosphono-carboxylic Acids by Michael Addition A number of phosphono-carboxylic acid esters are available by means of alkaline catalytic addition of P? H and C? H acidic esters to activated double and triple bonds. These may be transformed into complexing agents by hydrolysis.     

Thermische Cyclisierung von α-Alkinonen zu 2-Cyclopentenonen

Thermal Cyclization of α-Alkynones to 2-Cyclopentenones Gas phase thermolysis at 600–740° of substituted 1-pentyn-3-ones (α-alkynones), which are easily prepared by acylation of trimethylsilyl acetylenes, leads to substituted 2-cyclopentenones. The intramolecular formation of a new C, C-bond between an acetylenic and a non-activated carbon atom is accompanied by a [1,2]-migration of one of the substituents at the triple bond. This novel ‘-alkynone cyclization’ reaction may be explained by postulating an alkylidene carbene intermediate which inserts into a C,H-bond five carbon atoms away at the non-acetylenic part of the ketone. Several examples demonstrate that the α-alkynone cyclization offers a simple tool for the preparation of certain monocyclic, bicyclic and spiro compounds containing a 2-cyclopentenone moiety.     

Polyaddition und Cyclisierung von 5-Isocyanatocarbons?uren

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