Double bond migration cyclic alkenes

Selective double-bond migration of linear and cyclic alkenes without skeletal rearrangement is achieved by treatment with basic reagents ([Eq. (1.29)] see also Chapter 4) ... 

Cyclic alkenes Suppressed double-bond migration [52]... 

Pd-catalyzed isomerizations are often efficiently suppressed by addition of thallium or silver salts (Sect. B.v). Moreover, additions of both acetate " " or watert" are reported to suppress double bond migration in certain systems. Cyclic alkenes give different regioiso-mers and often product mixtures owing to double bond isomerizations after arylation. For example, in Scheme 18, arylation of cycloheptene gives entirely the homoallylic product. Addition of silver carbonate cleanly suppresses the double bond migration (Scheme 18).b ... 

Metathesis of ene-ynes having alkene and alkyne moieties in a molecule is an extremely interesting reaction [2]. In this reaction, the double bond of ene-yne 1 is cleaved and a carbon-carbon bond is formed between the double and triple bonds, and the cleaved alkyUdene part of the double bond migrates onto the alkyne carbon to produce a cyclic compound 2 having a 1,3-diene moiety (Equation 6.2). 

The addition, therefore, follows Markovnikov s rule. Primary alcohols give better results than secondary, and tertiary alcohols are very inactive. This is a convenient method for the preparation of tertiary ethers by the use of a suitable alkene such as Me2C=CH2. Alcohols add intramolecularly to alkenes to generate cyclic ethers, often bearing a hydroxyl unit as well. This addition can be promoted by a palladium catalyst, with migration of the double bond in the final product. Rhenium compounds also facilitate this cyclization reaction to form functionalized tetrahydrofurans. 

The above are in class of cascade of reactions, that involve two successive transformations Ru-catalyzed coupling of 1,6-diynes with acyclic alkenes forming bicyclic cyclohexadiene through electrocyclic ring closure and the migration of the double bond. Under the same reaction conditions, the [2-b2-b2] cycloaddition with cyclic olefins results in tricyclic cyclohexadienes with another arrangement of conjugated double bonds. 

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