Bicyclic compounds Wagner-Meerwein rearrangment

Expecting that acidic isomerization involving a double Wagner-Meerwein rearrangement would transform the bicyclic olefin 74 into supposedly stable [10.10]betweena-nene and its (Z)[10.10] isomer, they treated 74 with H2S04-AcOH in benzene only to find that the product was an 85 15 mixture of 75 and 76. Solvolysis of the spiro compound 77 was also found to yield a 60 40 mixture of 75 and 76 which was totally free from the fused (Z)[10.10] and ( )[10.10] olefins. 

Wagner-Meerwein rearrangements were first discovered in the bicyclic terpenes, and most of the early development of this reaction was with these compounds.81 An example is... 

An ehmination/double Wagner-Meerwein rearrangement process has recently been developed by Langer and coworkers [39]. Treatment of compound 1-136, obtained by reaction of 1-134 and 1-135, with trifluoroacetic add (TFA) led to the cationic spedes 1-137, which then underwent a twofold Wagner-Meerwein rearrangement to give the bicyclic compound 1-139 via 1-138 (Scheme 1.34). 

Reaction with unsaturated bicyclic hydrocarbons. From a study of the chlorination of unsaturated bicyclic compounds, Masson and Thuillier1 conclude that the reaction follows, a radical addition mechanism when initiated thermally or photo-chemically. The stereochemistry of the addition is markedly influenced by steric effects. No Wagner-Meerwein rearrangements are observed under these conditions. An ionic mechanism is involved without initiation or in the presence of trifluoroacetic acid in this case the usual carbonium ion rearrangements are observed. 

The cyclization of geranyl-OPP (3) to produce monocyclic and bicyclic monoterpenes proceeds via enzyme-bound intermediates that are probably similar to those postulated as intermediates in Wagner-Meerwein rearrangements. These reactions (catalyzed by strong acid) result in the formation of many types of monoterpenes when compounds similar to the precursors of cyclic monoterpenes are used as reactants. These enzymes, called monoterpene cyclases, largely deter-... 

Terpene synthesis in nature is a complex process involving successive electrophilic additions followed by a variety of skeletal rearrangements, including those of the Wagner-Meerwein variety. These reactions are typically catalyzed by enzymes and are responsible for the wide array of structural diversity in these compounds, including 6-6-6-5 tetracycles, 6-6-6-6-5 pentacycles, 6-6-6-6-6 pentacycles, and the less abundant acyclic, monocyclic, bicyclic, tricyclic, and hexacyclic triterpenoids. Each of the more than 100 triterpene skeletons identified in nature are formed through the involvement of several multifunctional triterpene synthases. 

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