Wagner-Meerwein

Oxabicyclo[2.2.1 ]heptyl 2-cation Wagner-Meerwein rearrangement, 1, 418... 

The Bamford-Stevens decomposition of tosylhydrazones by base has been applied to steroids, although not extensively. It has been demonstrated that the reaction proceeds via a diazo compound which undergoes rapid decomposition. The course of this decomposition depends upon the conditions in proton-donating solvents the reaction has the characteristics of a process involving carbonium ions, and olefins are formed, often accompanied by Wagner-Meerwein-type rearrangement. In aprotic solvents the diazo compound appears to give carbene intermediates which form olefins and insertion products ... 

A mechanism for formation of the first product by Wagner-Meerwein rearrangement has been proposed. ... 

Dehydration to olefins, which sometimes accompanies the reaction of alcohols with DAST [95, 108], is seldom as extensive as with a-fluoroamines (FAR and 1,1,2,3,3,3 hexafluoropropyldiethylamine) but occurs in a few cases to the exclusion of fluonnation, thus, 9a-fluoro-11-hydroxysteroids give 9a fluoro-A -steroids [127, 128] Dehydration accompanied by Wagner-Meerwein rearrangement occurs during the fluonnation of testosterone [129] Intermolecular dehydration to form ethers in addition to fluorides is observed in the reaction of benzhydryl alcohols [104] (Table 6)... 

From 5 the formation of alkene 2 is possible through loss of a proton. However, carbenium ions can easily undergo a Wagner-Meerwein rearrangement, and the corresponding rearrangement products may be thus obtained. In case of the Bamford-Stevens reaction under protic conditions, the yield of non-rearranged olefins may be low, which is why this reaction is applied only if other methods (e.g. dehydration of alcohols under acidic conditions) are not practicable. 

Skeletal rearrangements of carbenium ion species 2, that involve nucleophilic 1,2-migrations of alkyl groups, are called Wagner-Meerwein rearrangements... 

Of synthetic importance is the Wagner-Meerwein rearrangement especially in the chemistry of terpenes and related compounds." For example isoborneol 5 can be dehydrated and rearranged under acidic conditions to yield camphene 6 ... 

Except for terpene chemistry, the Wagner-Meerwein rearrangement is of limited synthetic importance. It is rather found as an undesired side-reaction with other reactions, for example in the synthesis of alkenes by elimination reactions. 

Diazomethanc undergoes addition of xanthylium perchlorate to afford dibenz[6,/]oxepin (4).193 The formation of this product can be rationalized by a carbenium ion that undergoes a Wagner Meerwein rearrangement. 

The formation of the isocorrolecarbaldehyde 5 may be best explained if one invokes 1,2-diol 4 as an intermediate of the McMurry coupling which would then react in a titanium(IV) chloride induced Wagner-Meerwein rearrangement to yield the isocorrole 5 as a minor product during... 

Addition of bromine to 1 in chloroform solution at 10°C led in high yield to the formation of the exo-5-a/ih -7-dibromide 2. No other products were isolated. The formation of this rearranged product can be explained in terms of Wagner-Meerwein rearrangement where migration of the aryl group is involved (eqn. 1). 

Wagner-Meerwein rearrangements were first discovered in the bicyclic terpenes. 

It was mentioned above that even alkanes undergo Wagner-Meerwein rearrangements if treated with Lewis acids and a small amount of initiator. An interesting application of this reaction is the conversion of tricyclic molecules to adamantane and its derivatives. It has been found that all tricyclic alkanes containing 10 carbons are converted to adamantane by treatment with a Lewis acid such as AICI3. If the substrate contains more than 10 carbons, alkyl-substituted adamantanes are produced. The lUPAC name for these reactions is Schleyer adamantization. Two examples are... 

Wagner-Meerwein rearrangements to give cyclic products... 

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