Wagner-Meerwein rearrangement Subject

The Pirrung synthesis is notable for its brevity and clever amalgamation of [2 + 2] photocycloaddition and Wagner-Meerwein rearrangement chemistry Enol ether 757 was reacted with the Grignard rea nt from 5-bromo-2-methyl-l-pentene, subjected to acid hydrolysis, and irradiated to generate the tricycle 738. Wittig olefination of this ketone and treatment with p-toluenesulfonic acid provided racemic isocomene. 

Since the initial studies by Wagner at the turn of the century, the Wagner-Meerwein rearrangement has been the subject of almost continuous investigation. The reaction was initially examined in terms of the rearrangement of a-pinene (1) to bomyl chloride (2 Scheme 1), and of camphene (3) via camphene hydrochloride (4) to isobomyl chloride (5). 

Collins has made a detailed research into the pinacolic rearrangement of 2-endo-phenyl-2,3-ds-exo-norbomandiol 91. If a 3,2-endo-hydride shift were possible, the diol 91 would yield the ketone 92. The reaction product, however, is an isomeric ketone 93. occuring from the 3,2-hydride shift initiated from the exo side. The absence of exo-H in the initially formed carbocation causes the latter to undergo a series of Wagner-Meerwein rearrangements and 6,2-hydride shifts result near the cation centre and at the exo-position of a hydrogen atom this is subjected to a 3,2-hydride shift. The formation of ketone 93 is not determined by thermodynamic factors because it is less stable than ketone 92. 

Piuacolyl chloride. The conversion of pinacolyl alcohol (la) into the chloride (2) has presented difficulties because (2) is subject to Wagner-Meerwein rearrangement to 2,3-dimethyl-2-chlorobutane, which has practically the same... 

Very recently an alternative utilization of the intramolecular DieIs-Alder reaction for the synthesis of seychellene (10) was reported. In this case an isomeric tricyclic intermediate was prepared and subjected to a Wagner-Meerwein rearrangement to give seychellene. As outlined below, the intramolecular Diels-Alder reaction utilized the cyclohexadienone portion of the molecule as the dienophile rather than the diene as had been done in Fukamiya s approach. 

As mentioned previously, primary alcohols, when subjected to 1, form the corresponding carbamates, via an Sn2 mechanism, to form the corresponding olefins. For instance, 17 forms an N-carbomethoxysulfamate salt intermediate that rearranges to urethane 18 when heated. When primary sulfamate esters (19) are formed in a sterically hindered environment, the El mechanism prevails followed by rearrangement via Wagner-Meerwein, to form olefin 20.2... 

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