Natural products Wagner-Meerwein rearrangement

The proposed transition states have been supported by deuterium isotope studies Evidence such as the decomposition behaviour in solution and the nature of the increases in the rates of decomposition along the series of chloro-formates methyl, ethyl, isopropyl, 2-butyl, /-butyl suggests that the transition states are somewhat polar °> . Lewis and Herndon found 2-methylbut-1-ene and 2-methylbut-2-ene as the olefinic products of the elimination reaction of neopentyl chloroformate, and the kinetic evidence supports a Wagner-Meerwein rearrangement in the gas-phase as in the case of neopentyl chloride pyrolysis (refs. 407, 408, 566). 

A Wagner-Meerwein rearrangement via a bridged carbenium ion has been observed in the electrodecarboxylation of bicyclo[2.2.1]heptane-2-carboxylic acids (CXVIIa, CXVIIb, and CXVIIc), leading to the formation of the same products (CXVIII and CXIX) [Eq. (58)] [174]. This method has been successfully applied to synthesis of useful intermediates for natural product synthesis. Some examples are given in Eqs. (59) and (60) [175-179]. 

These variously substituted camphor derivatives have in turn been used in a number of syntheses of natural products, some of which also involve Wagner-Meerwein rearrangements in their later stages. Examples drawn from the syntheses of (+)-a-santalene (34),(-)-3-santalene (35), (-)-copacamphene (36) and (-)-sativene (37) are given in Schemes 12-14. 

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