Migration of alkyl groups

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

However, 1,2 migration of alkyl groups has been shown to occur in certain diradicalsFor example, the following rearrangement has been established by tritium labeling. 

In important recent work, Shriver has demonstrated that electrophiles can promote the migration of alkyl groups to coordinated CO. Lewis acid adducts of metal acyl complexes are isolated [37]. Thus it is possible that electrophilic species might also facilitate the generation of catalyst-bound formyls. 

The migration of alkyl groups was found to be general and several examples53 are outlined in equation 20. As noted in equation 20, a competing reaction is the common 1,5-... 

Reaction intermediates formed in the nitration of a series of a,/i-unsaturatcd esters, such as (47), with N02BF4 have been reported to exhibit the expected behaviour of a-carbonyl cations. Three diagnostic reaction types were observed (1) Ritter reaction (2) cyclopropane formation from propyl cations (3) Wagner-Meerwein migration of alkyl groups. Semi-empirical calculations of the relative gas-phase stabilities of the proposed intermediate cations have also been performed.53... 

Scheme 2.5 1,2-Migration of alkyl group (R) with bonding electron pair with retention of configuration.

Note that the three migrations of alkyl groups from boron to carbon which occur in Equation B3.15 fall into the general class of reactivity represented in Equation B2.2. 

As indicated in Table 5, the [1,2] reaction of carbonium ions is allowed and is energetically favored (Table 9). The migration of alkyl groups to... 

The migration of alkyl groups to carbene centres has much in common with the migration of alkyl groups to cationic centres discussed in Chapter 37—after all, both carbenes and carbocations are electron-deficient species with a carbon atom carrying only six electrons in its outer shelJ. 

Boron is electrophilic because of its empty p orbital Boron forms strong B-O bonds and weak B-C bonds J Migration of alkyl groups from boron to O, N, or C is stereospecific... 

Many carbon—carbon bond formation reactions, where migration of alkyl groups from boron to carbon with the concurrent elimination of leaving groups occur, have been reported. Some of such earlier representative syntheses are shown in Eqs. 19 20 and 21 >. 

Migration of alkyl groups from boron to O, N, or C is stereospecific... 

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