And alkyl migration

For instance, if the metal is lost by Sn2 attack on coordinated carbon, this constitutes R loss, and alkyl migration to an electrophilic centre such as coordinated CO may resemble R loss. R- loss may take place by simple homolysis, or by alkyl group transfer. Moreover, as Yamamoto has pointed out an electroneutral metal-carbon bond lengthening may be a prelude to more complex processes such as 0-elimination, or may lead to internal hydrogen abstraction rather than to actual free ligand release. 

In this chapter, SN l reactions were introduced, compared to SN2 reactions and discussed mechanistically. Through these discussions, the involvement of electron orbitals, and their various hybrids, was addressed. Furthermore, complicating side reactions such as hydride and alkyl migrations were presented. As discussions move into more advanced mechanistic types, it is important to maintain awareness of the involvement and orientation of orbitals, the steric environment at reactive centers, and the overall reactivity of nucleophiles and electrophilic centers. 

The indanone oximes (7) gave the aryl- and alkyl-migrated products (8) and (9) (equation 6), with the proportion of (9) itKteasing with increasing steric demand of arenc substituents at the 4- and 7-positions. Exposure of the ( )-oxime (10) to phosphorus pentoxide and methanesulfonic acid gave the product (11) of migration of the yn-alkyl group, presumably via the (Z)-isomer (equation 7). 

Aryl and alkyl migration aptitudes were compared in the photolysis and in the thermolysis of 1,1-diphenylethyl azide (37) and 2-phenyl-2-propyl azide (38). For the compound 38 phenyl migration was the... 

Zimmerman, H. E., Pratt, A. C. Organic photochemistry. Llll. Directionality of the singlet di-p-methane. Rearrangement and alkyl migration in a unique photochemical vinylcyclopropane transformation. J. Am. Chem. Soc. 1970, 92,1407-1409. 

Mechanisms of Reverse Reactions for CO Migration and Alkyl Migration Related to Experiment II... 

A basic knowledge of the reaction types described in this section allows us to proceed to a discussion of the chemistry of selected organometallic complexes and (in Chapter 26) catalysis. Oxidative additions and alkyl migrations in particular are very important in the catalytic processes used in the manufacture of many organic chemicals selected important organometallic compounds used as catalysts are summarized in Box 23.3. 

The first item in Table 8.7 is the toluenesulfonic acid ester (toluenesulfonate, tosylate,-OTs) of 3- Hi-3-methyl-2-butanol, which is permitted to undergo solvolysis in an acetic acid solvent. As might be anticipated (and as shown in Scheme 8.76), the secondary tosylate group leaves and the secondary carbocation suffers a hydride migration (in this case, a deuteride, i.e., rather than H) to generate the more stable tertiary carbocation. The latter is then captured by the nucleophilic solvent. The acetic acid ester of 2-methyl-2-butanol (i.e., 2-acetoxy-2-methylbutane) results. Hydride and alkyl migrations from a less stable carbocation to a more stable carbocation have been used before (Chapter 7) to explain product mixtures resulting from solvolysis of alkyl halides. 

The hydride shifts and alkyl migrations discussed in Section 9.9 are not arcane examples fit only for the nether regions of an organic text (and for especially vexing problems). They are going on all the time as part of many of the enzyme-driven reactions in your body. So, as you read this, hydrides are migrating somewhere deep inside you. 

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