Neopentyl compounds rearrangement

For some tertiary substrates, the rate of SnI reactions is greatly increased by the relief of B strain in the formation of the carbocation (see p. 366). Except where B strain is involved, P branching has little effect on the SnI mechanism, except that carbocations with P branching undergo rearrangements readily. Of course, isobutyl and neopentyl are primary substrates, and for this reason they react very slowly by the SnI mechanism, but not more slowly than the corresponding ethyl or propyl compounds. 

The first step is not a free-radical process, and its actual mechanism is not known. Compound 30 is an acyl hypohalite and is presumed to be an intermediate, though it has never been isolated from the reaction mixture. Among the evidence for the mechanism is that optical activity at R is lost (except when a neighboring bromine atom is present, see p. 899) if R is neopentyl, there is no rearrangement, which would certainly happen with a carbocation and the side products, notably RR, are consistent with a free-radical mechanism. There is evidence that the Simonini... 

The reactions were between the alkyl bronude and OEt . The rate for isopropyl bromide was actually greater than that for ethyl bromide, if the temperature differenee is eonsidered. Neopentyl bromide, the next compound in the P-branching series, cannot be compared because it has no p-hydrogen and cannot give an elimination product without rearrangement. 

ControUed-potential oxidations of a number of primary, secondary, and tertiary alkyl bromides at platinum electrodes in acetonitrile have been investigated [10]. For compounds such as 2-bromopropane, 2-bromobutane, tert-butyl bromide, and neopentyl bromide, a single Ai-alkylacetamide is produced. On the other hand, for 1-bromobutane, 1-bromopentane, 1-bromohexane, 1-bromo-3-methylbutane, and 3-bromohexane, a mixture of amides arises. It was proposed that one electron is removed from each molecule of starting material and that the resulting cation radical (RBr+ ) decomposes to yield a carbocation (R" "). Once formed, the carbocation can react (either directly or after rearrangement) with acetonitrile eventually to form an Al-alkylacetamide, as described above for alkyl iodides. In later work, Becker [11] studied the oxidation of 1-bromoalkanes ranging from methyl to heptyl bromide. He observed that, as the carbon-chain length is increased, the coulombic yield of amides decreases as the number of different amides increases. 

Neopentyl tosylate reacts with LiCl in HMPA and gives the chloride with clean inversion without rearrangement (equation 5). Another example of this reaction is the conversion of allylic tosylates to chlorides without rearrangement or reaction of the sensitive acetal (equation 6). Dimethylaminopy-ridine is a useful catalyst for the transformation of hydroxy compounds to chlorides with tosyl chloride. ... 

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