Alkylation isomerization, during

C. Masters, J. A. van Doom, C. van der Woude, and J. P. Visser, Inorg. Chim. Acta, 1976,19. L21. Alkyl isomerization during transfer from ctr-[PtR2(PPh3)2] to [Rh2Cl2(CO)4l. 

In a more recent study Co(dppe)I2 was used as a catalyst for reductive additions of primary, secondary, and tertiary alkyl bromides or iodides 249 to alkyl acrylates, acrylonitrile, methyl vinyl ketone, or vinylsulfone 248 in an acetonitrile/water mixture using zinc as a stoichiometric reducing agent [305]. The yields of the resulting esters 252 were mostly good. The authors tested radical probes, such as cyclopropylmethyl bromide or 6-bromo-1-hexene (cf. Part 1, Fig. 8). However, the latter did not cyclize, but isomerized during addition, while the former afforded complicated mixtures. On this basis the authors proposed a traditional two-electron mechanism to be operative the results do not, however, exclude a radical-based Co(I) catalytic cycle convincingly (Fig. 61). 

As indicated earlier (2,3) for sulfuric acid alkylations, the rates of reaction for olefins are often higher during the initial stages of alkylation than the rates of reaction for Isobutane. In the case of n-butenes, isomerization of the n-butenes occurs readily in the presence of sulfuric acid, see Reactions H-1 and H-2. Considerable information on these isomerizations were reported earlier (5) the rates of isomerization Increase as the amounts of excess acid or as the acidity of the acid phase increase. Certainly at the conditions employed in commercial alkylators, isomerization would be very rapid. 

Diacyloxy compounds are intermediates in the conversion of olefins and 1,2-dihalides to glycols (method 95). Although the diesters are seldom isolated, yields are good where their isolation has been attempted. The well-known reaction of an alkyl halide with a silver salt of an acid is used infrequently. It is sometimes valuable in making esters from acids which isomerize during direct esterification. Thus, the labile double bond of 3 niethyl-3-butenoic acid is unaffected by conversion to the methyl ester by this method. ... 

Organozinc reagents are useful for the transfer of alkyl groups, more so than their organotin analogs. Isomerization during the alkylation reaction, or elimination reactions due to the presence of a hydrogen on a /3-carbon to the metal, may lead to side reactions. Palladium catalysts are... 

Reversible formation of a cobalt-alkyl complex from HCo(CO) and olefin has been established. The reversible formation of a cobalt alkyl is required to explain observations of alkene isomerization during hydroformylation by HCo(CO) and scrambling of deuterium in substrates, such as CD3(CHj)3CH=CH2, mider relatively low pressures of the mixture of CO and (Equation 17.4). Little deuterium is lost during transformation of the alkene to product, but the deuterium atoms are distributed nearly statistically along the chain. ... 

With our Rh(CO) complex bearing the anionic CNC hgand 5, we could show that Rh-catalyzed allyl transfer can be the source of isomerization during the allylic alkylation catalyzed by the same complex, especially when using linear allyl carbonates. The potential of this complex with regard to optimization of the catalyst, substrate scope, and asymmetric variations is not yet revealed, nor that of the respective Ir catalyst. 

The general theory of molecular rearrangements as outlined by Whitmore offers an alternative explanation of the isomerizations of alkyl groups during alkylation. ... 

Identification. The many possibilities for the formation of isomeric or anomalous products due to rearrangement, unusual orientation, or degradation of alkyl groups during the Friedel-Crafts reaction, coupled with the fact that the products are usually liquids, difficult to separate and identify, frequently necessitate particular care in establishing the structure and the purity of the products. The most effective method... 

Acyl-pyrroles, -furans and -thiophenes in general have a similar pattern of reactivity to benzenoid ketones. Acyl groups in 2,5-disubstituted derivatives are sometimes displaced during the course of electrophilic substitution reactions. iV-Alkyl-2-acylpyrroles are converted by strong anhydrous acid to A-alkyl-3-acylpyrroles. Similar treatment of N-unsubstituted 2- or 3-acyIpyrroles yields an equilibrium mixture of 2- and 3-acylpyrroles pyrrolecarbaldehydes also afford isomeric mixtures 81JOC839). The probable mechanism of these rearrangements is shown in Scheme 65. A similar mechanism has been proposed for the isomerization of acetylindoles. 

The demand for aviation gasoline during World War II was so great that isobutanc from alkylation feedstock was insufficient. This deficiency was remedied by isomerization of abundant normal butane into isobutane using the isomerization catalyst aluminum chloride on alumina promoted by hydrogen chloride gas. 

Evidence in support of a carbocation mechanism for electrophilic additions comes from the observation that structural rearrangements often take place during reaction. Rearrangements occur by shift of either a hydride ion, H (a hydride shift), or an alkyl anion, R-, from a carbon atom to the adjacent positively charged carbon. The result is isomerization of a less stable carbocation to a more stable one. 

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