Acid-catalyzed alkyl group migration

Acid-catalyzed alkyl group migration of alcohols to give more substituted olefins. 

When the reaction was performed on a 100 mg scale, the diene was obtained in 55% yield as a mixture of ( )- and (Z)-stereoisomers. However, when the scale was increased to lOOg, various by-products, such as cyclized products or alkyl group-migrated compounds, were produced presumably because of acid-catalyzed reactions of the diene. The formation of such by-products can be reduced using a microflow system composed of a micromixer and a microtube reactor. Thus, a solution of the allylic alcohol in tetrahydrofuran (THF) was mixed with a solution of p-toluenesulfonic acid (p-TsOH) in THF/toluene at 90 °C. After the reaction mixture was allowed to flow for 47 s, the reaction was quenched with a saturated NaHCOs solution at room temperature. In this case the desired diene was obtained in 80% yield. It is noteworthy that the acid-mediated by-products were not detected. This process was applied to the synthesis of pristane, a biologically important natural product that is widely used as an adjuvant for monoclonal antibody production. 

CHAlUHGtl Humulene and a-caryophyllene alcohol are terpene constituents of carnation extracts. The former is converted into the latter hy acid-catalyzed hydration in one step. Write a mechanism. (Hint The mechanism includes cation-induced double-bond isomerization, cyclizations, and rearrangements that may involve hydrogen and alkyl-group migrations. Two of the intermediates in the mechanistic sequence are shown five carbon atoms are identified by starts to help you track their positions through the process.)... 

Attention may be drawn, moreover, to acid-catalyzed rearrangements of pyrethrosin described by Barton and oo-worltera involving migration of a double bond -electrons) instead of the mere customary hydride ion or alkyl group (o-electronB). The transformation shown in Eq. (486) illustrates this point. 

Although it is now almost fifty years since Speier and his colleagues first announced the chloroplatinic acid-catalyzed hydrosilation of olefins, we are still far from complete control of the chemistry. A particular problem is the suppression of double bond migration. A solution of this problem will require a more detailed understanding of the factors affecting the relative rates of P-hydride elimination from an alkyl group and of the reductive elimination of Si-H from a platinum silyl hydride complex. Another factor which is poorly understood is suppression of the irreversible reduction of the platinum catalyst to Pt° metal. Both of these problems can greatly increase costs of production of certain products. 

Acylphosphonic acids (1-oxoalkylphosphonic acids) and their dialkyl esters undergo acid-catalyzed fission with the formation of carboxylic acids (or their alkyl esters) using a suiphonic acid as the catalyst the formation of an alkyl carboxylace is accompanied by that of an alkyl sulphonate. The reaction may be visualized as occurring through protonation on the carbonyl oxygen and migration of an alkoxy group from phosphorus... 

P-Amino ketone synthesis. The benzotriazole derivatives enable 9-vinylcar-bazole to become an acetaldehyde 1,2-dianion equivalent. The acid-catalyzed reaction gives rise to 1,1,3-trifunctionalized propanes in which the migrated benzotriazolyl group activates the a-carbon for alkylation. Subsequent hydrolysis of the aminal unit reveals the keto group. 

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