1,2-Rearrangement reaction pinacol type

The reaction of crotonaldehyde and methyl vinyl ketone with thiophenol in the presence of anhydrous hydrogen chloride effects conjugate addition of thiophenol as well as acetal formation. The resulting j3-phenylthio thioacetals are converted to 1-phenylthio-and 2-phenylthio-1,3-butadiene, respectively, upon reaction with 2 equivalents of copper(I) trifluoromethanesulfonate (Table I). The copper(I)-induced heterolysis of carbon-sulfur bonds has also been used to effect pinacol-type rearrangements of bis(phenyl-thio)methyl carbinols. Thus the addition of bis(phenyl-thio)methyllithium to ketones and aldehydes followed by copper(I)-induced rearrangement results in a one-carbon ring expansion or chain-insertion transformation which gives a-phenylthio ketones. Monothioketals of 1,4-diketones are cyclized to 2,5-disubstituted furans by the action of copper(I) trifluoromethanesulfonate. ... 

But now commonly associated with Tiffeneau-Demianov rearrangement The classification now covers many reactions of the "pinacol type", including ... 

Exercise 16-40 Write a sequence of reactions whereby 2-methylpropene may be converted to 2-methylpropanal by way of a pinacol-type rearrangement. Would you expect any concomitant formation of 2-butanone Explain. 

The diterpene derivative 1 was treated with BF3-OEt2 and AC2O in an attempt to induce a "pinacol-type rearrangement leading to a ring B-homo derivative. No such reaction was observed. Instead, the only product which could be isolated (33%) was shown to be 2, formed by "a profound backbone rearrangement" of 1. 

Asymmetricpinacol-type rearrangement. Oiiral P-mesyloxy tertiary alcohols undergo a stereospecific pinacol-type rearrangement in the presence of triethylaluminum (excess) to furnish optically pure a-aryl or a-vinyl ketones (equation I). The reaction is particularly... 

Intramolecular reaction of an allylsilane and an aldehyde was performed to prepare cyclic compounds as illustrated in Eq. (90) [233], which shows a high diastereoselec-tivity. The cyclization of optically active allylsilane proceeds stereoselectively in a manner consistent with the antiS l mechanism (Eq. 91) [234]. Development of a new reagent with a bis-allylsilane moiety effected tandem inter- and intramolecular cyclizations to give cyclic compounds as exemplified in Eqs (92) [235] and (93) [236-238]. In Eq. (92), the double addition product initially formed underwent a pinacol-type rearrangement under the influence of TiCU to give, eventually, the methyl cyclopentyl ketone. Further examples of intramolecular cyclization of allylsilanes are summarized in Table 8. 

This C-C bond cleavage is avoided when the oxidation is performed in the presence of chloride ions. In this case, pinacol-type rearrangement products involving a C-S bond cleavage are obtained, as in Eq. (72) [125]. A chlorosulfonium intermediate is believed to participate in this type of reaction. 

Some evidence for the mechanism being reaction mode (a) comes from the conversion of optically active oxazolidine (42) to a racemic mixture of pyrrolidine Scheme 22), obviously via the achird intermediate (44), since in a pinacolic-type rearrangement via (45), the chiral information would have been... 

A different outcome in the presence of an additional vinylic oxygen was observed by Overman s group (Scheme 52). The formation of the five-membered cyclic ether (108) is rationalized in terms of an SnCU-mediated acetal ring opening of (105), subsequent cyclization of (106) to (107), followed by a ring contraction to (108) by a pinacol-type rearrangement. This stereocontrolled reaction proved to be applicable to the synthesis of related natural products. ... 

The usefulness of the organoaluminum-mediated pinacol-type rearrangement is demonstrated in the synthesis of (+ )-eldanolide (354), a wing-gland pheromone of the African sugar-cane borer [112] (Scheme 48). The key reaction, the rearrangement of 350 351,... 

Although hydroxylation of phenylalanine to tyrosine looks like a typical electrophilic aromatic substitution, scientists at the U.S. National Institutes of Health discovered that the biochemical pathway combines epoxidation of the benzene ring followed by epoxide ring-opening with rearrangement. This rearrangement, which is the biochemical analog of the pinacol-type reactions described earlier, is known as the NIH shift. ... 

Figure 2 shows time conversion curves of 7 in CIXI3 at 100 C. In the absence of TsOH, the disappearance of the diol monotosylate star aft heating for 200 min or longer and occurred in a non-linear manner. The addition of TsC resulted in the marked reduction of heating time for the abrupt consumption of 7, indicating that the acidolysis reaction of 7 t es place autocatalytically. The determination of product distribution showed that 2-phenylcyclohexanone-l and benzoylcyclopentane are obtained in 36 % and 44 % yields, respectively, while TsOH is formed almost quantitatively (Scheme 4). Considering the chemical structures of the ketonic products, it is very likely that 7 imdergoes pinacol-type rearrangement...

When alkyne TT-activation meets pinacol-type [l,2]-rearrangement On the invention of domino reactions for the synthesis of carbocycles and heterocycles 13SL1471. 

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