Intramolecular Bronsted acid catalysis

An intramolecular phosphoric acid-catalyzed asymmetric 5 2-type alkylation reaction of alcohols with racemic secondary benzylic ethers resulted in a catalytic asymmetric transetherification reaction to form benzo[c]furan species via the potential of asymmetric Bronsted acid catalysis for the activation of normally unreactive functional groups such as ethers and potentially other less reactive substrates (13AGE3490). 

The rate constant for the reaction of penicillin with the monocation of 1,2-diaminoethane is ca 100-fold greater than that predicted from the Bronsted plot for a monoamine of the same basicity. The rate enhancement is attributed to intramolecular general acid catalysis of aminolysis by the protonated amine (Morris and Page, 1980a Martin et al., 1979). Breakdown of the tetrahedral intermediate, T, is facilitated by proton donation from the terminal protonated amino group to the P-lactam nitrogen [59]. It is not known whether proton transfer and carbon—nitrogen bond fission are concerted or occur by a stepwise process. 

In 2010, List reported a catalytic enantioselective intramolecular trans-acetalization reaction via Bronsted acid catalysis [37a]. Chiral 0,0-acetals, which are usually synthesized by enzymatic resolutions or metal-catalyzed desymmetri-zations, could now be easily obtained by catalysis with phosphoric acid 107. Alcohols 108 with both aUphatic and aromatic substitutions are suitable substrates, furnishing the tetrahydrofurans 109 in high yields and enantioselectivity (Scheme 36.29). 

The ionization of (E)-diazo methyl ethers is catalyzed by the general acid mechanism, as shown by Broxton and Stray (1980, 1982) using acetic acid and six other aliphatic and aromatic carboxylic acids. The observation of general acid catalysis is evidence that proton transfer occurs in the rate-determining part of the reaction (Scheme 6-5). The Bronsted a value is 0.32, which indicates that in the transition state the proton is still closer to the carboxylic acid than to the oxygen atom of the methanol to be formed. If the benzene ring of the diazo ether (Ar in Scheme 6-5) contains a carboxy group in the 2-position, intramolecular acid catalysis is observed (Broxton and McLeish, 1983). 

The relative sizes of the Hammett p and Bronsted a constants will determine the relative rate of 5-nitrosalicylamide. If intramolecular base catalysis applies, then 5-nitrosalicylamide should hydrolyse more rapidly, since the nitro group will increase the susceptibility of the amide bond to attack by hydroxide ion and increase the efficiency of the phenolic hydroxyl as a general acid catalyst. The value of Jtobs at the plateau region was found to be 18 times smaller for the 5-nitrosalicylamide than for salicylamide a mechanism of intramolecular general base catalysis is, therefore, the preferred mechanism. 

The latter isomerization via an intramolecular hydride shift is catalyzed by Lewis acids. Tin-containing P-zeoHte exhibits remarkable activity for the glucose-fructose isomerization in water. and NMR studies have elucidated this Lewis acid-catalyzed isomerization mechanism, and show a clear difference between Sn-fl (Lewis acid catalysis) and NaOH (Bronsted base catalysis). 

The asymmetric Bronsted acid (242-245) catalysis of efficient, intramolecular hydroamination and hydroarylation reactions involving dienes or allenes (240), led to chiral pyrrolidines and isoxazolidines (241) in excellent yields and ee values (Scheme 63). ... 

Dunn and Bruice (1970, 1971) presented evidence that the mechanism of hydrolysis of methoxymethoxybenzoic acid is actually A-1. Evidence included a Bronsted coefficient for intramolecular catalysis of DO, based upon points for the unsubstituted compound and the 5-NO2 derivative, and p -values that were the same (—3-0) for both the methyl ester and the carboxyl derivatives of [72] when... 

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