Bronsted-Acid Catalysis

Hodous BL, Fu GC (2002) Enantioselective addition of amines to ketenes catalyzed by a planar-chiral derivative of PPY possible intervention of chiral Bronsted-acid catalysis. J Am Chem Soc 124 10006-10007... 

Hydrogen-Bond Catalysis or Bronsted-Acid Catalysis General Considerations... 

Recent progress in chiral Bronsted-acid catalysis. (T. Akiyama, 2006) [Igj. 

The difference between hydrogen-bond catalysis and Br0nsted-acid catalysis is not always clear in the literatures. In this chapter, the differences and similarities of the hydrogen-bond catalysis and Bronsted-acid catalysis will be addressed. 

Scheme 2.5 Hydrogen-bond catalysis versus Bronsted-acid catalysis.

In summary, the differences between Br0nsted-acid catalysis and hydrogen-bond catalysis were discussed. Because there is a gradual transition from hydro-gen-bond catalysis to Bronsted-acid catalysis, it is not always easy to differentiate the two modes of catalysis. However, the combination of a stronger acid and an imine will be a Bronsted-acid-catalyzed reachon, while the combination of a neutral acid and an aldehyde will be a hydrogen-bond-catalyzed reaction. 

Scheme 3.2 Specific and general Bronsted-acid catalysis.

In contrast to some related reviews, which use reaction class or electrophiles as organizational elements, this chapter is divided into three main sections according to catalyst class (i) Bronsted acid catalysis by phosphoric acid and phosphoramide derivatives, (ii) N—H hydrogen bond catalysis by organic base and ammonium systems, and (iii) combined acid catalysis including Bronsted-acid-assisted Bronsted acid, Lewis-acid-assisted Bronsted acid, and Lewis-acid-assisted Br0nsted acid systems (Figure 5.1). 

Lewis-Acid-Assisted Bronsted Acid Catalysis [124]... 

These experimental results suggested a hydrogen-bonding mediated cooperative Bronsted acid catalysis mechanism (Scheme 6.28). Thiourea cocatalyst 9 is viewed to coordinate to mandelic acid 20 through double hydrogen-bonding, stabilizes the acid in the chelate-hke cis-hydroxy conformation, and acidifies the a-OH proton via an... 

As will be seen later, benzoyl fluoride exhibits Bronsted-acid catalysis in aqueous media86 and was thought to be the only acyl derivative to do so although alkyl fluorides are known to behave in this way also. For benzyl fluoride, the acid-catalysed rate is reported to show dependence on /i0104 105. Satchell87 studied the solvolysis of benzoyl and butyryl fluoride in 60 40 (v/v) dioxan-water mixtures (for which h0 data are known)106. The solvolysis of each compound is catalysed by acid, but does not follow h0. With excdss of solvent the observed first-order loss of acyl derivative obeys the expression... 

New Developments in Enantioselective Bronsted Acid Catalysis Chiral Ion Pair Catalysis and Beyond... 

Bronsted acid catalysis in electron transfer reactions can also be applied to catalysis of metal ions in electron transfer reactions, since not only protons but also metal... 

Bronsted acid catalysis in electron transfer described in Section 1.3.1 has also been effective for redox reactions via the electron transfer step. As shown in the case of metal ion-catalyzed hydride transfer reactions (see above), hydride transfer reactions from an NADH analogue to /7-benzoquinones also proceed via Bronsted acid-catalyzed electron transfer [255, 256]. Since NADH and ordinary NADH model compounds are subjected to the acid-catalyzed hydration [98, 257, 258], an acid-stable NADH model compound, 10-methyl-9,10-dihydroacridine (AcrH2), was used as a hydride donor to / -benzoquinone (Eq. 24) ... 

Following the pioneering reports on chiral Bronsted acid catalysis, a range of chiral phosphoric acid-catalyzed reactions have been reported [76]. 

AAButadiene Dimerization. The production of vinylcyclohexene is of a significant industrial importance as it is a route to styrene manufacture via the dehydrogenation of VCH. Cu zeolites, particularly Cu(I) Y zeolites proved to be active, selective and stable. They prevented the formation of cycloocta 1,5 diene and divinyl cyclobutane and also the formation of trimers. MAXWELL et al. (47) have studied the deactivation of this cuprous catalyst and found that the lower the acidity, the longer the lifetime. Consequently they devised a preparation procedure that involved reduction of cupric ions with NH3 at moderate temperature so that the Bronsted acidity generated by the reduction of cupric ions is neutralized by ammonia. As the temperature is increased little NH3 reamined as NH4 ions. These observations confirm that indeed this is not a Bronsted acid catalysis and confirm the involvement of the cuprous ions. 

---