Br0nsted acids strong chiral

In summary, chiral Br0nsted acids have been used to protonate prochiral intermediates that were photochemically produced. Optimization of the chiral amino alcohols and the conditions led to excellent enantioselectivities of up to 91% ee employing only 0.1 equivalent of chiral inductor with respect to the substrate. These results demonstrate that the desirable goal of chiral amplification can be reached with chiral templates. The asymmetric induction varies strongly for different substrates, and therefore the general applicability as a synthetic tool seems to be limited. 

Realizing the high potential of both strong Br0nsted acids and weaker hydrogen bond donors as (chiral or achiral) small-molecule catalysts to activate electrophiles... 

Enantioenriched indolines are very important compounds, which exist extensively in natural alkaloids or unnatural bioactive compounds. The development of facile methods toward chiral indolines continues to be a challenge for organic chemists. Unprotected indole 106 could be considered as a special enamine in an aromatic system. Inspired by the possible shift between enamine and imine of indole in the presence of strong acid. Sun and Chen et al. envisioned that a direct reduction of indole 106 to indoline 107 by a combined catalysis of Lewis base and Br0nsted acid would be highly possible (Scheme 32.24). Indeed, using the strategy... 

Takemoto and colleagues demonstrated that bifunctional ammonium-thiourea catalyst 110, prepared in situ by treatment of a chiral thiourea precatalyst with a strong Br0nsted acid, is also able to effect the same sequential transformation enantioselectively (Scheme 42.40). With ee-values of up to 69%, however, the enantiodiscrimination remained comparatively modest [90]. 

---