Access to chiral 1-aminoindene derivatives by asymmetric Brønsted acid catalysis

Asymmetric organocatalysis is emerging as an elegant tool for accelerating chemical reactions and creating specific types of molecules. Chiral Brønsted acid catalysis is an important area of organocatalysis. Recently we described a chiral Brønsted acid (N-triflyl phosphoramide) catalyzed intramolecular iminium ion cyclization reaction of 2-alkenylbenzaldimines for the synthesis of chiral 1-aminoindenes and tetracyclic 1-aminoindanes in good yields and high enantioselectivities. The obtained 1-aminoindene can be utilized as useful synthetic intermediate for synthesis of (S)-rasagiline, an effective drug for the symptomatic treatment of Parkinson's disease. And the obtained tetracyclic 1-aminoindanes are the skeleton of homoisoflavanoid natural products such as brazilin.

Chiral Brønsted acid-controlled intermolecular asymmetric [2 + 2] photocycloadditions

Control over the stereochemistry of excited-state photoreactions remains a significant challenge in organic synthesis. Recently, it has become recognized that the photophysical properties of simple organic substrates can be altered upon coordination to Lewis acid catalysts, and that these changes can be exploited in the design of highly enantioselective catalytic photoreactions. Chromophore activation strategies, wherein simple organic substrates are activated towards photoexcitation upon binding to a Lewis acid catalyst, rank among the most successful asymmetric photoreactions. Herein, we show that chiral Brønsted acids can also catalyze asymmetric excited-state photoreactions by chromophore activation. This principle is demonstrated in the context of a highly enantio- and diastereoselective [2+2] photocycloaddition catalyzed by a chiral phosphoramide organocatalyst. Notably, the cyclobutane products arising from this method feature a trans-cis stereochemistry that is complementary to other enantioselective catalytic [2+2] photocycloadditions reported to date.

Asymmetric Synthesis of Fused Tetrahydroquinolines via Intramolecular Aza-Diels-Alder Reaction of ortho-Quinone Methide Imines

Aza-Diels Alder reactions are straightforward processes in the construction of N-heterocycles, featuring inherent atom-economy and stereospecificity. Intramolecular strategies allow formation of bicyclic core structures with up to three stereocenters within a single step. Herein, this concept is combined with the chemistry of chiral Brønsted acid-bound ortho-quinone methide imines generating a range of interesting fused tetrahydro-quinolines in a diastereo- and enantioselective manner.

Practical catalytic enantioselective synthesis of 2,3-dihydroquin-azolinones by chiral brønsted acid catalysis

An efficient, practical and scalable protocol to prepare chiral 2,3-dihydroquinazolinones was developed under catalysis of spirocyclic SPINOL-phosphoric acid.

Dynamic Parallel Kinetic Resolution of α-Ferrocenyl Cation Initiated by Chiral Brønsted Acid Catalyst

The dynamic parallel kinetic resolution (DPKR) of an α-ferrocenyl cation intermediate under the influence of a chiral conjugate base of a chiral phosphoric acid catalyst has been demonstrated in an...