Substrate-selective catalysis.

Substrate selectivity is an important output function for the validation of different enzyme models, catalytic cavity compounds, and reaction mechanisms as demonstrated in this review. In contrast to stereo-, regio-, and chemoselective catalysis, the field of substrate-selective catalysis is under-researched and has to date generated only a few, but important, industrial applications. This review points out the broad spectrum of different reaction types that have been investigated in substrate-selective catalysis. The present review is the first one covering substrate-selective catalysis and deals with reactions in which the substrates involved have the same reacting functionality and the catalysts is used in catalytic or in stoichiometric amounts. The review covers real substrate-selective catalysis, thus only including cases in which substrate-selective catalysis has been observed in competition between substrates

Synthesis of Cr(III) Salen Complexes as Supramolecular Catalytic Systems for Ring-Opening Reactions of Epoxides

The synthesis of two conformationally restricted Cr(III) salen complexes, 2 and 3, is described. Together, they constitute a supramolecular hydrogen-bonding catalytic system for the recently reported asymmetric ring-opening reactions of epoxides by a dynamic supramolecular catalyst. The synthesis involves state-of-the art transformations in frontline synthetic chemistry applied to heterocyclic chemistry. Hence, palladium-catalyzed reactions were employed, including carbonylative annelation and Suzuki cross-coupling reactions, for the formation of one of the heterocyclic rings (quinolone) and the functionalization of the formed rings. For the construction of the second heterocyclic ring (isoquinolone), a Curtius rearrangement was employed. The corresponding salen ligands were then prepared by Schiff-base reactions, yielding the final complexes after metal insertion. For reference purposes the less conformationally restricted Cr(III) complexes 4 and 5 were also synthesized

Mono endo-6- And bis endo,endo-12-N,N-diethylcarbamoyl derivatives of Tröger’s Base. Synthesis and exo-endo isomerization study

An efficient synthetic route to the mono-endo-6- and bis-endo,endo-6,12-N,N-diethylcarbamoyl derivatives of Tröger’s base (TB), endo-7 and endo-8, is reported. Studies of reaction time, proton source, and additive allowed establishment of optimized conditions for the conversion of exo-7 into the corresponding isomer endo-7. With a longer reaction time, the exo,exo-6,12 bis-carbamoyl derivative exo-8 was converted into the corresponding endo,endo-bis-carbamoyl product endo-8. Single crystal X-ray crystallographic analysis confirmed the structural and stereochemical assignments made on the basis of 1H NMR, mechanistic, and calculational studies. Deuterium quench experiments using LDA, CD3ONa/CD3OD and DCl/CD3OD conditions of both exo-7 and exo-8 afforded exo-7d1 and exo-8d2, respectively (> 95% deuterium incorporation), supporting an enolate mechanism for the isomerization. In contrast, when repeating the experiment with DCl/CD3OD, no deuterium was incorporated, suggesting the traditional ring-opening mechanism involving an iminium ion