Discovery of novel 5,6,7,8-tetrahydro[1,2,4]triazolo[4,3-a]pyridine derivatives as γ-secretase modulators (Part 2)

Tandem reduction and trifluoroethylation of quinolines and quinoxalines with trifluoroacetic acid and trimethylamine borane

A metal-free tandem reduction and N-trifluoroethylation of quinolines and quinoxalines has been developed. It provided a convenient route to access trifluoroethylated tetrahydroquinolines and tetrahydroquinoxalines. This one-pot method avoids the purification process of the intermediate. Mechanistically, the in situ-generated boryl acetal species reacted with tetrahydroquinolines to generate iminiums followed by reduction to give the target compounds.

Identifying a Hidden Conglomerate Chiral Pool in the CSD

Conglomerate crystallization is the spontaneous generation of individually enantioenriched crystals from a nonenantioenriched material. This behavior is responsible for spontaneous resolution and the discovery of molecular chirality by Pasteur. The phenomenon of conglomerate crystallization of chiral organic molecules has been left largely undocumented, with no actively curated list available in the literature. While other crystallographic behaviors can be interrogated by automated searching, conglomerate crystallizations are not identified within the Cambridge Structural Database (CSD) and are therefore not accessible by conventional automated searching. By conducting a manual search of the CSD and literature, a list of over 1800 chiral species capable of conglomerate crystallization was curated by inspection of the racemic synthetic routes described in each publication. The majority of chiral conglomerate crystals are produced and published by synthetic chemists who seldom note and rarely exploit the implications this phenomenon can have on the enantiopurity of their crystalline materials. With their structures revealed, we propose that this list of compounds represents a new chiral pool which is not tied to biological sources of chirality.

Switchable Reductive N-Trifluoroethylation and N-Trifluoroacetylation of Indoles with Trifluoroacetic Acid and Trimethylamine Borane

The metal-free reductive N-trifluoroethylation and N-trifluoroacetylation of indoles have been developed. Bench stable and inexpensive trimethylamine borane and trifluoroacetic acid (TFA) were utilized as the reductive and fluorinating reagents, respectively. These transformations were switchable on the basis of altering the loading of trimethylamine borane and TFA. Preliminary experiments indicated indoline was the common intermediate in these two transformations.

Copper-Catalyzed [2+2+2] Modular Synthesis of Multisubstituted Pyridines: Alkenylation of Nitriles with Vinyliodonium Salts

A [2+2+2] modular synthesis of multisubstituted pyridines, with excellent regioselectivity, has been realized by copper catalysisand involves three distinct components: vinyliodonium salts, nitriles, and alkynes. The reactions proceeded with the facile formation of an aza-butadienylium intermediate by alkenylation of the nitrile with a vinyliodonium salt. Moreover, the alkynes in the reaction were extended to alkenes, which are an advantage of expense and relative scarceness of alkynes.