An efficient microwave-assisted solvent-free synthesis of pyrido-fused ring systems applying the tert-amino effect

A Stereoselective Reductive Hosomi-Sakurai Reaction

A novel reductive variant of the classical Hosomi-Sakurai reaction is reported. This transformation hinges on a redox-neutral, stereoselective internal reduction event under mild conditions. This operationally simple reaction relies on readily available starting materials and leads to useful products in diastereoselectivities of up to 7:1. The versatility of this new method is demonstrated through the stereoselective one-step synthesis of an AChE inhibitor.

Efficient construction of tetrahydroquinolines via fluorinated alcohol mediated cascade [1,5]-hydride transfer/cyclization

An environmentally benign cascade redox-neutral process was developed for the efficient construction of pharmaceutically important spirocyclic tetrahydroquinolines via a 3-step cascade Knoevenagel condensation/[1,5]-hydride transfer/cyclization.

Hydride transfer initiated ring expansion of pyrrolidines toward highly functionalized tetrahydro-1-benzazepines

The first example of ring expansion from a five-membered nitrogen-containing ring to a seven-membered heterocyclic ring has been developed.

Redox-neutral α-oxygenation of amines: reaction development and elucidation of the mechanism

Cyclic secondary amines and 2-hydroxybenzaldehydes or related ketones react to furnish benzo[e][1,3]oxazine structures in generally good yields. This overall redox-neutral amine α-C-H functionalization features a combined reductive N-alkylation/oxidative α-functionalization and is catalyzed by acetic acid. In contrast to previous reports, no external oxidants or metal catalysts are required. Reactions performed under modified conditions lead to an apparent reductive amination and the formation of o-hydroxybenzylamines in a process that involves the oxidation of a second equivalent of amine. A detailed computational study employing density functional theory compares different mechanistic pathways and is used to explain the observed experimental findings. Furthermore, these results also reveal the origin of the catalytic efficiency of acetic acid in these transformations.

Selective activation of enantiotopic C(sp3)-hydrogen by means of chiral phosphoric acid: asymmetric synthesis of tetrahydroquinoline derivatives

Chiral phosphoric acid-catalyzed asymmetric C-H functionalization has been achieved. In this process, enantiotopic C(sp(3))-hydrogen is selectively activated by chiral phosphoric acid to afford tetrahydroquinoline derivatives with excellent enantioselectivities (up to 97% ee).

Diastereo- and enantioselective synthesis of oxazine and oxazolidine derivatives with a chiral quaternary carbon center under multifunctional catalysis

An easy one-pot, multistep cascade reaction which could afford a series of substituted benzo[d]pyrido[2,1-b]oxazolidine and [1,3]oxazine derivatives in a highly enantio- (up to 98% ee) and diastereoselective (4:1 to >20:1 dr) manner with generally good to excellent yields (up to 99%) has been developed. This well designed strategy could be applied to a wide scope of substrates under mild conditions with simple operations.

Enantioselective organocatalytic C-H bond functionalization via tandem 1,5-hydride transfer/ring closure: asymmetric synthesis of tetrahydroquinolines

The first organocatalytic enantioselective intramolecular 1,5-hydride transfer/ring closure reaction is described. This redox neutral reaction cascade allows for the efficient formation of ring-fused tetrahydroquinolines in high enantioselectivities.

Catalytic enantioselective intramolecular redox reactions: ring-fused tetrahydroquinolines

The first example of a catalytic enantioselective intramolecular hydride shift/ring closure reaction is reported. This redox neutral reaction cascade allows for the efficient formation of ring-fused tetrahydroquinolines in high enantioselectivities.

Lewis acid catalyzed formation of tetrahydroquinolines via an intramolecular redox process

Polycyclic tetrahydroquinolines were prepared by an efficient Lewis acid catalyzed 1,5-hydride shift, ring closure sequence. Gadolinium triflate was identified as a catalyst that is superior to scandium triflate as well as other Lewis acids. An approach toward a catalytic enantioselective variant is also described.