Activation of enamine by photoexcited organocatalyst assisted singlet oxygen: synthesis of oxazoles and quinoxalines.

Herein, a novel transition-metal-free thiol-based donor-acceptor organophotocatalyst-assisted, singlet-oxygen-mediated tandem oxidative cyclization for the synthesis of substituted oxazoles in moderate-to-good yields is described. The developed method demonstrates applicability for the synthesis of various substituted quinoxalines in good-to-excellent yields. The metal-free methodology shows a practical route for the synthesis of oxazole and quinoxaline derivatives, which are privileged moieties prevalent in various biologically active compounds and natural products.

Visible Light Driven Metal-Free Photoredox Catalyzed α-benzylation and α-oxygenation of N-substituted Tetrahydroisoquinolines: Applications to Synthesis of Natural Products.

Herein, visible light mediated organophoto redox catalysed simple and convenient method for the α-benzylation and α-oxygenation of tertiary amines is demonstrated. Synthesis of novel thiophenol based donor acceptor organophotoredox catalysts 4 a-4 d were investigated along with commercial catalyst 4-CzIPN (4 e). A diverse biologically active α-benzylated tetrahydroisoquinolines and natural products such as (±)-Norlaudanosine, (±)-laudanosine and (±)-xylopinine have been synthesized under the optimized conditions in yields ranging from from 62-91%.

Plant-growth-promoting rhizobacteria Bacillus subtilis RR4 isolated from rice rhizosphere induces malic acid biosynthesis in rice roots.

Malic acid (MA), one of the major organic acid exudates from roots, plays a significant role in the chemotaxis of beneficial bacteria to the plant's rhizosphere. In this study, the effect of a plant-growth-promoting rhizobacterium, Bacillus subtilis RR4, on the synthesis and exudation of MA from roots is demonstrated in rice. To test the chemotactic ability of strain RR4 towards MA, a capillary chemotaxis assay was performed, which revealed a positive response (relative chemotactic ratio of 6.

Natural product biosynthesis inspired concise and stereoselective synthesis of benzopyrones and related scaffolds.

A natural product biosynthesis-inspired strategy to explore biologically relevant chemical space is presented. A phosphine-catalyzed cascade and stereoselective annulation provides a common tricyclic benzopyrone intermediate that was efficiently transformed into diverse and related naturally occurring scaffolds.

Gold(I)-catalyzed divergence in the reactivity of 3-silyloxy 1,6-enynes: pinacol-terminated vs claisen-terminated cyclization cascades.

On activation with catalytic amounts of gold(I) complexes, 3-silyloxy 1,6-enynes can react through two alternative pathways. In one, a cascade reaction consisting of carbocyclization and subsequent pinacol rearrangement takes place. In the second pathway, a heterocyclization is followed by a Claisen rearrangement.

Air-stable racemization catalysts for the dynamic kinetic resolution of secondary alcohols.

The substitution of a carbonyl ligand with PPh(3) in cyclopentadienylruthenium dicarbonyl complexes produces a new class of recyclable alcohol racemization catalysts. The catalysts are active at room temperature under aerobic conditions in the presence of silver oxide. Furthermore, the catalysts are compatible with the use of a lipase and isopropenyl acetate for the dynamic kinetic resolution (DKR) of secondary alcohols under ambient conditions.