Substituent-Directed Regioselective Azidation: Copper-Catalyzed C–H Azidation and Iodine-Catalyzed Dearomatizative Azidation of Indole

Azidation of indoles using iodine and copper bromide as catalysts under ambient reaction conditions is presented. The regioselectivity is directed by the substituent at the C3-position of indole. A radical stabilizing group such as an ester or ketone moiety at the C3-position of indole leads to azidation at the C2-position, whereas a less radical stabilizing group such as an alkyl or amide group at the C3-position of indole furnishes the 3-azidooxindole product. This protocol is mild and efficient to obtain several 2-azidoindole derivatives and 3-azidooxindole derivatives in moderate to good yields. The reaction conditions hold well for gram-scale synthesis

Sulfenylation of β‑Diketones Using C–<i>H</i> Functionalization Strategy

Sulfenylation of β-diketones is challenging as β-diketones undergo deacylation after sulfenylation in the reaction medium. The sulfenylation of β-diketones without deacylation under metal-free conditions at ambient temperature via a cross dehydrogenative coupling (CDC) strategy is reported. The resultant products can be further manipulated to form α,α-disubstituted β-diketones and pyrazoles

Generation of Hydrogen from Water: A Pd-Catalyzed Reduction of Water Using Diboron Reagent at Ambient Conditions

Production of hydrogen from renewable sources, particularly from water, is an intensive area of research, which has far-reaching relevance in hydrogen economy. A homogeneous catalytic method is presented for producing clean hydrogen gas from water, in a reaction of water with a diboron compound as the reductant, under ambient reaction conditions. The Pd-catalytic system is stable in water and displays excellent recyclability. Hydroxy analogues such as alcohols are compatible with the Pd/B₂Pin₂ system and generate hydrogen gas efficiently. The B₂Pin₂–H₂O system, in the presence of palladium, is an excellent catalytic system for selective hydrogenation of olefins

Directed Palladium-Catalyzed γ‑C(sp³)–H Alkenylation of (Aza and Oxa) Cyclohexanamines with Bromoalkenes: Bromide Precipitation as an Alternative to Silver Scavenging

Directed palladium-catalyzed coupling of remote C(sp3)–H bonds of aliphatic amines with organohalides is a powerful synthetic tool. However, these reactions still possess limitations with respect to cost and resource efficiency, requiring more reactive iodinated reactants and superstoichiometric silver salt reagents. In this work, an efficient regio- and stereospecific silver-free Pd-catalyzed γ-C(sp3)–H alkenylation of cyclohexanamines and heterocyclic analogues with bromoalkenes is reported, which can also be applied on five- and seven-membered rings. DFT methods revealed that the oxidative addition of the organobromide to Pd(II) is not the rate-limiting step but rather γ-C(sp3)–H bond activation in the substrate. The lowest energy complex in the catalytic cycle is a Pd(II)-Br complex coordinated with the reaction product (η2-alkene and a bidentate directing group). The stability of this complex defines the overall energy span of the reaction. Co-catalyst KOPiv plays a pivotal role by exchanging bromide for pivalate in the complex, via precipitation of the KBr coproduct. This removal of bromide from the reaction media decreases the energy span, avoiding the use of superstoichiometric silver salt reagents and allowing decoordination of the reaction product. In addition, pivalate facilitates the C(sp3)–H bond activation in the substrate once another substrate molecule is coordinated. The reaction conditions could be directly applied for (hetero)arylation given the weaker coordination of the reaction product, featuring a (hetero)aryl versus alkenyl and change in resting state. The picolinoyl directing group can be removed via amide esterification