Effects of Silver Carbonate and p-Nitrobenzoic Acid for Accelerating Palladium-Catalyzed Allylic C-H Acyloxylation.

An allylic C-H acyloxylation of terminal alkenes with 4-nitrobenzoic acid was assisted by a bidentate-sulfoxide-ligated palladium catalyst combined with 1,4-benzoquinone and Ag2CO3 under mild reaction conditions. The catalytic activity was remarkably enhanced by Ag2CO3 as an additive and 4-nitrobenzoic acid as a carboxylate source; both components were essential to exhibiting high catalytic activity, high branch selectivity, and a wide substrate scope with low loading of the palladium catalyst. Branch-selective allylic acyloxylation of ethyl 7-octenoate (1a) gave the product which was led to ethyl 6,8-dihydroxyoctanoate (5), a useful synthetic intermediate of (R)-α-lipoic acid.

Nickel-Catalyzed Reaction of Benzamides with Bicylic Alkenes: Cleavage of C-H and C-N Bonds.

The nickel-catalyzed reaction of aromatic amides that contain an 8-aminoquinoline as a directing group with bicyclic alkenes, such as norbornene and 1,4-dihydro-1,4-epoxynaphthalene, results in the cleavage of both the C-H bond at the ortho-position of the benzene ring and the C(O)-N bond to give methanofluoren-9-one and 1,4-epoxyfluoren-9-one derivatives. Both Ni(OTf)2 and Ni(cod)2 show a high catalytic activity. The presence of AgOAc is essential for the reaction to proceed. In the meta-substituted aromatic amides, a less hindered C-H bond is exclusively functionalized.

Unprecedented Access to ß-Arylated Selenophenes through Palladium-Catalysed Direct Arylation.

Several reported methods allow access to α-arylated selenophenes, whereas the synthesis of ß-arylated selenophenes remains very challenging. Here, the Pd-catalysed coupling of benzenesulfonyl chlorides with selenophenes affording regiospecific ß-arylated selenophenes is reported. The reaction proceeds with easily accessible catalyst, base and substrates, and tolerates a variety of substituents both on the benzene and selenophene moieties. This transformation allows the programmed synthesis of polyarylated selenophenes with potential applications in pharmaceutical and materials chemistry, as the installation of aryl groups at the desired positions can be achieved.

Reactivity of bromoselenophenes in palladium-catalyzed direct arylations.

The reactivity of 2-bromo- and 2,5-dibromoselenophenes in Pd-catalyzed direct heteroarylation was investigated. From 2-bromoselenophene, only the most reactive heteroarenes could be employed to prepare 2-heteroarylated selenophenes; whereas, 2,5-dibromoselenophene generally gave 2,5-di(heteroarylated) selenophenes in high yields using both thiazole and thiophene derivatives. Moreover, sequential catalytic C2 heteroarylation, bromination, catalytic C5 arylation reactions allowed the synthesis of unsymmetrical 2,5-di(hetero)arylated selenophene derivatives in three steps from selenophene.