Palladium-Catalyzed Cascade Allylative Dicarbofunctionalization of Aryl Phenol-Tethered Alkynes with Allyl Iodides: Synthesis of Skipped Dienes

Construction of Conjugated 1,3-Enynes via Pd-Catalyzed Cascade Alkynylation of Aryl Phenol-Tethered Alkynes with Alkynyl Bromides

An efficient Pd-catalyzed cascade alkynylation of aryl phenol-tethered alkynes with alkynyl bromides is described. This protocol could provide various conjugated 1,3-enynes possessing a polysubstituted spirocyclohexadienone, as well as an all-carbon tetrasubstituted alkene moiety. The products could also undergo ring-expansion and cyclization transformations under different conditions to convert to diverse fused cyclic scaffolds.

Pd-Catalyzed Cascade Intramolecular Heck Cyclization/Dearomatization of Indoles for the Construction of Two All-Carbon Quaternary Centers

A facile Pd-catalyzed cascade of intramolecular Heck cyclization/alkylpalladium activated dearomatization of aryl alkyne-tethered indole is described. In this single step two nonadjacent all-carbon quaternary centers, two nitrogen-containing heterocycles, and three C(sp²)-C(sp³) bonds are efficiently furnished. These products could also undergo 5-to-6 ring migration-expansion reaction under Brønsted-acid conditions to transform into the benzo[c]carbazole skeletons.

Synthesis of 1,4-benzoxazines via Y(OTf)3-catalyzed ring opening/annulation cascade reaction of benzoxazoles with propargylic alcohols

A convenient Y(OTf)₃-catalyzed cascade formal [4 + 2] cyclization approach for the formation of 1,4-benzoxazine scaffolds from benzoxazoles and propargyl alcohols through a ring-opening and regioselective ring-closure process has been developed. By using this mild and practical protocol, a broad range of aldehyde-containing 1,4-benzoxazine compounds were prepared in moderate to excellent yields with good functional group tolerance. Mechanistic studies indicated that an S_N1 nucleophilic substitution of benzoxazole with a propargyl cation was involved in this transformation.

imethyl 2-Benzylmalonate

An electrochemical dearomatizing spirocyclization of alkynes with dimethyl 2-benzylmalonates for the preparation of spiro[4.5]deca-trienones has been developed. This approach adopts ferrocene (Cp₂Fe) as an electrocatalyst to produce carbon-centered radical intermediates from C-H-based malonates, which obviates the forthputting of noble-metal reagents, sacrificial chemical oxidants and 2-bromomalonates. A wide variety of spiro compounds are efficiently prepared with satisfactory results under mild conditions.

Pd-Catalyzed C-H Functionalization of Indole-Containing Alkene-Tethered Aryl Halides with Alkynes To Construct Indole Alkaloid Scaffolds

A convenient and straightforward approach for the construction of indole alkaloid scaffolds from indole-containing alkene-tethered aryl halides and alkynes through a sequential C-H activation, five-membered palladacycle formation, and alkyne insertion process has been described. The approach provides a series of indole alkaloid compounds in moderate to excellent yields with good functional tolerance.