The Suzuki-Miyaura cross-coupling of unprotected, nitrogen-rich heterocycles using precatalysts P1 or P2 is reported. The procedure allows for the reaction of variously substituted indazole, benzimidazole, pyrazole, indole, oxindole and azaindole halides under mild conditions in good to excellent yields. Additionally, the mechanism behind the inhibitory effect of unprotected azoles on Pd-catalyzed cross-coupling reactions is described based on evidence gained through experimental, crystallographic, and theoretical investigations.

The Suzuki−Miyaura reaction is one of the most widely employed transformations in synthetic chemistry. Despite extensive investigation, questions remain about the mechanistic nature of the transmetalation step when catalysts based on advanced ligands such as biaryl monophosphines are used, impeding the development of improved catalysts. Here we demonstrate that the often overlooked halide salt (KX) generated as a byproduct of cross-coupling renders the transmetalation step reversible with SPhos-based catalysts, leading to severe reaction inhibition with (hetero)aryl iodides. Stoichiometric and kinetic studies reveal that halide inhibition likely originates from disfavoring the formation of a highly reactive Pd−OH intermediate. We demonstrate that changing the organic solvent in the biphasic reaction mixture from tetrahydrofuran to toluene is sufficient to minimize this inhibition and enable the general Suzuki−Miyaura coupling of (hetero)aryl iodides. Our studies suggest that halide inhibition may be a more general problem in cross-coupling reactions, especially those involving reversible transmetalation processes.

Molecular switches based on helical tetrasubstituted alkenes, substituted with either electron-withdrawing (CF(3), F, CN; 2a-c, 3a,c) or -donating substituents (Me, OMe; 2d,e), have been synthesized from acyclic precursors 4 and 5 in a domino carbopalladation/Stille reaction. This palladium-catalyzed process allowed the rapid assembly of two C-C bonds, two six-membered rings, and the tetrasubstituted double bond in a completely diastereoselective fashion. The electronic effects of the substituents on the overall switching process were investigated by alternating irradiation of two different wavelength regions. Although the substituents had only a small influence on the absorption maxima, drastic differences in the switching behavior were observed.

The three‐component domino Knoevenagel/hetero‐Diels–Alder reaction of nitroacetone (6), formaldehyde and ethoxyvinylacetate (4) leads to dihydropyrans 10 and 11, which after hydrogenation of the double bond as well as consecutive reduction of the nitro group and reductive amination give the desired forosamine‐type 2‐acetoxyamino sugars 21–24 and ossamine‐type 25.

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