Bimetallic Pd/Cu and Pd/Ag catalytic systems were used for borylation of propargylic alcohol derivatives. The substrate scope includes even terminal alkynes. The reactions proceed stererospecifically with formal SN2' pathways to give allenyl boronates. Opening of propargyl epoxides leads to 1,2-diborylated butadienes probably via en allenylboronate intermediate.

SummaryThe pH-activated E/Z isomerization of a series of hydrazone-based systems having different functional groups as part of the rotor (R = COMe, CN, Me, H), was studied. The switching efficiency of these systems was compared to that of a hydrazone-based molecular switch (R = COOEt) whose E/Z isomerization is fully reversible. It was found that the nature of the R group is critical for efficient switching to occur; the R group should be a moderate H-bond acceptor in order to (i) provide enough driving force for the rotor to move upon protonation, and (ii) stabilize the obtained Z configuration, to achieve full conversion.

(Hetero)aryl bis-acid chlorides and terminal alkynes, or likewise acid chlorides and terminal dialkynes, and ethyl 2-mercaptoacetate can be reacted to give highly luminescent symmetrical terthiophenes and quinquethiophenes in the sense of a consecutive pseudo-five-component reaction in good to excellent yields. Further functionalization of the obtained oligomers can be readily achieved by halogenation followed by a metal-catalyzed coupling reaction to give α,ω-diester substrates for subsequent transformations into highly functionalized materials.

Sequentially Pd-catalyzed processes are excellent entries to heterocycle synthesis. The broad mechanistic variety combined with often very mild reaction conditions allow the concatenation of elementary organic and organometallic steps to novel sequences in the sense of one-pot domino and multicomponent reactions. Given the numerous opportunities of alkyne coordination and their Pd-mediated transformations, alkynylation and carbometallation play a key role, both for purely organometallic sequences as well as in those processes that are intercepted by cyclocondensation. Pd-catalyzed aminations also find more and more entry into novel heterocycle syntheses based upon this theme.

1,2,5-Trisubstituted 7-azaindoles are rapidly and efficiently prepared in a one-pot, copper-free alkynylation–cyclization–alkylation sequence starting from unprotected 2-aminopyridyl halides in a consecutive three-component fashion. By extension to a consecutive four-component coupling–cyclization–iodination–alkylation synthesis of 3-iodo-1-methyl-2-phenyl-1H-pyrrolo[2,3-b]pyridine, a concise synthesis of SIS3, a selective TGF-β1 and signaling inhibitor, was realized.

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Substituted 1H-1,2,3-triazol-4-yl-pyrrolo[2,3-b]pyridines are efficiently prepared by a one-pot coupling/cyclization/desilylation Cu alkyne/azide cycloaddition (CuAAC) sequence in the sense of a consecutive three-component fashion. The key feature of this new de novo formation of azole and triazole anellation is the sequentially Pd/Cu-catalyzed process employing tri(iso-propyl)silyl (TIPS) butadiyne as a four-carbon building block. In addition, the sequence can be expanded in a four-component fashion also employing the in situ formation of the required azides.

2-Substituted 7-azaindoles are rapidly and efficiently prepared in a one-pot copper-free alkynylation-cyclization sequence starting from 2-aminopyridyl halides and terminal alkynes. Most importantly the amino nitrogen atom neither requires activation nor protection throughout the sequence.