Synlett

The present article presents a personalized Account on the synthesis of nitrogen heterocycles by domino C–N coupling/hydroamination reactions and related processes. The starting materials, 2-alkynyl-1-halohetarenes, are regioselectively available by Sonogashira reactions of various 1,2-dihalogenated heterocycles, such as thiophenes, benzothiophenes, furans and benzofurans, pyridines, quinolines, pyrimidines, and other ring systems. More complex products are formed by domino C–N coupling/hydroamination/C–H arylation reactions of 2-alkynyl-1-halohetarenes with 2-bromoanilines. In these reactions, not only two, but three bonds are formed in one step. In many cases, the products constitute new heterocyclic core structures and show interesting pharmacological or fluorescence properties.1 Introduction2 Domino C–N Coupling/Hydroamination Reactions3 Domino C–N Coupling/Hydroamination/C–H Arylation Reactions4 Conclusions

The addition of boron trifluoride etherate (BF3·OEt2) to allenic ketones has led to the isolation of the isolated boron difluoride enolates. The single-crystal structure of boron enolate has been solved. The unprecedented C1–C10 migration of (Z)-β-difluoroboryloxy ether derivatives is observed to deliver rearranged phenol derivatives which are functionalized to C-2 alkyl-chromenones. Interestingly the isolated boron enolates have exhibited significant anticancer properties.

A Grubbs II catalyst mediated ring-closing metathesis (RCM) of monobrominated dienes is reported to proceed in moderate to good yields (40–80%) where the linking chain contains five atoms, leading to carbocyclic and heterocyclic seven-membered bromoolefins. Notably, RCM to form five-, six-, or eight-membered bromoolefins was unsuccessful, with the exception of one example where RCM afforded diethyl 3-bromocyclohex-3-ene-1,1-dicarboxylate. In this case, a bromomethyl-substituted cyclohexene was obtained as a byproduct. The utility of selected bromoolefin RCM products was demonstrated through their participation in Suzuki–Miyaura reactions. Vinylic halide exchange (Br → Cl) was noted as a side reaction under RCM conditions.

The synthesis of common cyclopropenes has been widely studied, but the synthesis of cyclopropenols is a significant challenge. Here, we highlight our recent work on the synthesis of trifluoromethylated cyclopropenols through a [2+1] cycloaddition reaction between alkynes and (trifluoroacetyl)silanes under visible-light-induced organocatalysis. The novel amphiphilic donor–acceptor carbenes derived from (trifluoroacetyl)silanes can react effectively with both activated and nonactivated alkynes. A broad substrate scope and a good functional-group tolerance have been achieved. Moreover, the synthetic potential of this reaction was highlighted by a gram-scale reaction and the one-pot diastereoselective synthesis of trifluoromethylated cyclopropanols.

The simple combination of readily available, recoverable, and recyclable magnetite (Fe3O4) nanoparticles and an environmentally friendly oxidant (H2O2) induced the effective functional group transformation of arylboronic acids into their corresponding phenols under mild conditions. Moreover, subsequent treatment of the reaction intermediate with appropriate electrophiles was accomplished in a one-pot system, leading to the formation of halophenols and phenolic derivatives.

Synlett 2022; 33: V-DOI: 10.1055/s-0041-1737491Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, GermanyArticle in Thieme eJournals:Table of contents

A sustainable, practical, and direct strategy for the reduction of carbonyl compounds, including aldehydes and ketones, by an electrochemical pathway is presented, affording a variety of alcohols or diols as major products with decent yields. The reaction proceeds smoothly in the air at ambient temperatures with DABCO as the sacrificial reductant. Mechanistic studies revealed that direct electrochemical reduction followed by either protonation or radical–radical homocoupling is the main pathway.

Benzimidazole atropisomers bearing a C–N axis are privileged structural frameworks in pharmaceutical and natural products, thus appealing an increasing interest for its asymmetric synthesis. Here, we briefly discuss recent advances in the asymmetric synthesis of benzimidazole atropisomers with a C–N axis, with particular attention to our recently developed palladium-catalyzed intramolecular Buchwald–Hartwig amination strategy.

A CuCl-catalyzed hydrosilylation of allenes with PhSiH3 has been developed. It is the first example of using readily available cheap silane reagents to generate branched allylsilanes in copper-catalyzed allene hydrosilylation. This base-metal catalyst offered an atom-economical and efficient route to branched allylsilanes with excellent regioselectivity.

The synthesis of cyclopropyl pinacol boronic esters from dibromocyclopropanes via Matteson–Pasto rearrangement is reported. The method is readily scalable and shows limited levels of stereoinduction, with a selectivity that is in part complementary to that observed in existing stereoselective borylcyclopropanation strategies. The method can be used to rapidly access borylcyclopropanes as interesting building blocks for diversely functionalized cyclopropanes.