Using alcohols as simple H2-equivalents for copper-catalysed transfer semihydrogenations of alkynes

Copper(I)/N-heterocyclic carbene complexes enable a transfer semihydrogenation of alkynes employing simple and readily available alcohols such as isopropanol. The practical overall protocol circumvents the use of commonly employed high pressure equipment when using dihydrogen (H2) on the one hand, and avoids the generation of stoichiometric silicon-based waste on the other hand, when hydrosilanes are used as terminal reductants.DFG, 352364740, Diwasserstoff-vermittelte nachhaltige BindungsknüpfungsreaktionenDFG, 53182490, EXC 314: Unifying Concepts in CatalysisTU Berlin, Open-Access-Mittel - 201

Using Alcohols As Simple H2-Equivalents for Copper-Catalysed Transfer Hydrogenations

Catalytic transfer hydrogenations are among the most practical synthetic methods for the selective reduction of functional groups. Cheap and readily available dihydrogen (H2) equivalents are highly desirable for catalytic transfer hydrogenations, as inevitably, waste is generated by the formal H2 source. Copper hydride catalysis generally relies on stoichiometric use of waste-generating hydrosilanes. Here, we demonstrate that simple alcohols can be employed as H2 equivalents in stereoselective alkyne semihydrogenations, prototypical copper hydride-catalysed transformations

Metal-Free, Bronsted Acid-Catalyzed Formal 3+2] Annulation of Quinone Monoacetals with 2-Naphthols

An operationally simple and metal-free crosscoupling of quinone monoacetals (QMAs) with 2-naphthols catalyzed by triflic acid is reported, This formal 3+2] annulation allowed the synthesis of diverse naphtho2,1b]benzofuran derivatives in moderate to good yields. Preliminary mechanistic studies reveal the initial nucleophilic substitution of QMAs with 2-naphthols in preference to die mixed acetal formation and subsequent. 3,3] sigmatropic rearrangement

Efficient Diels–Alder Reaction of 1,2-Benzoquinones with Arynes and Its Utility in One-Pot Reactions

A new protocol for the efficient Diels–Alder reaction of 1,2-benzoquinones with arynes is reported. The aryne generated by the fluoride-induced 1,2-elimination of 2-(trimethylsilyl)aryl triflates undergoes a facile Diels–Alder reaction with 1,2-benzoquinones, affording the dioxobenzobicyclooctadienes in moderate to excellent yields. In addition, this methodology has been applied to the one-pot synthesis of benzoquinoxalinobarrelene and naphthalene derivatives

Employing Arynes in Transition-Metal-Free Monoarylation of Aromatic Tertiary Amines

The highly monoselective N-arylation of aromatic tertiary amines using a transition-metal-free approach using arynes has been developed. The reaction afforded functionalized diaryl amines in moderate to excellent yield. High levels of functional group compatibility especially with halogen containing substrates, dyes and donor–acceptor systems, and high yields of products are the notable features of the present reaction

AgOTf-catalyzed dehydrative 3+2] annulation of aziridines with 2-naphthols

The reaction of 2-naphthols with aziridines in the presence of AgOTf resulting in a dehydrative, formal 3+2] annulation is reported. The reaction allows the synthesis of functionalized benzoindolines, and tolerates a broad range of functional groups. A preliminary study on themechanism of this reaction indicates an SN1-type ring-opening of aziridines. This method is demonstrated for the one-pot synthesis of benzoindoles

Practical Synthesis of Phthalimides and Benzamides by a Multicomponent Reaction Involving Arynes, Isocyanides, and CO₂/H₂O

Transition-metal-free multicomponent reactions involving arynes and isocyanides with either CO₂ or H₂O have been reported. With CO₂ as the third component, the reactions resulted in the formation of <i>N</i>-substituted phthalimides. The utility of water as the third component furnished benzamide derivatives in moderate to good yields. These reactions took place under mild conditions with broad scope

Stereoselective Alkyne Hydrohalogenation by Trapping of Transfer Hydrogenation Intermediates

A catalytically generated vinylcopper complex, the reactive intermediate of a copper­(I)-catalyzed alkyne transfer hydrogenation, can be trapped by commercially available halogen electrophiles. In this manner, internal alkynes can stereoselectively be hydrohalogenated to the corresponding vinyl chlorides, bromides, and iodides

Stereoselective Alkyne Hydrohalogenation by Trapping of Transfer Hydrogenation Intermediates

A catalytically generated vinylcopper complex, the reactive intermediate of a copper­(I)-catalyzed alkyne transfer hydrogenation, can be trapped by commercially available halogen electrophiles. In this manner, internal alkynes can stereoselectively be hydrohalogenated to the corresponding vinyl chlorides, bromides, and iodides

A Bifunctional Copper Catalyst Enables Ester Reduction with H2: Expanding the Reactivity Space of Nucleophilic Copper Hydrides

Employing a bifunctional catalyst based on a copper(I)/NHC complex and a guanidine organocatalyst, catalytic ester reductions to alcohols with H2 as terminal reducing agent are facilitated. The approach taken here enables the simul-taneous activation of esters through hydrogen bonding and formation of nucleophilic copper(I) hydrides from H2, resulting in a catalytic hydride transfer to esters. The reduction step is further facilitated by a proton shuttle mediated by the guani-dinium subunit. This bifunctional approach to ester reductions for the first time shifts the reactivity of generally considered “soft” copper(I) hydrides to previously unreactive “hard” ester electrophiles and paves the way for a replacement of stoichi-ometric reducing agents by a catalyst and H2.<br /