Regio- and Stereoselective Hexafluoroisopropoxylation and Trifluoroethoxylation of Allenamides

Incorporating fluorinated moieties into organic molecules is an attractive strategy to enhance drug-like properties. Herein, we have developed a simple and self-promoted protocol for hexafluoroisopropoxylation and trifluoroethoxylation of allenamides with fluorinated alcohols such as HFIP and TFE. The reaction provided the fluoroalkoxylated products in a regio- and stereoselective manner in good to moderate yields under mild conditions.

Alcohols as Substrates in Transition-Metal-Catalyzed Arylation, Alkylation, and Related Reactions

Alcohols are abundant and attractive feedstock molecules for organic synthesis. Many methods for their functionalization require them to first be converted into a more activated derivative, while recent years have seen a vast increase in the number of complexity-building transformations that directly harness unprotected alcohols. This Review discusses how transition metal catalysis can be used toward this goal. These transformations are broadly classified into three categories. Deoxygenative functionalizations, representing derivatization of the C-O bond, enable the alcohol to act as a leaving group toward the formation of new C-C bonds. Etherifications, characterized by derivatization of the O-H bond, represent classical reactivity that has been modernized to include mild reaction conditions, diverse reaction partners, and high selectivities. Lastly, chain functionalization reactions are described, wherein the alcohol group acts as a mediator in formal C-H functionalization reactions of the alkyl backbone. Each of these three classes of transformation will be discussed in context of intermolecular arylation, alkylation, and related reactions, illustrating how catalysis can enable alcohols to be directly harnessed for organic synthesis.

Selective Hydrofunctionalization of N-Allenyl Derivatives with Heteronucleophiles Catalyzed by Brønsted Acids

In this study, we present a novel and environmentally sustainable protocol for the γ-hydrofunctionalization of N-allenyl compounds using various heteronucleophiles catalyzed solely by simple Brønsted acids. The method displays remarkable attributes, highlighting its sustainability, efficiency, regio- and stereoselectivity, as well as its versatile applicability to diverse heteroatom-containing enamides. Notably, our approach eliminates the need for metal catalysts and toxic solvents, representing a significant advancement in greener chemistry practices. We demonstrate the broad scope of our protocol by successfully scaling up reactions to gram-scale syntheses, underscoring its robustness for potential industrial implementation. The resulting γ-heterosubstituted enamides offer new possibilities for further synthetic transformations, yielding highly functionalized compounds with diverse applications. Mechanistic investigations reveal the pivotal role of CSA as a catalyst, enabling alcohol addition via a covalent activation mode.

AlCl3-catalyzed regioselective intermolecular α or γ mono- or α,γ bis-hydroalkoxylation of allenamides with alcohols

Regioselective intermolecular mono- or bis-hydroalkoxylation of allenamides with alcohols using simple aluminum-catalyzed reaction conditions is reported. When the reaction was carried out with 1.1 equivalents of alcohol at 50 °C, N,O-acetals were generated by 1,2-addition of an alcohol. An increase in temperature to 80 °C leads to γ-substituted ethers by an intermolecular isomerization process. Treatment with an excess of alcohol (3 equiv.) at 50 °C gave 1,3-bis(alkoxy)propanamines. The reactions exhibited good functional group tolerance and efficiency, affording the products in moderate to good yields.

A gold(i)-catalysed three-component reaction via trapping oxonium ylides with allenamides

A gold(i)-catalysed three-component reaction between alcohols (and water), α-aryl-α-diazoesters and allenamides is reported, affording tert-allylic ethers (and alcohols), in moderate to excellent yields with excellent geometric selectivity.

Chirality Transfer in Gold(I)-Catalysed Hydroalkoxylation of 1,3-Disubstituted Allenes

Gold(I)-catalysed intermolecular hydroalkoxylation of enantioenriched 1,3-disubstituted allenes was previously reported to occur with poor chirality transfer due to rapid allene racemisation. The first intermolecular hydroalkoxylation of allenes with efficient chirality transfer is reported here, exploiting conditions that suppress allene racemisation. A full substrate scope study reveals that excellent regio- and stereoselectivities are achieved when a σ-withdrawing substituent is present.

Gold(i)-catalyzed [2 + 2 + 2] cycloaddition of allenamides, alkenes and aldehydes: a straightforward approach to tetrahydropyrans

Allenamides participate as two-carbon components in an intermolecular [2 + 2 + 2] cycloaddition with alkenes and aldehydes when treated with catalytic amounts of a phosphite gold complex. The reaction is highly regio- and chemoselective, and works with different types of alkenes, including styrenes, enol ethers or enamides, as well as with aromatic and aliphatic aldehydes. Accordingly, different types of 2,6-disubstituted tetrahydropyrans can be stereoselectively assembled in a single step from commercial or very accessible starting materials.

Transition metal-catalysed intermolecular reaction of allenes with oxygen nucleophiles: a perspective

Transition metal catalysed hydroalkoxylation of allenes has received much attention in recent years, and both the intra- and intermolecular versions have been reported. Gold(I) complexes are among the most active catalysts for these processes. This critical perspective article will cover the progress in this field, analysing the intermolecular metal-catalysed reaction of allenes using palladium, iridium, rhodium, ruthenium, gold and platinum, in the presence of alcohols, water or carboxylic acids, and the mechanistic implications of these processes depending on the metal used.