Isomerization of propargylic alcohols catalyzed by an iridium complex

A Highly Stereoselective Redox Isomerization-Reductive Deuteration Sequence of Propargyl Amines to α-Deuterated Amino Acids

Herein, we report a Cu-catalyzed redox isomerization-reductive deuteration sequence, providing facile access to a range of α-deuterated amino acid esters featuring an Z-configured alkene moiety with high yields. The advantages of this sequence include mild conditions, broad substrate scope, and excellent stereoselectivity. This research also represents a rare example of the Z-selective redox isomerization of propargyl amines.

Electrophilic halogenations of propargyl alcohols: paths to α-haloenones, β-haloenones and mixed β,β-dihaloenones

The Meyer–Schuster rearrangement of propargyl alcohols or alkynols leading to α,β-unsaturated carbonyl compounds is well known. Yet, electrophilic halogenations of the same alkynols and their alkoxy, ester and halo derivatives are inconspicuous. This review on the halogenation reactions of propargyl alcohols and derivatives intends to give a perspective from its humble direct halogenation beginning to the present involving metal catalysis. The halogenation products of propargyl alcohols include α-fluoroenones, α-chloroenones, α-bromoenones and α-iodoenones, as well as β-haloenones and symmetrical and mixed β,β-dihaloenones. They are, in essence, tri and tetrasubstituted alkenes carrying halo-functionalization at the α- or β-carbon. This is a potential stepping stone for further construction towards challenging substituted alkenones via Pd-catalysed coupling reactions.

This review highlights the development of α-haloenone, β-haloenone and mixed β,β-dihaloenone formations from propargyl alcohols via direct electrophilic halogenations and metal catalysed-halonium interception rearrangements.

A New Class of Redox Isomerization of N-Alkylpropargylamines into N-Alkylideneallylamines Catalyzed by a ReBr(CO)5/Amine N-oxide System

Redox isomerization reaction wherein N-alkylpropargylamines are converted into N-alkylideneallylamines in the presence of rhenium(I) complexes as catalysts is described. Among the additives tested, certain pyridine N-oxides and tertiary amine N-oxides were effective for the reaction to proceed, and in particular, the use of 2,6-lutidine N-oxides gave the best results. The choice of a diphenylmethyl group as a substituent on the nitrogen atom was key to the success of the reaction, allowing it to reach completion.

Lu's [3 + 2] cycloaddition of allenes with electrophiles: discovery, development and synthetic application

The discovery of Lu's [3 + 2] cycloaddition reaction is briefly introduced, and the recent important developments and synthetic applications of Lu's [3 + 2] cycloaddition reaction are highlighted and overviewed.

Well-defined transition metal hydrides in catalytic isomerizations

This Feature Article intends to provide an overview of a variety of catalytic isomerization reactions that have been performed using well-defined transition metal hydride precatalysts. A particular emphasis is placed on the underlying mechanistic features of the transformations discussed. These have been categorized depending upon the nature of the substrate and in most cases discussed following a chronological order.

Stereoselective synthesis of enynones via base-catalyzed isomerization of 1,5-disubstituted-2,4-pentadiynyl silyl ethers or their alcohol derivatives

1,5-Disubstituted-2,4-pentadiynyl silyl ethers undergo smooth desilylative isomerization to afford cis-enynones as major products with moderate stereoselectivities in the presence of a catalytic amount of KO(t)Bu or DBU. While the isomerization reactions of their alcohol derivatives catalyzed by KOH, KO(t)Bu or NaH take place efficiently to produce trans-enynones with high stereoselectivities. These reactions provide convenient and practical routes for the synthesis of enynones with a wide range of substitution groups.

An atom-economic and selective ruthenium-catalyzed redox isomerization of propargylic alcohols. An efficient strategy for the synthesis of leukotrienes

Catalytic ruthenium complexes in conjunction with an indium cocatalyst and Bronsted acid isomerize primary and secondary propargylic alcohols in good yields to provide trans enals and enones exclusively. Readily available indenylbis(triphenylphosphine)ruthenium chloride, in the presence of indium triflate and camphorsulfonic acid, gives the best turnover numbers and reactivity with the broadest range of substrates. Deuterium labeling experiments suggest that the process occurs through propargylic hydride migration followed by protic cleavage of the resultant vinylruthenium intermediate. Application of this method to the synthesis of leukotriene B4 demonstrates its utility and extraordinary selectivity.

Ruthenium-catalyzed reactions--a treasure trove of atom-economic transformations

The demand for new chemicals spanning the fields of health care to materials science combined with the pressure to produce these substances in an environmentally benign fashion pose great challenges to the synthetic chemical community. The maximization of synthetic efficiency by the conversion of simple building blocks into complex targets remains a fundamental goal. In this context, ruthenium complexes catalyze a number of non-metathesis conversions and allow the rapid assembly of complex molecules with high selectivity and atom economy. These complexes often exhibit unusual reactivity. Careful consideration of the mechanistic underpinnings of the transformations can lead to the design of new reactions and the discovery of new reactivity.