Stereoselective Propargylations with Transition-Metal-Stabilized Propargyl Cations

Abstract

Cationic propargylations have been known for quite some time but only the advent of transition metal stabilization has initiated their stereoselective applications. The introduction of nucleophilic additions to dicobalthexacarbonyl‐complexed propargyl cations, known as the Nicholas reaction, has led to widespread applications in the synthesis of complex molecules. Besides the stabilization by direct complexation of the triple bond, the complementary mode, i.e. transition metal complex substituents as propargyl cation stabilizing functional groups, is almost unknown. However, upon ionization, ferrocenyl‐ and (arene)chromiumcarbonyl‐substituted propargyl derivatives give the desired cationic species, and these cations can be regarded as quite reactive propargyl cations without simultaneous complexation of the triple bond, thus enabling highly diastereoselective nucleophilic additions with the potential of exploiting the ambident nature of propargyl cations.

Lewis Acid-Catalyzed Propargylic Etherification and Sulfanylation from Alcohols in MeNO2-H2O

“…This method involves Lewis acid-catalyzed C-C bond formation and thiazole synthesis via a propargyl cation stabilized by a unique structure. 39) A more versatile propargylation using the alcohol directly as a carbocation precursor would be a powerful tool leading to some useful compounds. In the present study, we report a unique Lewis acid-catalyzed etherification using both g-sulfur substituted and non-substituted propargyl alcohols in MeNO 2 -H 2 O.…”

Development of Palladium-Catalyzed Transformations Using Propargylic Compounds

“…[1][2][3][4][5][6][7][8][9][10][11] Reactions via the propargylic organometallics are the representative transformations, in which metal complexes react with propargylic compounds to form the propargylmetal species. Stoichiometric amounts of metal complexes are required in typical metalpromoted reactions, 3,4) and most of the reactions can proceed catalytically by the use of transition metal complexes.…”

“…[1][2][3][4][5][6][7][8][9][10][11] Reactions via the propargylic organometallics are the representative transformations, in which metal complexes react with propargylic compounds to form the propargylmetal species. Stoichiometric amounts of metal complexes are required in typical metalpromoted reactions, 3,4) and most of the reactions can proceed catalytically by the use of transition metal complexes. [5][6][7][8][9][10][11] For example, propargylic compounds containing an ester or a halide at the propargylic positions react with palladium complexes leading to π-propargylpalladium and allenylpalladium complexes (Chart 1), which further cause various transformations in the presence of the reactants to produce the corresponding products along with the regenerated palladium complexes.…”

Some reactions of Ni–Mo and Ni–W propargylic cations with nucleophiles

“…Many examples of such species ligated onto Co-Co bonds have been recognized and they are synthetically useful [2][3][4][5]. Carbocations (propargylic cations) have also been stabilized over Mo-Mo, and W-W centers.…”