Propargylation of aromatic compounds

Propargylation of Aromatic Compounds with Propargylic Alcohols... 

Scheme 7.26 Propargylation of aromatic compounds with propargylic alcohols.

Quite recently, some mononuclear ruthenium complexes such as [(p-cymene)RuX-(CO)(PR3)]OTf (X = Cl, OTf, R = Ph, Cy) have been found to work as catalysts for the propargylation of aromatic compounds such as furans, where some ruthenium complexes were isolated as catalytically active species from the stoichiometric reactions of propargylic alcohols (Scheme 7.27) [31]. The produced active species promoted the propargylation of furans vdth propargylic alcohols bearing not only a terminal alkyne moiety but also an internal alkyne moiety, indicating that this propargylation does not proceed via allenylidene complexes as key intermediates. 

Use of cationic thiolate-bridged diruthenium complexes 84 promotes the catalytic propargylation of aromatic compounds with propargylic alcohols bearing not only a terminal alkyne but also an internal alkyne unit (Equation (34)). " A variety of propargylated aromatic compounds are isolated in high to excellent yields. Although... 

As described in the previous sections, a variety of nucleophiles attack the Cy atom of ruthenium-allenylidene intermediates. Aromatic compounds should also be suitable candidates and this was found to be the case [30]. Thus, reactions of propargylic alcohols with heteroaromatic compounds such as furans, thiophenes, pyrroles, and indoles in the presence of a diruthenium catalyst such as la proceeded smoothly to afford the corresponding propargylated heteroaromatic compounds in high yields with complete regioselectivity (Scheme 7.25). The reaction is considered to be an electrophilic aromatic substitution if viewed from the side of aromatic compounds. 

In 2003, Torre and his co-workers prepared new terpene-aromatic hybrids 47 in high yields in the reactions of cobalt-coordinated propargylic compounds, derived from commercial (7iJ)-myrtenal, with a variety of aromatic compounds (Equation (23)). Interestingly, any terpene-aromatic hybrids are not produced from propargylic compounds without cobalt coordination. 

Propargylation (8, 148-149). The propargylation of aromatics and /1-dicarbonyl compounds with (propargyl)dicobalt hexacarbonyl cations (I) is now used for selective alkylation of ketones and their Irimethylsilyl enol ethers and enol acetates. The reaction is regiospccific and involves attack of the more thermodynamically stable enol, In the case of ketones, yields are substantially reduced by use of a solvent. In the case of enol derivatives, CH2C12 can be used.1... 

From InCl3, highly reactive low-valent indium(i) species are electrochemically generated and regenerated. These are used for allylation and propargylation of carbonyl compounds (Scheme 3). Of special interest are bisallylations of aromatic and aliphatic esters, since such conversions cannot be achieved by using conventional stoichiometric allylations of esters by means of indium metal or Ini.66... 

Propargylation. Propargylic alcohols can be converted into stabilized cations by reaction with Co2(CO)s and then with tetralluoroboric acid. The resulting cation propargylates activated aromatic compounds. The —Co2(CO)g unit is removed by treatment with ferric nitrate. An example is shown in equation (1). The steps can be conducted in sequence without purification of intermediates. The complex of propargyl alcohol itself reacts at both the ortho- andpara-positions of anisole. 

Propargylic alcohols bearing a terminal triple bond react with electron-rich aromatic compounds in the presence of thiolate-bridged diruthenium complexes to give the propargylated aromatic compounds.30 l-Phenylprop-2-yn-l-ol, for example, reacts with 2-methylfuran to form (15). Intramolecular examples of the reaction were also reported. The process is believed to involve electrophilic attack by the ruthenium-stabilized propargyl cation. 

Thiolate-bridged diruthenium complexes such as Cp RuCl(p2-SR)2RuCp Cl catalyze the propargylic substitution reaction of propargylic alcohol derivatives with various carbon-centered nucleophiles [118-120]. Ketones [119] (Eq. 88), aromatic compounds [120] (Eq. 89), or alkenes thus selectively afford the corresponding propargylated products with C-C bond formation. An allenylidene intermediate is proposed in these reactions. They are detailed in the chapter Ruthenium Vinylidenes and Allenylidenes in Catalysis of this volume. 

Electron-rich aromatic componnds are readily alkylated at room temperature with propargyl complexes to form, after demetallation, 2-propyne-snbstituted aromatic compounds. Depending on the snbstitution pattern of the alkyne complex and the aromatic substrate, alkylation occurs at times with very high regioselectivity. This type of annulation was used in a synthesis of psendoipterosin... 

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