Ruthenium‐Catalyzed Enantioselective Propargylation of Aromatic Compounds with Propargylic Alcohols via Allenylidene Intermediates

Abstract

The Friedel-Crafts reaction is one of the most reliable and powerful CÀC bond forming tools in organic synthesis. [1] Recently, the development of an asymmetric Friedel-Crafts alkylation of aromatic compounds has received a great deal of attention. This reaction introduces chiral centers at the benzylic position of aromatic compounds, [2] and a variety of Lewis acids and organocatalysts are available to promote the reaction. [2,3] However, the successful examples of asymmetric Friedel-Crafts alkylation are still limited to reactions with three types of electrophiles such as epoxides, carbonyl compounds, activated alkenes, and their analogues. [2,3] We have recently disclosed the novel catalytic activity [4] of chalcogenolate-bridged diruthenium complexes [5] such as [{Cp*RuCl(m 2 -YR) }2 ] (Cp* = h 5 -C 5 Me 5 ; Y= S, Se, Te; R = Me, nPr, iPr) and [Cp*RuCl(m 2 -YR) 2 RuCp*(OH 2 )]OTf (Tf = trifluoromethanesulfonyl) for many organic transformations via ruthenium-allenylidene intermediates.[6] One of these transformations is the propargylation of aromatic compounds with propargylic alcohols. [7][8][9] We envisaged the development of a catalytic enantioselective propargylation of aromatic compounds as a new type of asymmetric FriedelCrafts alkylation of aromatic compounds by taking account of our previous development of the ruthenium-catalyzed enantioselective propargylic substitution reactions of propargylic alcohols with acetone (up to 82 % ee).[10] We report here a successful example of an asymmetric Friedel-Crafts alkylation by using propargylic alcohols as electrophiles.Treatment of 1-phenyl-2-propyn-1-ol (1 a) with 2-methylfuran (10 equiv) in ClCH 2 CH 2 Cl in the presence of a catalytic amount of a chiral thiolate-bridged diruthenium complex 2 a, (prepared in situ from the tetranuclear ruthenium(II) complex [Cp*RuCl] 4 and a chiral disulfide [10b] in THF at room temperature for 12 h), and NH 4 BF 4 at 60 8C for 3 h afforded 2-methyl-5-(1-phenyl-2-propynyl)furan (3 a), which was isolated in 75 % yield with 77 %

Desilylation‐Activated Propargylic Transformation: Enantioselective Copper‐Catalyzed [3+2] Cycloaddition of Propargylic Esters with β‐Naphthol or Phenol Derivatives

“…[1][2][3][4] Very recently,wedisclosed the first copper-catalyzed asymmetric formal [3+ +2] cycloaddition of propargylic esters as C 2 synthons with C,O-bis(nucleophile)s, b-ketoesters,b yasequential propargylic alkylation/intramolecular hydroalkoxylation process. [5] However,t he use of other bis(nucleophile)s for this cycloaddition remains unexplored.…”

Iridium catalysis: application of asymmetric reductive hydrogenation

“…25 While ruthenium has been used in this process for 1,4-addition, sometimes in good enantioselectivities, the substrate scope remains small overall. 26 Similarly, Rh catalysts have been used, to obtain diarylethanes, but again the substrate 35 scope was limited. 27 The application of asymmetric hydrogenation to these substrates was highly successful as shown in Table 2.…”

Transition Metal Complexes of Neutral eta1-Carbon Ligands

“…Intramolecular cyclization reactions were also operative leading to the tricyclic species 124 (Fig. The asymmetric version of these reactions, using as catalyst a chiral diruthenium derivative, has recently been described [335][336][337]. Once again, the involvement of allenylidene intermediates was demonstrated through the stoichiometric reaction of isolated [Cp*RuCl(m-SMe) 2 Ru{=C=C=C(H)Ph}Cp*][BF 4 ] with 2-methylfuran, which led to the expected propargylated species 2-methyl-5-(1-phenyl-2-propynyl)furan as the sole reaction product.…”