(CDC)–Rhodium-Catalyzed Hydroallylation of Vinylarenes and 1,3-Dienes with AllylTrifluoroborates

Abstract

Catalytic site-selective hydroallylation of vinyl arenes and 1,3-dienes is reported. Transformations are promoted by a readily accessible bidentate carbodicarbene− rhodium complex and involve commercially available allyltrifluoroborates and an alcohol. The reaction is applicable to vinyl arenes and aryl-or alkyl-substituted 1,3-dienes (30 examples). Allyl addition products are generated in 40−78% yield and in up to >98:2 site selectivity. Reaction outcomes are consistent with the intermediacy of a Rh(III)−hydride generated by protonation of Rh(I) by an acid. A number of key mechanistic details of the reaction are presented: (1) Deuterium scrambling into the product and starting alkene indicates reversible Rh(III)−H migratory insertion. (2) A large primary kinetic isotope effect is observed. ( 3) With substituted allyltrifluoroborates (e.g., crotyl-BF 3 K) mixtures of site isomers are generated as a result of transmetalation followed by Rh−(allyl) complex equilibration, consequently disproving outer-sphere addition of the allyl nucleophile to Rh(III)−(η 3 -allyl). ( 4) Stereochemical analysis of a cyclohexadiene allyl addition product supports a syn Rh(III)−hydride addition. (5) A Hammett plot shows a negative slope. Finally, utility is highlighted by a iodocyclization and cross metathesis.

Enantioselective Synthesis of Functionalized Arenes by Nickel‐Catalyzed Site‐Selective Hydroarylation of 1,3‐Dienes with Aryl Boronates

“…We have previously reported catalytic site-and enantioselective reactions between N-heteroarenes and terminal or internal 1,3-dienes promoted by a carbodicarbene-Rh complex that proceeds via an electrophilic Rh III -p-allyl species (Scheme 1 A). [10,11] Although the method is efficient and siteand enantioselective, the scope of the reaction centers on nucleophilic arenes, since C À C bond formation occurs by outer-sphere nucleophile addition. In 2019, Zhou and co-workers reported a strategy for the catalytic hydroarylation of alkenyl arenes that involves reaction between an olefin, aryl boronic acid, and an alcohol in the presence of a phosphinenickel complex.…”

Enantioselective Synthesis of Functionalized Arenes by Nickel‐Catalyzed Site‐Selective Hydroarylation of 1,3‐Dienes with Aryl Boronates

“…We have previously reported catalytic site‐ and enantioselective reactions between N‐heteroarenes and terminal or internal 1,3‐dienes promoted by a carbodicarbene–Rh complex that proceeds via an electrophilic Rh III –π‐allyl species (Scheme A) . Although the method is efficient and site‐ and enantioselective, the scope of the reaction centers on nucleophilic arenes, since C−C bond formation occurs by outer‐sphere nucleophile addition.…”

Copper-Catalyzed Highly Enantioselective 1,4-Protoboration of Terminal 1,3-Dienes

“…Due to the utility of allylic boron reagents in organic synthesis, chemists are increasingly attentive to their preparations. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] Usually, basic main-group organometallics, such as organolithium or Grignard reagent, are necessary for traditional methods to make allylboranes. [19][20][21][22][23][24][25] The disadvantage of these strategies is their incompatibility with electrophilic functional groups.…”