Experimental and Computational Studies on Cobalt(I)-Catalyzed Regioselective Allylic Alkylation Reactions

Reductive coupling of allenyl/allyl carbonate with alkyne under dual cobalt-photoredox catalysis

Skipped dienes are among the most prevalent motifs in a vast array of natural products, medicinal compounds, and fatty acids. Herein, we disclose a straightforward one-step reductive protocol under Co/PC for the synthesis of diverse 1,4-dienes with excellent regio- and stereoselectivity. The protocol employs allenyl or allyl carbonate as π-allyl source, allowing for the direct synthesis of skipped diene with a broad range of alkynes including terminal alkynes, propargylic alcohols, and internal alkynes. The method also demonstrated the biomimetic homologation of natural terpenols into synthetic counterparts via iterative allylation of three-carbon allyl units, employing propargylic alcohol as a readily available alkyne source. Experimental studies, control experiments, and DFT calculations suggest the dual catalytic process generates 1,3-diene from allenyl carbonate, followed by proton and electron transfer leading to Co(II)-π-allyl species prior to the alkyne coupling. The catalytic cycle transitions through Co(II), Co(I), and Co(III).

Chemoselective and Stereoselective Allylation of Bis(alkenyl)boronates

Bis(alkenyl)boronates react with optically active Ir(π-allyl) species in a process that involves allylation of the more substituted olefin and 1,2-metalate shift of the less substituted olefin. The method constructs valuable enantioenriched tertiary allylic boronic esters with high chemoselectivity, enantioselectivity and diastereoselectivity. Allylic functionalization reactions transform the 1,3-stereodiad to 1,5- and 1,6-stereochemical relationships.

Cobalt-Catalyzed Allylic Alkylation at sp3-Carbon Centers

The rising demand and financial costs of noble transition metal catalysts have emphasized the need for sustainable catalytic approaches. Over the past few years, base-metal catalysts have emerged as ideal candidates to replace their noble-metal counterparts because of their abundance and easiness of handling. Despite the significant advancements achieved with precious transition metals, earth-abundant cobalt catalysts have emerged as efficient alternatives for allylic substitution reactions. In this review, allylic alkylations at sp3-carbon centers mediated by cobalt will be discussed, with a special focus on the mechanistic features, scope, and limitations.

Synthesis of Homoallylamines Enabled by Cobalt or Palladium Catalyzed Allylic Substitution of Azaarylmethylamines

Pd(OAc)2/Nixantphos or CoI2/Nixantphos catalyzed allylic substitutions with weakly acidic C(sp)3-H bonds of azaarylmethylamines are described. This method facilitates access to various kinds of heteroaryl rings containing homoallylamines (39 examples, 30-98% yields) with excellent functional group tolerance and diastereoselectivity. Compared with the Pd/Nixantphos complex, the Co/Nixantphos catalysis could obtain the cyclic products with good to excellent diastereoselectivities. Importantly, the CoI2/(R,R)-Me-Duphos catalyzed reactions exhibit moderate enantioselectivity. Additionally, the scalability of this transformation is successfully demonstrated.