Cobalt-Catalyzed Allylic C(sp³)–H Carboxylation with CO₂

Abstract

Catalytic carboxylation of the allylic C(sp)-H bond of terminal alkenes with CO was developed with the aid of a Co/Xantphos complex. A wide range of allylarenes and 1,4-dienes were successfully transformed into the linear styrylacetic acid and hexa-3,5-dienoic acid derivatives in moderate to high yields, with excellent regioselectivity. The carboxylation showed remarkable functional group tolerability, so that selective addition to CO occurred in the presence of other carbonyl groups such as amide, ester, and ketone. Since styrylacetic acid derivatives can be readily converted into optically active γ-butyrolactones through Sharpless asymmetric dihydroxylation, this allylic C(sp)-H carboxylation showcases a facile synthesis of γ-butyrolactones from simple allylarenes via short steps.

Cobalt-catalyzed nucleophilic addition of the allylic C(sp3)–H bond of simple alkenes to ketones

“…4). First, methylcobalt(I) I should be generated from Co(acac) 2 , Xantphos, and AlMe 3 [28–29]. Oxidative addition of the allylic C(sp 3 )–H bond to I would proceed to afford η 3 -allylcobalt(III) intermediate II , which is tautomerized to η 1 -allylcobalt(III) III by the assistance of the oxygen atom in the Xantphos ligand [30].…”

“…Therefore, it would be a formidable challenge for the generation of a nucleophilic π-allylmetal complex that reacts with electrophiles, triggered by allylic C(sp 3 )–H activation. To this end, Schneider [26], Kanai [27], and we [28–29] reported in 2017 catalytic allylic C(sp 3 )–H activation of alkenes to react carbonyl electrophiles such as imines, ketones, and CO 2 via nucleophilic allylmetal species (Fig. 1).…”

Direct Carboxylation of C(sp3)-H and C(sp2)-H Bonds with CO2 by Transition-Metal-Catalyzed and Base-Mediated Reactions

“…As shown in Scheme 11a, silylation of 2-(o-tolyl) pyridine exhibited a different regioselectivity toward C(sp 2 )-H and C(sp 3 )-H bonds functionalization in the presence of [Ir(cod)Cl] 2 and Ru 3 (CO) 12 Catalysts 2017, 7, 380 8 of 53 catalysts. While the Ir catalyst was found to afford selectively the C(sp 2 )-silylated product (8), the Ru catalyst afforded both C(sp 2 )-and C(sp 3 )-silylated derivative (6).…”

“…Very recently Mita and Sato have reported the catalytic carboxylation of allylic C(sp 3 )-H bond of terminal alkenes with CO 2 in the presence of a Co(acac) 2 /Xantophos/AlMe 3 /CsF system [53] (Scheme 12). Allylarenes (15 examples) were carboxylated to linear trans-styrylacetic acids (9) with moderate to good yields (41-84%) and 100% regioselectivity.…”

“…It is worth citing very recent examples of hydrocarboxylation reactions involving substrate reduction by a "formal hydride donor": (i) in Scheme 1f, [43] hydride is formally generated from H 2 O and Mn; (ii) in Scheme 1g, [44] the substrate is reduced by photo-induced transfer of 2e − and 2H + from a sacrificial amine; (iii) in Scheme 1h, [45] the substrate is carboxylated and subsequently reduced with H 2 in a Poly-NHC/Ag/Pd mediated process; (3) use of CO 2 in conjunction with alkenes, alkynes, dienes, allenes, diynes, in oxidative cycloaddition reaction of low valent metal complexes to form five-membered metallacycles [46][47][48][49][50][51][52] as exemplified in Scheme 1i; (4) direct carboxylation of C-H bonds with CO 2 avoiding C-H pre-functionalization, hydrocarboxylation or metallacycle formation as exemplified in Scheme 1j [53]). …”