Domino Heck/borylation sequence towards indolinone-3-methyl boronic esters: trapping of the σ-alkylpalladium intermediate with boron

Abstract

Pd-catalyzed domino Heck/borylation of acrylamides with B2pin2 is reported to generate synthetically useful indolinone-3-methyl boronic esters, via capturing σ-alkyl palladium with boron. Further functionalization of the obtained boronic ester qualify it as a new starting point for the functionalization of specific C(sp(3))-H bond. Moreover, the application of an Ugi-adduct as starting material or B2nep2 as an alternative boron source works equally well, making this a broadly applicable and robust method for the formation of a C-C and C-B bond in a single operation.

Pd(0)‐Catalyzed Dearomative Diarylation of Indoles

“…This led to the formation of the desired 1,2-diarylation product 2a in 20 %y ield in > 20:1 d.r., albeit with 63 %o ft he direct Suzuki coupling product 2a'.T he use of an aqueous solvent mixture lead to ad ecrease in the amounto f2a' formed (entry 2). Decreasing the reaction time to 2.5 hl ed to an increase in yield of 2a to 71 % (entry 9), and nearly quantitative mass recovery.T he use of other potassium-containing bases, such as KOH, KOAc, or K 3 PO 4 ,a ll lead to marked decreases in yield and/orc onversions (entries [10][11][12]. [27] Changing the organic component of the solvent from PhMe to dioxaneo rD MF led to decreased conversion and yields (entries 3a nd 4).…”

“…[1] The ability of Pd to react through multiple oxidation state manifolds has resulted in the development of ar emarkably broad range of difunctionalizationsw herein mostp roceed via Pd 0 /Pd II [2] or Pd II /Pd 0 cycles. [11] The 1,2-diarylation involving at erminating Suzuki coupling [12] of arylboronic acids [13,14] is the most widely explored variant to date(Scheme 1a). These processes are important as they allow for straightforward formation and functionalization of difficult-to-access organopalladium species, [6] and their utility has been made evident by the large number of reports, which include formal hydroarylations, [6a,b] arylcarbonylations, [6e] aminations, [6d, 7] alkenylations, [8] cyanations, [6d, 9] halogenations, [10] and borylations.…”

ChemInform Abstract: Pd(0)‐Catalyzed Dearomative Diarylation of Indoles.

“…Lowering the reactiont emperature to 100 8Cl ed to better overall mass recovery and as light increasei nt he yield of 2a to 64 % (entry 6), whereas deviatingf rom a0 .1 m concentrationo f1a only led to inferior results (entries 7a nd 8). Decreasing the reaction time to 2.5 hl ed to an increase in yield of 2a to 71 % (entry 9), and nearly quantitative mass recovery.T he use of other potassium-containing bases, such as KOH, KOAc, or K 3 PO 4 ,a ll lead to marked decreases in yield and/orc onversions (entries [10][11][12]. In the case of KOH, severe decomposition was observed.…”

“…These processes are important as they allow for straightforward formation and functionalization of difficult-to-access organopalladium species, [6] and their utility has been made evident by the large number of reports, which include formal hydroarylations, [6a,b] arylcarbonylations, [6e] aminations, [6d, 7] alkenylations, [8] cyanations, [6d, 9] halogenations, [10] and borylations. [11] The 1,2-diarylation involving at erminating Suzuki coupling [12] of arylboronic acids [13,14] is the most widely explored variant to date(Scheme 1a). This process is mechanistically distinct from the corresponding 1,2-diarylation arisingf rom at er-minatingC ÀHf unctionalization event (Scheme 1b), [15] or the Pd(II)-catalyzed 1,1-or 1,2-diarylation reactions using arylboron or aryltin reagents (Scheme 1c).…”

Trapping σ‐Alkyl–Palladium(II) Intermediates with Arynes Encompassing Intramolecular C−H Activation: Spirobiaryls through Pd‐Catalyzed Cascade Reactions

“…[3] Pioneering work from Grigg in the trapping of transient salkyl Pd II intermediates arising from intramolecular Heck reactions opened up awide range of organic transformations according to the terminating step of the cascade. [4] For instance,t he intermediate complex A (Scheme 1) can be trapped with different nucleophilic coupling partners such as hydride, [4,5] boron derivatives, [6] organotin reagents, [7] hydrazones, [8] or cyanides among others [9,10] (path a, Scheme 1).…”