Tandem β‐Boration/Arylation of α,β‐Unsaturated Carbonyl Compounds by Using a Single Palladium Complex To Catalyse Both Steps

Abstract

Diphenyl(3-methyl-2-indolyl)phosphine (C(9)H(8)NPPh(2), 1) gives stable dimeric palladium(II) complexes that contain the phosphine in P,N-bridging coordination mode. On treating 1 with [Pd(O(2)CCH(3))(2)], the new complexes [Pd(mu-C(9)H(7)NPPh(2))(NCCH(3))](2) (2) or [Pd(mu-C(9)H(7)NPPh(2))(mu-O(2)CCH(3))](2) (3) were isolated, depending on the solvent used, acetonitrile or toluene, respectively. Further reaction of 3 with the ammonium salt of 1 led to the substitution of one carboxylate ligand to afford [Pd(mu-C(9)H(7)NPPh(2))(3)(mu-O(2)CCH(3))] (4), in which the bimetallic unit is bonded by three C(9)H(7)NPPh(2)(-) moieties and one carboxylate group. Using this methodology, [Pd(2)(mu-C(6)H(4)PPh(2))(2)(mu-C(9)H(7)NPPh(2))(mu-O(2)CCX(3))] (X=H (7); X=F (8)) were synthesised from the ortho-metalated compounds [Pd(C(6)H(4)PPh(2))(mu-O(2)CCX(3))](2) (X=H (5); X=F (6)). Complexes 3, 4, 7, and 8 have been found to be active in the catalytic beta-boration of alpha,beta-unsaturated esters and ketones under mild reaction conditions. Hindrance of the carbonyl moiety has an influence on the reaction rate, but quantitative conversion was achieved in many cases. More remarkably, when aryl bromides were added to the reaction media, complex 7 induced a highly successful consecutive beta-boration/cross-coupling reaction with dimethyl acrylamide as the substrate (99% conversion, 89% isolated yield).

Highly Enantio‐ and Diastereoselective Synthesis of γ‐Amino Alcohols from α,β‐Unsaturated Imines through a One‐Pot β‐Boration/Reduction/Oxidation Sequence

“…In all solvents where the formation of the syn-product was preferred (including in EtOH), we observed one single 11 B NMR resonance with very similar chemical shifts Table 2. 1,3-Diastereocontrolled reduction of the C=N bond in the b-boryl imines 2 followed by CA C H T U N G T R E N N U N G (Bpin) oxidation.…”

“…The enantioselectivies could only be unambiguously determined from the analysis of the corresponding aminoalcohols (3c) (vide infra). An interesting spectroscopic feature of the three b-boronate imine derivatives 2a-c is that their 11 B NMR chemical shifts are around d = 22 ppm, significantly different from that of the corresponding ketone (d = 37.2 ppm). Such a Dd is characteristic of a loss of planarity at the boron, a shift from pure sp 2 towards sp 3 -character [17] indicating a weak intramolecular B !…”

“…Alternatively, nickel and palladium complexes modified with chiral ligands, can also catalyze the bboration reaction providing enantioenriched a-chiral boron compounds, [10] and opening new possibilities for tandem catalytic cross-coupling reactions. [11] Rhodium-catalyzed asymmetric b-boration of a,b-unsaturated carbonyl compounds has also been reported. [12] Most recently, the b-boration of a,b-unsaturated esters and ketones has also been efficiently carried out by asymmetric organocatalysis with tertiary phosphorus compounds as chiral auxiliaries.…”

When cross-coupling partners meet indolylphosphines

“…Fernández, Ubeda and co-workers reported new dinuclear Pd(II) complexes containing diphenyl(3-methyl-2-indolyl)phosphine [77]. Palladium complexes of 1a, 1b, 2a…”

Palladium‐Catalyzed Borylation of Aryl Mesylates and Tosylates and Their Applications in One‐Pot Sequential Suzuki–Miyaura Biaryl Synthesis

“…The one-pot, two-step coupling reactions [14] were successfully achieved by adding the second electrophilic partners (e.g. ArOTs, ArOMs, ArCl, or ArBr) and K 3 PO 4 after the borylation process.…”