First enantiopure imine CN-palladacycle of non-metallocenic planar chirality with the [2.2]paracyclophane backbone

Cyclopalladation of 2-tert-butyl-4,4-dimethyl-2-oxazoline in solution and on silica gel

“…Recently, our group demonstrated that cyclopalladation of structurally different N-containing compounds could be carried out on SiO 2 using solvents only during the purification step [3]. In addition to our study, there have been four reports on the formation of a carbon-metal bond in reactions on SiO 2 or Al 2 O 3 ; in all cases the (sp 2 )C-H bond activation was observed [4][5][6][7][8]. In particular, formation of (sp 2 )C-Ru and (sp 2 )C-Pd bonds on SiO 2 at 50 and 75°C, respectively, were reported by the Chakravorty et al [4,5].…”

“…Transformations of Pt(II) coordination complexes to the corresponding cycloplatinated derivatives on SiO 2 at 150-200°C were described by the Eisenberg and Kukushkin [6]. Most recently, Dunina et al reported preparation of a C,N-palladacycle in 70% yield using our procedure for cyclopalladation on SiO 2 at 85°C [7]. Metalation during chromatographic purification on Al 2 O 3 has also been reported [8].…”

[2.2]Paracyclophane‐Derived Planar‐Chiral Hydrogen‐Bond Receptors

“…The compound was subject to a borane reduction, using a chiral oxazaborolidine (CBS) catalyst. Other preparative methods for the resolution of [2.2]paracyclophane derivatives involve the separation of diastereomeric 4‐(4‐tert‐butyl‐2‐oxazolinyl)‐[2.2]paracyclophanes, available in two steps from [2.2]paracyclophane carboxylic acid and ( S )‐ tert ‐leucinol,44 as well as the diastereoselective decomplexation of a ( R )‐valinate ligand in dimeric [2.2]paracyclophane‐based CN ‐palladacycles 45. Apart from these strategies, resolution by enzymatic methodologies have been developed for 4‐acetoxy[2.2]paracyclophane,46 4,12‐bisacetoxy[2.2]paracyclophane,17c and 4‐formyl[2.2]paracyclophane 47.…”

Solvent-free cyclopalladation on silica gel

“…In addition, reactions carried out on SiO 2 often proceed with high regio-and stereoselectivity and generally under milder conditions than those in solution [2][3][4][5][6]. Although organic transformations on silica gel are well documented, there have been only several reports regarding metalation reactions on SiO 2 or Al 2 O 3 [7][8][9][10][11]. Transformations of Pt(II) coordination complexes with benzophenone-derived ligands to the corresponding cycloplatinated derivatives on SiO 2 at 150-200°C were studied by the Eisenberg and Kukushkin groups [7].…”

“…Ortho-palladation of a triarylphosphite during chromatographic purification on aluminum oxide was reported by Tune and Werner [10]. Most recently, the Dunina group reported preparation of a C,N-palladacycle on SiO 2 [11] using our general procedure reported at the ACS conference [12].…”