Complete Retention of Configuration in a Cobaloxime π-Cation-Mediated Cyclization of an (ω-Hydroxy-β-hydroxyalkyl)cobaloxime

Stereochemistry and Mechanistic Study of Intramolecular PdII‐Catalyzed Oxypalladation and 1,3‐Chirality‐Transfer Reactions

“…The compound 3 was obtained in six steps from 5‐benzoyloxy‐1,2‐pentanediol ( 16 )12 as shown in Scheme . Monoprotection of the primary alcohol function of 16 with TBDMSCl followed by the (second) protection of the secondary alcohol with TBDPSCl gave 18 in 77 % yield in two steps.…”

“…17 : TBDMSCl (2.52 g, 16.7 mmol) was added to a mixture of ( S )‐4,5‐dihydroxypentyl benzoate 16 12 (3.42 g, 15.25 mmol), DMAP (186 mg, 1.5 mmol), and NEt 3 (10.6 mL, 76.3 mmol) in CH 2 Cl 2 (50 mL) at 0 °C. The mixture was stirred for 6 h at the same temperature, quenched with aqueous NaHSO 4 (15 mL, 1 M solution) and extracted with Et 2 O (3×20 mL).…”

Bridged (β-alkoxyalkyl)CoIII(salen) complexes by intramolecular alkoxycobaltation of unactivated alkenes: new models for coenzyme B12

“…Mechanisms that have been proposed for these reactions involve Co()-olefin π-cations, 22,25 β-cobaltoethyl cations stabilised by cobalt-carbon hyperconjugation, 25 and a concerted elimination of alcohol or water and cobalt(). 24 More recently, cobaloxime π-cations have also been suggested as intermediates in the reaction of (β-hydroxyalkyl)cobaloximes with nucleophiles 26 and in cobalt-mediated carbocyclic ring constructions. 27 Considering these proposals, it seems that a structure-dependent mechanistic continuum exists, similar to that implied for the solvomercuration-demercuration reaction for which arguments in favour and against bridged mercurinium and unsymmetrical mercury-stabilised carbocations, respectively, have been advanced.…”

Dialkyl Carbonates in the Green Synthesis of Heterocycles

“…These procedures generally employ heavy metals (Sharma et al, 2002; Shibata et al, 2005; Panda and Sarkar, 2008; Gadda et al, 2010; Tsui et al, 2012) or chlorine chemistry in the form of leaving groups, i.e., tosylate, mesylate etc. (Grubb and Branchaud, 1997; Lindner and Rodefeld, 2001; Adaligil et al, 2007).…”