Atom-efficient transition-metal-free arylation of N,O-acetals using diarylzinc reagents through Zn/Zn cooperativity

Abstract

Exploiting the cooperative action of Lewis acid Zn(C6F5)2 with diarylzinc reagents, the efficent arylation of N,O-acetals to access diarylmethylamines is reported. Reactions take place under mild reaction conditions without the...

An Illustrated Guide to Schlenk Line Techniques

“…Rotating the solid addition tube and gently tapping it will encourage the solid to enter the reaction flask (Figure c). This method is best suited for the addition of crystalline solids or salts (such as ZnCl 2 ) , that will not stick to the solid addition tube.…”

Atom-efficient arylation of N-tosylimines mediated by cooperative ZnAr2/Zn(C6F5)2 combinations

“…0.5 equivalents each of ZnPh 2 and Zn(C 6 F 5 ) 2 ] which effectively regenerates the more nucleophilic diarylzinc reagent. 10,11 In the case of 5a, the RZn(C 6 F 5 ) and ''PhZn(C 6 F 5 )'' components are retained together, at least in the solid-state under the conditions employed for crystallisation. In solution however, it is proposed that ''PhZn(C 6 F 5 )'' dissociates from 5 which gives compound 6 as the ultimate product of the reaction, which affords the corresponding amine 2 upon acidic quench.…”

“…9 Nevertheless, the high selectivity of organozinc reagents comes with the drawback of reduced reactivity, meaning that transition-metal catalysts, additives, or harsh reaction conditions are often needed to facilitate C-C bond formation when using these reagents. 7,8 To overcome these limitations, we have previously exploited the use of diarylzinc reagents in combination with the Lewis acidic species Zn(C 6 F 5 ) 2 to enable the atom-efficient functionalisation of glycosyl bromides 10 or N,O-acetals 11 without the need for transition-metal catalysts. Key for the success of these approaches is the lack of co-complexation or ligand scrambling between both types of Zn reagents.…”

“…Numerous reports have demonstrated that non-donor solvents work best for nucleophilic substitution reactions involving diarylzinc reagents. 10,11,18 This solvent dependence suggests that the pre-coordination of the imine substrate to the Lewis acidic zinc centre plays an essential role in the reaction (vide infra). Lowering the equivalents of ZnPh 2 to 0.5, only 45% yield of 2 was obtained, indicating that only one phenyl-substituent from ZnPh 2 is transferred.…”

“…To overcome these limitations, we have previously exploited the use of diarylzinc reagents in combination with the Lewis acidic species Zn(C 6 F 5 ) 2 to enable the atom-efficient functionalisation of glycosyl bromides 10 or N , O -acetals 11 without the need for transition-metal catalysts. Key for the success of these approaches is the lack of co-complexation or ligand scrambling between both types of Zn reagents.…”