Details

Autor(en) / Beteiligte

• Shu, Chao
• Noble, Adam
• Aggarwal, Varinder K

Titel

Metal-free photoinduced C(sp 3 )-H borylation of alkanes

Ist Teil von

• Nature (London), 2020-10, Vol.586 (7831), p.714-719

Ort / Verlag

England: Nature Publishing Group

Erscheinungsjahr

2020

Link zum Volltext

Beschreibungen/Notizen

• Boronic acids and their derivatives are some of the most useful reagents in the chemical sciences , with applications spanning pharmaceuticals, agrochemicals and functional materials. Catalytic C-H borylation is a powerful method for introducing these and other boron groups into organic molecules because it can be used to directly functionalize C-H bonds of feedstock chemicals without the need for substrate pre-activation . These reactions have traditionally relied on precious-metal catalysts for C-H bond cleavage and, as a result, display high selectivity for borylation of aromatic C(sp )-H bonds over aliphatic C(sp )-H bonds . Here we report a mechanistically distinct, metal-free borylation using hydrogen atom transfer catalysis , in which homolytic cleavage of C(sp )-H bonds produces alkyl radicals that are borylated by direct reaction with a diboron reagent. The reaction proceeds by violet-light photoinduced electron transfer between an N-alkoxyphthalimide-based oxidant and a chloride hydrogen atom transfer catalyst. Unusually, stronger methyl C-H bonds are borylated preferentially over weaker secondary, tertiary and even benzylic C-H bonds. Mechanistic studies indicate that the high methyl selectivity is a result of the formation of a chlorine radical-boron 'ate' complex that selectively cleaves sterically unhindered C-H bonds. By using a photoinduced hydrogen atom transfer strategy, this metal-free C(sp )-H borylation enables unreactive alkanes to be transformed into valuable organoboron reagents under mild conditions and with selectivities that contrast with those of established metal-catalysed protocols.