solid and air stable 2‑Pyridylzinc reagents – Real alternative to 2-pyridyl boronates?


A collaborative publication from Buchwald and Knochel trying to solve the ever recurring issue faced when using 2-pyridyl boronate. From past experience, 2-pyridyl boronates have always been problematic when used in ‘Suzuki’ type cross coupling and often prone to fast protodeborylation.

The recent development of Burke’s MIDA boronate is neat but far from widely applicable. Here Buchwald & Knochel are taking on solid and air-stable 2-pyridylzinc reagents

Their initial examples are forming a range of simple Air Stable 2-Pyridylzinc Pivalates by lithium or magnesium (Turbo Grignard) halogen exchange followed by transmetalation to Zn(OPiv)2

 

MP1

Very simple process but the scope is rather limited. The 2-Pyridylzinc Pivalates are reported as ‘free-flowing solids, indefinitely stable when stored under an inert atmosphere, and comparable in reactivity to organozinc halides in Negishi reactions’ which they clearly demonstrate in the later part of their publication.

The second part of the article focuses on alternative means to produce air stable and solid 2-pyridylzinc reagents. The small reported ‘screen’ identified dioxane as a stabilizing ligand forming a dioxanate complex, retaining reasonable air stability over a 24 hour period.

MP2Overall, an interesting and readily applicable alternative methodology to the problematic 2-pyridyl boronate by forming solid and air stable solid 2-Pyridylzinc reagents.