n‐Butyllithium Catalyzed Hydroboration of Nitriles and Carbodiimides

Abstract

Highly efficient and selective hydroboration of nitriles and carbodiimides with pinacolborane (HBpin) is achieved by using the simple and convenient n‐BuLi as a catalyst. Solvent‐free and good functional group tolerance under mild conditions have been achieved. A possible mechanistic pathway of the n‐BuLi catalyzed hydroboration of nitriles with HBpin is proposed.

Molecular Main Group Metal Hydrides

“…Analogous studies in tetrahydrofuran were proposed to result in a complex equilibrium between several different boron-containing species in which the trialkoxy­borohydride, [( t BuO)­B­(H)­pin] − , was the major species participating in hydride delivery (Scheme ). On the basis of this precedent, a number of closely related studies have been described during the last decade, derived variously from the use of NaOH, n BuLi, − (also imines, alkynes, nitriles, and carbodiimides), , NaH, KH, Li­[O t Bu], K­[O t Bu], K 2 CO 3 , KCH 2 Ph, M­[N­(SiMe 3 ) 2 ] (M = Li, Na, K), LiBr, , MF (M = K, Cs), 2,6-di- tert -butylphenolate lithium, 1,1-dilithioferrocene, ( Dipp Nacnac)­Li, and l-lithio-2-alkyl-1,2-dihydropyridine . In a very recent advance, Newman and Melen have shown that the simple bases, lithium di- iso -propylamide and tert- butoxide catalyze the hydroboration of ketones, but with some enantioselectivity (er up to 70:30) when used in conjunction with enantiopure BINOL-type ligands .…”

Applications of catalysis in hydroboration of imines, nitriles, and carbodiimides

“…In addition, high chemoselectivity of imine over nitrile reduction was observed under this procedure. 137 Very recently in 2022, Mandal group reported a Bicyclic (alkyl)(amino)carbene (BICAAC) catalyst in metal free and solvent free hydroboration of nitriles. A wide scope of substrates including aromatic, heteroaromatic, and aliphatic nitriles (40 examples) were studied using 5 mol% catalyst with 30-92% isolated yield as ammonium salt.…”

“…In the same year of 2021, Ma and Yang reported n-BuLi as catalyst in monohydroboration of carbodiimides under neat condition at 80 °C. Both aliphatic and aromatic carbodiimides (3 examples) underwent reduction with yield of 97-99% within 24-48 h. 137 The Sen group reported lithium complexes, 2,6-di-tert-butyl phenolate lithium and 1,1′-dilithioferrocene (Fig. 12k) in carbodiimide hydroboration in 2021.…”

“…In addition, high chemoselectivity of imine over nitrile reduction was observed under this procedure. 137…”

“…In the same year of 2021, Ma and Yang reported n -BuLi as catalyst in monohydroboration of carbodiimides under neat condition at 80 °C. Both aliphatic and aromatic carbodiimides (3 examples) underwent reduction with yield of 97–99% within 24–48 h. 137…”