In situ generated aminodiborane as a reagent for deoxygenative reduction of carboxamides to amines

Abstract

Herein, we report a new method for the synthesis of aminodiborane (µ-NH2B2H5), by the reaction of NH3BH3 and elemental iodine (I2). The in situ generated aminodiborane is used as a...

Catalyst- and Stoichiometry-Dependent Deoxygenative Reduction of Esters to Ethers or Alcohols with Borane–Ammonia

“…A great deal of work has been performed exploring BH 3 −NH 3 as a hydrogen source, 18,19 but it is also gaining prominence as a useful reducing agent. 20,21 Using appropriate catalysts and activators, it has been applied for the reduction of carbonyls, 22,23 esters, 24,25 amides, 26,27 and a variety of other functional groups. 28,29 As part of our program on borane−amines for organic synthesis, we recently reported efficient room temperature (RT) reductions of ketones 30 and carboxylic acids 31 to alcohols with BH 3 −NH 3 using catalytic (10 mol %) TiCl 4 .…”

“…Borane–ammonia (BH 3 –NH 3 , 1a ) is an easily prepared, air and moisture stable alternative to borane–tetrahydrofuran (BTHF) and borane–dimethyl sulfide (BMS). A great deal of work has been performed exploring BH 3 –NH 3 as a hydrogen source, , but it is also gaining prominence as a useful reducing agent. , Using appropriate catalysts and activators, it has been applied for the reduction of carbonyls, , esters, , amides, , and a variety of other functional groups. , As part of our program on borane–amines for organic synthesis, we recently reported efficient room temperature (RT) reductions of ketones and carboxylic acids to alcohols with BH 3 –NH 3 using catalytic (10 mol %) TiCl 4 . During these projects, ketones or acids were selectively reduced in the presence of esters, which is not surprising given the fact that esters are poor substrates for reduction with BTHF or BMS .…”

“…This coordination is followed by a borane–ammonia hydroboration of the carbonyl, forming a tetrahedral intermediate. In the case of BF 3 , an alternate reaction with aminodiborane is feasible, , as a reaction between BF 3 –Et 2 O and borane–ammonia was observed to produce this species. The mechanisms diverge following the recoordination of the Lewis acid to the acetal intermediate.…”

Reduction of esters to alcohols and iodides using aminodiborane (μ-NH2B2H5): scope and mechanistic investigations

“…[5][6][7] Among the various B-N dehydrogenated species, 8 aminodiborane (m-NH 2 B 2 H 5 , ADB) has received recent interest in organic and inorganic syntheses. [9][10][11][12][13][14] ADB is a strained molecule, which is sensitive to moisture and air. The isolation of pure ADB as a reagent is cumbersome due to the high reactivity of the compound.…”

“…11,12 So, in situ generation of ADB has been found to be a better alternative for the reduction reactions of various organic functional groups. [12][13][14] The in situ generated ADB has been reported for reduction of carboxylic acids to alcohols 12 and nitriles to amines. 13 Very recently, our group reported that by combining iodine and AB, ADB can be in situ generated which can be used to reduce amides to amines (Scheme 1).…”