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Catalytic Reductions Without External Hydrogen Gas: Broad Scope Hydrogenations with Tetrahydroxydiboron and a Tertiary Amine
Author(s) -
Korvinson Kirill A.,
Akula Hari K.,
Malinchak Casina T.,
Sebastian Dellamol,
Wei Wei,
Khandaker Tashrique A.,
Andrzejewska Magdalena R.,
Zajc Barbara,
Lakshman Mahesh K.
Publication year - 2020
Publication title -
advanced synthesis and catalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.541
H-Index - 155
eISSN - 1615-4169
pISSN - 1615-4150
DOI - 10.1002/adsc.201901099
Subject(s) - chemistry , aryl , reagent , halide , nitro , catalysis , amine gas treating , halogen , medicinal chemistry , tertiary amine , ketone , aryl halide , organic chemistry , alkyl
Abstract Facile reduction of aryl halides with a combination of 5% Pd/C, B 2 (OH) 4 , and 4‐methylmorpholine is reported. Aryl bromides, iodides, and chlorides were efficiently reduced. Aryl dihalides containing two different halogen atoms underwent selective reduction: I over Br and Cl, and Br over Cl. Beyond these, aryl triflates were efficiently reduced. This combination was broadly general, effectuating reductions of benzylic halides and ethers, alkenes, alkynes, aldehydes, and azides, as well as for N ‐Cbz deprotection. A cyano group was unaffected, but a nitro group and a ketone underwent reduction to a low extent. When B 2 (OD) 4 was used for aryl halide reduction, a significant amount of deuteriation occurred. However, H atom incorporation competed and increased in slower reactions. 4‐Methylmorpholine was identified as a possible source of H atoms in this, but a combination of only 4‐methylmorpholine and Pd/C did not result in reduction. Hydrogen gas has been observed to form with this reagent combination. Experiments aimed at understanding the chemistry led to the proposal of a plausible mechanism and to the identification of N , N ‐bis(methyl‐ d 3 )pyridin‐4‐amine (DMAP‐ d 6 ) and B 2 (OD) 4 as an effective combination for full aromatic deuteriation.