An exceptionally general electrophilic amination, which directly transforms commercially available nitroarenes into alkylated aromatic aminoboranes with zinc organyl compounds was developed. The reaction starts with a two-step partial reduction of the nitro group to a nitrenoid, which is used in situ as the electrophilic amination reagent. To facilitate isolation, the resulting air- and moisture-sensitive aminoboranes were reacted with a range of electrophiles. The method not only represents a direct transformation of nitro compounds into electrophilic amination reagents but also provides an elegant alternative to dehydrocoupling methods for the generation of aminoboranes.
Supercritical carbon dioxide is the preferred reaction medium for catalyst synthesis as exemplified for the hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL).
Ar are reductive coupling of nitro compounds with organohalides has been realized. The reaction is initiated by ap artial reduction of the nitro group to an itrenoid intermediate.T herefore,n ot only aromatic but also aliphatic nitro compounds are efficiently transformed into monoalkylated amines,w ith organohalides as the alkylating agent. Given the innate reactivity of the nitrenoid, ac atalyst is not required, resulting in ahigh tolerance for aryl halide substituents in both starting materials. Scheme 1. Reductivec oupling strategies. Table 2: Scope of the reductive coupling of nitro compounds with organohalides.Reaction conditions: Zn powder (4 equiv) and LiCl (2.2 equiv) were dried in vacuo, 1mLTHF was added, followed by pretreatment with catalytic amounts of TMSCl and dibromoethane. R 1 X 2 (0.6 mmol, 3equiv), the nitro compound 1 (0.2 mmol), and B 2 pin 2 (0.4 mmol, 2equiv) were added and the reaction was stirred for 12 hatRT. The aminoborane D was hydrolyzed by addition of water.[a] Carried out at 50 8 8C.[b] Reaction stirred for 1hat 50 8 8Cbefore the addition of 1a.[c] Carried out at 70 8 8C. Structures, compound numbers, and yields of isolatedproducts after column chromatography are given.
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