A unique nickel/organic photoredox co‐catalyzed asymmetric reductive cross‐coupling between α‐chloro esters and aryl iodides is developed. This cross‐electrophile coupling reaction employs an organic reductant (Hantzsch ester), whereas most reductive cross‐coupling reactions use stoichiometric metals. A diverse array of valuable α‐aryl esters is formed under these conditions with high enantioselectivities (up to 94 %) and good yields (up to 88 %). α‐Aryl esters represent an important family of nonsteroidal anti‐inflammatory drugs. This novel synergistic strategy expands the scope of Ni‐catalyzed reductive asymmetric cross‐coupling reactions.
Indoles are essential heterocycles in medicinal chemistry,a nd therefore,n ovel and efficient approaches to their synthesis are in high demand. Among indoles,2 -aryl indoles have been described as privileged scaffolds.Advanced herein is astraightforward, practical, and transition-metal-free assembly of 2-aryl indoles.Simply combining readily available 2-fluorotoluenes,n itriles,L iN(SiMe 3 ) 2 ,a nd CsF enables the generation of adiverse arrayofindoles (38 examples,48-92 % yield). Ar ange of substituents can be introduced into each position of the indole backbone (C4 to C7, and aryl groups at C2), providing handles for further elaboration. Scheme 1. Transition-metal-free synthesis of indoles.
Amines are fundamental motifs in bioactive natural products and pharmaceuticals. Using simple toluene derivatives, a one-pot aminobenzylation of aldehydes is introduced that provides rapid access to amines. Simply combining benzaldehydes, toluenes, NaN(SiMe3)2, and additive Cs(O2CCF3) (0.35 equiv.) generates a diverse array of 1,2-diarylethylamine derivatives (36 examples, 56–98% yield). Furthermore, suitably functionalized 1,2-diarylethylamines were transformed into 2-aryl-substituted indoline derivatives via Buchwald–Hartwig amination. It is proposed that the successful deprotonation of toluene by MN(SiMe3)2 is facilitated by cation–π interactions between the arene and the group(I) cation that acidify the benzylic C–Hs.
The first cobalt-catalyzed asymmetric Kumada cross-coupling with high enantioselectivity has been developed. The reaction affords a unique strategy for the enantioselective arylation of α-bromo esters catalyzed by a cobalt-bisoxazoline complex. A variety of chiral α-arylalkanoic esters were prepared in excellent enantioselectivity and yield (up to 97% ee and 96% yield). The arylated products were transformed into α-arylcarboxylic acids and primary alcohols without erosion of ee. The new enantioenriched α-arylpropionic esters synthesized herein are potentially useful in the development of nonsteroidal anti-inflammatory drugs. This method was conducted on gram-scale and applied to the synthesis of highly enantioenriched (S)-fenoprofen and (S)-ar-turmerone.
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