Abstract
Atropisomers are important organic frameworks in bioactive natural products, drugs as well as chiral catalysts. Meanwhile, silanols display unique properties compared to their alcohol analogs, however, the catalytic synthesis of atropisomers bearing silanol groups is challenging. Here, we show a rhodium-catalyzed torsional strain-promoted asymmetric ring-opening reaction for the synthesis of α-silyl biaryl atropisomers. The reaction features a dynamic kinetic resolution of C(Ar)-Si bond cleavage, whose stereochemistry was controlled by a phosphoramidite ligand derived from (S)-3-methyl-1-((2,4,6-triisopropylphenyl)sulfonyl)piperazine. This work is a demonstration of an aryl-Narasaka acylation, where the C(Ar)-Si bond cleavage is promoted by the torsional strain of α, α’-disubstituted silafluorene.
Highlights
Atropisomers are important organic frameworks in bioactive natural products, drugs as well as chiral catalysts
Organo-catalyzed transformation showed its strong power in organic synthesis and it have been successfully applied to axially chiral molecules construction[35,36,37,38,39,40]
In comparison with the classic asymmetric couplings, which proceed via a highly bulky metal intermediate (Fig. 1a), the ringopening strategy surcumvented this key intermediate and it provided an efficient protocol for construction of biaryl atropisomers
Summary
Atropisomers are important organic frameworks in bioactive natural products, drugs as well as chiral catalysts. Under the catalysis of nickel, copper, and palladium, the groups of Hayashi, Gu and others realized the ring-opening of dibenzo[b,d]thiophenes[44], diaryliodoniums[45,46,47,48], and 9H-fluoren9-ols (Fig. 1b)[49] This ring-opening reactions showed particular advantages in the preparation of sterically hindered ortho tetrasubstituted atropisomeric biaryls; these ringopening reactions displayed excellent diversity: hydroxyl, hydroxymethyl, thiol, iodine, and keto groups were efficiently introduced to the position adjacent to the chiral axis. The releasing of noncyclic aryl ring is the undesired pathway; (c) the classic Narasaka acylation is steric sensitive, and vinyltriphenylsilane displayed extremely low reactivity (Fig. 2c) It is forseeable, the reaction would be more challenging if tetra(arylsilanes) were used. The torsional strain enabled to differentiate one of four C(aryl)–Si bonds to give desired products
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