Rhodium-Catalyzed Boron Arylation of 1,2-Azaborines
摘要:
A Sn-phony in B!: BN isosteres of biphenyl compounds are prepared through Rh-catalyzed cross-coupling between 2-chloro-1,2-azaborines and arylstannanes (see scheme). The synthetic method should enable investigations of structure–activity relationships (SARs) by expanding the chemical space of the pharmaceutically relevant biphenyl structure through BN/CC isosterism.
Catalytic Cycle of Rhodium-Catalyzed Asymmetric 1,4-Addition of Organoboronic Acids. Arylrhodium, Oxa-π-allylrhodium, and Hydroxorhodium Intermediates
摘要:
The catalytic cycle of asymmetric 1,4-addition of phenylboronic acid to an alpha,beta-unsaturated ketone catalyzed by a rhodium-binap complex was established by use of RhPh(PPh3)(binap) as a key intermediate. The reaction proceeds through three intermediates, phenylrhodium, oxa-pi-allylrhodium, and hydroxorhodium complexes, all of which were observed in NMR spectroscopic studies. The transformations between the three intermediates, that is, insertion, hydrolysis, and transmetalation, were also observed. On the basis of the catalytic cycle, a more active chiral catalyst, [Rh(OH)(binap)](2), was found and used successfully for the asymmetric 1,4-addition reactions.