167773-12-8Relevant articles and documents
Chemoselective Cross-Coupling of gem-Borazirconocene Alkanes with Aryl Halides
Bai, Songlin,Gao, Yadong,Jiang, Chao,Qi, Xiangbing,Yang, Chao
supporting information, p. 11506 - 11513 (2020/07/14)
The direct and chemoselective conversion of the carbon-metal bond of gem-dimetallic reagents enables rapid and sequential formation of multiple carbon-carbon and carbon-heteroatom bonds, thus representing a powerful method for efficiently increasing structural complexity. Herein, we report a visible-light-induced, nickel-catalyzed, chemoselective cross-coupling reaction between gem-borazirconocene alkanes and diverse aryl halides, affording a wide range of alkyl Bpin derivatives in high yields with excellent regioselectivity. This practical method features attractively simple reaction conditions and a broad substrate scope. Additionally, we systematically investigated a Bpin-directed chain walking process underlying the regioselectivity of alkylzirconocenes, thus uncovering the mechanism of the remote functionalization of internal olefins achieved with our method. Finally, DFT calculations indicate that the high regioselectivity of this reaction originates from the directing effect of the Bpin group.
Total synthesis of epothilones B and D: Stannane equivalents for β-keto ester dianions
Keck, Gary E.,Giles, Robert L.,Cee, Victor J.,Wager, Carrie A.,Yu, Tao,Kraft, Matthew B.
supporting information; experimental part, p. 9675 - 9691 (2009/04/07)
(Chemical Equation Presented) Studies leading to a total synthesis of epothilones B and D are described. The overall synthetic plan was based on late-stage fragment assembly of two segments representing C1-C 9 and C10-C21 of the structure. The C 1-C9 fragment was prepared by elaboration of commercially available (2R)-3-hydroxy-2-methylpropanoate at both ends of the three-carbon unit. Introduction of carbons 1-4 containing the gem-dimethyl unit was achieved in a convergent manner using a diastereoselective addition of a stannane equivalent of a β-keto ester dianion. An enantioselective addition of such a stannane equivalent for a β-keto ester dianion was also used to fashion one version of the C10-C21 subunit; however, the fragment assembly (using bimolecular esterification followed by ring-closing metathesis) with this subunit failed. Therefore, fragment assembly was achieved using a Wittig reaction; this was followed by macrolactonization to close the macrocycle. The C10-C21 subunit needed for this approach was prepared in an efficient manner using the Corey-Kim reaction as a key element. Other key reactions in the synthesis include a stereoselective SmI 2 reduction of a β-hydroxy ketone and a critical opening of a valerolactone with aniline which required extensive investigation.
