72824-04-5Relevant articles and documents
Umpolung of B?H Bonds by Metal–Ligand Cooperation with Cyclopentadienone Iridium Complexes
Higashi, Takuya,Kusumoto, Shuhei,Nozaki, Kyoko
supporting information, p. 2844 - 2848 (2020/12/18)
In contrast to conventional metal–ligand cooperative cleavage of a B?H bond, which provides a B cation on the ligand and an H anion on the metal, we report herein the umpolung of B?H bonds by novel cyclopentadienone iridium complexes. The B?H bonds of 4,4,5,5-tetramethyl-1,3,2-dioxaborolane (HBpin) and 1,8-naphthalenediaminatoborane (HBdan) were cleaved to give a B anion on the metal and an H cation on the phenolic oxygen atom of the ligand. Mechanistic investigation by DFT calculations revealed that the alkoxycarbonyl-substituted cyclopentadienone ligand facilitated deprotonation from Ir?H after oxidative addition of the B?H bond to give the umpolung product. The generated boryliridium complex was found to undergo borylation of an allyl halide in the presence of base, thus showing the nucleophilic nature of the boron atom.
Mechanism-based enhancement of scope and enantioselectivity for reactions involving a copper-substituted stereogenic carbon centre
Lee, Jaehee,Radomkit, Suttipol,Torker, Sebastian,Pozo, Juandel,Hoveyda, Amir H.
, p. 99 - 108 (2017/12/27)
A rapidly emerging set of catalytic reactions involves intermediates that contain a copper-substituted stereogenic carbon centre. Here, we demonstrate that an intimate understanding of this distinction provides ways for addressing limitations in reaction scope and explaining why unexpected variations in enantioselectivity often occur. By using catalytic enantioselective Cu-boryl addition to alkenes as the model process, we elucidate several key mechanistic principles. We show that higher electrophile concentration can lead to elevated enantioselectivity. This is because diastereoselective Cu-H elimination may be avoided and/or achiral Cu-boryl intermediates can be converted to allyl-B(pin) rather than add to an alkene. We illustrate that lower alkene amounts and/or higher chiral ligand concentration can minimize the deleterious influence of achiral Cu-alkyl species, resulting in improved enantiomeric ratios. Moreover, and surprisingly, we find that enantioselectivities are higher with the less reactive allylphenyl carbonates as chemoselective copper-hydride elimination is faster with an achiral Cu-alkyl species.
Enantioselective syn and anti homocrotylation of aldehydes: Application to the formal synthesis of spongidepsin
Lin, Hongkun,Tian, Leiming,Krauss, Isaac J.
supporting information, p. 13176 - 13182 (2015/10/28)
Whereas crotylboration has been a useful method for synthesis of stereochemically complex products, we have shown that homocrotylboration can be achieved with cyclopropanated crotylation reagents, and that the stereoselectivity of the reaction can be predicted by analogous models. This paper presents a full account of this work, including the first examples of asymmetric anti homocrotylation. The scope of this reaction is demonstrated with highly enantioselective homocrotylation of both aliphatic and aromatic aldehydes, as well as double diastereoselection studies. An application of the synthesis of the marine natural product spongidepsin is presented, as well as streamlined syntheses of homocrotylation reagents.
