Complexes of Borane and N-Heterocyclic Carbenes: A New Class of Radical Hydrogen Atom Donor
摘要:
Calculations suggest that complexes of borane with N-heterocyclic carbenes (NHC) have B-H bond dissocation energies more then 20 Kcal/mol less than free borane, diborane, borane-THF, and related complexes. Values are in the range of popular radical hydrogen atom donors like tin hydrides (70-80 Kcal/mol). The resulting prediction that NHC borane complexes could be used as radical hydrogen atom donors was verified by radical deoxygenations of xanthates by using either AIBN or triethylborane as initiator.
development of one-pot organocatalytic dominoMichael/alpha-alkylation reactions between bromomalonates or bromoacetoacetate esters and alpha,beta-unsaturated aldehydes is presented. The chiral-amine-catalyzed reactions with bromomalonates as substrates give access to the corresponding 2-formylcyclopropane derivatives in high yields with excellent diastereoselectivity and up to 99 % ee. The catalytic domino
N-Heterocyclic Carbene-Catalyzed Hydrosilylation of Styryl and Propargylic Alcohols with Dihydrosilanes
作者:Qiwu Zhao、Dennis P. Curran、Max Malacria、Louis Fensterbank、Jean-Philippe Goddard、Emmanuel Lacôte
DOI:10.1002/chem.201101822
日期:2011.8.29
Reducing alkenes to tears: Addition of structurally diverse N‐heterocyclic carbenes (NHCs) to silicon allows the reduction of propargylic and styryl alcohols through an organocatalyzed silylation/direct hydride transfer tandem reaction (see scheme). Catalytic turnover is enabled by the switch to and from hypervalent silicon. This provides a new synthetic application of NHC–main group element complexes
Catalytic Generation of Activated Carboxylates: Direct, Stereoselective Synthesis of β-Hydroxyesters from Epoxyaldehydes
作者:Kenneth Yu-Kin Chow、Jeffrey W. Bode
DOI:10.1021/ja047407e
日期:2004.7.1
The catalytic generation of activated carboxylates from epoxyaldehydes enables the direct, stereoselective synthesis of beta-hydroxyesters under mild, convenient reaction conditions. In addition to providing a new method for the synthesis of anti-aldol adducts, this chemistry unveils a mechanistically viable solution to the catalytic, waste-free synthesis of esters.
A new reaction, closely related to both the classical Mannich reaction and the benzoin condensation, affords α-aminoketones from aldehydes and in situ prepared N-methylenemorpholinium or N-methylenepiperidinium salts.
Total Syntheses of the Histone Deacetylase Inhibitors Largazole and 2-<i>epi</i>-Largazole: Application of <i>N</i>-Heterocyclic Carbene Mediated Acylations in Complex Molecule Synthesis
作者:Bo Wang、Po-Hsien Huang、Ching-Shih Chen、Craig J. Forsyth
DOI:10.1021/jo102478x
日期:2011.2.18
Details of the evolution of strategies toward convergent assembly of the histone deacetylase inhibiting natural product largazole exploiting gamma,delta-unsaturated-alpha,beta-epoxy-aldehydes and a thiazole-thiazoline containing omega-amino-acid are described. The initial N-heterocyclic carbene mediated redox amidation exploying these two types of building blocks representing largazole's structural domains of distinct biosynthetic origin directly afforded the seco-acid of largazole. This was accomplished without any protecting groups resident upon either thioester bearing epoxy-aldehyde or the tetrapeptide. However, the ineffective production of largazole via the final macrolactonization led to an alternative intramolecular esterification/macrolactamization strategy employing the established two building blocks. This provided largazole along with its C2-epimer via an unexpected inversion of the alpha-stereocenter at the valine residue. The biological evaluation demonstrated that both largazole and 2-epi-largazole led to dose-dependent increases of acetylation of histone H3, indicating their potencies as class I histone deacetylase selective inhibitiors. Enhanced p21 expression was also induced by largazole and its C2 epimer. In addition, 2-epi-largazole displayed more potent activity than largazole in cell viability assays against PC-3 and LNCaP prostate cancer cell lines.