Probing the Efficiency of N-Heterocyclic Carbene Promoted O- to C-Carboxyl Transfer of Oxazolyl Carbonates
摘要:
Screening of a range of azolium salts, bases and solvents for reactivity indicates that triazolinylidenes, generated in situ with KHMDS in THF, promote the Steglich rearrangement of oxazolyl carbonates with high catalytic efficiency (typical reaction time 5 min at < 1.5 mol % NHC). This protocol shows wide substrate applicability, even allowing the efficient generation of vicinal quaternary centers. An improved experimental procedure is also described that allows a simplified one-pot reaction protocol to be employed with similarly high catalytic efficiency.
Enantioselective TADMAP-Catalyzed Carboxyl Migration Reactions for the Synthesis of Stereogenic Quaternary Carbon
作者:Scott A. Shaw、Pedro Aleman、Justin Christy、Jeff W. Kampf、Porino Va、Edwin Vedejs
DOI:10.1021/ja056150x
日期:2006.1.1
efficient and are used to prepare chiral lactams (23) and lactones (30) containing a quaternary asymmetric carbon. TADMAP-catalyzed carboxyl migrations in the indole series are relatively slow and proceed with inconsistent enantioselectivity. Modeling studies (B3LYP/6-31G*) have been used in qualitative correlations of catalyst conformation, reactivity, and enantioselectivity.
Amidine catalysed O- to C-carboxyl transfer of heterocyclic carbonate derivatives
作者:Caroline Joannesse、Carmen Simal、Carmen Concellón、Jennifer E. Thomson、Craig D. Campbell、Alexandra M. Z. Slawin、Andrew D. Smith
DOI:10.1039/b805850d
日期:——
The structural requirements of amidines necessary to act as efficient O- to C-carboxyl transfer agents are delineated and the scope of this process outlined through its application to a range of oxazolyl, benzofuranyl and indolyl carbonates.
Carbene‐Catalyzed Enantioselective Aldol Reaction: Post‐Aldol Stereochemistry Control and Formation of Quaternary Stereogenic Centers
作者:Xing Yang、Pankaj Kumar Majhi、Huifang Chai、Bin Liu、Jun Sun、Ting Liu、Yonggui Liu、Liejin Zhou、Jun Xu、Jiawei Liu、Dongdong Wang、Yanli Zhao、Zhichao Jin、Yonggui Robin Chi
DOI:10.1002/anie.202008369
日期:2021.1.4
The dominated approaches for asymmetric aldol reactions have primarily focused on the aldol carbon–carbon bond‐forming events. Here we postulate and develop a new catalytic strategy that seeks to modulate the reaction thermodynamics and control the product enantioselectivities via post‐aldol processes. Specifically, an NHC catalyst is used to activate a masked enolate substrate (vinyl carbonate) to
Isothiourea-Catalyzed Enantioselective Carboxy Group Transfer
作者:Caroline Joannesse、Craig P. Johnston、Carmen Concellón、Carmen Simal、Douglas Philp、Andrew D. Smith
DOI:10.1002/anie.200904333
日期:2009.11.9
Transferable skills: Enantiomerically pure isothioureas promote the O‐ to C‐carboxyl grouptransfer of oxazolyl carbonates with excellent levels of enantiocontrol (see scheme). The origin of the enantioselectivity of this process was probed mechanistically and rationalized computationally.
Isothiourea-Mediated Asymmetric O- to C-Carboxyl Transfer of Oxazolyl Carbonates: Structure-Selectivity Profiles and Mechanistic Studies
作者:Caroline Joannesse、Craig P. Johnston、Louis C. Morrill、Philip A. Woods、Madeleine Kieffer、Tobias A. Nigst、Herbert Mayr、Tomas Lebl、Douglas Philp、Ryan A. Bragg、Andrew D. Smith
DOI:10.1002/chem.201102847
日期:2012.2.20
The structural motif within a series of tetrahydropyrimidine‐based isothioureas necessary for generating high asymmetric induction in the asymmetric Steglich rearrangement of oxazolylcarbonates is fully explored, with crossover and dynamic 19F NMR experiments used to develop a mechanistic understanding of this transformation.
充分探索了一系列四氢嘧啶基异硫脲中的结构基序,这些结构对于恶唑碳酸酯的不对称Steglich重排产生高不对称诱导是必要的,并使用交叉和动态19 F NMR实验来发展对该转变的机理理解。