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.
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.
Tandem multi-step synthesis of C-carboxyazlactones promoted by N-heterocyclic carbenes
作者:Craig D. Campbell、Nicolas Duguet、Katherine A. Gallagher、Jennifer E. Thomson、Anita G. Lindsay、AnnMarie C. O’Donoghue、Andrew D. Smith
DOI:10.1039/b806816j
日期:——
Cascade reaction sequences incorporating N-heterocyclic carbene-based organocatalysis have been developed that allow the direct preparation of a range of (±)-4-phenoxycarbonylazlactones in good isolated yields (66–84%) from the corresponding N-p-anisoyl amino acids.
Probing the Efficiency of N-Heterocyclic Carbene Promoted <i>O</i>- to C-Carboxyl Transfer of Oxazolyl Carbonates
作者:Jennifer E. Thomson、Craig D. Campbell、Carmen Concellón、Nicolas Duguet、Kathryn Rix、Alexandra M. Z. Slawin、Andrew D. Smith
DOI:10.1021/jo702720a
日期:2008.4.1
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.
Organic base effects in NHC promoted O- to C-carboxyl transfer; chemoselectivity profiles, mechanistic studies and domino catalysis
作者:Craig D. Campbell、Christopher J. Collett、Jennifer E. Thomson、Alexandra M. Z. Slawin、Andrew D. Smith
DOI:10.1039/c1ob05160a
日期:——
The O- to C-carboxyltransfer of oxazolylcarbonates promoted by triazolinylidenes, generated in situ with NEt3, shows a markedly different rate and chemoselectivity profile to the same reaction promoted by triazolinylidenes generated using KHMDS. The mechanism of these pathways has been probed through extensive crossover studies to understand this process. The use of NEt3 as a base allows domino multi-step