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
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.
Efficient N-Heterocyclic Carbene-Catalyzed <i>O</i>- to C-Acyl Transfer
作者:Jennifer E. Thomson、Kathryn Rix、Andrew D. Smith
DOI:10.1021/ol061380h
日期:2006.8.1
An N-heterocyclic carbene promotes the rearrangement of alpha-amino acid derived O-acyl carbonates to their corresponding C-acylated isomers, generating a C-C bond and a quaternary stereocenter with high efficiency, under mild reaction conditions and with low catalyst loadings.