Enantioselective synthesis of pyrano[2,3-<i>c</i>]pyrrole <i>via</i> an organocatalytic [4 + 2] cyclization reaction of dioxopyrrolidines and azlactones
cyclization reaction of dioxopyrrolidines and azlactones has been successfully developed through a squaramide catalysis strategy. This protocol provides an efficient and mild access to obtain pyrano[2,3-c]pyrrole scaffolds containing contiguous quaternary and tertiary stereogenic centers in excellent yields (up to 99%) with high levels of diastereo- and enantioselectivities (up to 99% ee). Two possible pathways
二氧吡咯烷和氮杂内酯的对映选择性[4 + 2]环化反应已通过方酰胺催化策略成功开发。该协议提供了高效,温和的途径来获得吡喃并[2,3- c ]吡咯支架,该支架包含连续的四级和三级立体异构中心,产率高(高达99%),非对映和对映选择性高(ee高达99%) )。提出了两种可能的途径来解释观察到的立体选择性。
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.
Regiodivergent Enantioselective γ-Additions of Oxazolones to 2,3-Butadienoates Catalyzed by Phosphines: Synthesis of α,α-Disubstituted α-Amino Acids and <i>N</i>,<i>O</i>-Acetal Derivatives
作者:Tianli Wang、Zhaoyuan Yu、Ding Long Hoon、Claire Yan Phee、Yu Lan、Yixin Lu
DOI:10.1021/jacs.5b10524
日期:2016.1.13
Phosphine-catalyzed regiodivergent enantioselective C-2- and C-4-selective gamma-additions of oxazolones to 2,3-butadienoates have been developed. The C-4-selective gamma-addition of oxazolones occurred in a highly enantioselective manner when 2-aryl-4-alkyloxazol-5-(4H)-ones were employed as pronudeophiles. With the employment of 2-alkyl-4-aryloxazol-5-(4H)-ones as the donor, C-2-selective gamma-addition of oxazolones took place in a highly enantioselective manner. The C-4-selective adducts provided rapid access to optically enriched alpha,alpha-disubstituted alpha-amino acid derivatives, and the C-2-selective products led to facile synthesis of chiral N,O-acetals and gamma-lactols. Theoretical studies via DFT calculations suggested that the origin of the observed regioselectivity was due to the distortion energy that resulted from the interaction between the nudeophilic oxazolide and the electrophilic phosphonium intermediate.
Rational Design of 2-Substituted DMAP-<i>N</i>-oxides as Acyl Transfer Catalysts: Dynamic Kinetic Resolution of Azlactones
A novel concept that conversion of chiral 2-substituted DMAP into its DMAP-N-oxide could significantly enhance the catalytic activity and still be used as an acyltransfercatalyst is presented. A new type of chiral 2-substituted DMAP-N-oxides, derived from l-prolinamides, has been rationally designed, facilely synthesized, and applied in the dynamic kinetic resolution of azlactones. Using simple MeOH