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.
A Metallocene-Pyrrolidinopyridine Nucleophilic Catalyst for Asymmetric Synthesis
摘要:
A highly active chiral 4-aminopyridine nucleophilic catalyst, available in three steps from (S,S)-hexane-2,5-diol, was applied to the asymmetric Steglich rearrangement of O-aceylated azlactones (1 mol % loading, up to 76% ee).
Chiral Bicycle Imidazole Nucleophilic Catalysts: Rational Design, Facile Synthesis, and Successful Application in Asymmetric Steglich Rearrangement
作者:Zhenfeng Zhang、Fang Xie、Jia Jia、Wanbin Zhang
DOI:10.1021/ja109069k
日期:2010.11.17
A new type of chiral bicycle imidazole nucleophilic catalyst was rationally designed, facilely synthesized, and successfully applied in an asymmetric Steglich rearrangement with good to excellent yield and enantioselectivity at ambient temperature. Moreover, it can be easily recycled with almost no reduction of catalytic efficiency. This is the first example for the successful chiral imidazole nucleophilic
A pseudo-enantiomeric pair of optically switchable helicenes containing a catalytic 4-N-methylaminopyridine (MAP) bottom unit and a C2-symmetric, (10R,11R)-dimethoxymethyl-dibenzosuberane top template was synthesized. They underwent complementary photoswitching at 290 nm (P/M′, <1/>99) and 340 nm (P/M′, 91/9) and unidirectional thermo-rotation at 130 °C (P/M′, >99/<1). They were utilized to catalyze
合成了含有催化的4- N-甲基氨基吡啶(MAP)底部单元和C 2对称(10 R,11 R)-二甲氧基甲基-二苯并亚戊烷顶部模板的可光学转换的螺旋对映体的对映体对映体。他们在290 nm(P / M ',<1 /> 99)和340 nm(P / M ',91/9)处进行互补光开关,并在130°C(P / M ',> 99 / <1)。它们被用来催化O-对C的对映异构Steglich重排。-羧基内酯,形成两种对映体,分别具有高达91%ee(R)和94%ee(S)的对映体。
Chiral DMAP‐
<i>N</i>
‐oxides as Acyl Transfer Catalysts: Design, Synthesis, and Application in Asymmetric Steglich Rearrangement
pyridine nitrogen, which serves as the nucleophilic site in the asymmetric acyltransfer reaction, we discovered that chiral DMAP‐N‐oxides, in which the oxygen now acts as the nucleophilic site, are efficient acyltransfercatalysts. Our finding might open a new door for the development of chiral DMAP‐N‐oxides for asymmetric acyltransfer reactions.