已成功实现了碱促进的杂环烯胺和2,3-环氧丙烷-1-酮的环过环化反应,为具有结构选择性和立体选择性的结构多样的稠合吡啶和吡咯提供了新途径。在微波加热下用N-芳基4-氨基呋喃-2(5 H)-one和2,3-环氧丙烷-1-酮处理可得到高产率的功能性呋喃[3,2- b ]吡啶。带有吸电子基团的N-芳基4-氨基吡咯-2(5 H)-参与反应,得到吡咯并[3,2- b ]吡啶,而其对应物带有电子中性基团或给电子基团经历了不同的反应途径形成吡咯并[3,2- b通过C–C键断裂产生的吡咯。
from l‐ and d‐xylose, and l‐ and d‐arabinose, respectively. These monosaccharide‐based chiral macrocycles were tested as phase transfer catalysts in a few asymmetric reactions. The xylal‐based crown compounds proved to be efficient catalysts in a few liquid‐liquid phase reactions. The epoxidation of trans‐chalcone and the Darzens condensation of α‐chloroacetophenone with benzaldehyde took place with
The chiral monoaza-15-crown-5 lariat ethers annellated to methyl-4,6-O-benzylidene-α-d-glucopyranoside-1 or mannopyranoside 2 have been applied as phase-transfercatalysts in the epoxidation of substituted chalcones and chalcone analogues with tert-butylhydroperoxide resulting in significant asymmetricinduction. It was found that the position of the substituents in the aromatic ring of the chalcone
Synthesis, applications and mechanistic investigations of C2 symmetric guanidinium salts
作者:Matthew T. Allingham、Elliot L. Bennett、Deniol H. Davies、Philip M. Harper、Andrew Howard-Jones、Yassin T.H. Mehdar、Patrick J. Murphy、Dafydd A. Thomas、Peter W.R. Caulkett、David Potter、Casey M. Lam、AnnMarie C. O'Donoghue
DOI:10.1016/j.tet.2015.11.058
日期:2016.1
epoxidation of somechalcones in 85–94% ee. Using a spectrophotometric method, pKa values in the range 13.2–13.9 in DMSO have been determined for some of the catalysts highlighting an increase in basicity relative to achiral tetramethylguanidine (pKa=13.0) and a mechanism involving the protonated guanidinium ion as a phase transfer catalyst is proposed. The use of two of the catalysts for the addition of nucleophiles
在六个或七个合成步骤中制备了一系列胍鎓催化剂,并用于21-86%ee的甘氨酸Schiff碱的相转移烷基化,以及85-94%ee的一些查耳酮的相转移环氧化。使用分光光度法,对于某些催化剂,确定了DMSO中p K a值在13.2–13.9范围内,从而突出了相对于非手性四甲基胍的碱度增加(p K a= 13.0),提出了一种以质子化的胍鎓离子作为相转移催化剂的机理。研究了使用两种催化剂在迈克尔加成反应中添加亲核试剂,发现两者都是有效的催化剂。在这些反应中抗衡离子作用是明显的,但是没有观察到对映选择性。
Asymmetric C–C bond forming reactions with chiral crown catalysts derived from d-glucose and d-galactose
induction as phase transfer catalysts in the Michael addition of 2-nitropropane to chalcone (87% ee), in the Darzenscondensation of phenacyl chloride with benzaldehyde (71% ee) and in the self-condensation of phenacyl chloride (64% ee) to give 14. The absolute configurations of (−)-(2R,3S)-epoxy-3-(4-chlorophenyl)-1-phenyl-1-propanone 12 and (−)-4-chloro-(2R,3S)-epoxy-1,3-diphenyl-1-butanone 14 have
one-pot, two-step process was disclosed for production of chiral α,β-epoxy ketonesfrom benzaldehydes and acetophenones catalyzed by imidazolium-modified poly(l-leucine). Two effective reaction systems with complementary high enantioselectivities (up to 98% ee) or satisfactory yields (up to 89%) have been developed. Importantly, the poly(aminoacid) catalyst can be easily recovered and recycled for ten