From meso-Lactide to Isotactic Polylactide: Epimerization by B/N Lewis Pairs and Kinetic Resolution by Organic Catalysts
摘要:
B/N Lewis pairs have been discovered to catalyze rapid epimerization of meso-lactide (LA) or LA diastereomers quantitatively into rac-LA. The obtained rac-LA is kinetically polymerized into poly(L-lactide) and optically resolved n-LA, with a high stereoselectivity k(L)/k(D) of 53 and an ee of 91% at 50.6% monomer conversion, by newly designed bifunctional chiral catalyst 4 that incorporates three key elements (beta-isocupreidine core, thiourea functionality, and chiral BINAM) into a single organic molecule. The epimerization and enantioselective polymerization can be coupled into a one-pot process for transforming mesa-LA directly into poly(L-lactide) and D-LA.
The cinchona alkaloids are a privileged class of natural products and are endowed with diverse bioactivities. However, for compounds with the closely‐related oxazatricyclo[4.4.0.0]decane (“oxazatwistane”) scaffold, which are accessible from cinchonidine and quinidine by means of ring distortion and modification, biological activity has not been identified. We report the synthesis of an oxazatwistane
Novel Quinidine-Derived Organocatalysts for the Asymmetric Substitutions of O-Boc-Protected Morita-Baylis-Hillman Adducts
作者:Cheng-Kui Pei、Xiu-Chun Zhang、Min Shi
DOI:10.1002/ejoc.201100501
日期:2011.8
A series of novelquinidine-derivedorganocatalysts was synthesized and utilized for the asymmetricsubstitution of O-Boc-protectedMorita–Baylis–Hillmanadducts with various carbamates and tosylcarbamates, affording the corresponding products in good to high yields (up to 91 % yield) with moderate to high ee values (up to 96 % ee) under mild conditions.
Tertiary Amine-Catalyzed Difluoromethylthiolation of Morita-Baylis-Hillman Carbonates of Isatins with Zard's Trifluoromethylthiolation Reagent
作者:Xing Fan、Haibin Yang、Min Shi
DOI:10.1002/adsc.201600954
日期:2017.1.4
tertiary amine‐catalyzed [3+2] annulation between Morita–Baylis–Hillman (MBH) carbonates derived from isatins with thiocarbonyl fluoride (F2C=S) in situ generated from Zard's reagent proceeds smoothly under mild conditions, affording difluoromethylthiolated spirocyclic oxindoles in good to excellent yields. Moreover, the asymmetric variant could be realized with a modified Cinchonaalkaloid, giving the
在本文中,我们报道了一种新的叔胺催化的[3 + 2]环化反应,该反应是由Isards衍生的Morita–Baylis–Hillman(MBH)碳酸酯与异硫氰酸羰基氟化物(F 2 C = S)从Zard试剂原位生成的在温和的条件下,以良好或优异的收率得到二氟甲基硫醇化的螺环羟吲哚。此外,可以用修饰的金鸡纳生物碱实现不对称变体,从而以良好的对映体选择性以及良好的产率获得所需的环状加合物。
Quinidine derived organocatalysts for the nucleophile promoted asymmetric [4+2] cycloaddition reaction of salicyl N-tosylimine with allenic esters
作者:Cheng-Kui Pei、Min Shi
DOI:10.1016/j.tetasy.2011.06.030
日期:2011.6
Cinchona alkaloid derived catalyst cat. 5 prepared fromβ-isocupreidine (β-ICD) was found to be a fairly effective organocatalyst for the nucleophilic promoted asymmetric [4+2] cycloaddition reaction of salicyl N-tosylimines and allenic esters to give the corresponding adducts in up to 80% yield, 87% ee.
Invertible Enantioselectivity in 6′-Deoxy-6′-acylamino-β-isocupreidine-Catalyzed Asymmetric Aza-Morita−Baylis−Hillman Reaction: Key Role of Achiral Additive
作者:Nacim Abermil、Géraldine Masson、Jieping Zhu
DOI:10.1021/ol901920s
日期:2009.10.15
(1e)-catalyzed aza-Morita−Baylis−Hillmanreaction between N-sulfonylimines 3 and alkyl vinyl ketones 4 produced the (R)-enriched adducts 5. By adding a catalytic amount of β-naphthol (2a), the enantioselectivity of the same reaction was inversed leading to (S)-5 in excellent yields and enantioselectivities. Both aromatic and aliphaticimines are accepted as substrates for this reaction.