Synthesis of polyhydroxylated xanthones via acyl radical cyclizations
摘要:
2-Formylphenoxy quinones can be converted into xanthones via an acyl radical intermediate with NBS and AIBN. (C) 2011 Elsevier Ltd. All rights reserved.
Lanthanide cation exchanged resins were used as catalysts for the acetalization of sucrose. Ytterbium(III)- and erbium(III)-exchanged resins promote the transacetalization of dialkyl acetals of α,β-unsaturated aldehydes. A two-step one-pot procedure provides direct access from the unsaturated aldehyde to a series of sucrose 4,6-acetals in good yields from unprotected sucrose without concomitant glycosidic bond cleavage.
d-Camphor-derived triazolium salts for catalytic intramolecular crossed aldehyde–ketone benzoin reactions
作者:Yi Li、Zhen Feng、Shu-Li You
DOI:10.1039/b801004h
日期:——
A series of triazolium salts has been synthesized from d-camphor and found to be efficient catalysts for intramolecular crossedaldehyde-ketonebenzoin reactions, affording alpha-ketols bearing a quaternary carbon center with up to 93% ee.
Readily available 1,2-amino alcohols provide the framework for a new generation of chiral carboxylicacid catalysts that rival the acidity of the widely used chiral phosphoric acid catalyst (S)-TRIP. Covalently linked thiourea sites stabilize the carboxylate conjugate bases of these catalysts via anion-binding, an interaction that is largely responsible for the low pKa values. The utility of the new
Catalytic Enantioselective [4+2] Cycloadditions of Salicylaldehyde Acetals with Enol Ethers
作者:Xiaojun Hu、Zhengbo Zhu、Zhongzheng Li、Alafate Adili、Minami Odagi、Khalil A. Abboud、Daniel Seidel
DOI:10.1002/anie.202315759
日期:2024.1.22
A readily accessible conjugate-base-stabilized carboxylic acid (CBSCA) catalyst facilitates highly enantioselective [4+2] cycloaddition reactions of salicylaldehyde-derived acetals and cyclic enol ethers, resulting in the formation of polycyclic chromanes with oxygenation in the 2- and 4-positions. Spirocyclic products are also accessible.