Stereoselective Entry into α,α’‐C‐Oxepane Scaffolds through a Chalcogen Bonding Catalyzed Strain‐Release C‐Septanosylation Strategy
摘要:
The utility of unconventional noncovalent interactions (NCIs) such as chalcogen bonding has lately emerged as a robust platform to access synthetically difficult glycosides stereoselectively. Herein, we disclose the versatility of a phosphonochalcogenide (PCH) catalyst to facilitate access into the challenging, but biologically interesting 7‐membered ring α,α’‐C‐disubstituted oxepane core through an α‐selective strain‐release C‐glycosylation. Methodically, this strategy represents a switch from more common but entropically less desired macrocyclizations to a thermodynamically favored ring‐expansion approach. In light of the general lack of stereoselective methods to access C‐septanosides, a remarkable palette of silyl‐based nucleophiles can be reliably employed in our method. This include a broad variety of useful synthons, such as easily available silyl‐allyl, silyl‐enol ether, silyl‐ketene acetal, vinylogous silyl‐ketene acetal, silyl‐alkyne and silylazide reagents. Mechanistic investigations suggest that a mechanistic shift towards an intramolecular aglycone transposition involving a pentacoordinate silicon intermediate is likely responsible in steering the stereoselectivity.
Ionic Liquid-Promoted, Highly Regioselective Heck Arylation of Electron-Rich Olefins by Aryl Halides
作者:Jun Mo、Lijin Xu、Jianliang Xiao
DOI:10.1021/ja0450861
日期:2005.1.1
arylation reaction in molecular solvents led to mixtures of regioisomers under similar conditions. Several lines of evidence point to the unique regiocontrol stemming from the ionic environment provided by the ionic liquid that alters the reaction pathway. The chemistry provides a simple, effective method for preparing branched, arylated olefins and contributes to the extension of Heckreaction to a wider
Pd-Catalyzed C(sp<sup>3</sup>)–C(sp<sup>2</sup>) cross-coupling of Y(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>3</sub>(THF)<sub>2</sub> with vinyl bromides and triflates
作者:Guilong Cai、Zhibing Zhou、Wenchao Wu、Bo Yao、Shaowen Zhang、Xiaofang Li
DOI:10.1039/c6ob01765g
日期:——
with vinyl bromides and triflates has been developed for efficient synthesis of various allyltrimethylsilanes. The cross-coupling reaction was conducted at room temperature with low catalyst loading of either Pd(PPh3)4 or Pd(PPh3)2Cl2, and exhibited high efficiency and a broad substrate scope. In combination with the cross-coupling by the Lewis-acid catalyzed Hosomi–Sakurai reaction, a novel three-component
A Stereoselective Reductive Hosomi–Sakurai Reaction
作者:Adriano Bauer、Nuno Maulide
DOI:10.1021/acs.orglett.8b00276
日期:2018.3.2
reaction is reported. This transformation hinges on a redox-neutral, stereoselective internal reduction event under mild conditions. This operationally simple reaction relies on readily available starting materials and leads to useful products in diastereoselectivities of up to 7:1. The versatility of this new method is demonstrated through the stereoselective one-step synthesis of an AChE inhibitor.
The application of cyclic and acyclic enol ethers as electrophiles in cross coupling reactions offers new possibilities for the preparation of functional compounds.
作者:Manuel Mahlau、Pilar García-García、Benjamin List
DOI:10.1002/chem.201203623
日期:2012.12.14
Lewis acid catalyzed Hosomi–Sakuraireaction of (hetero)aromatic aldehydes and allylsilanes using an easily handled disulfonimide precatalyst (see scheme). The key to the success of this system is to turn the usually undesired silylium ion catalysis into the desired catalytic regime and pair the cation with an enantiopure disulfonimide anion, thereby applying the concept of asymmetric counteranion‐directed