Abstract
Electronic modifications within Ru-based olefin metathesis precatalysts have provided a number of new complexes with significant differences in reactivity profiles. So far, this aspect has not been studied for neutral 16 VE allenylidenes. The first synthesis of electronically altered complexes of this type is reported. Following the classical dehydration approach (vide infra) modified propargyl alcohols were transformed to the targeted allenylidene systems in the presence of PCy3. The catalytic performance was investigated in RCM reaction (ring closing metathesis) of benchmark substrates such as diallyltosylamide (6) and diethyl diallylmalonate (7).
Highlights
IntroductionMetathesis represents one of the ground-breaking achievements in modern synthetic chemistry
Metathesis represents one of the ground-breaking achievements in modern synthetic chemistry.This powerful tool for carbon-carbon bond formation in hands of synthetic chemists renders the possibility to cut an olefinic double bond in retrosynthetic studies of target molecules [1,2]
The discovery of Selegue and coworkers that Ru(II)-complexes promote the dehydration of propargyl alcohols of type 8 (Scheme 1, dehydration approach) marks the inception of a straightforward access to a new metathetically active Ru-based catalyst class, the cationic allenylidenes (IV, Figure 1) [16]
Summary
Metathesis represents one of the ground-breaking achievements in modern synthetic chemistry. This powerful tool for carbon-carbon bond formation in hands of synthetic chemists renders the possibility to cut an (strategically introduced) olefinic double bond in retrosynthetic studies of target molecules [1,2]. Milestones in catalyst development have been the introduction of NHC ligands (N-heterocyclic carbenes) and the usage of chelating carbene moieties to provide highly active catalysts of improved stability (e.g., II, L = NHC). Electron withdrawing para-substituents successfully improve the initiation rate by means of decreasing both the electron density on the benzylidene (increased electrophilicity) and the chelating isopropoxy moiety (decreased Lewis basicity)
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