Cyclization Reactions of Ruthenium Vinylidene Complexes with Terminal Aromatic Alkynes Containing Aldehyde, Ketone, and Ester Functionality
Date Issued
2010
Date
2010
Author(s)
Chang, Wei-Chen
Abstract
Terminal arylalkynes containing aldehyde, ketone, and ester functionality (1a-c and 6), were reacted with [Ru]-Cl ([Ru] = (η5-C5H5)(PPh3)2Ru) to investigate the specific influence of different carbonyl groups. Dissimilar types of hetrocyclic complexes were obtained, including a six-membered ring alkoxycarbene complex 2 from 1, an isobenzofuran carbene complex 3 from 1, or furan complexes 11c and 12a-c from 6, respectively. For the o-alkynyl benzaldehyde 1a, the reaction with [Ru]-Cl takes place at the terminal alkyne first giving the vinylidene-intermediate II which could undergo an intramolecular cyclization to yield the six-membered ring carbene complex 2a. By changing the aldehyde gourp to a ketone group, the reaction gives the five-membered ring carbene complex 3 as the major product and the six-membered ring complex 2 as the minor product. The reaction proceeds via formation of a π-coordinated intermediate followed by a cyclization at Cβ. The presence of ketone group clearly controls the reaction pathway to give different products. For the ethynylbenzoate compound 6, the vinylidene complex 7 is isolated, and then deprotonation followed by alkylation with various haloacetates yield complex 9. Base induced cyclization of complex 9 leads to two types of products. In the first type, formation of complex 12, through a formal methanol elimination accompanied with one sp2-sp2 C-C bond formation, is via a tandem intramolecular cyclization and a vinylidene intermediate V. The intramolecular cyclization at Cα of complex 9c accompanied with a [1,3]-benzyl group migration process to yield complex 11c is the second type reaction. These two types of reaction pathways could be controlled by the amount of base used in the reaction. Better understanding of these chemical reactions and their mechanisms involved are corroborated by structure determination of the two ruthenium complexes using single crystal X-ray diffraction analysis.
Subjects
Ruthenium
vinylidene
carbene
cyclization
furan
rearrangement
Type
thesis
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