123772-77-0Relevant academic research and scientific papers
Ruthenium-catalyzed propargylic substitution reactions of propargylic alcohols with oxygen-, nitrogen-, and phosphorus-centered nucleophiles
Nishibayashi, Yoshiaki,Milton, Marilyn Daisy,Inada, Youichi,Yoshikawa, Masato,Wakiji, Issei,Hidai, Masanobu,Uemura, Sakae
, p. 1433 - 1451 (2007/10/03)
The scope and limitations of the ruthenium-catalyzed propargylic substitution reaction of propargylic alcohols with heteroatom-centered nucleophiles are presented. Oxygen-, nitrogen-, and phosphorus-centered nucleophiles such as alcohols, amines, amides, and phosphine oxide are available for this catalytic reaction. Only the thiolate-bridged diruthenium complexes can work as catalysts for this reaction. Results of some stoichiometric and catalytic reactions indicate that the catalytic propargylic substitution reaction proceeds via an allenylidene complex formed in situ, whereby the attack of nucleophiles to the allenylidene Cγ atom is a key step. Investigation of the relative rate constants for the reaction of propargylic alcohols with several para-substituted anilines reveals that the attack of anilines on the allenylidene Cγ atom is not involved in the rate-determining step and rather the acidity of conjugated anilines of an alkynyl complex, which is formed after the attack of aniline on the C γ atom, is considered to be the most important factor to determine the rate of this catalytic reaction. The key point to promote this catalytic reaction by using the thiolate-bridged diruthenium complexes is considered to be the ease of the ligand exchange step between a vinylidene ligand on the diruthenium complexes and another propargylic alcohol in the catalytic cycle. The reason why only the thiolate-bridged diruthenium complexes promote the ligand exchange step more easily with respect to other monoruthenium complexes in this catalytic reaction should be that one Ru moiety, which is not involved in the allenylidene formation, works as an electron pool or a mobile ligand to another Ru site. The catalytic procedure presented here provides a versatile, direct, and one-step method for propargylic substitution of propargylic alcohols in contrast to the so far well-known stoichiometric and stepwise Nicholas reaction.
Base-Catalyzed Cyclization of N-Propargylamides to Oxazoles
Nilsson, Bjoern M.,Hacksell, Uli
, p. 269 - 275 (2007/10/02)
The base-catalyzed cyclization of some N-propargylamides to oxazoles has been studied in the presence of sodium hydride and potassium carbonate.The α-arylsubstituted propargylamides 1c-d (Ar = p-OMeC6H4 (1c), C6H5 (1d), and p-O2NC6H4 (1e)) cyclized with markedly higher rates (1e > 1d > 1c) than the unsubstituted and α-methyl substituted propargylamides 1a and 1b.A 1H nmr spectroscopic experiment demonstrated the presence of an allenic intermediate in the potassium carbonate-catalyzed ring closure of 1e.The observed rank order of reactivities correlates well withthe acidities of the respective propargylic hydrogens of the amides and with the ability of the ring closed intermediates to stabilize an oxazole anion.The results demonstrate that the base-catalyzed formation of oxazoles from propargylamides may proceed via an allenic intermediate.
