74636-51-4Relevant articles and documents
Imidazolidene carboxylate bound MBPh4 complexes (M = Li, Na) and their relevance in transcarboxylation reactions
Van Ausdall, Bret R.,Poth, Nils F.,Kincaid, Virginia A.,Arif, Atta M.,Louie, Janis
, p. 8413 - 8420 (2011)
Combination of 1,3-bis(2,6-diisopropylphenyl)imidazolum-2-carboxylate (IPrCO2) with the Lewis acids MBPh4, where M = Li or Na, provided two separate complexes. The crystal structures of these complexes revealed that coordination to NaBPh4 yielded a dimeric species, yet coordination of IPrCO2 with LiBPh4 yielded a monomeric species. Combination of 1,3-bis(2,4,6-trimethylphenyl)imidazolum-2-carboxylate (IMesCO2) with LiBPh4 also afforded a dimeric species that was similar in global structure to that of the IPrCO2+NaBPh 4 dimer. In all three cases, the cation of the organic salt was coordinated to the oxyanion of the zwitterionic carboxylate. Thermogravimetric analysis of the crystals demonstrated that decarboxylation occurred at lower temperatures than the decarboxylation temperature of the parent NHC·CO2 (NHC = N-heterocyclic carbene). Kinetic analysis of the transcarboxylation of IPrCO2 to acetophenone with NaBPh 4 to yield sodium benzoylacetate was performed. First-order dependences were observed for IPrCO2 and acetophenone, whereas zero -order dependence was observed for NaBPh4. Direct dicarboxylation was observed when ItBuCO2 was added to MeCN in the absence of added MBPh4.
Tropylium Ion Catalyzes Hydration Reactions of Alkynes
Oss, Giulia,Ho, Junming,Nguyen, Thanh Vinh
supporting information, p. 3974 - 3981 (2018/08/17)
The hydration of alkynes is one of the most atom-economic and versatile synthetic protocols to access carbonyl compounds. This fundamental reaction, however, often requires transition-metal catalysts or harsh reaction conditions to promote the addition of water to the carbon–carbon triple bond. In this work, it is demonstrated that the non-benzenoid aromatic tropylium ion can be used as an organic Lewis acid promoter for the hydration of alkynes under simple reaction conditions with excellent outcomes.
On the mechanism of ylide-mediated cyclopropanations: Evidence for a proton-transfer step and its effect on stereoselectivity
Riches, Samantha L.,Saha, Chandreyee,Filgueira, Noelia Fontan,Grange, Emma,McGarrigle, Eoghan M.,Aggarwal, Varinder K.
supporting information; experimental part, p. 7626 - 7630 (2010/07/09)
In this paper, we describe studies on the cyclopropanation of Michael acceptors with chiral sulfur ylides. It had previously been found that semi-stabilized sulfonium ylides (e.g., Ph-stabilized) reacted with cyclic and acyclic enones and substituted acrylates with high ee and that stabilized sulfonium ylides (e.g., ester-stabilized) reacted with cyclic enones again with high ee. The current study has focused on the reactions of stabilized sulfonium ylides with acyclic enones which unexpectedly gave low ee. Furthermore, a clear correlation of ee with ylide stability was observed in reactions with methyl vinyl ketone (MVK): ketone-stabilized ylide gave 25% ee, ester-stabilized ylide gave 46% ee, and amide-stabilized ylide gave 89% ee. It is believed that following betaine formation an unusual proton transfer step intervenes which compromises the enantioselectivity of the process. Thus, following addition of a stabilized ylide to the Michael acceptor, rapid and reversible intramolecular proton transfer within the betaine intermediate, prior to ring closure, results in an erosion of ee. Proton transfer occurred to the greatest extent with the most stabilized ylide (ketone). When the same reactions were carried out with deuterium-labeled sulfonium ylides, higher ees were observed in all cases since proton/deuteron transfer was slowed down. The competing proton transfer or direct ring-closure pathways that are open to the betaine intermediate apply not only to all sulfur ylides but potentially to all ylides. By applying this model to S-, N-, and P-ylides we have been able to rationalize the outcome of different ylide reactions bearing a variety of substituents in terms of chemo- and enantioselectivity.
