863977-77-9Relevant academic research and scientific papers
Metal-catalyzed 1,2-shift of diverse migrating groups in allenyl systems as a new paradigm toward densely functionalized heterocycles
Dudnik, Alexander S.,Sromek, Anna W.,Rubina, Marina,Kim, Joseph T.,Kel'in, Alexander V.,Gevorgyan, Vladimir
, p. 1440 - 1452 (2008/10/09)
A general, mild, and efficient 1,2-migration/cycloisomerization methodology toward multisubstituted 3-thio-, seleno-, halo-, aryl-, and alkyl-furans and pyrroles, as well as fused heterocycles, valuable building blocks for synthetic chemistry, has been developed. Moreover, regiodivergent conditions have been identified for C-4 bromo- and thio-substituted allenones and alkynones for the assembly of regioisomeric 2-hetero substituted furans selectively. It was demonstrated that, depending on reaction conditions, ambident substrates can be selectively transformed into furan products, as well as undergo selective 6-exo-dig or Nazarov cyclizations. Our mechanistic investigations have revealed that the transformation proceeds via allenylcarbonyl or allenylimine intermediates followed by 1,2-group migration to the allenyl sp carbon during cycloisomerization. It was found that 1,2-migration of chalcogens and halogens predominantly proceeds via formation of irenium intermediates. Analogous intermediate can also be proposed for 1,2-aryl shift. Furthermore, it was shown that the cycloisomerization cascade can be catalyzed by Bransted acids, albeit less efficiently, and commonly observed reactivity of Lewis acid catalysts cannot be attributed to the eventual formation of proton. Undoubtedly, thermally induced or Lewis acid-catalyzed transformations proceed via intramolecular Michael addition or activation of the enone moiety pathways, whereas certain carbophilic metals trigger carbenoid/oxonium type pathway. However, a facile cycloisomerization in the presence of cationic complexes, as well as observed migratory aptitude in the cycloisomerization of unsymmetrically disubstituted aryl- and alkylallenes, strongly supports electrophilic nature for this transformation. Full mechanistic details, as well as the scope of this transformation, are discussed.
1,2-Halogen migration in haloallenyl ketones: Regiodivergent synthesis of halofurans
Sromek, Anna W.,Rubina, Marina,Gevorgyan, Vladimir
, p. 10500 - 10501 (2007/10/03)
Selective 1,2-iodine, bromine, and chlorine migration in haloallenyl ketones in the presence of Au catalyst has been demonstrated. It was found that, depending on the nature of the Au catalyst used, either selective bromine migration or hydrogen shift occ
