Synthesis of a new example of the pyridazine annelated bis(N-heterocyclic carbene) ligand 3b (vegi) bearing benzyl substituents is reported, as well as the synthesis of its cationic Rh(cod) complex 5b. The mechanism of formation of the [Rh(cod)(vegi)] + complexes was investigated, showing a stepwise deprotonation of the imidazolium moieties via the mono-carbene imidazolium Rh(cod)Cl species 4. The [Rh-(cod)(vegi)] + complexes 5a,b show catalytic activity in the transfer hydrogenation of even sterically hindered ketones.
Metal-free halogen, chalcogen, or oxocarbenium ion mediated yne-carbonyl or yne-thioxo transformations of a range of N-and O-propargylic compounds have been studied. This investigation has led to the development of a mild, economic, and effective method for the synthesis of functionalized 4H-
Kabachnik-Fields reactions of various carbocyclic or heterocyclic acetylenic aldehydes together with subsequent Lewis acid catalyzed cyclizations have been studied. It was found that 5-exo-dig versus 6-endo-dig cyclization mode strongly depends on the structure of starting materials. Thus, nonaromatic acetylenic α-anilinomethylphosphonates underwent gold(III)-catalyzed or iodine-mediated 5-exo-dig cyclization to 1H-pyrrol-2-ylphosphonates. In contrast, electron-withdrawing heteroaromatic substrates formed 1,2-dihydropyridin-2-ylphosphonate ring containing materials via an exclusive 6-endo-dig ring-closure process. The dual mode of cyclization is possible only for α-amino (2-alkynylphenyl)methylphosphonates containing a benzene ring.
Cyclopropyl‐tethered 3‐alkynyl imines react with polarized‐covalent‐bond‐containing compounds to give polyfunctionalized pyrroles. This provides a mild and effective method for the simultaneous introduction of halogen, chalcogen, or hydrogen groups to the 3‐position of the pyrrole ring, together with the incorporation of halogen, azide, or alkoxy/aryloxy groups into the ethyl side‐chain.
The regio‐ and stereoselective nucleophilic addition of primary aliphatic amines to 2‐(1‐alkynyl)‐2‐alken‐1‐ones was found to proceed through double‐bond migration. In particular, this is a mild and atom‐economical route for the preparation of (Z)‐β‐enaminones having cycloalkene rings.
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