ABSTRACT
An unprecedented way to extend the synthetic utility of the Diels-Alder reaction to include a vinylogous reactivity space is described. A commercially available chiral phosphoric acid catalyst effectively activates cyclic 2,4-dienones towards a vinylogous [4+2] cycloaddition with 2-vinylindoles, which leads to stereochemically dense tetrahydrocarbazoles. The reaction proceeds with a high level of remote stereocontrol and exclusive chemoselectivity for the more distant double bond of the dienone.
ABSTRACT
Ruthenium catalysts enabled C-H bond functionalizations on arenes with challenging secondary alkyl halides. Particularly, ruthenium(II) biscarboxylate complexes proved to be the key to success for direct alkylations with excellent levels of unusual meta-selectivity. The direct alkylations occurred under mild reaction conditions with ample scope and tolerated valuable functional groups. Detailed mechanistic studies were performed, including various competition experiments as well as reactions with isotopically labeled substrates. These studies provided strong support for an initial reversible cyclometalation. The cycloruthenation thereby activates the arene for a subsequent remote electrophilic-type substitution with the secondary alkyl halides. Independently prepared cycloruthenated complexes were found to be catalytically active provided that a carboxylate ligand was present, thereby highlighting the key importance of carboxylate assistance for effective meta-selective C-H bond alkylations.
Subject(s)
Alkanes/chemistry , Carbon/chemistry , Halogenation , Hydrogen/chemistry , Alkylation , Substrate SpecificityABSTRACT
An inexpensive ruthenium catalyst enabled oxidative annulations of alkynes by acrylamides with ample scope, which allowed for the preparation of 2-pyridones employing various electron-rich and electron-deficient acrylamides as well as (di)aryl- and (di)alkyl-substituted alkynes.
Subject(s)
Pyridones/chemical synthesis , Ruthenium/chemistry , Alkynes/chemistry , Catalysis , Chemistry, Organic/economics , Chemistry, Organic/methods , Molecular Structure , Oxidation-Reduction , Pyridones/chemistry , StereoisomerismABSTRACT
The mechanism of carboxylate-assisted ruthenium(II)-catalyzed direct alkylations of ketimines with unactivated alkyl halides was probed through experimental studies. The remarkable chemoselectivity of the broadly applicable catalyst also enabled direct alkylations among others on H(2)O or under solvent-free reaction conditions.
ABSTRACT
A palladium catalyst derived from air-stable secondary phosphine oxide (1-Ad)(2)P(O)H enabled efficient intramolecular alpha-arylations of amides with aryl chlorides, which allowed for the synthesis of diversely substituted (aza)oxindoles.
