ABSTRACT
An efficient and selective bis(amidate)bis(amido) titanium precatalyst for the anti-Markovnikov hydroamination of alkynes is reported. Hydroamination of terminal and internal alkynes with primary alkylamines, arylamines, and hydrazines is promoted by 5-10 mol % of Ti catalyst. Various functional groups are tolerated including esters, protected alcohols, and imines. The in situ generated complex shows comparable catalytic activity, demonstrating its synthetic versatility for benchtop application. Applications of this catalyst for the synthesis of amino alcohols and a one-pot procedure for indole synthesis are described. A mechanistic proposal that invokes turnover-limiting protonolysis is presented to rationalize the observed regioselectivities.
Subject(s)
Alkynes/chemistry , Imines/chemistry , Organometallic Compounds/chemical synthesis , Titanium/chemistry , Amination , Catalysis , Molecular StructureABSTRACT
A new bis(amidate)zirconium bis(amido) hydroamination pre-catalyst using 6-tert-butyl-3-phenyl-2-pyridone as a proligand has been prepared and characterized. This rare example of an early transition metal complex incorporating a 2-pyridonate derivative as an ancillary ligand was found to be effective for the cyclohydroamination of aminoalkenes, including more challenging substrates bearing unactivated internal C=C bonds.
Subject(s)
Alkenes/chemistry , Pyridones/chemistry , Zirconium/chemistry , Amination , Catalysis , Cyclization , Molecular ConformationABSTRACT
Selective alpha-C-H activation results in the synthesis of the first bridging metallaaziridine complex for the catalytic alpha-alkylation of primary amines. Reaction development led to the preparation of new Zr 2-pyridonate complexes for this useful transformation. No nitrogen protecting groups are required for this reaction, which is capable of assembling quaternary chiral centers alpha to nitrogen. Preliminary mechanistic investigations suggest bridging metallaaziridine species are the catalytically active intermediates for this alpha-functionalization reaction, while monomeric imido complexes furnish azepane hydroamination products.
Subject(s)
Alkenes/chemistry , Amines/chemical synthesis , Aziridines/chemical synthesis , Hydrocarbons, Cyclic/chemical synthesis , Alkylation , Amines/chemistry , Catalysis , Titanium/chemistryABSTRACT
Commercially available Ti(NMe(2))(4) has been used effectively as a precatalyst in a facile protocol for the intramolecular hydroamination of aminoalkenes to yield pyrrolidine and piperidine heterocyclic products with isolated yields up to 92%. Geminally substituted substrates display the highest reactivity. This precatalyst is also effective for the hydroamination of activated internal alkenes, providing access to more complex heterocyclic target molecules.
