ABSTRACT
We present a copper-catalyzed oxidative cyclization of ß,γ-unsaturated hydrazones, utilizing molecular oxygen as a stoichiometric oxidant. The methodology provides distinct classes of pyrazoles simply by changing the reaction solvent. Tris-substituted pyrazoles, having a ketone functionality at the C-5 position, were obtained as the major product in ethanol, while di-substituted pyrazoles were predominantly formed in 1,1,1,3,3,3-hexafluoro-2-propanol.
Subject(s)
Copper/chemistry , Oxygen/chemistry , Pyrazoles/chemical synthesis , Catalysis , Molecular Structure , Oxidation-Reduction , Pyrazoles/chemistry , Solvents/chemistryABSTRACT
The [4 + 2] cross-benzannulation of conjugated enynes and diynes under cobalt-catalysis led to 1,2,3-trisubstituted benzene derivatives in good yields. The reaction proceeds smoothly in absolute regiospecific control when symmetrical diynes are applied. Moreover, the use of unsymmetrical diynes was investigated, resulting in the formation of the unprecedented regioisomers as major products, which is in contrast to the results obtained in palladium-catalyzed benzannulation reactions. Also, 4-bromophenyl-substituted starting materials could be applied successfully in the cobalt-catalyzed process, which can be problematic in the palladium-catalyzed counterpart.
ABSTRACT
The CH-activation of THF is realized in a zinc-mediated process using a dibromocyclopropane as a crucial additive. The highly regioselective addition to aryl-substituted propiolates as well as the regio- and stereoselective addition to diynes are described.
ABSTRACT
Fluorenone derivatives were generated from aryl-substituted propiolates via a cobalt-catalyzed Diels-Alder reaction/DDQ-oxidation and Friedel-Crafts-type cyclization. Several functional groups are tolerated, and good to excellent overall yields (up to 89%) could be achieved. For the synthesis of anthraquinone derivatives, aroyl-substituted propiolates were applied in a zinc iodide catalyzed Diels-Alder reaction with 1,3-dienes. The subsequent DDQ oxidation and Friedel-Crafts-type cyclization led to symmetrical as well as some unsymmetrical anthraquinones in good to excellent yields of up to 87% over the three-step reaction sequence.
Subject(s)
Alkadienes/chemistry , Anthraquinones/chemical synthesis , Fluorenes/chemical synthesis , Iodides/chemistry , Propionates/chemistry , Zinc Compounds/chemistry , Anthraquinones/chemistry , Catalysis , Cobalt/chemistry , Combinatorial Chemistry Techniques , Cyclization , Cycloaddition Reaction , Fluorenes/chemistry , Molecular StructureABSTRACT
The transformation of enynes under cobalt-catalysis leads to symmetrical benzannulation products in dichloromethane. In tetrahydrofuran the cobalt-catalysed reactions afforded the unprecedented unsymmetrical benzannulation products in moderate to good yields and good regioselectivities. In addition, cyclotrimerisation of the alkyne subunit can be realised when electron-deficient enynes are applied in the cobalt-catalysed transformations to generate 1,2,4-trivinylbenzene derivatives using tetrahydrofuran as solvent.
