ABSTRACT
The unexpected ability of arylzinc reagents bearing electron-donating substituents to react in a Friedel-Crafts fashion (cine) with electrophiles like perpivaloylated glucoside bromide and benzhydryl bromides in competition with organometallic coupling (ipso) is shown. The stereoelectronic factors required to promote the cine reactivity versus the classical ipso, and the mechanism of this alternative pathway, have been investigated. The Wheland intermediate is deprotonated intramolecularly in a 1,2-shift but also in a longer-range shift, leaving in this case the C-Zn untouched. In the latter case, it is possible to take advantage of this result for further functionalization.
ABSTRACT
The reaction scope of iron- and cobalt-catalyzed cross-coupling reactions in the presence of isoquinoline (quinoline) in the solvent mixture tBuOMe/THF has been further investigated. Various 2-halogenated pyridine, pyrimidine, and triazine derivatives were arylated under these mild conditions in excellent yields. The presence of isoquinoline allows us to perform Fe-catalyzed cross-coupling reactions between 6-chloroquinoline and aryl magnesium reagents. Furthermore, it was found that the use of 10% N,N-dimethylquinoline-8-amine increases the yields of some Co-catalyzed cross-coupling reactions with chloropyridines bearing electron-withdrawing substituents.
ABSTRACT
The zincation of various 1-(trimethylsilyl)-3-aryl-1-propynes with TMPZnCl·LiCl followed by a Pd-catalyzed coupling with aryl halides provides arylated allenes in 52-92% yield. Subsequent metalation with TMPZnCl·LiCl and cross-coupling with a second different aryl halide provides regioselectively tetrasubstituted allenes in 42-70% yield. This sequence can be performed in a one-pot procedure. DFT calculations and NMR studies support the formation of allenylzinc and propargyllithium intermediates starting from 1-(trimethylsilyl)-3-phenyl-1-propyne.
ABSTRACT
Chromium(II) chloride catalyzes the chemoselective cross-coupling reaction of dichloropyridines with a range of functionalized (hetero)aromatic Grignard reagents at room temperature. Functional groups, such as esters and acetals, are well tolerated in this transformation. Previously challenging substrates, quinolines and isoquinolines, participate in the selective Cr-catalyzed cross-coupling in cyclopentyl methyl ether (CPME) as the solvent. The effective purging of Cr salts is demonstrated by using various solid supports.
Subject(s)
Chromium/chemistry , Catalysis , Indicators and Reagents , Molecular StructureABSTRACT
Cyclic TBS-protected iodohydrins (and bromohydrins) undergo a highly diastereoselective cross-coupling with various aryl- and heteroarylmagnesium reagents in the presence of THF-soluble CoCl2·2LiCl and TMEDA as a ligand leading to trans-2-arylcyclohexanol derivatives in good yields and dr up to >99:1. A range of functional groups are tolerated in the Grignard reagent (e.g., COOR, CN, CF3, SF5). The use of heterocyclic iodohydrins leads to trans-3,4-disubstituted pyrrolidines and tetrahydrofurans.
ABSTRACT
Low-toxicity chromium(II) chloride catalyzes at 25 °C within minutes the coupling reactions of various (hetero)arylmagnesium reagents with N-heterocyclic halides, aromatic halogenated ketones or imines, and alkenyl iodides. Remarkably, much lower amounts of homo-coupling side products are obtained compared to related iron, cobalt, or manganese cross-couplings.
Subject(s)
Chlorides/chemistry , Chromium Compounds/chemistry , Catalysis , Molecular Structure , Organometallic Compounds/chemistrySubject(s)
Cobalt/chemistry , Iron/chemistry , Ligands , Catalysis , Cyclization , Isoquinolines/chemistry , Magnesium , Quinolines/chemistry , Transition Elements/chemistryABSTRACT
A simple, practical iron salt catalyzed procedure allows fast cross-couplings of N-heterocyclic chlorides and bromides with various electron-rich and -poor arylmagnesium reagents. A solvent mixture of THF and tBuOMe is found to be essential for achieving high yields mainly by avoiding homocoupling side reactions.
Subject(s)
Boron Compounds/chemistry , Boronic Acids/chemistry , Hydrocarbons, Brominated/chemistry , Hydrocarbons, Chlorinated/chemistry , Iron/chemistry , Magnesium/chemistry , Organometallic Compounds/chemistry , Catalysis , Hydrocarbons, Brominated/chemical synthesis , Hydrocarbons, Chlorinated/chemical synthesis , Indicators and Reagents , Molecular StructureABSTRACT
A new general Pd-catalyzed arylation of various 2-methyl-5-membered heterocycles is reported. This novel method requires Li-, Mg-, or Zn-TMP bases and allows selective metalation of the benzylic position. Subsequent Negishi cross-coupling provides the corresponding arylated heterocycles.
Subject(s)
Heterocyclic Compounds/chemical synthesis , Hydrocarbons, Brominated/chemistry , Palladium/chemistry , Catalysis , Heterocyclic Compounds/chemistry , Molecular StructureABSTRACT
Sulfoxide-alkene hybrids are introduced as a new class of chiral heterodentate ligands for the Hayashi-Miyaura reaction. The synthesis of these ligands was achieved without the use of protecting groups. A chiral resolution was performed via simple column-chromatographic separation of the diastereomeric ligands. Both diastereomers proved to be excellent ligands in Rh-catalyzed 1,4-addition reactions, furnishing chiral products with high enantioselectivities and, remarkably, opposite stereoconfigurations.
