Highly enantioselective conjugate addition of fluoromalonates to nitroalkenes using bifunctional organocatalysts

The enantioselective conjugate addition of fluoromalonates to aromatic nitroalkenes catalyzed by chiral amine-thiourea bifunctional organocatalysts generated a stereocenter at the carbon bearing the aromatic group and an adjacent prochiral center from the fluoromalonate. Treatment of fluoromalonates with aromatic nitroalkenes under mild reaction conditions afforded the corresponding 2-fluoro-2-(2-nitro-1-arylethyl)malonates with high yields (72-93%) and excellent enantioselectivities (91-98% ee).     

Organocatalyzed stereoselective construction of N-formylpiperidines via a Michael-aza-Henry-hemiaminalization reaction cascade

An efficient asymmetric synthesis of N-formylpiperidines via an organocatalytic Michael-aza-Henry-hemiaminalization reaction cascade of an aldehyde, a nitroalkene, and an N-arylideneformamide is reported. The reaction is triggered by diphenylprolinol trimethylsilyl ether and creates two C-C and one C-N bonds leading to the formation of highly enantio-enriched N-formylpiperidines with five contiguous chiral centers in a one-pot operation.     

Synthesis of 9,9′-biphenanthryl-10,10′-bis(oxazoline)s and their preliminary evaluations in the Friedel-Crafts alkylations of indoles with nitroalkenes

Chiral 9,9′-biphenanthryl-10,10′-bis(oxazoline)s 6a-d were firstly prepared. These new chiral compounds were evaluated as ligands for the Friedel-Crafts alkylations of indoles with nitroalkenes, excellent yields and modest to good enantioselectivities were achieved.     

Improved preparation of alkyl 2-(3-indolyl)-3-nitroalkanoates under fully heterogeneous conditions: stereoselective synthesis of alkyl (E)-2-(3-indolyl)-2-alkenoates

Ethyl 3-nitro-2-alkenoates can be generated starting from nitroalkanes and ethyl 2-oxoacetate under heterogeneous conditions that minimize work-up procedures, avoid any purification step and direct manipulation of the nitroalkene system. Reaction of ethyl 3-nitro-2-alkenoates, formed in situ from their acetoxy precursors, with indoles in the presence of basic alumina affords ethyl 2-(3-indolyl)-3-nitroalkanoates that are central intermediates for the preparation of tryptamines and carboline alkaloids. A base promoted elimination of nitrous acid from these nitroindolyl derivatives readily produces ethyl 2-(3-indolyl)-2-alkenoates with high E stereoselectivity. The latter compounds can be used as Michael acceptors in intra- and intermolecular reactions with nucleophilic reagents.     

Stereoselective intramolecular 1,3-dipolar nitrile oxide cycloaddition reaction of N-formyl-β-nitroamides

The stereoselective intramolecular nitrile oxide cycloaddition (INOC) reaction was achieved from N-formyl-β-nitroamides, which were prepared through the Michael addition of allylic formamides to nitroalkenes, and cis-pyrroroisoxazoles and trans-piperidinoisoxazoles were obtained in a stereoselective manner.     

NCC Pincer Ni (II) Complexes Catalyzed Hydrophosphination of Nitroalkenes with Diphenylphosphine

An efficient NCC pincer Ni (II)-catalyzed hydrophosphination of nitroalkenes with diphenylphosphine has been developed. Under the optimized conditions, both (hetero)aromatic and aliphatic nitroalkenes were well tolerated, irrespective of electronic effect, to provide the corresponding products in up to 99% yield.     

A simple and convenient synthesis of 4-methyl-3-nitro-2-trihalomethyl-2H-chromenes from N-unsubstituted imines of 2-hydroxyacetophenones and trichloro(trifluoro)ethylidene nitromethanes

The reaction of N-unsubstituted imines of 2-hydroxyacetophenones with trichloro(trifluoro)ethylidene nitromethanes in the presence of DABCO proceeds via tandem oxa-Michael/aza-Henry additions (in dichloromethane) or aza-Michael addition (in benzene) to give 4-methyl-3-nitro-2-trichloro(trifluoro)methyl-2H-chromenes or 1,1,1-trichloro(trifluoro)-3-nitro-N-[1-(2-hydroxyaryl)ethylidene]propan-2-amines, respectively.     

Organocatalytic synthesis of quaternary stereocenter bearing a fluorine atom: enantioselective conjugate addition of α-fluoro-β-ketoesters to nitroalkenes

The catalytic enantioselective conjugate addition reaction of α-fluoro-β-ketoesters to nitroalkenes promoted by chiral bifunctional organocatalysts is described. The treatment of α-fluoro-β-ketoesters with nitroalkenes under mild reaction conditions afforded the corresponding Michael adducts containing a fluorinated quaternary stereogenic center with excellent enantioselectivity (up to >99% ee).