Search

Low-valent titanium-mediated cyclization of bis-unsaturated compounds with a conjugated ester moiety is a versatile method for producing mono- and bicyclic compounds. Diastereoselective reaction of carbonyl compounds allows extending side chains from the cyclization product, stereoselective cyclization allows constructing the ring structure of the defined stereochemistry and these transformations enable regioselective aldol formation from a symmetrical ketone. These advantages make this method very viable for preparing stereogenic centers with a cyclic structure.

LiCl acts as a highly effective catalyst for cyanosilylation of various aldehydes and ketones to the corresponding silylated cyanohydrins. The reaction proceeds smoothly with a substrate/catalyst under ratio of 100-100000 at 20-25 degree Celsius under solvent-free conditions.

A novel type of cyclizations of acyclic precursors for the preparation of bicyclic systems, consisting of two different kinds of cyclizations in tandem, starting from the title unsaturated compounds, is presented. The initial step is based on the titanium-mediated cyclization of dienes and enynes, followed by the second ring closure through the addition of the resulting carbon-titanium bond to an electron-deficient moiety in the same molecule with accompanying incorporation of an electrophile. Substrates determine the patterns of reactions, with type I occurring with alpha,beta-olefinic esters and type II involving the reactions of alpha,beta-acetylenic esters.

The enhanced reactivity of alpha,beta-unsaturated ester and amide towards radical addition comes because of the presence of Lewis acid. The effect of LA (Lewis acid) was experimented in butyl radical addition to alpha,beta-unsaturated ester and amide. The chemoselectivity of the substrate changed due to the complexation of LA to the substrate. The alpha, beta-unsaturated ester is a more reactive accepter than the corresponding amide, because the former has more electron deficient enone moiety.

The oxidative transformation of primary amines to their corresponding oximes proceeds with high efficiency under molecular oxygen diluted with molecular nitrogen (O2/N2 = 7/93 v/v, 5 MPa) in the presence of the catalysts 1,1-diphenyl-2-picrylhydrazyl (DPPH) and tungusten oxide/alumina (WO3/Al2O3). The method is environmentally benign, because the reaction requires only molecular oxygen as the terminal oxidant and gives water as a side product. Various alicyclic amines and aliphatic amines can be converted to their corresponding oximes in excellent yields. It is noteworthy that the oxidative transformation of primary amines proceeds chemoselectively in the presence of other functional groups. The key step of the present oxidation is a fast electron transfer from the primary amine to DPPH followed by proton transfer to give the α-aminoalkyl radical intermediate, which undergoes reaction with molecular oxygen and hydrogen abstraction to give α-aminoalkyl hydroperoxide. Subsequent reaction of the peroxide with WO3/Al2O3 gives oximes. The aerobic oxidation of secondary amines gives the corresponding nitrones. Aerobic oxidative transformation of cyclohexylamines to cyclohexanone oximes is important as a method for industrial production of ε-caprolactam, a raw material for Nylon 6. [ABSTRACT FROM AUTHOR]

Ring-opening polymerizations of THF using V(NR)(CH2SiMe3)(OAr)2[R = 2,6-Me2C6H3, 1-adamantyl (Ad), Ph; Ar = 2,6-Me2C6H3, C6F5] proceededin a livingmanner in the presence of [Ph3C][B(C6F5)4], affording high molecular weight polymers with lowPDI (Mw/Mn) values: the observed activity (initiation efficiency) was affectedby the arylimido and aryloxo ligands employed. A new vanadium(V)-alkylidene,V(CHSiMe3)(NAd)(OC6F5)(PMe3)2, prepared from V(NAd)(CH2SiMe3)2(OC6F5) by α-hydrogen eliminationin n-hexane in the presence of PMe3at25 °C, exhibited remarkable catalytic activity for ring-openingmetathesis polymerization of norbornene: the activity at 25 °Cwas higher than those by the reported vanadium(V)-alkylidenes andordinary Mo(CHCMe2Ph)(N-2,6-iPr2-C6H3)(OtBu)2. [ABSTRACT FROM AUTHOR]

The oxidative transformation of primary amines to their corresponding oximes proceeds with high efficiency under molecular oxygen diluted with molecular nitrogen (O2/N2 = 7/93 v/v, 5 MPa) in the presence of the catalysts 1,1-diphenyl-2-picrylhydrazyl (DPPH) and tungusten oxide/alumina (WO3/Al2O3). The method is environmentally benign, because the reaction requires only molecular oxygen as the terminal oxidant and gives water as a side product. Various alicyclic amines and aliphatic amines can be converted to their corresponding oximes in excellent yields. It is noteworthy that the oxidative transformation of primary amines proceeds chemoselectively in the presence of other functional groups. The key step of the present oxidation is a fast electron transfer from the primary amine to DPPH followed by proton transfer to give the α-aminoalkyl radical intermediate, which undergoes reaction with molecular oxygen and hydrogen abstraction to give α-aminoalkyl hydroperoxide. Subsequent reaction of the peroxide with WO3/Al2O3 gives oximes. The aerobic oxidation of secondary amines gives the corresponding nitrones. Aerobic oxidative transformation of cyclohexylamines to cyclohexanone oximes is important as a method for industrial production of ε-caprolactam, a raw material for Nylon 6.