Synthesis of new imidazole 3-Oxides; unexpected deoxygenation of some derivatives in the reaction with 2,2,4,4-Tetramethylcyclobutane-1,3-dithione

Whereas the reaction of a series of 1,4,5-trisubstituted imidazole 3-oxides with 2,2,4,4-tetramethylcyclobutane-1,3-dithione gave the corresponding imidazole-2-thiones by a sulfur-transfer reaction via [2+3] cycloaddition, an unexpected deoxygenation occurred in the case of 4-acetyl- 1-(adamantan-1-yl)- 5-methylimidazole 3-oxide. It was shown that the presence of an electron- withdrawing substituent at C(4) and the bulky 1-adamantyl group at N(1) are necessary to enable this reaction course. A reaction mechanism via a zwitterion, followed by a 1,3-cyclization and elimination of an oxathiirane, is proposed

Formation of phosphonylated thiiranes in the reaction of a diazomethanephosphonate and cycloaliphatic thioketones

The reaction of diethyl diazomethanephosphonate (1) with cycloaliphatic thioketones (6) in THF at room temperature leads to the corresponding thiirane-2-phosphonates (7) in good yield. A reaction mechanism via 1,3-dipolar cycloaddition of the diazo compound with the C=S group to give the 2,5-dihydro-1,3,4-thiadiazole-2-phosphonate as an intermediate, which spontaneously eliminates nitrogen is most likely. The resulting thiocarbonyl ylide undergoes a 1,3-dipolar electrocyclization to yield a thiirane. These products can be desulfurized smoothly by treatment with tris(diethylamino)phosphine to give alpha,beta-unsaturated phosphonates

[2+3]-Cycloadditions of diazoalkanes with imines of hexafluoroacetone and chloral

The reactions of N-arylimines 1 and 2 of hexafluoroacetone and chloral, respectively, with diazoalkanes at –60°C to room temperature led to the corresponding 4,5-dihydro-1H-[1,2,3]triazoles 4 and 5, respectively, in a regioselective [2+3]-cycloaddition. The structure of one example in each case has been established by X-ray crystallography. The thermal decomposition of these adducts yielded the corresponding aziridines, bearing two trifluoromethyl and one trichloromethyl group, respectively, at C(2)

Preparation and Structure of Optically Active Imidazolium Tetrafluoroborates; in Search of New Chiral Liquids

Enantiomerically pure (R)-1-(1-phenylethyl)imidazoles 4a,b can be prepared conveniently from alpha-(hydroxyimino)ketones 1, (R)-1-phenylethylamine and formaldehyde, followed by deoxygenation with Raney-Ni. Similarly, the reaction with (R,R)-trans-cyclohexane-1,2-diamine yields enantiomerically pure (R,R)-trans-1,1'-cyclohexane-1,2-diyl)imidazoles 4c,d. Alkylation of these imidazole derivatives with alkylbromides leads to the corresponding 3-alkylimidazolium bromides 6 and 8, respectively, which on treatment with sodium tetrafluoroborate are transformed into the corresponding tetrafluoroborates 7 and 9. Whereas some of the imidazolium salts 7 show properties of chiral ionic liquids, the bis-imidazolium tetrafluoroborates 9 are high-melting crystalline materials

Phosphonylated thiocarbonyl ylides from the reaction of aromatic thioketones with diethyl diazomethylphosphonates

The reaction of diazomethylphosphonates with aromatic thioketones at 65 °C to room temperature yields 2,5-dihydro-1,3,4-thiadiazole-2-phosphonates, which eliminates N2 to give phosphonylated thiocarbonyl ylides as reactive intermediates. These sulfur-centered 1,3-dipoles undergo typical reactions of thiocarbonyl ylides, i.e., 1,3-dipolar cycloadditions, cyclodimerization, and electrocyclic ring closure, depending on the involved thioketone and, therefore, on the reaction conditions. In the case of the most reactive thiofluorenone, the phsophonylated thiocarbonyl methanide can be intercepted with thiobenzophenone, a phosphonodithioformate, and tetracyanoethylene. In the absence of such reactive dipolarophiles, cyclodimerization occurs to give the corresponding 1,4-dithiane

Chemoselective insertion of dimethoxycarbene into the N-H bond of thiolactams with diverse ring size

Thermal decomposition of 2,5-dihydro-1,3,4-oxadiazole 4 in toluene solution in the presence of thiolactams 7 or corresponding lactams 11 result in the chemoselective formation of the N-(dimethoxy)methyl derivatives 8 and 12, respectively. The products of both types are formed via insertion of dimethoxycarbene 2a into the N−H bonds. A reaction mechanism via the intermediate ion pair 14/15 or a complex of type 13 is postulated to explain the formation of the products

Reaction of 1-azabicyclo[1.1.0]butanes with 2,3-dicyanofumarates; interception of the intermediate zwitterions with methanol

The reaction of 3-phenyl-1-azabicyclo[1.1.0]butane (1c) with 2,3-dicyanofumarates ((E)-5) in dichloromethane at room temperature yields mixtures of cis- and trans-2,3-dicyano-4-phenyl-1-azabicyclo[2.1.1]hexane- 2,3-dicarboxylates (cis,trans-4). The proposed two-step reaction mechanism via a zwitterionic intermediate of type (6) is supported by trapping experiments with methanol: when the reactions of 1-azabicyclo[1.1.0]butanes (1) with dimethyl 2,3-dicyanofumarate ((E)-5a) are carried out in methanol, dimethyl (E)-2-(azetidin-1-yl)-3-cyanobut-2-enedioates (7) are formed as the only products