Necdet Coşkun

Regio and diastereoselective addition of imidazoline 3-oxides to aryl isocyanates

Δ3-Imidazoline 3-oxides 1 underwent regio and diastereoselective cycloaddition with aryl isocyanates 2 to give 5,6,7,7a-tetrahydroimidazo[1,5-b][1.2.4]oxadiazol-2(1H)-ones 3 in excellent yields. Thermally and chemically induced retro cycloaddition of compounds 3 was demonstrated.

Synthesis of di- and cis-triaryl-3a,4,5,6-tetrahydroimidazo[1,5-b]isoxazoles and their ring-opening reactions

Abstract The Δ3-imidazoline 3-oxides 1 undergo diastereoselective cycloaddition with dimethyl acetylenedicarboxylate 2 to give 3a,4,5,6-tetrahydroimidazo[1,5-b]isoxazoles 3. Thermally and base induced ring-opening reactions of compounds 3 were demonstrated. cis-6-Phenyl substituted adducts 3d,e undergo ring opening with secondary but not with tertiary amines. The same adducts undergo regio- and diastereoselective Michael addition with sodium methoxide to give 2-methoxy-3a,5,6-triphenyl-hexahydro-imidazo[1,5-b]isoxazole-2,3-dicarboxylic acid dimethyl esters 6.

The first examples of di- and cis triaryl-3a,4,5,6-tetrahydroimidazo[1,5-b]isoxazoles and their ring-opening reactions

Abstract The Δ 3 -imidazoline 3-oxides 1 undergo diastereoselective cycloaddition with dimethyl acetylenedicarboxylate 2 to give 3a,4,5,6-tetrahydroimidazo[1,5- b ]isoxazoles 3 . Thermal and base induced ring-opening reactions of compounds 3 were demonstrated.

The first regio- and diastereoselective synthesis of homochiral perhydroimidazoisoxazoles via the 1,3-dipolar cycloaddition of imidazoline 3-oxides with (1S)-(−)-β-pinene

Abstract The 1,3-dipolar cycloaddition of imidazoline 3-oxides 1 with (1 S )-(−)-β-pinene proceeds regio- and diastereoselectively to give homochiral perhydroimidazoisoxazole derivatives 3 in high yields in the cases of imidazoline 3-oxides 1a – e but in low yields in the reactions of 1f – g . The preferred attack of (1 S )-(−)-β-pinene to the cyclic nitrone was shown to be anti–endo. The reaction of racemic nitrones (±)- 1f – g with the homochiral β-pinene gave the adduct from the ( S )-nitrone and the corresponding imidazole. The adducts 3 undergo retro-1,3-dipolar cycloaddition when heated in the condensed phase or in diphenyl ether to give the corresponding imidazole and β-pinene.

New Methods for the Synthesis of Imidazoline-N-Oxides

Abstract Δ3-lmidazoline-3-oxides were prepared by the reaction of corresponding aromatic Schiff bases with syn-2-bromoacetophenone oxime. 5,6-Dihydro-4H-1,2,5-oxadiazines were isolated as byproduct in some instances.

Direct conversion of aldehydes into nitriles via O-phenylcarbamoylated aldoximes

Abstract O-Arylcarbamoylated hydroxylamine tosylate reacts with aldehydes at room temperature to give the corresponding O-carbamoylated oximes. The reaction of carbamoylated hydroxylamine with aromatic aldehydes in THF or in toluene at reflux affords the corresponding nitriles and anilinium tosylate in high yield. Attempts to cyclize compounds 2 in the presence of AcCl lead again to the formation of nitriles.

Synthesis and Ring Opening Reactions of Tetrahydroimidazo[1,5- b ][1,2,4]oxadiazol-2(1 H )-thiones

1,3-Dipolar cycloaddition of imidazoline 3-oxides 1 with methylisothiocyanate proceeds regio- and diastereoselectively to give tetrahydroimidazo[1,5- b ][1,2,4]oxadiazol-2(1 H )-thiones 3 in high yields. The cis configuration of the adducts were proved by our double cis elimination test as well as by NOESY experiments. The imidazooxadiazol-2-thiones 3a-e were treated with concentrated HCl in ethanol at 50°;C to give the corresponding 4 H -[1,2,4]oxadiazole-5-thione only in the cases where the substituent at C-6 is an aryl.

Mild and Efficient Method for the Synthesis of Nitriles

Abstract The treatment of aldoximes with a mixture of DMAD and triethylamine serve as an efficient and mild method for the synthesis of aromatic and α,β‐unsaturated nitriles in high yields at room temperature.

Synthesis of 4‐Oxo‐3a,4,5,6‐tetrahydroimidazo[1,5‐b]isoxazole‐3‐carboxylic Acid Esters

Abstract 3‐Imidazoline 3‐oxides react regioselectively with 3‐phenylpropanoic acid alkyl esters to give the corresponding 2‐phenyl‐3a,4,5,6‐tetrahydroimidazo[1,5‐b]isoxazole‐3‐carboxylic acid alkyl esters. This adducts convert to imidazole and the corresponding alkyl 3‐oxo‐3‐phenylpropanoic acid esters when treated with alkoxides or heated under vacuum. Attempts to oxidise the carbon–carbon double bond using KMnO4–FeSO4 led to the formation of heretofore unknown 4‐oxo‐3a,4,5,6‐tetrahydroimidazo[1,5‐b]isoxazoles.

One-pot synthesis and hydroxylaminolysis of asymmetrical acyclic nitrones

Abstract Aromatic aldehydes 1 were reductively aminated to the corresponding secondary amines 2 using NaBH4 in methanol in good yields. Amines 2 were oxidized with H2O2‐WO4 2− regioselectively to nitrones 3, the structures of which were easily determined by reacting them with hydroxylamine hydrochloride as well as by spectral means. The products of hydroxylaminolysis in ether proved to be the corresponding benzaldehyde oximes 4 and benzyl or methyl hydroxylamine hydrochlorides 5.