[3+2] Cycloadditions of Metallo Nitrile Ylides and Metallo Nitrile Imines with Metal Carbonyl,Thiocarbonyl, and Isocyanide Complexes: Heterodimetallic Systems with Bridging Heterocycles [1]

The reactions of [Re(CO)₆]⁺, [FeCp(CO)₂CS]⁺ and [FeCp(CNPh)₃]⁺ with the metallo nitrile ylides [M^–{C⁺=N–C^–(H)CO₂Et}(CO)₅]^– (M = Cr, W) and the chromio nitrile imine [Cr^–{C⁺=N–N^–H}(CO)₅]^– (generated by mono‐α‐deprotonation of the parent isocyanide complexes) to give neutral 5‐metallated 1,3‐oxazolin‐ ( 1 ), 1,3‐thiazolin‐ ( 2 ), imidazolin‐ ( 3 , 4 ), 1,3,4‐oxdiazolin‐ ( 5 ), 1,3,4‐thiadiazolin‐ ( 6 ) and 1,3,4‐triazolin‐2‐ylidene ( 8 ) chromium and tungsten complexes represent the first all‐organometallic versions of Huisgen’s 1,3‐dipolar cycloadditions. The formation of 6 and 8 is accompanied by partial decomposition to (OC)₅Cr–C≡N–FeCpL₂ {L = CO ( 7 ), CNPh ( 9 )}. The structures of 4a and 5 have been characterized by X‐ray diffraction.     

A novel one-pot synthesis of hydroximoyl chlorides and 2-isoxazolines using N-tert-butyl-N-chlorocyanamide

Treatment of aldoximes with N-tert-butyl-N-chlorocyanamide gave hydroximoyl chlorides in quantitative yields in less than a minute, which on dehydrohalogenation in the presence of triethylamine gave the corresponding nitrile oxides. The nitrile oxides underwent 1,3-dipolar addition to dipolarophiles and gave 2-isoxazolines in excellent yields under mild conditions.     

Cycloadditions of α-(4-[2.2]paracyclophanyl)-N-methyl nitrone

Cycloadditions of the newly synthesized α-(4-[2.2]paracyclophanyl)-N-methyl nitrone (9) with selected dipolarophiles such as phenyl isocyanate (10), styrene (13), dimethyl acetylenedicarboxylate (15) and methylene sulfene (17) are reported. Two isolated diastereomeric oxadiazolones 11 and 12 are obtained by the reaction of 9 with 10, whereas the reaction of 9 with either 13 and/or 15 gives only one diastereomer isoxazole 14 and/or 16. 4-([2.2]Paracylophanyl)-N-methylamine (20) was obtained by the reaction of 9 with 17. The structure of compounds 9, 11 and 14 are assigned by X-ray structural analysis.     

An intramolecular one-pot synthesis of steroidal triazoles via 1,3-dipolar cycloadditions of in situ generated diazo compounds

A novel synthetic route is reported for the preparation of steroidal triazoles via intramolecular 1,3-dipolar cycloaddition of a steroidal 16,17-seco-17-diazo-16-nitrile system. The structures of the products are established by X-ray and NMR studies. The in vitro antiproliferative activity of the steroidal triazoles against three tumor cell lines was evaluated.     

One-pot synthesis of vinylisoxazolidines from simple hydroxylamines and conjugated carbonyls

Herein is reported the highly chemo- and regioselective synthesis of 3-vinyl-4-formyl and 3-vinyl-5-formylisoxazolidines from enals, hydroxylamines and dipolarophiles under thermal conditions. The reaction works in high yields for a large array of substituted enals and a variety of dipolarophiles. The reaction provides the respective isoxazolidines with high chemoselectivity, stereospecificity and diastereoselectivity without significant purification. The substitution pattern on the dipolarophile directs the regioselectivity of the reaction to provide either 3,4- or 3,5-substituted isoxazolidine isomers. This method provides access to a wide variety of highly substituted, stereochemically dense isoxazolidine scaffolds from the selective reaction of the three proposed components.     

An Alternative Method to Prepare Nitrile Oxides from Primary Nitro Compounds by Using Thionyl Chloride and Triethylamine

The dehydration of PhCH₂NO₂ (1a), PhCOCH₂NO₂ (1b), and MeOOCCH₂NO₂ (1c) with SOCl₂ in the presence of Et₃N gave three corresponding nitrile oxides. Each nitrile oxide was trapped by various dipolarophiles to obtain the cycloadducts of 2-isoxazolines.