Synthesis of Pyrazolo[1,5-a]quinoxalines

4‐Isoxazolines: Scaffolds for Organic Synthesis

“…Scheme 2. 1,3-Dipolar cycloadditions between nitrones and the electron-deficient allenes 12 take place regioselectively to give the 5-methylene-isoxazolidines 13, which can be converted into the corresponding 4-isoxazolines 14 upon treatment with base or through thermolysis, by 1,3-hydrogen shifts (Scheme 3). [11][12][13][14][15] Scheme 3.…”

Synthesis, reactivity, and electronic structure of multifarious, five-membered heteroaryl and heteroaroyl azides

“…(see Scheme 32, path I, Het = 2-thienyl, 3-thienyl, and 2-benzo [b]thienyl) These acyl azides are converted in fairly good yields (52,70, and 79%, respectively) into the appropriate isocyanates when heated in a sealed tube at 90°C for 1 h (Scheme 32, path I). On the other hand, in refluxing CCl 4 with excess TMSA, the same reaction preferentially yields the 1,4-disubstituted heteroaryl(trimethylsilyl)tetrazol-5-ones A; through regioselective azido 1,3-DC addition of the 1,3-dipolar azido group of the TMSA to the N-C bond of the former heteroaryl isocyanates.…”

“…70 To our knowledge, no report has described the intermolecular 1,3-DCs of the azido component of azido(heteroaryl)methanones with dipolarophiles as a possible route to acyl triazoles. Related examples would be the known 1,3-DCs involving arenesulphonyl azide and ethyl azidoformate with strained dipolarophiles.…”

Synthesis of isomeric 2,3,5‐trisubstituted perhydropyrrolo[3,4‐d]‐isoxazole‐4,6‐diones via 1,3‐dipolar cycloaddition reactions

“…The nitrone‐olefin 1,3‐dipolar cycloaddition reaction is interesting, as it can create as many as three new contiguous stereogenic centers in a single step [7, 8]. Both inter and intramolecular nitrone–alkene cycloaddition reactions have received attention because they are useful methods for the formation of heterocycles of biological interest [9–12].…”