Isoxazole-azirine isomerization as a reactivity switch in the synthesis of heterocycles

Thermal Kinetic Performance and Thermal Safety of 3,3’‐Bis‐Oxadiazole‐5,5’‐Bis‐Methylene Dinitrate

“…In recent years, focus has shift to the compounds of isoxazoles and oxadiazoles which have practical uses in many civilian and military applications [22][23][24][25][26][27][28][29]. Various bis-isoxazoles and bis-oxazoles have been synthesized which show potential for melt-castable applications, including the compound of 3,3'-bis-oxadiazole-5,5'-bis-methylene dinitrate (BODN, Figure 1) [30].…”

Isomerization of 5-(2H-Azirin-2-yl)oxazoles: An Atom-Economic Approach to 4H-Pyrrolo[2,3-d]oxazoles

“…Intramolecular ring-to-ring isomerization of azirines with the formation of five-membered nitrogen heterocyles most often occurs under conditions of metal catalysis or thermolysis at high temperatures [ 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 ]. Using azirine 2a as a test compound, various isomerization conditions (catalysts, solvents, temperatures) were tested to achieve maximum yield of 4 H -pyrrolo[2,3- d ]oxazole 3a .…”

“…Synthesis of 5,5-heterobicyclic systems via isomerization of 2H-azirines. 5,5-Heterobicyclic systems with three and more heteroatoms in the bicyclic framework, as far as we know, have not been prepared by using the azirine methodology. This is not least due to the difficulties in the synthesis of polyheteroatomic azoles bearing an azirin-2-yl substituent.…”

“…Such isomerization of substituted azirines, which occurs easily due to the high strain of the three-membered ring under thermolysis, photolysis or catalysis, is widely used for the synthesis of various heterocycles [ 2 , 3 , 4 ]. 2-Carbonyl-substituted 2 H -azirines can be isomerized to isoxazoles [ 2 , 3 , 4 , 5 , 6 , 7 , 8 ] or oxazoles [ 2 , 3 , 4 , 5 , 8 ], 2-vinyl-2 H -azirines to pyrroles [ 9 , 10 , 11 , 12 ], and 2-(hydrazonomethyl) and 2-(iminomethyl)-2 H -azirines to pyrazoles [ 13 , 14 ]. The isomerization can lead also to six-membered rings, thus, variously substituted pyridines were prepared from 2-propargyl [ 15 , 16 , 17 , 18 ], 2-allyl [ 19 ] or 2-vinyl-substituted 2 H -azirines [ 10 ].…”

Diazocarbonyl and Related Compounds in the Synthesis of Azoles

“…This heterocycle serves as a masked equivalent of a 1,3-dicarbonyl compound, which can be useful in total synthesis of natural compounds [ 44 ]. Moreover, other heterocycles are available from isoxazoles, such as 1,3-oxazoles, azirines [ 45 ], pyridines, and pyrroles [ 46 ]. Biological profile of isoxazoles is somewhat similar to 1,3-oxazoles [ 47 ].…”