Reaction of difluorocarbene with 2H-azirines: generation and transformations of strained azomethine ylides — aziriniodifluoromethanides

Synthesis and Reactivity of 2-(Carboxymethyl)aziridine Derivatives

“…Besides cycloaddition reactions with 2 H -azirines as 1,3-dipolarophiles, 1,3-dipolar cycloadditions with ylides derived from 3-arylazirines have also been investigated. , Reaction of 2 H -azirines 265 with difluorocarbene involved formation of azirinium difluoromethanides 266 which underwent a 1,3-dipolar cycloaddition with dimethyl acetylenedicarboxylate 55 (Scheme ). The cycloaddition reaction of these strained azomethine ylides 266 furnished the corresponding fluorinated fused aziridinopyrrole derivatives 267 in 27–40% yield. , …”

“…Crystalline azabicyclohexanes 267 could be stored indefinitely at −20 °C, but upon storage at room temperature, a quantitative dehydrofluorination and ring expansion to give pyridines 527 was observed, with release of the aziridine ring strain (Scheme ). , …”

“…All attempts to convert aziridine 528 into dihydropyridine 529 failed. Therefore, it was concluded that aziridine 528 is not a precursor for the six-membered ring compound 529 (Scheme ) . An explanation for the difference in reactivity between the nitrogen nucleophiles was not given.…”

“…However, this reaction showed low regioselectivity and two isomers 530 and 531 were formed, which proved to be unstable. Dehydrofluorination and ring expansion afforded dihydropyridines 532 and 533 , which were hydrolyzed to piperidinones 534 and 535 in the presence of water albeit in low yield (4–8%) (Scheme ) …”

Synthesis of 3-cyano-2-fluoropyridines

“…Electrophilic fluorination has also been employed to prepare 2-fluoropyridines; however, fluorination of pyridine with XeF 2 or XeF 6 has shown to yield a mixture of 2-and 3-fluropyridines and 2,6-difluoropyridine [9]. 5-Aryl-3,4-dimethoxycabonyl-2-fluoropyridines have been prepared by the reaction of difluromethylaziridinium salts with dimethyl acetylenedicarboxylate [12].…”