Difluoro -2//-azirine

Ethane 2-Atnino-1,1-difluoro-1-phenyl- ElOb, 288F. (Azirine - 2-N ll, -1.I-F,)... 

Propane 2-Amino-l,l-difluoro-l-phenyl- ElOa. 288f. (Azirine ->... 

Propanoate Methyl 2-Amino-3.3-difluoro-3-phenyl- ElOb, 288f. (Azirine -< 2-NH2 — 3,3-F, ... 

The 5,7-diaryl-2-fluoro-4/7-l,3-diazepines have been synthesized from 3-aryl-substituted 277-azirines and difluoro-carbene (Scheme 13). The reaction involves isomerization of azirinium ylide into a 2-aza-l,3-diene, which undergoes [4+2] cycloaddition with the starting azirine, followed by ring expansion and dehydrofluorination <2006TL639>. 

Fluorinations of other functionalities containing C = N bonds, such as 2//-azirines and imines, are included in this section. Certain 2Ff-azirines and imines yield a-fluoro ketones. With other 2Ff-azirines, /i,/(-difluoro amines are the main reaction products. In a strict sense, these reactions cannot be considered as examples of substitution of nitrogen-containing functional groups no substitution takes place when /S. -difluoro amines are the reaction products. However, these methods have been included. 

The reaction of 2//-azirines (e.g.. 1) with hydrogen fluoride in pyridine [pyridinium poly(hy-drogen fluoride). Olah s reagent] gives /f,/f-difluoro amines (e.g., 7) or a-fluoro ketones (e.g., 5) (Table 10). In some cases, pyrazines (e.g.. 9) are the main reaction products (Table IQj 31-35 2//-Azirines arc more reactive than aziridines towards pyridinium poly(hydrogcn... 

In the mechanism proposed to explain the formation of /l,y difluoro amines and a-fluoro ketones, two main, competing pathways are possible, after protonation of the 2//-azirine 1. One pathway leads to the / ,/ -difluoro amine 7 via the intermediates 2 and 6. A second possibility, via 2, 3 and 4, gives the observed a-fluoro ketone 5. Pyrazines are formed by the intermoleciilar reaction of the intermediates corresponding to 3, lo give diprotonated intermediates, e.g. 8. 

Difluoro Amines and a-Fluoro Ketones by the Reaction of 2//-Azirines with Pyridinium Poly(hydrogen fluoride) General Procedure ... 

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