Synthesis of Rings with One Nitrogen Atom

Aziridine 12 was obtained as a by-product in the reaction of imine 13 and CF2 derived from perfluoropropylene oxide to give 14 (79IZV1826). It is unclear whether the reaction mechanism includes the addition of. CF2, the most electrophilic dihalogenocarbene, onto the C=N bond of imine 13. 

A ring-contraction reaction is rarely used to produce an aziridine. A Wolff ring contraction of a carbene generated from 6-diazopenicillanate 21 forms the intermediate ketene, which is then trapped by imines to give spiroaziridines 22 (86CC584). 

Intramolecular insertion of carbenes into N —H and C—H bond are most frequently used for generating azetidine derivatives. But while carbene 

N — H insertion generally proceeds unidirectionally, C—H insertion leading to a four-membered ring is not infrequently accompanied by C—H insertion, yielding a five-membered ring, and also by aromatic cycloaddition, ylide formation, etc. Few other carbene reactions are employed in the synthesis of azetidines, and their mechanisms are not always clear. 

Rhodium(II) carboxylate-catalyzed decomposition of diazoacetoace-tamides (versus diazoacetamides) is a more efficient method for generating a jQ-lactam ring by carbenoid C—H insertion. Treatment of ring-substituted A-benzyl-A-ferf-butyl diazoacetamides 25 ( = 0) with Rh2(AcO)4 results in the exclusive production of /Q-lactams 26 (n = 0) in 90-98% yield 

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