Heterocycles from ketenimines. IV. 3‐iminosubstituted‐1,2‐oxazetidines

Copper‐Catalyzed Enantioselective [2+2] Cycloadditions of 2‐Nitrosopyridine with Ketenes

“…[3] Whereas compounds of type 1 can be isolated, regioisomers 2 further react by CO 2 elimination to give the corresponding imines. Ketenimines [4] and electron-rich olefins [5] also undergo [2 + 2] cycloadditions with nitroso derivatives. To the best of our knowledge, only a single report on stereoselective cycloadditions of ketenes with aryl nitroso derivatives has been published to date: [6] Fu reported very recently that chiral Lewis bases are able to catalyze the stereoselective formation of 1,2-oxazetidine-3-ones 1.…”

“…This was documented by the transformation of a 1,2-oxazetidine-3-one to the corresponding 1,2-diol. Many other interesting reactions with these 4 ] PF 6 (10 mol%) were added to a flame dried Schlenk tube under an argon atmosphere. The catalyst was dried at room temperature for 10 min under vacuum.…”

“…Reactions were conducted in CH 2 Cl 2 by using 10 mol% of [CuA C H T U N G T R E N N U N G (MeCN) 4 ] PF 6 in the presence of vari-ous phosphines (10 mol%) with 2-nitrosopyridine to give 1a. The ketene was added by a syringe pump at À70 8C for 3.5 h and the reaction mixture was then allowed to warm to À50 8C and stirring was continued for 12 h at À50 8C.…”

Merging strain-release and copper catalysis: the selective ring-opening cross-coupling of 1,2-oxazetidines with boronic acids

“…10 Despite their high ring strain, 1,2-oxazetidines are sufficiently stable and can be easily obtained, which opens an avenue to ring-opening transformations. Although the synthesis of N -alkyl substituted 1,2-oxazetidines was firstly reported in 1970, 11 the investigation of their chemical reactivities is a recent achievement and only five examples have been reported to date. In 2015, Orentas et al firstly applied 1,2-oxazetidines as a source of electrophilic oxygen to couple with organometallic (Li or Mg) reagents (Scheme 1b, left).…”