Chemistry of Four-Membered Cyclic Nitrones. 3. Reaction with Nucleophilic Reagents and Stereospecific Conversion into 1-Hydroxyazetidines

Article abstract of DOI:10.1021/jo00144a006

Four-membered cyclic nitrones (¹) react with a variety of nucleophiles (MeMgI, CN^-, OH^-, MeO^-, and H^-) by stereospecific addition to the C=N bond.Reaction of 1a with potassium cyanide and with methylmagnesium iodide yields the 1-hydroxyazetidines 2a and 2b, respectively.Reduction of 1b with lithium aluminum hydride and with sodium borohydride affords the 1-hydroxyazetidine derivatives 3 and 4, respectively.Sodium hydroxide in methanol-water reacts with 1a to give a mixture of two isomeric 5-hydroxyisoxazolidines 5a and 5b, but under similar reaction conditions 1b and 1c rearrange to the oximes 6 and 7.In acetic acid at room temperature 6a cyclizes to the 6H-1,2-oxazin-6-one derivative 8, whereas 6b yields 5-methyl-3,4-diphenylisoxazole (9) after being refluxed in acetic acid, probably by carbon monoxide elimination from the intermediate oxazin-6-one derivative.Reaction of 1a with sodium hydroxide for 2 min gives exclusively the 1-hydroxy-4-methoxyazetidine 13a, whereas prolonged reaction gives the isomeric azetidine 13b together with 5 (mixture of 5a and 5b in a ratio 4:1).Single-crystal X-ray analysis of 13b reveals that all three relatively bulky substituents at C-2, C-3, and C-4 are on the same face of the azetidine ring.Treatment of 13b with acetic acid at room temperature gives the 5-methoxyisoxazolidine 15.The 1-hydroxyazetidines 2-4 are oxidized with yellow mercury(II) oxide to the corresponding four-membered cyclic nitrones 1b, 16 and 17.