Some new aspects on the chemistry of 1,4‐benzoxazines

Abstract

3‐Methyl (3a) and 3‐t‐butyl‐1,4‐2H‐benzoxazine (3b) were synthesized by cyclization of the appropriate acetamidoketone (Scheme 1). The former is a highly unstable molecule which rapidly converts in an intractable mixture, while the latter slowly undergoes aerial oxidation affording the hemiacetal 4. The 4H‐forms of the same 3‐methyl (6a) and of the parent 1,4‐benzoxazine (9) could be obtained as 4‐acetyl derivatives. This latter, by hydrolysis, gave the cyclic trimer 10.

Heck Reaction as Key Step in the Synthesis of Hydrogenated 2‐benzazepin‐1‐ones

“…Similar cyclization by intramolecular attack of a carboxamide at an aldehyde or ketone has been reported in literature [12,13]. For the synthesis of benzamides 2 two routes were envisaged: According to the first route, the carboxamido group will be introduced starting with (2-halophenyl) propionaldehyde derivatives 3.…”

Phenacyl Bromide: An Organic Intermediate for Synthesis of Five- and Six-Membered Bioactive Heterocycles

“…In addition of above information these compounds also served as precursors for the synthesis of many medicinally important drugs [53]. The skeleton of these type of structures are synthesized by the direct intramolecular reductive cyclization of appropriate nitroketones or by intramolecular annulation of 2-aminophenoxy ketones [54]. Benzoxazines are also prepared by the condensation reaction of 2-aminophenols with substituted phenacyl halides [55].…”

A New Convenient Method for the Synthesis of 2H‐1,4‐Benzoxazine Derivatives from Nitroketones via Intramolecular Reductive Cyclization.

“…2H-1,4-Benzoxazine is a useful prochiral cyclic imine [2][3][4] for the synthesis of chiral cyclic amines, and especially 3-aryl-2H-1,4-benzoxazines are found to have an anti-inflammatory activity [5]. The 2H-1,4-benzoxazines have been classically prepared by base [6] or acid [7] catalyzed intramolecular condensation of 2-aminophenoxyketones or directly by the reaction of 2-aminophenol with phenacyl bromide derivatives under basic condition [8][9][10]. However, the direct synthesis of cyclic imines from the corresponding nitroketones by reductive cyclization would be more attractive.…”