Übergänge aus der Benzoxazol‐ in die Benzoxazin‐Reihe und umgekehrt, II¹⁾ Benzoxazol‐2‐carbonsäure‐Derivate aus 2.3‐Dioxo‐1.4‐benzoxazinen

Abstract

2.3-Dioxo-1.4-benzoxazine 1 reagieren mit Thionylchlorid zu den Imidchloriden 2. Daraus erhalt man mit nucleophilen Reaktionspartnern entweder 3-substituierte Benzoxazinone, wie die Thioxo-Derivate 16 sowie die Quartarsalze 14 und 15, oder unter Ringverengung die Ester 3 und Amide 9 der Benzoxazol-2-carbonsaure. Bei der Umsetzung von 2 mit Aminen entstehen haufig das Isomerenpaar 9 und Aminobenzoxazinon 10 nebeneinander. Umgekehrt beobachtet man bei der Reaktion der Ester 3 mit Aminen bisweilen auch eine Ringerweiterung zu 10. Fur Benzoxazol-2-aldoxim 13 wird eine neue Synthese angegeben. Conversions from the Benzoxarole into the Benzoxazine Series and vice versa, I1 1). Benzoxazole-2-carboxylic Acid Derivatives from 2,3-Dioxo-I ,I-benzoxazines2,3-Dioxo-1,4-benzoxazines 1 react with thionyl chloride to form the imide chlorides 2. With nucleophilic reactants one obtains either 3-substituted benzoxazinones such as the thioxo derivatives 16 as well as the quarternary salts 14 and 15; or, with ring contraction, esters 3 and amides 9 of the benzoxazole-2-carboxylic acid. In the case of reaction of 2 with amines, the isomer pair 9 and aminobenzoxazinone 10 are frequently obtained together. Conversely, if the esters 3 are reacted with amines, ring enlargement to 10 is also sometimes observed. A new synthesis is given for benzoxazole-2-aldoxime 13.

Crystal structure of methyl 1,3-benzoxazole-2-carboxylate

“…This compound was first prepared by a multi-step synthesis starting from 2,3-dioxo-1,4-benzoxazine (Dickore ´et al, 1970) and 2-cyanobenzoxazole (Mo ¨ller, 1970), but it can be obtained much more simply from condensation of 2-aminophenol with methyl 2,2,2-trimethoxyacetate (Musser, Hudec et al, 1984;Koshelev et al, 2019). It has been synthesized in high yields by direct carboxylation of benzoxazole using carbon dioxide (CO 2 ) as a naturally abundant and renewable C1 source, with (Zhang et al, 2010;Inomata et al, 2012) or without any metal catalyst (Vechorkin et al, 2010;Fenner & Ackermann, 2016).…”

Notes. Studies on copper(II) complexes of ortho-quinone mono-oximes: reaction of bis(4-chloro-1,2-benzoquinone 2-oximato)copper(II) with dimethyl acetylenedicarboxylate under various experimental conditions

“…Preparation of Starting Materials.-Bis(4-chloro-l ,2-benzoquinone 2-oximato)copper(11), bis(4-chloro-l,2-benzoquinone-2-oximato)(pyridine)copper(ri), and bis(4-chloro-I ,2-benzoquinone 2-oximato)nickel(rr) were prepared as described and dimethyl acetyIenedicarboxylate (1 cm3) in anhydrous methanol (60 cm3) were heated under reflux for about 1 h; the reaction mixture was filtered, treated with activated charcoal, and evaporated under vacuum to give a crude oil, from which pure methyl 5-chloro-1,3-benzoxazole-2-carboxylate was isolated by column chromatography [silica gel, carbon tetrachloride-ethyl acetate (19 : l)] and repeated crystallizations from n-hexane, m.p. 120-121 "C (Found: C, 51.15; H, 2.85; N, 6 (b) In 99.5% methanol the 6-chloro-4-hydroxy-2,3-dimethoxycarbonyl-l,4benzoxazine was formed in about 30 min; the reaction mixture was filtered and evaporated to dryness to give the crude product which was crystallized from ethyl acetate-n-hexane (identity confirmed by analysis, m.p., and i.r. spectroscopy).…”

Reaction of 1-Nitroso-2-naphthols with α-Functionalized Ketones and Related Compounds: The Unexpected Formation of Decarbonylated 2-Substituted Naphtho[1,2-d][1,3]oxazoles

“…However, it seems that scope and limitations of this method have not been explored in depth. Apart from the synthesis of 2-alkylated and 2-arylated derivatives, the preparation of annulated oxazoles carrying a functional group such as a carbonyl, an ester, or a nitrile group at C-2 is also of great interest. , …”