Of benzoxazinone acetal

Kluge, M. and Sicker, D. 1996. Double diastereoselective glucosidation of cyclic hemiacetals synthesis of the 1,4-benzoxazinone acetal glucosides GDIBOA and GDIMBOA from Gramineae. Tetrahedron 52, 10389-10398... 

It is the aim of this review to present a detailed overview on natural sources of benzoxazinones and their enzymatic and chemical degradation, on the synthetic access both to aglycones and acetal glucosides, on medical effects and on the molecular allelopathy of these bioactive natural products. 

This new procedure is especially valuable in the synthesis of benzoxazinones bearing one or two methoxy substituents or a 6,7-methylenedioxy unit at the aromatic ring. A drawback of the former methyl acetal cleavage method (Fig. (7), [110]) consisted in an insufficient selectivity of the boron trichloride mediated 2-methoxy group... 

Kluge M, Schneider B, Sicker D (1997) Diastereoselective synthesis of the benzoxazinone acetal ghnxrside ent-GDlMBOA The first enantiomer of a natural acetal ghicoside Carbohydrate Research 298 147 152... 

An attempt to ringclose the free acid 8 to the benzoxazinone 3 with the help of acetic anhydride led to an unexpected result If 8 (or preferable 3) is heated in acetic anhydride the oxadiazolyl benzoxazine 12 is obtained. However, the outcome of this reaction is not surprising since R. Huisgen [68AG359] and others, have shown, that the acylation of tetrazoles give 1,3,4-oxadiazoles via N-acylnitrilimines (such as 11) by 1,5-dipolar electrocyclic ringclosure. 

The discovery of natural benzoxazinones was based on the finding that rye plants showed an increased resistance towards pathogenic fungi. Hence, the first aglucone and the first glucoside were reported from rye in two successive papers [1,2]. Acetal glycosides of the 2-hydroxy-2/f-l,4-... 

Alkyl- and aryl-substituted carboxylic acid derivatives such as ethyl 4-methoxybenzoate, diethyl phthalate,104 aryl- and alkylcarboxylic add halides or anhydrides10,2 5 8 give benzoxazinones (193). When IA was brominated in glacial acetic acid, 193 (R2 = CHBr2) was obtained.259 Anthranilic acid (4) with A-methyl IA (24) leads to 194, which cyclizes in sulfuric acid to the benzoxazinone 195134 (Scheme 33). Reaction of /V-formylanthranilic acid (196) (available from 1A and formic acid) with IA again yields the quina-zolinone 19710 260 (Eq. 19). 

The described method was expanded to provide an easy access to quinoline alkaloid analogues by using one-step reaction between benzoxazinones and ketene silyl-acetals in the presence of titatium tetrachloride. ... 

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