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Benzoxazinoids (BXs), alkaloids frequently found in Gramineae species, are natural defensives that can potentially be exploited to the development of novel antimicrobial agents. Here, BXs analogs were synthesized from 2-nitrophenol (benzoxazinone series)

An unprecedented aryne 1,2,3-trifunctionalization protocol from 2,6-bis(silyl)aryl triflates was developed under transition-metal-free conditions. The reaction of generated 3-silylaryne with both pyridine N-oxide and N-hydroxylamide afforded o-silyl triflate/tosylate in a one-pot transformation, allowing the formation of 2,3-aryne precursors with various vicinal pyridinyl/amido substituents. These pyridinyl-substituted 2,3-aryne intermediates exhibit a broad scope of reactivity with diverse arynophiles in good yields and high selectivity.

The utility of benzoxazinones and some of their synthetic derivatives in the search for new leads for herbicide model development has been widely discussed. As the benzoxazinone skeleton contains three different potential areas for functionalization (C-2,

Compounds with a (2H)-1,4-benzoxazin-3(4H)-one skeleton have attracted the attention of phytochemistry researchers since 2,4-dihydroxy-(2H)-1,4-benzoxazin- 3(4H)-one (DIBOA) and 2,4-dihydroxy-7-methoxy-(2H)-1,4-benzoxazin-3(4H)-one (DIMBOA) were isolated from plants belonging to the Poaceae family. These compounds exhibit interesting biological properties, such as phytotoxic, antimicrobial, antifeedant, antifungal, and insecticidal properties. These chemicals, in addition to a wide variety of related compounds involved in their metabolism, detoxification mechanisms, and degradation on crop soils and other systems, have high interest and in some cases potential agronomic utility. This paper presents a complete review of the methods employed for their synthetic obtention in addition to some of the authors' own contributions to their chemistry. The degradation and phytotoxicity experiments carried out in ongoing research into the potential agronomic utility of these compounds required large amounts of them, which were obtained from natural sources. This paper presents a modified methodology to access DIMBOA from Zea mays cv. Apache and to obtain 2-O-β-D-glucopyranosyl-2,4-dihydroxy-(2H)-1,4-benzoxazin-3(4H)-one (DIBOA-Glc) and DIBOA from Secale cereale L. New synthetic methodologies were employed for the obtention of the lactams 2-hydroxy-(2H)-1,4-benzoxazin-3(4H)- one and 2-hydroxy-7-methoxy-(2H)-1,4-benzoxazin-3(4H)-one and the malonamic acids N-(2-hydroxyphenyl)malonamic acid and N-(2-hydroxy-7-methoxyphenyl)- malonamic acid. The aminophenoxazines 2-amino-7-methoxyphenoxazin-3-one and 2-acetamido-7-methoxyphenoxazin-3-one have been synthesized in the authors' laboratory by novel procedures. All of the methodologies employed allowed the desired compounds to be obtained in high yield and in an easy-to-scale manner.

Benzoxazinones 2,4-dihydroxy-7-methoxy-(2H)-1,4-benzoxazin-3(4H)-one (DIMBOA) and 2,4-dihydroxy-(2H)-1,4-benzoxazin-3(4H)-one (DIBOA) have been considered key compounds for understanding allelopathic phenomena in Gramineae crop plants such as corn (Zea mays L.), wheat (Triticum aestivum L.), and rye (Secale cereale L.). The degradation processes in the environment observed for these compounds, in which soil microbes are directly involved, could affect potential allelopathic activity of these plants. We present in this work a complete structure-activity relationships study based on the phytotoxic effects observed for DIMBOA, DIBOA, and their main degradation products, in addition to several synthetic analogues of them. Their effects were evaluated on standard target species (STS), which include Triticum aestivum L. (wheat) and Allium cepa L. (onion) as monocots and Lepidium sativum L. (cress), Lactuca sativa L. (lettuce), and Lycopersicon esculentum Will, (tomato) as dicots. This permitted us to elucidate their ecological role and to propose new herbicide models based on their structures. The best phytotoxicity results were shown by the degradation chemical 2-aminophenoxazin-3-one (APO) and several 2-deoxy derivatives of natural benzoxazinones, including 4-acetoxy-(2H)-1,4-benzoxazin- 3(4H)-one (ABOA), 4-hydroxy-(2H)-1,4-benzoxazin-3(4H)-one (D-DIBOA), and 4-hydroxy-7-methoxy-(2H)-1,4-benzoxazin-3(4H)-one (D-DIMBOA). They showed high inhibitory activity over almost all species growth. The fact that APO is a degradation product from DIBOA with high phytotoxicity and stability makes it possible to assign an important ecological role regarding plant defense mechanisms. 2-Deoxy derivatives of natural benzoxazinones display a wide range of activities that allow proposing them as new leads for natural herbicide models with a 1,4-benzoxazine skeleton.

Some 4-hydroxy-2H-1,4-benzoxazin-3(4H)-ones were synthesized and evaluated for their antimicrobial activities against Staphylococcus aureus, Escherichia coli and Candida albicans. Compounds 9, and 10 exhibited the best activity against Candida albicans. C

Electrophilic intramolecular aromatic substitution with an N-methoxy- or an N-allyloxyacylnitrenium ion, generated by treatment of an N-methoxy- or an N-allyloxy-N-chloroamide with anhydrous zinc acetate in nitromethane, leads to formation of a nitrogen h

Naturally occurring hemiacetals DIBOA and DIMBOA were synthesized by the first α-hydroxylation of N-hydroxylactams via m-chloroperbenzoic acid oxidation of corresponding cyclosilyl enol ethers.

Analogues of the aglucones of naturally occurring cyclic hydroxamic acids (2,4-dihydroxy-1,4-benzoxazin-3-ones) from Gramineae (Poaceae) have been synthesized by the reductive cyclization of the ring-substituted methyl α-(o-nitrophenoxy)-α-methoxyacetates, followed by demethylation of the C-2 methoxy group with BBr3 or BCl3 to reveal the 2-hydroxy group.A structure-activity series was produced by varying the substituent at C-7 on the aromatic ring .The pKa values for the hydroxamic acid and the phenol moieties were determined for each member of the C-7 series.They correlated well with ? in a linear free energy relationship (LFER) yielding values of ρ = 0.71 (with ?p) for pKa1 (the hydroxamic acid) and ρ = 1.6 (with ρm) for pKa2 (the phenol).A LFER also existed between the rate constants for the unimolecular decomposition of these hydroxamic acids to benzoxazolinones and ?+ (ρ = -1.1).The rates of hydroxamic acid reduction to lactams by β-mercaptoethanol were also investigated.It was found that only compounds with electron-rich aromatic rings and specifically an oxa functionality para to the hydroxamic acid nitrogen atom (compounds 1 and 3 - 5) had measurable rates of reduction. 1H NMR spectra recorded during this reaction in D2O buffers (pD 9), however, showed that compounds 1, 2, 6 - 9 (the only ones investigated) formed a hemithioacetal at C-2 even though only 1 has a measurable rate of reduction by the same thiol.The remarkable rate enhancement provided by an oxa functionality suggests that reduction occurs by direct attack of thiolate on the hydroxamic nitrogen of a resonance-stabilized ion pair.

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