Piero Tedeschi

Group IVB organometallic derivatives: Synthesis and 13C NMR spectra of new silyl and stannyl isoxazoles

Abstract Several new organomettalic isoxazoles, silylated and stannylated in the heterocyclic ring or in a side chain have been made. Their 13C NMR spectra are consistent with the previous conclusions on the electronic effects of MR3 and CH2MR3 (M = Si, Sn) groups, and indicate the importance of the pπ-dπ and σ-π mechanisms in the various ring positions.

Carbon‐13 NMR studies on azolopyridines 2—The oxazolopyridine systems

The 13C NMR spectra of oxazolopyridine systems are discussed, and a simple method for distinguishing between 2‐methyloxazolo‐ and 3‐methylisoxazolo‐pyridines is suggested, based on the chemical shift of the methyl group. The effect of the 2‐methyloxazole fusion on the pyridine ring is comparable to that of 3‐methylisoxazole, judging by 1J(CH) values determined from line splittings.

Permanganate oxidation of 3-methyl-4-nitro-5-styrilisoxazole: a correction

Abstract In contrast with a previous report, permanganate oxidation of the title compound 3 gives the nitroisoxazolone 8 and not 3-methyl-4- nitroisoxazole-5-carboxylic acid 2 ; a reaction pathway, involving the spirocyclisation of the carboxylate 10 , is suggested.

A New One Step Synthetic Approach to the Isoxazolo[4,5-b]Pyridine System

Abstract A convenient direct entry to the title ring system by condensation-cyclization processes of 3,5-dimethyl-4-nitroisoxazole (1) with the enamines 2 and 8 is reported; some reactions of the resulting N-oxides 5 and 10 are also described.

Side-chain silylation of heterocyclic derivatives. The sythesis of 3-methyl-5-(trimethylsilylmethyl)-1,2,4-oxa-diazole and the atttempted synthesis of 3-methyl-4-nitro-5(trimethylsilymethyl)isoxazole via organolithium reagents

Abstract Silylation of activated heterocyclic systems via treatment with organolithium reagents followed by coupling with Me 3 SiCl, leads to the expected product in the case of 3,5-dimethyl-1,2,4-oxadiazole, whereas for 3,5-dimethyl-4-nitroiso-xazole the predominant reaction is addition of the lithiating agent, to give after work-up 3,5-dimethyl-5-butyl-4-nitro-4,5-isoxazoline.

AROMATIC ISOTHIAZOLOPYRIDINES : NEW DIRECT SYNTHETIC APPROACHES

Abstract Alternative synthetic routes to the title ring systems were examined: the isothiazolopyridines 5a,b and 10 were obtained by single step procedures from pyridine derivatives.

BH3 THF reduction of 3-methylisoxazolo [4,5-c]pyridines

Abstract 3-Methylisoxazolo[4,5-c]pyridine 1 on reduction with BH3:THF gave, via the isolable complex 4 , the tetrahydroisoxazolopyridine 5 . The presence of two chlorine atoms at the 4 and 6 positions directed borane attact to the isoxazole ring, yielding the aminoethylpyridine 8 . Both types of reduction were obtained with 6-chloroisoxazolo[4,5-c]pyridine 7 .

A new spiro annellation reaction in the isoxazole series: applications and limits. Part 2. Reactivity of ethyl 4-nitro-3-phenylisoxazole-5-carboxylate with nitrogen binucleophiles

Treatment of the title compound (5) with benzamidine and 1,3-diphenylguanidine afforded in good yields the spiro nitronate (6) and a mixture of the regioisomeric salts (12) and (13), respectively; these products were easily converted into the corresponding nitro derivatives (7), (14), and (15), respectively, with hydrochloric acid. The same nitro ester (5) reacted smoothly with o-phenylenediamine and NaH to give, after acidification, the heterospiran (16). Some limits of this spiro annellation process are emphasized. The structures of the new compounds have been established on the basis of spectral data.

Thermal behaviour of 3-phenyl-1,2,4-oxadiazol-5-ylhydrazines

Depending on the substitution on the hydrazine moiety, thermolysis of 3-phenyl-1,2,4-oxadiazol-5-ylhydrazines (1)–(5) gives variable amounts of 1-amino-Δ2-1,2,4-triazolin-5-ones (13) or (17), Δ2- or Δ3-1,2,4-triazolin-5-ones (12), (18), or (19), and the s-triazine (20). A possible mechanism accounting for the products and the effects is discussed. A diradical intermediate and a hydrogen transfer from the reaction medium are suggested on the basis of the effect of benzoyl peroxide on the reaction and on the behaviour of the hydrazines (1)–(4) towards catalytic hydrogenation.

Thermally induced isomerisation of isoxazol-5-ylhydrazines

The thermal isomerisation of isoxazol-5-ylhydrazines (I) led to 1-aminopyrazolin-5-ones (II), 4-aminopyrazolin-5-ones (III), and 1,2,4-triazin-6-ones (IV), in ratios depending on the nature of the substituents and the solvents used. A reaction mechanism involving a bicyclic intermediate, is suggested on the basis of the behaviour of isoxazolyl hydrazines methylated on the hydrazine moiety towards heating. Heating the methylated isoxazolyl-hydrazines (IXg and h) afforded the corresponding azirinecarbohydrazides (XII).