Stefania Turchi

Reactions of 4,5-dicyanopyridazine with alkynes and enamines: A new straightforward complementary route to 4-mono- and 4,5-disubstituted phthalonitriles

The preparation of the 1,2-dicyanobenzenes 6a-m in fairly good to excellent yields by one-pot procedures based on [4 + 2] cycloaddition processes of the title compound 1 with acetylenic or enamine dienophiles, is reported; some features of this new synthetic strategy are emphasized.

Hetero Diels-Aler reactions of 4,5-dicyanopyridazine with alkenes

Abstract The behaviour of the title compound 1 with some linear and cyclic olefins has been investigated. Except for the reaction with diphenylcyclopropenone 22, affording 24 and 26 through cyclization processes of the primary Michael adduct 23, a remarkable reactivity as azadiene was observed. The structures of the resulting dicyanocyclohexa-1,3-dienes, aromatic phthalonitriles, and polycyclic bis-adducts were established on the basis of spectral data.

4-Nitroisoxazoles as nitroalkene heterodienes: diastereoselective synthesis of spiro tricyclic nitroso acetals by thermal reactions with ethyl vinyl ether

Abstract A few 4-nitroisoxazoles were found to undergo highly diastereoselective pericyclic homodomino processes with the title enol ether affording 1,6,9-trioxa-5,9a-diazacyclopenta[d]indenes through bicyclic nitronates as key intermediates. Formation of isoxazolo–oxepine systems is also reported together with a domino reaction with the above reagent and methyl acrylate. Two X-ray analyses of compounds 8 and 13 were carried out to firmly establish their stereochemistry.

Phthalonitriles by hetero Diels-Alder reactions of 4,5-dicyanopyridazine with enamines: isolation and characterization of unprecedented intermediates

Abstract The title conversions were shown to involve as key intermediates new dicyanodiene systems, that can be isolated in high yields under mild conditions; their structures, inferred from analytical and spectral data, were confirmed by an X-ray study. Some improvements for the synthetic methodology connected with this finding are discussed.

[4+2]- and [2+4]-cycloaddition processes of 4,5-dicyanopyridazine with 2,3-dimethylbuta-1,3-diene

Abstract The title compounds afforded under relatively mild conditions the polycyclic systems 3a, 4, and 5 through alternative concomitant cycloadditions; the reactivity of the dicyanopyridazine system was critically influenced by the presence of methyl groups at the 3 and 6 positions. The skeleton of 3a and the stereochemistry of 5 were established by X-ray experiments.

[2+4] Cycloaddition reactions of 4-Nitro-3-phenylisoxazole with Carbo- and heterodienes

Abstract The title compound 4 reacted as a dienophile with open-chain and cyclic carbodienes as well as the 1-azadiene 16, to yield different polynuclear isoxazole systems. On the contrary, it gave rise preferentially to a Michael-type reaction with the dimethyluracil derivative 19 affording the cine-substitution product 23, whose structure was determined by an X-ray analysis. Some mechanistic features and synthetic opportunities are emphasized.

4-Nitro-2-phenyloxazole: an electrophilic dienophile for normal Diels–Alder reactions in the oxazole series

The title compound 2, obtained by thermal isomerization of the corresponding nitroisoxazole 1, is found to undergo [2 + 4] cycloaddition processes with 2,3-dimethylbuta-1,3-diene and cyclohexa-1,3-diene, respectively.

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.

Reaction of 1-diethylaminopropyne with difunctionalized 4-nitroisoxazoles: a single step access to the Novel isoxazolo[4,5-c]isoxazole system

The nitroderivatives 1a–c were found to react with the title ynamine 2 under mild conditions to give the corresponding fused isoxazoles 3a–c, as proved by an X-ray diffraction of 3a; a plausible mechanistic pattern for these conversions is presented. Treatment of the nitroderivatives 1a–c with the ynamine 2 afforded the new bicyclic isoxazoles 3a–c as proved by an X-ray analysis of 3a.

Reactions of 3,5-dimethyl-4-nitroisoxazole with cyclic enamines and 1-diethylaminopropyne

3,5-Dimethyl-4-nitroisoxazole (1) was found to undergo tandem condensation-cyclization processes with 4-(1-cylopenten-1-yl)- and 4-(1-cyclohexen-1-yl)morpholine in ethanol solution to give, through the intermediates (4) and (7), the N-oxides (5) and (9) respectively. The reactivity of 1 towards 1-diethylamino-propyne in different solvents was also investigated; the structure of the unexpected acycloxime (13), coming from the above reagents in acetonitrile, was determined by an X-ray analysis. Plausible mechanistic pathways for these new reactions are suggested