Franco Serra-Zanetti

Effect of metal ions in organic synthesis : Part XXXIII. 2-hydroxy-4-pyrrolines as stable intermediates in the synthesis of 1-aminopyrrole derivatives

Abstract The reactions of conjugated aroylazoalkenes with β-diketones and β-ketoesters in the presence and in the absence of copper(II) chloride as catalyst have been studied. In the first case, 1-aminopyrrole derivatives have been obtained, while in the second case the formation of 2-hydroxy-4-pyrrolines as stable intermediates has been frequently detected. The observations on the conditions of the formation of either or both products, as well as the proof of the easy conversion of 2-hydroxy-4-pyrrolines into pyrrole derivatives elucidate the much debated behaviour of these reactions.

Synthesis and transition metal catalysed reactions of 1-Ureido-3-propargyl-2,3-dihydropyrrol-2-ols, 1-ureido-3-propargylpyrroles and 1-ureido-3-propargyl-3-phosphono-1H-pyrrol-2(3H)-ones

Abstract The title compounds were obtained by reaction of conjugated azoalkenes with activated methinic derivatives bearing a propargylic residue. 1-Ureido-3-propargyl-2,3-dihydropyrrol-2-ols gave in the presence of Cu(I) catalyst the 2,5-dimethyl-3-ethoxycarbonyl-4-(2-oxopropyl)-1-(N′-phenylureido)-pyrrole, while in the presence of Pd(0) or Au3+ the 3,6-dimethyl-5-ethoxycarbonyl-4-propargyl-1,4-dihydropyridazine was obtained by ring opening and ring expansion reaction. The propargylic side chain of 1-ureido-3-propargylpyrroles and 1-ureido-3-propargyl-3-phosphono-1H-pyrrol-2(3H)-ones was functionalised by means of palladium and/or copper catalysed coupling reactions with aryl or vinyl triflates and halides.

Effect of Metal Ions in Organic Synthesis. Part XXX. Synthesis of New 3-Carbonyl- and 3-Carboxy-1-Alkoxycarbonylaminopyrroles from Reaction Catalyzed by Copper(II) Chloride of Alkoxycarbonylazoalkenes with β-Diketones and β-Ketoesters

Abstract In the course of our previous investigations, we dealt with the direct synthesis of unknown 1-aminopyrroie derivatives, obtained by reaction of some azoalkenes with B-diketones, 8- ketoesters, or B-ketoamides under copper (II) ionscatalysis. 1-9

Conjugated azoalkenes. Part XVI. Reaction of some conjugated azoalkenes with β-nitrocarbonyl derivatives.

Abstract Unknown 2-hydroxy-3-nitro-2,3-dihydro-1-aminopyrrole derivatives were directly obtained by easy reaction of conjugated azoalkenes with 2-nitro-1,3-indanedione. The treatment of the same reagents with benzoylnitromethane or β-nitroesters gave α,β-olefinated-γ-carbonyl- or α,β-olefinated-γ-alkoxycarbonylhydrazone derivatives, respectively. New asymmetric α-azinohydrazones were isolated from the reaction of the above-mentioned materials with some β-nitroketone tosylhydrazones.

Conjugated Azoalkenesi Part III. Synthesis of Sone Phosphorous Azoalkenes

Abstract Recently, some of us reviewed the synthes is and chemical reactions of conjugated azoalkenes.1 Emphasis was placed on the fact that these derivatives represent at the same time interesting products and useful intermediates in organic chemistry. In fact, conjugated azoolefins undergo a wide range of 1,4-additions, (3+2)- and (4+2)-cycloadditions allowing various functionalizations of the carbon atom adjacent to the carbonyl group, and the construction of many types of interesting five - and six-membered heterocycles, such as widely substituted pyrrole and pyridazine rings. These relevant synthetic objectives appear not to be smoothly obtained by other procedures. In addition, many of the compounds produced from conjugated azoalkenes can profitably be employed in the preparation of natural, pharmaceutical, and phytopharmaceutical products.1

Easy one-pot conversion of 2-chlorohydrazone into 2-oxohydrazone derivatives via 2-azidohydrazone intermediates

Abstract The simple, mild and selective conversion in good yields of 2-chlorohydrazone into 2-oxohydrazone derivatives is reported. The reaction easily occurs via 2-azidohydrazone intermediates and represents a convenient procedure for the useful transformation of the methylene into carbonyl group.

Chapter 1 Polyfunctionalized pyrroles and pyrazoles from conjugated azoalkenes

Publisher Summary This chapter discusses polyfunctionalized pyrroles and pyrazoles from conjugated azoalkenes. Conjugated azoalkenes have been demonstrated to be valuable tools in organic synthesis both as acceptors in Michael additions and as partners in cycloaddition reactions. The azo-ene system of conjugated azoalkenes undergoes various nucleophilic attacks, frequently with high yield and under very mild reaction conditions, producing hydrazone derivatives by 1,4-conjugated addition (Michael-type). It is noteworthy that the hydrazones generated are useful intermediates, giving rise to spontaneous reactions (that is, eliminations, substitutions, internal nucleophilic attack with or without further elimination, heterocyclizations). The synthetic strategy elaborated by us for the polysubstituted title heterocycles from conjugated azoalkenes has made possible the direct preparation of pyrroles with four or five substituents, dihydropyrroles containing up to seven substituents, and fused pyrroles bearing eight substituents. In the case of pyrroles and dihydropyrroles, three substituents are from the azoolefinic substrates and the rest are derived from the nucleophilic reagents.

Conjugated azoalkenes. Part 14. Synthesis of new 1-amino- and 1,2-diaminopyrrole derivatives by reaction of some conjugated azoalkenes with activated methylene compounds RCH2Ac and RCH2CN (R = aryl, heteroaryl)

1-Amino- and 1,2-diamino-pyrrole derivatives are obtained in high yield by reaction of conjugated azoalkenes with ketones and cyanides containing methylene groups further activated by a 4-nitrophenyl, 2-fluorophenyl, benzothiazol-2-yl or benzimidazol-2-yl group. In some cases the heterocycles can be prepared in a one flask procedure, while in others a two step sequence is required, namely, formation of the 1, 4-conjugate adduct and then cyclization. Reaction of 2,4-dichloro- and 2,3,6-trichlorophenylacetonitrile with the azoalkenes gave the 1,4-conjugate adducts, but these could not be successfully cyclized.

Conjugated azoalkenes. Part 12. Synthesis of new 1-amino-3-cyanopyrrole, 1,2-diaminopyrrole and pyrrolo[2,3-b] pyrrole derivatives by reaction of some conjugated azoalkenes with activated nitriles

The reactions of a variety of conjugated azoalkenes with β-cyano ketones or β-cyano amides have been studied and, depending on the nature and the molar ratios of the reagents, new 1 -amino-3-cyanopyrroles, 1,2-diaminopyrroles and 1,3a,6,6a-tetrahydropyrrolo[2,3-b]pyrroles can be obtained in good yields and under mild reaction conditions.

Simple Direct Synthesis of New 1-Heterocyclamino-3-Carbonylaminopyrroles by Reaction of Heterocyclic Azoalkenes with β-Ketoamides

Abstract Pyrrole and several its derivatives have been subjected to extensive chemical investigations, while substituted 1-aminopyrroles remain a class of compounds about which relatively little is known due to the far from trivial problem sposed by their syntheis. In fact, 1-aminopyrroles appear to be prepared mainly by direct reactionfrom conjugated azoalkenes,2 that unfortunately represent a class of relatively little