Giorgio Abbiati

Silver and gold-catalyzed multicomponent reactions.

Summary Silver and gold salts and complexes mainly act as soft and carbophilic Lewis acids even if their use as σ-activators has been rarely reported. Recently, transformations involving Au(I)/Au(III)-redox catalytic systems have been reported in the literature. In this review we highlight all these aspects of silver and gold-mediated processes and their application in multicomponent reactions.

[Silver(I)(Pyridine-Containing Ligand)] Complexes As Unusual Catalysts for A3-Coupling Reactions

Two original macrocyclic silver(I)(pyridine-containing ligand) complexes [Ag(I)(Pc-L)] were synthesized and characterized. Their ability to catalyze the coupling among aldehydes, terminal alkynes and amines (A(3)-coupling) was demonstrated. The reaction could be performed under conventional as well as dielectric heating. The catalysts were effective in both cases, but dielectric heating allowed a lower catalyst loading and reduced ratio among reaction partners in shorter reaction times. The reaction scope was broad, including aryl/alkyl aldehydes, aryl/alkyl acetylenes and secondary aliphatic amines. Some unprecedented propargylamines have been prepared. The new catalytic system was also tested with more challenging coupling partners such as aniline and ketones.

[4+2] and [2+2] cycloaddition reactions of 1-(4-methylphenyl) and 1-benzyl-1,3-diaza-1,3-butadienes with ketenes

Abstract [4+2] and [2+2] cycloaddition reactions of 1-(4-methylphenyl) and 1-benzyl-1,3-diaza-1,3-butadienes with monophenyl, diphenyl, monochloro and ethoxycarbonylketenes are described. The mechanism of these reactions is also discussed.

Synthesis of functionalised pyrazolones and imidazolines/imidazoles through divergent cyclisation reactions

Abstract The base-promoted reactions of easily accessible α-aminohydrazones represent a simple and efficient method for the preparation of both 1-substituted and 1-unsubstituted-4-aminocarbonyl-1 H -pyrazol-5(2 H )-ones, whereas the copper promoted reactions provide a divergent facile regiocontrolled synthesis of the imidazoline/imidazole ring system. The copper-promoted reaction of the α-benzylaminohydrazone produces a 2-oxo-1,4-diazadiene derivative. Finally, the imidazolines can be easily hydrolyzed to α-ketohydrazones.

[2+2] Cycloaddition Reactions of 1-Benzyl-2,4-Diphenyl-1,3-Diazabuta-1,3-Diene with Chiral Ketenes

Abstract The [2+2] cycloaddition reactions of 1-benzyl-2,4-diphenyl-1,3-diaza-1,3-butadiene with β-(dimethylphenylsilyl)ketene, β-menthoxyketene and Evans–Sjogren ketene were investigated. The results and some chemical transformations of the obtained cycloadducts are reported.

Substituted 1 Benzyl-4-(benzylidenimino)-4-phenylazetidin-2-ones : synthesis, thermal and photochemical reactions

Abstract The title compounds were synthesised from 1,3-diazabuta-1,3-dienes and ketenes. Thermal and photochemical ring expansion reactions to 5,6-dihydro-3H-pyrimidin-4-ones are also described.

Gold(I) or silver catalyzed synthesis of α-indolylacrylates.

Methyl 2-acetamidoacrylate reacted with various 2-substituted indoles in the presence of catalytic amounts of AgSbF6 or AuPPh3NTf2 to provide the corresponding methyl 2-(2-substituted-1H-indol-3-yl)acrylates.

Novel intramolecular cyclization of N-alkynyl heterocycles containing proximate nucleophiles

Intramolecular cyclization of 2-acyl-1-propargyl-1H-indoles in the presence of ammonia provides an easy entry to pyrazino[1,2-a]indole nucleus.

Cycloaddition reactions of 2,4-diphenyl-1,3-diazabuta-1,3-dienes with isocyanates and isothiocyanates

The cycloaddition reactions of 1-p-tolyl and 1-benzyl- 2,4-diphenyl-1,3-diazabuta-1,3-dienes with a variety of aryl and alkyl isocyanate and isothiocyanate are described. The reaction mechanism is also discussed.

Concise synthesis of fused polycyclic quinolines

Abstract β-(2-Aminophenyl)-α,β-ynones react with enamines of cyclic ketones by domino [2+2]cycloaddition/annelation reaction giving rise to bicyclo[4.2.0]-octane[7,8- c ]-2-aryl quinolines or to c -fused quinolines. The reactivity of ynones towards acyclic enamines and thermal rearrangement of tetracyclic to the corresponding tricyclic derivatives are also described.