Stefano Tollari

Catalytic amination of unsaturated hydrocarbons : reactions of p-nitrophenylazide with alkenes catalysed by metallo-porphyrins

Abstract Porphyrin derivatives of transition metals such as Ru(TPP)CO, Ru(OEP)CO and Co(OEP)(TPP=dianion of 5, 10, 15, 20-tetraphenylporphyrin, OEP=dianion of 2, 3, 7, 8, 12, 13, 17, 18-octaetylporphyrin) catalyse the reaction of p-nitrophenylazide with cyclohexene to give the corresponding allylamine in good yields. With other olefins such as cyclooctene, 1-octene, styrene and substituted styrenes the main product becomes the corresponding aziridine. The reaction of p-nitrophenylazide with Ru(TPP)CO has been investigated and the mechanism of the catalytic reactions is discussed.

Synthesis of heterocycles via palladium-catalyzed carbonylation of ortho-substituted organic nitro compounds in relatively mild conditions

Abstract Carbonylation of o-nitroaniline in the presence of aldehydes catalyzed by the Pd (TMB)2/TMPhen/TMBH catalytic system (TMBH = 2,4,6-trimethyl benzoic acid; TMPhen = 3,4,7,8-tetramethyl-1,10-phenanthroline) at 140–180°C and 20–40 atm of carbon monoxide, gives the corresponding benzimidazoles, with a selectivity ranging from 10 to 80%, strongly depending on the aldehyde used. The main by-product was shown to be the 2(1H) benzimidazolone, derived by direct carbonylation of o-nitroaniline. The same catalytic system has been used in the carbonylation of o-nitrostyrenes at 120–180°C and 20–60 atm of carbon monoxide, obtaining the corresponding indoles with a selectivity generally ranging from 70 to 100%. Interestingly, in the latter case the presence of TMBH was not necessary in order to obtain good conversions and selectivities. On the contrary, the presence of excess TMBH is indispensable when nitrobenzene is catalytically converted to phenyl isocyanate. Moreover, in the catalytic synthesis of indoles no carbonylated products are formed. These observations suggest a catalytic cycle different from what has been proposed in the synthesis of phenyl isocyanate from nitrobenzene, catalyzed by palladium.

Synthesis of Indole Derivatives with Biological Activity by Reactions Between Unsaturated Hydrocarbons and N-Aromatic Precursors

The present review is devoted to illustrate the state of the art of the syntheses of indoles, focusing particularly on the most recent developments of new synthetic approaches. Emphasis is given to the preparation of natural products or bioactive compounds containing the indole unit. We present a historical perspective of indole synthesis showing the strategies by choosing the nitrogen precursors. The review is organized sharing the indole synthetic approaches by using different nitrogen-containing functional groups in aromatic substrates used as source of the nitrogen of the indole moiety. Some functional groups and some typical reactions are particularly stressed and highlighted because of the limited coverage given in previous reviews published on this topic. Other synthetic approaches more used and discussed in recent, complete and excellent reviews on the topic are summarized but the most recent published results are highlighted. Our interest is particularly focused on the indolization procedures and on the different methods used for the ring closure and no attention is given to modification of indole structures starting from molecules with a preformed indole unit. Intriguing indole syntheses are continually discovered and the importance that the scientific community gives to these new developments is connected with the strategic role of molecules containing the indole unit. Indoles are the class of heterocycles with more applications and extensive interest due to their biological and pharmacological activity.

Cyclometallation of indole derivatives: cyclopalladation of gramine and 1-methyl gramine and CO insertion

Abstract Li 2 PdCl 4 , in methanol, with gramine 1 and 1-methyl gramine 2 gave the dimeric complexes 1a and 2a with chlorine bridges and having the indole nucleus metallated at position 2. The corresponding bromo derivatives 1b and 2b were isolated from the reactions of Pd(OAc) 2 with 1 and 2 , followed by treatment with LiBr. Complexes 1a,b and 2a,b gave the monomeric, cyclometallated derivatives 3a-d by reaction with PPh 3 in methylene chloride. When the cyclopalladation of 1-methyl gramine 1 was attempted by reacting PdCl 2 , PPh 3 and 2 in methanol in the presence of AcOna, an unexpected compound 4 was obtained. A structural determination of 4 showed it consisted of the known [Pd(PPh 3 )Cl 3 ] − anion packed with the dimethyl-bis(3-methylene-1-methyl indole) ammonium cation. When compounds 1a and 2a were reacted with carbon monoxide at atmospheric pressure in methanol or ethanol and in the presence of Net 3 , the corresponding 2-carboalkoxy indole derivatives 5 and 6 were isolated in high yields.

Acyclic and cyclic urea formation via the cobalt-catalysed oxidative carbonylation of aromatic primary amines

Abstract The N,N-bis(salicylidene)ethylenediaminocobalt(II)-catalysed oxidative carbonylation of aromatic primary amines in methanol gives ureas in good yields, with small amounts of carbamates and azo derivatives. Ortho-substituted aromatic amines also give cyclic ureas via a metal-induced oxidative carbonylation-cyclisation pathway.

Ruthenium carbonyl-catalyzed deoxygenation by carbon monoidde of o-substituted nitrobenzenes. Synthesis of benzimidazoles

Abstract Ru3(CO)12 is a very efficient catalyst for the deoxygeiiation of 2-nitro-N-(phenylmethylene) benzeneamine derivatives to give the corresponding 2-substituted benzinmidazoles, at 220 °C and 50 bar of carbon monoxide. Main byproducts are the corresponding amines. The same benzimidazoles are also obtained starting from o-nitroaniline and the corresponding aldehyde. When N-(2-nitrophenyl)methylene benzeneamine derivatives are used as substrates, the reaction changes dramatically and only traces of the corresponding heterocyclic compounds are obtained, although complete conversion of the starting nitro compounds is achieved.

The bis(salicylaldehyde)ethylenediimine cobalt(II)-catalysed oxidative carbonylation of primary and secondary amines

Abstract Anilines are oxidized to azobenzenes in methanol or methylene chloride solution using dioxygen as the oxidant and bis(salicylaldehyde)ethylenediimine cobalt(II) (CoIIsalen) as catalyst. In the presence of carbon monoxide, isocyanates, urethanes and ureas are also obtained. The latter two are the only reaction products when the aliphatic amine 1-adamantylamine is used as a substrate. Increasing the pressures of dioxygen and carbon monoxide significantly improves reaction yields. Ortho-aminophenol give the corresponding azo derivative and an oxazolone. Aromatic secondary amines give secondary formamides in low yields.

Oxidation of primary benzylic amines by Mo(O) (O2)2 (H2O) (HMPA)

Abstract The stoichiometric reactions of MO (O)(O 2 ) 2 (H 2 O) (HMPA) ( 1 ) (HMPA = hexamethylphosphoramide) with primary benzylic amines, RNH 2 , [R=C 6 H 5 CH 2 ( 2 ); 2,4Cl 2 -C 6 H 3 CH 2 ( 3 ); 3,4(OCH 3 ) 2 -C 6 H 3 CH 2 ( 4 ); 2,Cl-C 6 H 4 CH 2 ( 5 )] yield the cis -dioxoperoxo complexes, Mo(O) 2 (O 2 )(RNH 2 ) 2 ,( 2a – 5a ), the corresponding oximes, RCHNOH, and/or the Schiff bases, RCHNCH 2 R. The complex Mo(O) 2 (O 2 )(C 6 H 5 CH 2 NH 2 ) 2 ( 2a ), obtained in the stoichiometric reaction of ( 1 ) with benzylamine, catalyzes the oxidation of ( 2 ) to benzaldehyde oxime, in the presence of H 2 O 2 (30% w/w) as oxidant.

Synthesis, X-ray structure and reactivity of cyclopalladated complexes of hydrazones of 1H-indole-3-carboxaldehyde

Abstract By reaction of Li 2 [PdCl 4 ] with substituted hydrazones of 1 H -indole-3-carboxaldehyde the corresponding cyclopalladated complexes have been isolated and characterized. Compound 1a [C 11 H 10 ClN 3 OPd] reacts with PPh 3 by halogen displacement giving the cationic complex 5 the X-ray structure of which has revealed metallation at position 4 of the indole hydrazone, which is terdentate forming a [5,6]-fused ring system.

The unprecedented detection of the intermediate formation of N-hydroxy derivatives during the carbonylation of 2'-nitrochalcones and 2-nitrostyrenes catalysed by palladium

Abstract The carbonylation of 2′-nitrochalcones ( 1 ) in tetrahydrofuran, catalysed by Pd(TMB) 2 (TMBH=2,4,6-trimethylbenzoic acid) at 30 atm of carbon monoxide and 170°C, gave the corresponding quinolones ( 2 ), together with the N -hydroxyquinolones ( 3 ). In some cases the latter become the most abundant products. Similar reactions have been observed in the carbonylation of 2-nitrostyrenes ( 4 ) with the same catalytic system but in the presence of TMPhen (3,4,7,8-tetramethyl-1,10-phenanthroline), which gave the corresponding indoles ( 5 ), together with the N -hydroxyindoles ( 6 ). This is the first case where the formation of N -hydroxy derivatives has been observed during the catalytic carbonylation of organic nitro compounds. The use of Pd/C without any additive as catalyst has also been investigated.