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The reactivity of the ynamide tert-butyl N-ethynyl-N-phenylcarbamate (1) in the 1,3-dipolar cycloaddition (1,3-DC) with C-carboxymethyl-N-phenylnitrilimine was investigated. This [3+2] cycloaddition affords the 5-amino pyrazole as a single regioisomer. The obtained cycloadduct has been activated at the 4-position of the pyrazole ring through bromination and subsequently coupled with a phenyl group under Pd catalysis. A detailed computational study has been performed to fully explain the complete regioselectivity observed.

The catalytic asymmetric inverse-electron-demand (IED) [4+2] cycloaddition of various salicylaldehyde-derived N-arylimines with electron-rich alkenes in the presence of chiral BINOL-derived phosphoric acid catalysts has been studied with the aim of obtaining optically active 4-aminobenzopyran derivatives. Dienophiles such as 2,3-dihydro-2H-furan, benzyl N-vinylcarbamate and 2-vinylindole have been employed.

1,3-Dipolar cycloadditions of C-carboxymethyl-N-arylnitrile imines with substituted acetylenes bearing thiol or sulfone groups were studied. The sulfur controls the regiochemistry of the reaction, and this protocol was applied to the synthesis of ring-fused thieno[2,3-c]pyrazoles.

Some N-Boc ynamides bearing a terminal ester or aryl group are treated with azides to produce the desired triazoles with complete regiocontrol.

The cyanobis(dibenzylamino)borane-mediated transformation of chiral aldehydes into the corresponding α-amino nitriles is described. Starting from these compounds short synthetic routes can be envisaged for obtaining diastereomerically pure functionalized 1,2-diamines and hydroxylated α-amino acids that are of interest as core key units of biologically active substances or as potential ligands for asymmetric catalysis. The stereochemical outcome of the aminative cyanation reaction is discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Several new ligands featuring a rigid three ring skeleton have been prepared for the first time following a modular approach. Chirality has been introduced by use of an oxazoline moiety fused with a cyclopenta[b]thiophene backbone. The efficiency and stereochemical impact of these ligands on the copper-catalyzed enantioselective addition of Et2Zn to chalcone was examined and enantiomeric excesses up to 79% were achieved using the ligand (R,R)-16 substituted with a methyl group at the cyclopenta moiety. Computational and ESI-mass spectral studies show that these new compounds behave as monodentate ligands towards Cu+. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Indoles (II) and (V) bearing Michael acceptors at the 4-position are used in enantioselective organocatalytic cascade reactions with enals (III) and (VI).

1,3-Dipolar cycloaddition of nitrile imines with α,β-unsaturated five- and six-membered lactones, thiolactones and lactams gave ring-fused pyrazoles. Regioisomeric mixtures have been obtained with the 5-substituted pyrazole as the major cycloadduct. Only with the five-membered lactone the major product was the 4-acyl derivative. Computational studies, the use of the topological analysis of the Fukui functions and the potential energy surfaces (PES) theory allowed a theoretical description of the local reactivity in agreement with the observed high regiochemistry and with the role of the heteroatom adjacent to the carbonyl group.

Several small organic molecule catalysts are reminiscent of natural enzymes in their mode of action and substrate interaction/activation. This striking similarity has been a great source of inspiration for the development of new organocatalytic asymmetric processes. A few representative examples, mostly dealing with catalysts interacting through multiple hydrogen-bonds (synthetic oxyanion holes), are highlighted in this perspective.

It is demonstrated, that the stereochemical outcome of Wittig olefinations of 4-substituted cyclohexanones can be controlled by hydrogen-bond donor catalysts such as (R,R)-TADDOL or 1,2-diaminocyclohexane derived bis-thioureas.

Aldimines (II) or (V) and dihydrofuran (III) or vinylindole (XII) give exclusively the desired enantioenriched aminobenzopyrans.

1,3-Dipolar cycloadditions of C-carboxymethyl-N-arylnitrile imines with substituted acetylenes bearing thiol or sulfone groups were studied. The sulfur controls the regiochemistry of the reaction, and this protocol was applied to the synthesis of ring-fused thieno[2,3-c]pyrazoles.

Photo-induced cycloadditions of phenyl triphenylsilyl thioketone 1 with electron-poor olefins (acrylonitrile, methyl acrylate and cis- and trans-1,2-dichloroethene) gave silyl thietanes in a regio- and highly stereo-selective manner. In contrast, reaction with vinyl ethers gave thietanes without any regio- or stereo-control. Reaction with α-methylstyrene and 2,3-dimethylbut-2-ene gave open chain products. Desilylation of silyl thietanes occurs with prevalent inversion of configuration at the carbon bearing the silicon group.

ω-Haloacylsilanes 1 were selectively transformed via thioacylsilanes into Z-silyl-enethiols 4 with solid sodium hydrogen carbonate or into 2-silylthiacycloalk-2-enes 5 of common to large ring size with solid sodium hydroxide. Compounds 5 underwent protiodesilylation.

Treatment of methyl 1-methylsulfanylvinyl sulfoxides with sodium thiophenolate in MeOH gives 1-methylsulfanylalk-1-en-3-ols.

A series of 4-acylamino-3-aryl substituted pyrazoles is synthesized and evaluated in vitro for their cytotoxicity against U87MG glioma cells.

The Rh complex catalysed hydrogenation of an α-(hydroxyalkyl)- N-methoxyacrylamide and the Ru complex catalysed hydrogenation of an α-(fluoroalkyl)acrylate both proceed with ≥90% selectivity to give the syn-isomer.

Structural variations in acylsilane molecules allow a number of new selective synthetic processes to be performed which lead to sulfur-containing heterocycles, highly functionalized and unsaturated polycarbonyl derivatives, polyenes, and β - and γ -aminoalcohols. The synthesis of these compounds, most of them not easily accessible through conventional routes, takes advantage of the site-selective reactions occurring at the C–Si bonds, of the increased stability of acylsilanes with respect to that of the corresponding aldehydes and of the high diastereofacial selectivity introduced by the SiR 3 group. Herein we report the different synthetic strategies leading to the synthesis of several functionalized acylsilanes and their synthetic applications. The use of new selective polymetallic reagents for the nucleophilic silylation will be presented as well.

The allylation of acylsilanes with tetraallyltin in the presence of catalytic amounts of Sc(OTf) 3 proceeded smoothly to afford the silylated homoallylic alcohols in good yields. Subsequent protiodesilylation gave the formal adducts of the corresponding aldehydes. The homochiral acylsilane 11 gave a reversal of asymmetric induction in the Sc(OTf) 3 catalyzed allylation and in the Sakurai reaction.

The new allylaminosilanes 2a – c , derived from chiral amines, react with benzaldehyde and pivalaldehyde in the presence of SnCl 4 to give homoallylic alcohols 4a – b with enantiomeric excesses of up to 30%.

A practical route is described for the synthesis of enantiopure β- and γ-amino alcohols with two stereocenters, starting from homochiral α- (1 and 5) and β- (13 and 16) -aminoacylsilanes, and involving stereoselective addition of allylmetal compounds and subsequent stereospecific protiodesilylation of the adducts. The degree of diastereoselectivity achieved in the nucleophilic addition step depends on both the nitrogen-protecting group and the reagents used. Diastereomeric excess (de) values equal to or higher than 98% were obtained in the TiCl4-promoted allylation of the N-Pht-aminoacylsilanes 1 and 13 and of the N-Ts-aminoacylsilane 5 with allyltrimethylsilane. Lower de values were obtained in the Sc(OTf)3-catalyzed allylation of 5 with tetraallyltin and in the additions of both allyltrimethylsilane and tetraallyltin to the N-Ts-β-aminoacylsilane 16. Protiodesilylation of the adducts, leading to the β- and γ-amino alcohols, was accomplished with TBAF, except in the case of the adducts obtained from 5. For these, a preliminary removal of the tosyl group was necessary, which was accomplished with simultaneous desilylation by treatment with Na in liquid ammonia.

Thioacylsilanes containing the ferrocene moiety, easily prepared from the corresponding acylsilanes with Lawesson's reagent at room temperature, can be transformed into vinyl silanes, sulfur heterocycles and sulfines.

The results of model investigations concerning 1,4-addition of higher-order cyanocuprate (n-Bu)2Cu(CN)Li2 to 3-alkyl-substituted butenolides are presented.

Enantiomerically pure β-hydroxyalkyl and β-aminoalkyl ferrocenyl sulfides have been synthesized in good yields from mercaptoferrocene and amino alcohol derivatives. Primary β-aminoalkyl sulfides allowed the synthesis of tetrahydro-1,4-thiazepines containing the ferrocene moiety with good diastereoselectivity and β-iminoalkyl sulfides. Some of these derivatives have successfully been employed as ligands for palladium-catalyzed allylic substitution, with asymmetric induction of up to 99% ee. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

1,3-Dipolar cycloaddition of C-aryl-N-aryl- and C-carboxymethyl-N-aryl-nitrile imines with functionalized acetylenes have been studied. Regioisomeric mixtures have been obtained with the 5-substituted pyrazole as the major cycloadduct. Under scandium triflate catalysis a reversal in the regiochemistry was observed, especially in the case of C-carboxymethyl-N-aryl-nitrile imines.

Enantiomerically pure 2-hydroxyalkyl, 2-aminoalkyl and 2-iminoalkyl ferrocenyl p-tolylsulfides are easily prepared in good yields and with complete diastereocontrol from (S)-(2-p-tolylthio)ferrocencarboxyaldehyde. 2-Iminoalkyl ferrocenyl derivatives can be used as ligands in asymmetric catalysis and as starting materials for asymmetric Staudinger reaction.

A nitrogen-containing superbase such as TMG was found to be an effective catalyst for the reaction between N-diphenylphosphinoyl imines and nitroalkanes. Exploiting a protocol that avoids the use of any solvent also during workup procedure, we synthesized a series of beta-nitroamines in excellent yields and high diastereomeric ratios. These results, combined with the capability of the indium in conjunction with Zn as the stoichiometric reducing agent to perform in aqueous medium reduction of the nitro group under mild reaction conditions, led us to devise a three-step, one-pot synthesis of a range of 1,2-diamines, making use of environmentally friendly procedures in the various steps.

Several new ligands featuring a rigid three ring skeleton have been prepared for the first time following a modular approach. Chirality has been introduced by use of an oxazoline moiety fused with a cyclopenta[b]thiophene backbone. The efficiency and stereochemical impact of these ligands on the copper-catalyzed enantioselective addition of Et2Zn to chalcone was examined and enantiomeric excesses up to 79% were achieved using the ligand (R,R)-16 substituted with a methyl group at the cyclopenta moiety. Computational and ESI-mass spectral studies show that these new compounds behave as monodentate ligands towards Cu+. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

N,N-Disubstituted α-aminonitriles undergo Bruylants reaction under Barbier and Reformatsky conditions with activated halides, in the presence of zinc and 10 mol% HOAc. The high yields and the simple operational conditions make this reaction an appealing, approach to N,N-disubstituted homoallylamines and β-aminoesters.