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Cyclocarbonylative Sonogashira reactions of ortho-ethynylbenzamides have been investigated. The process is carried out under CO pressure, in the presence of a very small amount of PdCl2(PPh3)2 (0.4 mol %) as a catalytic precursor and without the need for a Cu salt as the co-catalyst. 2-Ethynylbenzamide reacted successfully with iodoarenes bearing electron-withdrawing and electron-donating groups, giving rise to different classes of compounds depending on the solvent used. On the contrary, N-(4-chlorophenyl)-2-ethynylbenzamide afforded exclusively polyfunctionalized isoindolinones with high stereoselectivity toward (E) isomers.

In recent years, the immobilization of palladium nanoparticles on solid supports to prepare active and stable catalytic systems has been deeply investigated. Compared to inorganic materials, naturally occurring organic solids are inexpensive, available and abundant. Moreover, the surface of these solids is fully covered by chelating groups which can stabilize the metal nanoparticles. In the present review, we have focused our attention on natural biomaterials-supported metal catalysts applied to the formation of C–C bonds by Mizoroki–Heck, Suzuki–Miyaura and Sonogashira reactions. A systematic approach based on the nature of the organic matrix will be followed: (i) metal catalysts supported on cellulose; (ii) metal catalysts supported on starch; (iii) metal catalysts supported on pectin; (iv) metal catalysts supported on agarose; (v) metal catalysts supported on chitosan; (vi) metal catalysts supported on proteins and enzymes. We will emphasize the effective heterogeneity and recyclability of each catalyst, specifying which studies were carried out to evaluate these aspects.

In this study, we report on the synthesis of new organic fluorophores containing either the p-phenylene or the benzodithiophene cyclic nucleus connected to thiophene units via triple bonds and carbonyl group, and on their application for the fabrication of luminescent solar concentrators (LSCs). Their optical properties were evaluated. Independent of the core, dyes containing the CO-thiophene residues seem to be the most promising for LSCs applications. In fact , carbonyl groups slightly enhance the quantum yield but significantly increase the red-shift of the emission so that the superimposition between the absorbance spectrum and the emission one is diminished. In the case of the benzodithiophene centre, light emission in the yellow-red portion of the spectrum is achieved. The latter dye is then selected for tests in a poly(methyl methacrylate) (PMMA) matrix. It showed good compatibility and homogenous distribution, no auto-absorption phenomena, and optical efficiencies of about 8% at 1 wt. %, i.e. comparable with those PMMA/Lumogen Red films in the same range of concentration.

Oxygen and nitrogen heterocyclic systems are present in a large number of natural and synthetic compounds. In particular, oxa- and aza-silacyclane, tetrahydrofuran, benzofuran, cycloheptadifuranone, cycloheptadipyrrolone, pyrrolidine, lactone, lactam, phthalan, isochromanone, tetrahydroisoquinolinone, benzoindolizidinone, indoline and indolizidine scaffolds are present in many classes of biologically active molecules. Most of these contain a C=O moiety which can be easily introduced using carbonylative reaction conditions. In this field, intramolecular silylformylation and silylcarbocyclization reactions may afford heterocyclic compounds containing a carbonyl functional group together with a vinylsilane moiety which can be further transformed. Considering these two aspects, in this review a detailed analysis of the literature data regarding the application of silylformylation and silylcarbocyclization reactions to the synthesis of several heterocyclic derivatives is reported.

This work reports the first observation of circularly polarized electroluminescence (CPEL) in thin films of self-organized oligothiophenes. Four new 1,4-phenylene and 9H-carbazole-based oligothiophenes were ad hoc designed to ensure efficient spontaneous formation of chiral supramolecular order. They were easily synthesized and their chiroptical properties in thin films were measured. Circularly polarized luminescence (CPL) spectra revealed glum in the order of 10−2 on a wide wavelengths range, originating from their self-organized chiral supramolecular organization. These molecules have reasonable properties as organic semiconductors and for this reason they can constitute the active layer of circularly-polarized organic light-emitting diodes (CP-OLEDs). Thus, we could investigate directly their electroluminescence (EL) and CPEL, without resorting to blends, but rather in a simple multilayer device with basic architecture. This is the first example of a CP-OLED with active layer made only of a small organic compound.

Palladium nanoparticles (NP) immobilized on metal scavengers (Smopex®-234, Smopex®-111, PVPy, 1% w/w) have been tested in the acyl Sonogashira reactions between terminal acetylenes and acid chlorides. Pd/PVPy resulted especially effective in the synthesis of alkynyl ketones with different stereoelectronic properties, even working with a very low amount of palladium (0.2 mol%). Preliminary tests seem to indicate that Pd/PVPy could act as a reservoir of very active palladium NP which are partially released during the reaction and then recaptured from the resin at the end of the process, thus ensuring the possibility of reuse of the catalyst. Graphic Abstract: [Figure not available: see fulltext.]

New luminophores having different aryl nuclei and propynones moieties have been obtained via Sonogashira reactions. Their optical properties were evaluated and indicated that carbonyl groups are responsible for significant bathochromic effects and high Stokes shifts. The insertion of -OMe groups on the central benzene unit gives to the fluorophore high optical efficiency (7.7%) when homogeneously dispersed in a poly(cyclohexyl methacrylate) (PCMA) film and connected to a PV cell.

A chiral benzo[1, 2-b:4,5-b']dithiophene-based oligothiophene with the very uncommon chiroptical property of signal inversion on sample flipping was recently described. This property is due to the interference between linear dichroism and linear birefringence, called LDLB effect, which is theoretically well understood, but to date very rarely reported in the literature. Samples with very large LDLB effect lead to the unique possibility of discriminating the direction of sample illumination (i. e., from the front or back). This article presents a set of analogue compounds, in which small structural changes are introduced to uncover which factors determine the very large LDLB effect or true circular dichroism connected to supramolecular chirality. It also reveals the impact of the deposition technique, in which spin coating may exert a primary role, and results in films with outstanding chiroptical features. These features are made even more relevant due to the semiconducting properties of oligothiophenes, which are interesting for optical sensing applications

Oxygen and nitrogen heterocycle systems are found in a vast number of natural substrates and biologically active molecules. In particular, phthalan, isochroman, and isoindoline scaffolds are present in many classes of products such as antimycotics, antibiotics, antioxidants, pigments, and fluorophores. Therefore several procedure dedicated to the building of such heterocycles have been developed. In this review a detailed analysis of literature data relating to these scaffolds is described. Particular attention has been devoted to their biological and chemical potentiality, and an in-depth investigation into the most important synthetic methods is reported. Cyclocarbonylative Sonogashira coupling of suitable alcohols and amides has been carefully considered, because it represents a valuable and atom-economic route for the construction of alkylidenephthalans, -isochromans, and -isoindolines.

A new protocol for the synthesis of 3-isochromanone derivatives based on rhodium-promoted silylcarbocyclisation reactions of ethynylbenzyl alcohol with different arylsilanes is described. The structure of the isochromanone depends upon the reaction conditions used: when the reaction is carried out without base, (Z)-4-[(aryldimethylsilyl)methylene]isochroman-3-ones are obtained as major products. These compounds can be submitted to a desilylation/aryl migration reaction to give 4-(arylmethyl)isochroman-3-ones in high yields. In contrast, in the presence of DBU (1,8-diazabicyclo[5.4.0]undec-7-ene), hydrogenation of methyleneisochroman-3-ones takes place, and the corresponding β-(silylmethyl)-3-isochromanones are formed. Moreover, when internal alkynes are treated with hydrosilanes under silylcarbocyclisation reaction conditions, alcoholysis of the hydrosilanes occurs exclusively.

A new chiral benzo[1,2-b:4,5-b′]dithiophene-based oligothiophene has been synthesized and spectroscopically characterized in solution and in the solid state. The electronic circular dichroism (ECD) spectra of the thin films revealed the occurrence of an uncommon phenomenon, consisting of the inversion of the circular dichroism sign by sample flipping. To the best of our knowledge, this is unprecedented in samples where no preferential orientation of the chromophores has been induced, and must be due to spontaneous local anisotropies. It reveals peculiar features upon the usual solvent annealing procedure, but finally results in stable and very strong signals, which are perfectly reproduced in sign, and relative and even absolute magnitude. Although the recorded signal cannot be considered as a true ECD spectrum, it corresponds to a very large discrimination of light circular polarization, which is well explained by means of the Mueller matrix analysis and does not depend on instrumental defects. It is a genuine property of this material, which correlates with polarized optical microscopy (POM) images and only depends on the self-assembling properties of this molecule. This phenomenon may have relevant implications, on account of its strength and of the interest of oligothiophenes in current optoelectronic devices.

The acyl Sonogashira reaction represents an extension of Sonogashira cross-coupling to acid chlorides which replace aryl or vinyl halides, while terminal acetylenes are used as coupling partners in both reactions. The introduction of a carbonyl functional group on the alkyne backbone determines a radical change in the reactivity of the products. Indeed, α,β-alkynyl ketones can be easily converted into different heterocyclic compounds depending on the experimental conditions employed. Due to its potential, the acyl Sonogashira reaction has been deeply studied with particular attention to the nature of the catalysts and to the structures of both coupling compounds. Considering these two aspects, in this review, a detailed analysis of the literature data regarding the acyl Sonogashira reaction and its role in the synthesis of several heterocyclic derivatives is reported.

Supported catalysts are important tools for developing green-economy-based processes. Palladium nanoparticles (NPs) that are immobilized on two fibers developed as metal scavengers (i.e., Smopex®-234 and Smopex®-111, 1% w/w) have been prepared and tested in copper-free cyclocarbonylative Sonogashira reactions. Their catalytic activity has been compared with that of a homogeneous catalyst (i.e., PdCl2(PPh3)2). Pd/Smopex®-234 showed high activity and selectivity in the synthesis of functionalized heterocycles, such as phthalans and isochromans, even when working with a very low amount of palladium (0.2–0.5 mol%). The extension of Pd/Smopex®-234 promoted cyclocarbonylative reactions to propargyl and homopropargyl amides afforded the corresponding isoindoline and dihydrobenzazepine derivatives. A preliminary test on Pd NPs leaching into the solution (1.7 × 10−3 mg) seems to indicate that, at the end of the reaction, almost all of the active metal is present on the fiber surface.

Controlling circularly polarized (CP) emission is key for both fundamental understanding and applications in the field of chiral photonics and electronics. Here, a completely new way to achieve this goal is presented. A luminescent thin film, made from a chiral conjugated phenylene bis-thiophenylpropynone able to self-assemble into ordered structures, emits highly circularly polarized light with opposite handedness from its two opposite faces. Such emergent nonreciprocal behavior in CP emission, so far unprecedented, represents a fundamental advance, opening new opportunities in design, preparation, and applications of CP emitting materials.

Oxygen and nitrogen heterocycles are present in a vast number of natural substrates and biologically active molecules. In particular, phthalan and isoindoline subunits are found in many classes of products such as antibiotics, antioxidants, antimycotics, pigments, and fluorophores. Therefore several procedures dedicated to the construction of these heterocycles have been developed. In this review, a detailed analysis of the literature data regarding the synthesis of these nuclei via cyclization reactions is reported.1 Introduction2 Phthalans2.1 Oxa-Pictet–Spengler Reaction2.2 Garratt–Braverman Cyclization2.3 Diels–Alder and Related Reactions2.4 [2+2+2] Cyclotrimerization of Alkynes2.5 Cycloetherification of ortho-Substituted Aromatics2.6 Tandem Carbonylative Sonogashira Coupling–Cyclization Reactions3 Isoindolines3.1 Amination of Dihalides3.2 Intramolecular Hydroamination3.3 Diels–Alder and Related Reactions3.4 [2+2+2] Cycloaddition Reactions3.5 Tandem Carbonylative Sonogashira Coupling–Cyclization Reactions4 Conclusions

In this work, we present a carbonylative Sonogashira reaction of o-ethynyl benzyl alcohols and aryl iodides, followed by a cyclization process to selectively give carbonylmethylene isobenzofurans in high yields and in an atom-economic fashion. The reaction can be carried out in the absence of CuI, with a small amount of PdCl2(PPh3)2 (0.2–0.5 mol-%), using aryl iodides bearing both electron-withdrawing and electron-donating groups. Of the two possible stereoisomeric products, Z-isobenzofuran derivatives were obtained as major products. But, when the reaction was extended to a secondary alcohol, an interesting switch in stereoselectivity was observed.

A preliminary study was conducted on the hydrogenolysis of benzyl protected substrates using palladium nanoparticles supported on different inorganic and organic matrices, under mild experimental conditions (1 mol% Pd, T=358C, PH2=1 atm). The activity of commercially available Pd/C systems was compared with that of nanosized catalysts prepared by the Metal Vapour Synthesis (MVS) technique. MVS-derived systems resulted more efficient, affording phenols and aniline with complete chemoselectivity. Preliminary investigation on metal leaching during the reactions, indicated the presence of very low amount of palladium in solution, thus suggesting a heterogeneous behavior of the catalysts.

In this study we used a tandem carbonylative Sonogashira reaction/cyclisation process to construct alkylidene-functionalized isochromans in high yields with complete stereoselectivity (only Z isomers were formed). The reaction was performed in the absence of a CuI co-catalyst with a small amount of PdCl2(PPh3)2 (0.2–0.5 mol-%), and aryl iodides bearing both electron-donating and electron-withdrawing substituents were successfully employed.

In this chapter we intend to provide a synapsis of the synthesis of supported gold catalysts by the metal vapor synthesis (MVS) technique. In particular, the contribution includes the work undertaken till date in our and other research groups pointing out the key factors to control the size of Au nanoparticles by this synthetic approach.

Functionalised β-lactones were prepared starting from propargyl alcohols by means of an efficient rhodium-catalysed silylcarbocyclisation reaction. This process took place in high yields and complete stereoselectivity using DBU as the base, a sterically hindered alcohol and/or hydrosilane. Otherwise, a silylformylation competitive reaction occurred affording 3-hydroxy-2-[(aryldimethylsilyl)methylene]alkanals with complete regioselectivity. Indeed, while α-(aryldimethylsilylmethylene)-β-lactones were generated exclusively starting from an alkynol characterised by two alkyl groups on the propargyl carbon atom, significant amounts of the aldehydes were observed for secondary alcohols. In these cases, the use of ortho -substituted arylsilanes improved the chemoselectivity towards the α-methylene-β-lactones. Such molecules were then successfully converted into α-methylaryl-β-lactones by a fluoride-induced rearrangement of the aryl group that migrates from silicon to carbon with retention of configuration.

In the last 20 years, nanostructured gold species have received increasing attention due to their activity in many reactions such as selective oxidations and reductions of fine organic chemicals, both in gas phase and in liquid phase. Here, we report that gold nanoparticles prepared from Au/CH 3 COCH 3 solution (obtained from gold vapours and acetone by the Metal Vapour Synthesis technique) can be directly deposited on a wide series of different supports (C, Al 2 O 3 , Fe 2 O 3 , CeO 2 , TiO 2 and ZrO 2 ) with their small dimensions being maintained. The supported gold nanoclusters thus obtained are effective catalysts for the hydrosilylation of acetylenic compounds. The catalytic performance of Au is defined by two major factors: particle size and choice of support. For instance, the results obtained from the reaction of 1-hexyne with triethylsilane in the presence of Au/γ-Al 2 O 3 (0.05 mol%) demonstrate the high selectivity and the excellent specific activities typical of these gold catalysts.

The silylformylation reaction of unsaturated compounds consists of the rhodium-catalysed addition of a R3Si and a CHO moiety to a carbon–carbon multiple bond. The silylformylation process is applicable to both terminal and internal alkynes and is tolerant towards several functional groups. Many factors can influence the chemoselectivity of the reaction that generally affords β-silylalkenals with high yields and regioselectivity. The β-silylalkenals are polyfunctionalised substrates that can be submitted to several chemical transformations and in particular can undergo fluoride-promoted (TBAF) aryl migration from an aryldimethylsilyl group to the adjacent carbon atom thus generating 2-(arylmethyl)aldehydes, important industrial precursors of perfumes. This silylformylation-aryl migration two-steps sequence can be applied to functionalised alkyne precursors and chemo-, regio- and stereoselectivity of the products can be modulated according to the nature and the position of the functional group. When a good leaving group is present in the ω position of the aliphatic chain of the alkyne cyclisation products are obtained, while α,β-unsaturated aldehydes are generated from propargyl tosylamides, acetates and benzoates. α-Silylmethylene-β-lactams, prepared from p-tosylamides according to silylcarbocyclisation reaction, can be transformed into the corresponding arylmethyl-β-lactams by means of TBAF-induced rearrangement that takes place without involving the lactam ring. A plausible mechanism of the rearrangement reaction is reported that suggests the addition of the fluoride ion to the arylsilicon moiety and the consequent migration of the aryl group to the adjacent carbon atom. Both aryl and heteroaryl substituents can migrate without any loss of configuration further enhancing the high synthetic value of this protocol. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

In this work, we present a carbonylative Sonogashira reaction of o-ethynyl benzyl alcohols and aryl iodides, followed by a cyclization process to selectively give carbonylmethylene isobenzofurans in high yields and in an atom-economic fashion. The reaction can be carried out in the absence of CuI, with a small amount of PdCl2(PPh3)2 (0.2–0.5 mol-%), using aryl iodides bearing both electron-withdrawing and electron-donating groups. Of the two possible stereoisomeric products, Z-isobenzofuran derivatives were obtained as major products. But, when the reaction was extended to a secondary alcohol, an interesting switch in stereoselectivity was observed.

Solvated platinum atoms, obtained by metal vapour synthesis (MVS), were conveniently used to prepare γ-iron oxide and γ-alumina supported Pt catalysts containing small metal nanoparticles of controlled size, ranging 0.5–3.0 nm in diameter (HR-TEM). The γ-Fe 2 O 3 -supported Pt system showed higher catalytic activity and selectivity than those of a similarly prepared γ-Al 2 O 3 -supported system in the selective hydrogenation reactions of p - and o -chloronitrobenzene to the corresponding haloanilines, in mild reaction conditions (25 °C, 0.1 MPa hydrogen pressure) ( p -chloronitrobenzene: specific activity (SA) = 59.5 min −1 , Selectivity (Sel.) = 99.9%; o -chloronitrobenzene: SA = 42.8 min −1 , Sel. = 99.2%). The Pt/γ-Fe 2 O 3 system also showed high catalytic efficiency (Sel. > 98%, at 100% of conversion) in the selective hydrogenations of m -chloro-, p - and o -bromo- and p - and o -iodonitrobenzenes. XPS structural studies performed on a pristine Pt/γ-Fe 2 O 3 sample as well as on a sample recovered after the reaction, indicate that the catalytic process did not induce permanent modification in the chemical and/or electronic structure of the catalyst according with the high reusability of the system.

The advantages of the title synthesis are high yield, complete stereoselectivity, low catalyst loading (0.2-0.5 mol%), and no need for CuI as co-catalyst.

The performances of palladium metal catalysts supported by organic resins containing tertiary amino, cyano, carboxyl, and pyridyl groups have been investigated in standard Heck reactions. The catalysts were prepared by either immobilization in the resins of palladium(II) precursors and chemical reduction thereof or by deposition of solvated metal atoms obtained by means of metal vapor synthesis (MVS). Particular attention was paid to the nature of catalysis in the presence of these materials. As the observed catalytic activity turned out to be generally associated with metal leaching, the reaction was most likely catalyzed in solution by soluble, active palladium species. However, a MVS 1% (w/w) catalyst supported by a commercial polyvinylpyridine resin cross-linked with divinylbenzene exhibited an appreciable catalytic activity with a possible partial contribution from supported active palladium species.

A procedure to synthesize new Au–Pd bimetallic catalysts using Au and Pd vapours as reagents (metal vapour synthesis, MVS) is reported. The simultaneous co-condensation of Au and Pd vapours with acetone vapour affords Au–Pd/acetone-solvated metal atoms which have been used to deposit Au–Pd bimetallic nanoparticles on γ-alumina and titanium oxide supports. Transmission electron microscopy (TEM) analysis determined the nanoparticles dimensions (dm = 2.2–2.4 nm) and size distribution while the X-ray absorption spectroscopy (XAS) analysis showed the presence of small bimetallic Au–Pd nanoparticles with a large amount of Au–Pd bonds. The bimetallic co-condensed systems, tested in the selective oxidation of benzyl alcohol with molecular oxygen both in toluene solvent and in solvent-free conditions, showed higher catalytic activity and selectivity than the corresponding monometallic systems as well as of the analogous systems obtained by separate evaporation of the two metals.

Organobis(heterocuprates), 7 and 8 , have been prepared reacting in situ 1,4-dilithiobutane and di-Grignard reagents, obtained from 1,4-dibromobutane and 1,4-dibromobenzene, respectively, with CuSPh and LiCuBr 2 . The cross-coupling reaction of these di-cuprate reagents with 3-alkyl and 3,3-dialkyl 1-bromo-1,2-dienes ( 1 ) provides a general method for selective synthesis of 1,9-decadiynes ( 5 ) and 1,4-bis(2-propynyl)benzenes ( 6 ), characterized by two identical chiral centres in the α position to the triple bonds. The high 1,3- anti stereoselectivity of the coupling process allows us to obtain enantiomerically enriched α,ω-diynes 5 and 6 starting from optically active allenic substrates 1 .

Palladium nanoparticles supported on two Smopex® commercial metal scavengers (1% w/w) have been tested in the carbonylative Sonogashira reactions of aryl iodides with phenylacetylene. Their catalytic activity has been compared with those of more common catalysts (Pd/C, Pd/γ-Al2O3). Pd/Smopex®-234 resulted especially effective in the synthesis of alkynyl ketones even working with a low amount of palladium (0.2–0.5 mol%). Preliminary heterogeneity tests (i.e. hot filtration test, Pd leaching and recycle of the catalyst) have been performed in order to evaluate the catalytic behaviour of this system. The obtained results seem to indicate that Pd/Smopex®-234 could act as a truly heterogeneous catalyst.

the synthesis of 2-phenylsulphonyltetrahydrofuran (1), 2-phenyl sulphonyl-5-methoxy-2,5-dihydrofuran (2) and 2-phenylsulphonylfuran (3) was carried out in very good yields and short reaction times starting from easily available precursors.

vic -dibromides are quantitatively convened into alkenes by using a catalytic amount of NidppeCl 2 , in the presence of two molar equivalents of EtMgBr in THF. Stereochemical aspects of the reaction are given.

a catalytic amount of NidppeCl2 converts an acyl bromide directly into ketones at 0 °C in THF in the presence of a Grignard reagent. The described procedure represents a useful way to afford dialkyl, diaryl or alkyl aryl ketones as well as 1,2-diketones. In the adopted reaction conditions double bonds, esters and ketones are unaffected.

Functionalised β-lactones and β-lactams were prepared starting from propargyl alcohols and propargyl tosyl amides by means of efficient silylcarbocyclisation reactions catalysed by rhodium nanoparticles derived from mesitylene-solvated Rh atoms (Metal Vapour Synthesis technique, MVS) and deposited on inorganic (C, γ-Al2O3 Fe2O3) and organic matrices (PBI). All the MVS supported nanoclusters resulted more active than the analogous commercial Rh/C and Rh/γ-Al2O3, as well as homogeneous Rh4(CO)12 used as reference catalyst. In particular, metal vapour derived Rh/C afforded the β-lactones and β-lactams in high yields and chemoselectivity. Preliminary investigations on the nature of the real active metal species involved in the catalytic process showed that rhodium(0) naked nanoparticles are leached by the support. The high catalytic activity encountered with Rh/C could be ascribed to the easy leaching of metal nanoparticles from carbon into solution. Indeed, the presence of a more polar matrix determined a minor catalytic efficiency probably due to a stronger interaction between the metal and the support. Therefore MVS Rh/C species represents a source, stable with ageing at room temperature, of highly active metal nanoparticles.

α-Benzyl aldehydes are prepared from easily available β-silylalkenals and fluoride reagents, under mild experimental conditions; the reaction occurs instantaneously with almost quantitative yields. A plausible mechanism is suggested, which involves a 1,2-phenyl migration from the silicon to the adjacent carbon atom.

vic -dibromides are quantitatively convened into alkenes by using a catalytic amount of NidppeCl 2 , in the presence of two molar equivalents of EtMgBr in THF. Stereochemical aspects of the reaction are given.

α-Benzyl aldehydes are prepared from easily available β-silylalkenals and fluoride reagents, under mild experimental conditions; the reaction occurs instantaneously with almost quantitative yields. A plausible mechanism is suggested, which involves a 1,2-phenyl migration from the silicon to the adjacent carbon atom.

The tetracationic complex [Rh2(MeCN)2(Naft)4](BF4)4 (Naft = μ-1,8-naphthyridine) was found to be an efficient catalyst for the silylformylation of internal and functionalised alkynes to yield useful synthetic intermediates. The complex exhibits an unprecedented chemoselectivity towards alkyne silylformylation instead of simple hydrosilylation, as well as a good stereoselectivity. The catalytic efficiency of the complex is markedly superior compared to that of previously reported catalysts such as [ Rh + C 7 H 8 BPh 4 - ] or Rh4(CO)12; incidentally, the performance of the latter catalyst was found to vary dramatically with its shelf-life, which indicates that the catalyst evolves with ageing towards other species, most notably higher nuclearity rhodium carbonyl clusters, which are more chemoselective towards silylformylation. Preliminary results on the determination of the catalytically active species in the case of complex [Rh2(MeCN)2(Naft)4](BF4)4 indicate that the complex is reduced in situ to a dirhodium(I) species which maintains the dimeric, lantern-shaped structure.

The silylformylation reaction of unsaturated compounds consists of the rhodium-catalysed addition of a R3Si and a CHO moiety to a carbon–carbon multiple bond. The silylformylation process is applicable to both terminal and internal alkynes and is tolerant towards several functional groups. Many factors can influence the chemoselectivity of the reaction that generally affords β-silylalkenals with high yields and regioselectivity. The β-silylalkenals are polyfunctionalised substrates that can be submitted to several chemical transformations and in particular can undergo fluoride-promoted (TBAF) aryl migration from an aryldimethylsilyl group to the adjacent carbon atom thus generating 2-(arylmethyl)aldehydes, important industrial precursors of perfumes. This silylformylation-aryl migration two-steps sequence can be applied to functionalised alkyne precursors and chemo-, regio- and stereoselectivity of the products can be modulated according to the nature and the position of the functional group. When a good leaving group is present in the ω position of the aliphatic chain of the alkyne cyclisation products are obtained, while α,β-unsaturated aldehydes are generated from propargyl tosylamides, acetates and benzoates. α-Silylmethylene-β-lactams, prepared from p-tosylamides according to silylcarbocyclisation reaction, can be transformed into the corresponding arylmethyl-β-lactams by means of TBAF-induced rearrangement that takes place without involving the lactam ring. A plausible mechanism of the rearrangement reaction is reported that suggests the addition of the fluoride ion to the arylsilicon moiety and the consequent migration of the aryl group to the adjacent carbon atom. Both aryl and heteroaryl substituents can migrate without any loss of configuration further enhancing the high synthetic value of this protocol. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Propargyl functionalised β-silylalkenals were easily prepared starting from suitable propargyl compounds by a silylformylation process. In particular the use of propargyl tosyl amides allowed the synthesis of α,β-unsaturated aldehydes through a two-step sequence of silylformylation–desilylation reactions. TBAF was employed to induce the desilylation process that was performed under very mild experimental conditions and occurred along with an elimination step of the tosylamido moiety affording 2-methylaryl-2-alkenals with good yields and stereoselectivity. When the tosyl amides were reacted with a hydrosilane in the presence of catalytic amounts of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) α-silylmethylene-β-lactams were synthesised through a silylcarbocyclisation process. A high chemoselectivity towards the β-lactam was observed when dialkyl propargyl amides were employed. The obtained β-lactams were easily transformed into the corresponding methylaryl-β-lactams by fluoride induced aryl migration–desilylation with total retention of configuration of the migrating group and complete stereoselectivity towards the more stable β-lactam ( E )-isomer.

α,β-Unsaturated aldehydes are prepared from easily available propargyl amides through a two-step sequence of silylformylation–desilylation reactions. The substituent on the nitrogen atom markedly influences both reactions, β-silylalkenals being formed in the presence of tosyl or tert -butoxycarbonyl protected amines. TBAF is employed to induce the desilylation process that is performed under very mild experimental conditions. A contemporary elimination step occurs when tosylamido aldehydes are reacted affording 2-methylaryl-2-alkenals, while this process can be suppressed changing the functional group to NBOC, thus allowing the formation of β-amino carbonyl compounds.