Domino Addition/Cycloisomerization Reactions of 2-Alkynyl-Arylaldehydes: Silver Catalyzed Synthesis of 1,3-Dicarbo-Substituted Isochromenes

One of the most efficient methods for the construction of 1-substituted isochromenes (and related heteroaryl compounds) is the metal catalyzed regioselective domino cycloisomerization/nucleophilic addition reaction of a 2-alkynyl(hetero)arylaldehyde in the presence of a suitable nucleophile.(1) The reaction with oxygen nucleophiles is the probably the most studied one. Several metal catalyst have been used, and our group recently gave a contribution in the field of silver catalyzed(2) synthesis of 1-alkoxyisochromenes.(3) Conversely, the reaction with carbon nucleophiles, and in particular with enolizable carbonyl compounds, is relatively less investigated.(4) We report here our recent results regarding the silver catalyzed synthesis of 1,3-dicarbo-substituted isochromene derivatives starting from 2-alkynyl(hetero)arylaldehydes and enolizable carbonyl compounds.(5) The reaction proceeded in a cascade fashion under mild reaction conditions with absolute regioselectivity and moderate-to-good yields. In some cases, the reaction produced unexpected diastereoisomeric couple of homodimeric products. The divergent formation of the 1-carbosubstituted isochromenes and the alternative homodimeric products has been tentatively explained by some experiments and two conceivable competitive paths have been proposed

Silver Triflate/p-TSA Co-Catalysed Synthesis of 3-Substituted Isocoumarins from 2-Alkynylbenzoates

In this paper, we describe the silver triflate/p-toluensulfonic acid co-catalysed synthesis of seventeen isocoumarins and two thieno[2,3-c]pyran-7-ones starting from 2-alkynylbenzoates and 3-alkynylthiophene-2-carboxylates, respectively. The reactions proceed with absolute regioselectivity under mild reaction conditions and low catalyst loading, to give the desired products in good to excellent yields. A conceivable reaction mechanism is proposed and supported by isotope-exchange tests, and 1H NMR studies and ad-hoc experiments

Gold-catalyzed cascade reactions of 4H‐furo[3,2‐b]indoles with allenamides: synthesis of indolin-3-one derivatives

2-Spirocyclopentane-1,2-dihydro-3H-indol-3-ones (namely, spiropseudo-indoxyls) constitute privileged scaffolds in organic synthesis and represent core components of different indole alkaloids (e.g. aristotelone and brevianamide A) and of molecules applied as functional dyes. In addition, they have found also an application as useful intermediate in the total synthesis of minfiensine. Taking into account these premises and our expertise in gold-catalyzed indole functionalization, we tested the reactivity of 4H-furo[3,2-b]indoles in the presence of electrophilic gold(I) activate \u3c0-systems (allenamides) with the aim to develop a new cascade process for the synthesis of these relevant scaffolds (Scheme 1). In this poster we present the obtained results together with the scope and limitation of the method and the proposed reaction mechanism

Catalytic transformations of indoles: recent achievements and new perspectives for the synthesis of complex indole derivatives

Transformation of simple indoles into (polycyclic) complex scaffolds has become the object of intensive studies in synthetic organic chemistry due to ubiquitous occurrence of indole core in the structure of relevant molecules In particular, catalytic-promoted manipulation of indoles have become an incomparable tool to increase indole structural complexity working under exceedingly mild conditions and in a regio- and stereo-controlled fashion. In this context we reported in the last years the synthesis of complex carbazole derivatives through gold-catalyzed (4+2) cycloaddition reactions of vinylindoles with different \u3c0-systems and the functionalization of structurally simple indoles with challenging metal-activated electrophiles. Taking into account these premises, this oral communication will deal with our recent achievements in the field of cycloaddition reactions involving vinylindoles as 4\u3c0 systems and in gold-catalyzed cascade reactions on indole-based scaffolds. In particular we were able to extend cycloaddition of vinylindoles besides (4+2) processes to synthetize cyclohepta[b]indoles. Moreover, we explored the reactivity of 4H-furo[3,2-b]indoles with gold-activated \u3c0-systems to synthetize 2-spiro-3-oxindoles and 2-alkenyliden-indolin-3-ones selectively. Advantages of our methods as well as limitations and future perspectives will be discussed

Frequency Dielectric Spectroscopy and Dissipation Factor Measurements during Thermal Cycles on Different Types of MV Cable Joints

Results of periodic measurements of Dissipation Factor (DF) and Frequency Dielectric Spectroscopy (FDS) on Medium Voltage (MV) cables during thermal cycles, are reported and discussed in this paper. Twelve cables equipped with different types of joints were connected together to form a ring in short-circuit. The ring was energized at rated voltage and current. Temperature cycles with a period of one day (11 hours of heating) were applied by controlling the current. Periodically, each cable was tested separately using both DF and FDS techniques to monitor the ageing progression. This paper focuses on the experimental results obtained testing six new cables provided by different types of new joints while the other six coming from the field, are not considered here. Results obtained testing the six new cables indicate that FDS evaluation is a reliable tool to distinguish the aging progression of the insulation from the seasonal and reversible changes while DF values recorded at different voltage levels show a non-regular behavior particularly in XLPE cables. These results clearly suggest that the systematic use of FDS in condition assessment of underground cables can provide more information on the ageing progression than the traditional DF measurements

Mild AgOTf Catalyzed Synthesis of 1-Carbosubstituted-isochromenes

One of the most efficient methods for the construction of 1-substituted isochromenes (and related heteroaryl compounds such as pyrano[4,3-b]pyridines) is the metal catalyzed regioselective domino cycloisomerization/nucleophilic addition reaction of a properly substituted 2-alkynyl(hetero)arylaldehyde in the presence of a suitable nucleophile. The reaction with oxygen nucleophiles is the most studied and several metal catalyst, i.e., Pd(II), Cu(I), Ag(I), Au(I) and In(III), demonstrated to be effective for synthesis of 1-alkoxyisochromenes. Conversely, the reaction with carbon nucleophiles, and in particular with enolizable carbonyl compounds, is relatively less investigated. In connection with our ongoing interest in the development of silver catalysed domino approaches involving alkyne derivatives, we report here a silver catalyzed domino approach to isochromenes starting from 2-alkynyl(hetero)arylaldehydes and enolizable carbonyl compounds. The reaction yields range from fair to very good. The reaction mechanism is also investigated and the formation of by-products discussed