3-(Aryl)methyl-4-hydroxycoumarins were produced in good to excellent yields by reaction between 4-hydroxycoumarin and (hetero)aromatic aldehydes in the presence of Hantzsch 1,4-dihydropyridine (HEH) which works as an hydride donor (i.e., in a sequential Knoevenagel-reductive Michael addition). The sonochemical-assisted procedure (method B) provides an improved and accelerated conversion when compared to conventional silent reactions (method A). Experiments carried out according to method B showed that the reaction could be more efficiently run in the absence of organic solvents, at 30-40°C in open vessel, without the need of an excess HEH and with simplified work-up and separation procedures.
The thermal reaction between nitrosoarenes and alkynes under alkylating conditions produces Nalkoxyindoles as the major products in moderate to good yields and excellent regioselectivity. Various electrophiles are used affording different N-O-protected hydroxyindoles in a multi-component fashion. Privileged acetylenic subtrates used in reactions with substituted nitrosoarenes are arylalkynes or propiolates. Potentially bioactive compounds and other classes of highly functionalizable indole products were prepared. Reactions between o-carbomethoxy-nitrosoarenes and arylacetylenes provided tricyclic compounds containing an acylaziridine indoline skeleton.
Novel regioselective ring closing ene-yne metathesis provided an efficient access to different substituted 1-benzazepine scaffolds. The reported synthetic approach could also be used as a powerful tool for the selective formation of a highly functionalizable 2-benzazepine core. This synthetic protocol was even proved to be an efficient way to obtain a functionalizable benzazocine derivative. By modifying the structure of the starting materials, the optimized cyclization finally proved to be a suitable technique to obtain five-and six-membered lactams, enhancing the synthetic application of our method. Five-and six-membered lactams were efficiently prepared by ring-closing metathesis involving the loss of ethylene moiety and affording highly functionalizable compounds showing both electron-withdrawing substituents and electron-donor groups.
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