Insertion Reactions on Carbopalladated Benzyne: From Eight- to Nine- and Ten-Membered Palladacycles. Applications to the Synthesis of N‑Heterocycles

The ortho-metalated complexes [Pd­{<i>C</i>,<i>N</i>-C₆H₂CH₂CH₂NH₂-2,(OMe)₂-4,5}­(μ-Br)]₂ (<b>A</b>) and [Pd­{<i>C</i>,<i>N</i>-C₆H₄CH₂CMe₂NH₂-2}­(μ-Cl)]₂ (<b>B</b>), derived from homoveratrylamine and phentermine, respectively, react with benzyne generated in situ, to afford the previously reported eight-membered palladacycles <b>1a</b> and <b>1b</b>, respectively, arising from the insertion of one molecule of the aryne into the Pd–C_aryl bond. Complexes <b>1</b> react with isocyanides RNC (R = Xy, ^tBu) in 1:4 molar ratio to give the nine-membered iminoacyl palladacycles [Pd­(<i>C</i>,<i>N</i>-C­(NR)-C₆H₄{C₆H₂CH₂CH₂NH₂-2­(OMe)₂-4,5)-2′})­Br­(CNR)] (R = Xy (<b>2a)</b>, R = ^tBu (<b>3a</b>)) and [Pd­(<i>C</i>,<i>N</i>-C­(NXy)-C₆H₄{C₆H₄CH₂CMe₂NH₂-2)-2′})­Cl­(CNR)] (R = Xy (<b>2b</b>), R = ^tBu (<b>3b</b>)). Complex <b>2a</b> decomposes in refluxing toluene to afford palladium(0) and 7,8-dihydro-10,11-dimethoxy-5-[(2,6-dimethylphenyl)­imino]­dibenzo­[<i>c</i>,<i>e</i>]­azocinium triflate (<b>4a</b>). When <b>1b</b> reacts with TlOTf and XyNC (molar ratio 1:2:2), 7,8-dihydro-5-[(2,6-dimethylphenyl)­imino]-7,7-dimethyl­dibenzo­[<i>c</i>,<i>e</i>]­azocinium triflate (<b>4b</b>) is obtained, resulting from an isocyanide insertion/C–N reductive coupling sequence. The amidinium triflates <b>4a</b> and <b>4b</b> present <i>E</i>/<i>Z</i> isomerism in CHCl₃ solution. The stoichiometric carbonylation of dinuclear complexes <b>1</b> renders, after depalladation, the lactams 7,8-dihydro-10,11-dimethoxy­dibenzo­[<i>c</i>,<i>e</i>]­azocin-5­(6<i>H</i>)-one (<b>5a</b>) and 7,8-dihydro-7,7-dimethyl­dibenzo­[<i>c</i>,<i>e</i>]­azocin-5­(6<i>H</i>)-one (<b>5b</b>) or the previously reported ester derivative [2′-MeO₂CC₆H₄C₆H₂­CH₂CH₂NH₃-2-(OMe)₂-4,5]Br (<b>6a</b>) or [2′-MeO₂CC₆H₄C₆H₄­CH₂CMe₂NH₃-2]Cl (<b>6b</b>), depending on the reaction conditions. The eight-membered palladacycles <b>1</b> react with alkenes to afford complexes [PdCl₂(biarylamine)₂] (<b>7a</b>, <b>7b</b>, <b>8b</b>), containing the Heck-type functionalized phenethylamines. The reaction of <b>1b</b> with ^tBuOK in toluene at 95 °C, under a N₂ atmosphere, affords 6,7-dihydro-6,6-dimethyl-5<i>H</i>-dibenz­[<i>b</i>,<i>d</i>]­azepine (<b>9b</b>), resulting from a C–N reductive coupling process. The crystal structures of compounds [Pd­(<i>C</i>,<i>N</i>-C­(NXy)-C₆H₄­{C₆H₂CH₂CH₂NH₂-2­(OMe)₂-4,5)-2′})­Br­(CNXy)]·CH₂Cl₂·1/2H₂O (<b>2a</b>·CH₂Cl₂·1/2H₂O), [Pd­(<i>C</i>,<i>N</i>-C­(NXy)-C₆H₄­{C₆H₄CH₂CMe₂NH₂-2)-2′})­Cl­(CNXy)]·0.72Et₂O·0.28CHCl₃ (<b>2b</b>·0.72Et₂O·0.28CHCl₃), and 7,8-dihydro-10,11-dimethoxy­dibenzo­[<i>c</i>,<i>e</i>]­azocin-5­(6<i>H</i>)-one (<b>5a</b>) have been determined by X-ray diffraction studies