Metal-Mediated [6 + 2] Cycloadditions of Alkynes to Cycloheptatriene and N-Carbethoxyazepine

Nucleophilic addition reactions of bridged triene η6-chromiumtricarbonyl complexes

“…We chose to commence our study by preparing bridged complexes 6 and 7 from cycloheptatriene complex 5 10 using the photolytic conditions described by Sheridan and co-workers, Scheme 3. 7 Reaction of 5 in degassed hexane at room temperature using a 125 W medium pressure mercury lamp gave 6 in good yield, although we found the corresponding preparation of 7 more problematic (the reported yield is 85%). Analogous reactions involving bis-ethers or silyl ethers of 1,4-dihydroxybut-2-yne were not successful in our hands.…”

“…12 Bearing in mind the transformations described above, the potential for this methodology to provide a new route to anatoxin seemed clear, providing that analogous chemistry of aza-bridged complexes could be accomplished. With this in mind we prepared the known complexes 25 and 26, 13,7 and then established that addition of lithiated ethyl vinyl ether resulted in formation of methyl ketone 27 in reasonable yield, Scheme 7.…”

“…3 We became interested in exploring the nucleophilic addition chemistry of a much less common type of organometallic system, namely the bridged complexes generated by formal [6 ϩ 2] cycloaddition of seven-membered η 6 -chromiumtricarbonyl complexes 3, Scheme 2. [4][5][6][7] We were aware of no chemistry of the unusual η 6 -complexes 4, other than de-metallation to provide bridged products that have applications in natural products synthesis. 5 It seemed reasonable that the activating effect of the chromium tricarbonyl unit present in the bridged complexes would enable nucleophilic addition to these compounds in a similar fashion to that seen with the arene complexes.…”

Synthesis of New Functionally Substituted 9-Azabicyclo[4.2.1]nona-2,4,7-trienes by Cobalt(I)-Catalyzed [6π + 2π]-Cycloaddition of N-Carbocholesteroxyazepine to Alkynes

“…According to previously published data, an efficient method for the synthesis of 9-azabicyclo[4.2.1]nonane cages is based on the cycloaddition reactions of N -substituted azepines catalyzed by transition metal complexes [ 30 ]. However, these reactions have been studied rather superficially, being addressed in a few publications on the photoinduced cyclo-codimerization of tricarbonyl(η 6 - N -carboalkoxyazepine)chromium(0) [ 31 , 32 , 33 , 34 , 35 , 36 ] and tricarbonyl(η 6 - N -cyanoazepine)chromium(0) [ 37 ] with alkenes and alkynes. Meanwhile, data on catalytic versions of these reactions are scarcely reported in the literature, except for two examples of Cr(0)-catalyzed cycloaddition of N -carbomethoxyazepine [ 34 ] and N -carbethoxyazepine [ 38 ] to ethyl acrylate ( Scheme 1 ).…”

Cobalt(I)-Catalyzed [6π + 2π] Cycloaddition of 1,2-Dienes and 1,3-Diynes to N-Carbocholesteroxyazepine in the Synthesis of Previously Undescribed Heterofunctional 9-Azabicyclo[4.2.1]nonadi(tri)enes

“…Meanwhile, the synthesis of 9-azabicyclo[4.2.1]­nonanes applying metal-promoted and metal-catalyzed cycloaddition reactions of N-substituted 1 H -azepines remains almost unexplored field. So far, there are only a few reported studies on the photochemical cyclocodimerization of tricarbonyl­(η 6 - N -carboalkoxyazepine)­chromium­(0) and tricarbonyl­(η 6 - N -cyanoazepine)­chromium­(0) with alkenes, 1,3-dienes, and alkynes. Moreover, before our studies started, , there had been no information available on the catalytic transformations of N-substituted azepines, except for two reactions of Cr(0)-catalyzed cycloaddition of N -carbomethoxyazepine and N -carbethoxyazepine to ethyl acrylate (Scheme ).…”