Cycloocta pyrroles

Pyrroles 36 with n = 4, 8 have been isolated and characterized (Table XIX). These include4,5,6,7,8,9-hexahydro-l//-cycloocta >]pyrrole (yield 60%, optimal synthesis time about 3 hr), which shows a reduced stability as compared with other pyrroles of this series (n = 2,3,8). Nevertheless, the reason for the unsuccessful attempt to synthesize this compound from cyclooctanone oxime and acetylene [87JCS(P 1)2829] is not very clear. 

A 50-ml Schlenck tube equipped with a stirring bar containing bis(l,5-cyclooc-tadiene)-nickel(O) (4.48 mmol), 2,2 -bipyridyl (4.48 mmol), and 1,5-cycloocta-diene (4.48 mmol) was treated with 5 ml of DMF and the ensuing deep blue/ purple solution stirred at 60°C for 30 minutes. The mixture was then treated with 2,7-diiodo-9,9-bis(2-ethylhexyl)fluorene (1.68 mmol) and 2,5-bis(p-bromo-phenyl)-A-(p-hexylphenyl)pyrrole (0.56 mmol) in 20 ml of toluene by syringe and then stirred for 5 days at 75°C. The solution was cooled to ambient temperature and precipitated into a mixture of 100 ml apiece of methanol and acetone and 5 ml concentrated hydrochloric acid. After of the mixture was stirred for 2 hours, it was filtered the solid residue was dissolved in chloroform and re-precipitated in methanol and acetone solution, and re-filtered. The residue was successively washed with methanol, water and methanol, and dried the product was isolated having a Mj, of 47,200 daltons. 

In contrast with fluorenylidene, singlet-triplet equilibrium in the carbene derived by photoelimination of nitrogen from the diazodihydroboraanthracene (57) is slow. Direct irradiation affords singlet carbene which reacts with propan-2-ol to give the ether (58), whereas 2-acetonaphthone-sensitized irradiation yields triplet carbene which undergoes non-stereospecific addition to alkenes. Products obtained by irradiation of 3-diazo-2,5-diphenylpyrrole can arise via the intermediacy of singlet and triplet carbenes. Decomposition of the pyrrole (59) in the presence of benzene, for example, yields the 2H-cycloocta[c]pyiTole (60) as the major product. 

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