161375-33-3Relevant academic research and scientific papers
Metal-mediated [6 + 2] cycloadditions of alkynes to cycloheptatriene and N-carbethoxyazepine
Chaffee, Karen,Huo, Pei,Sheridan, John B.,Barbieri, Anthony,Aistars, Arnis,Lalancette, Roger A.,Ostrander, Robert L.,Rheingold, Arnold L.
, p. 1900 - 1907 (2007/10/02)
UV photolysis of [(η6-C7H7R)Cr(CO)3] (1, R = H, Ph, CH{CO2Me}2) and R?C=CR? (R? = Ph, Tol, SiMe3, Et) in toluene or n-hexane gives the [6 + 2] cycloadducts [(η2:4-C9H7{R}R?2)Cr(CO)3] (2). Heating 2 in toluene releases the 7,8-disubstituted bicyclo[4.2.1]nona-2,4,7-trienes 3 and [(η6-C6H5Me)Cr(CO)3]. Irradiation of solutions of 1 and dimethyl acetylenedicarboxylate at O °C yields the bicyclotriene as the major product but no organometallic complex. The diphenyl derivative 2a undergoes a reversible intramolecular metal migration to the η6-aryl species 4. Irradiation of the azepine complex [(η6-C6H6N{CO2Et})Cr(CO) 3] (5) and R?C≡CR? (R? = Ph, SiMe3) in toluene also forms [6 + 2] cycloadducts [(η2:4-C8H6N{CO2Et}R? 2)Cr(CO)3] (6). The heterobicyclotrienes 7 are isolated from 6 by treatment with iodine (R? = SiMe3) or by heating in toluene (R? = Ph). X-ray crystal structures are reported for 6b (R? = SiMe3) [orthorhombic, P212121, a = 8.871(1), b = 10.148(1), and c = 26.017(4) A, R = 0.041 for 2500 independent reflections] and a byproduct (8) that results from the endo [6 + 4] cycloaddition of N-carbethoxyazepine to 5; monoclinic, P21/c, a = 10.665(9), b = 14.976(7), and c = 13.004(7) A?,β= 100.05(7)°, R = 0.047 for 1044 independent reflections. Heating cycloheptatriene and alkynes R?≡CR? (R? = SiMe3, Me, Et) in dibutyl ether with a catalytic amount of Cr(CO)6 or Fe2(CO)9 also gives good yields of the [6 + 2] cycloadducts 3, whereas the thermal reaction with dimethyl acetylenedicarboxylate in the presence of Cr(CO)6 gives the known norcaradiene [4 + 2] adduct 9.
