Photoinduced [6 + 2] cycloadditions of alkynes to tricarbonyl(cycloheptatriene)chromium(0)

Article abstract of DOI:10.1021/om00037a010

Photolysis of [(η⁶-C₇H₈)Cr(CO)₃] (1) and RC≡ CR (2a, R = Ph; 2b, R = Tol) in toluene or n-hexane results in the formation of [(η²:η⁴-C₉H₈R ₂)Cr(CO)₃] (3a,b) in 70-85% isolated yield via a [6 + 2] cycloaddition reaction. Heating 3a,b in toluene gives the bicyclo[4.2.1]-nona-2,4,7-trienes 4a,b and [(η-C₆H₆Me)Cr(CO)₃]. Photolysis of 1 and excess DMAD (dimethyl acetylenedicarboxylate, 5) in toluene at 0°C yields the bicyclotriene 4c as the major product and small amounts of the arene C₆(CO₂Me)₆ and the [4 + 2] cycloadduct between 4c and 5.