Bellinger, Geoffrey C. A.; Campbell, William E.; Giles, Robin G. F., Journal of the Chemical Society. Perkin transactions I, 1982, # 12, p. 2819 - 2826
When 2-ethynylbenzoic acids were treated with a catalytic amount of a rhenium complex, such as ReCl(CO())5, 6-endo cyclization of 2-ethynylbenzoic acids proceeded with a high selectivity to give the corresponding isocoumarins in moderate to good yields.