Bromolactonization occurs with TMS bromide in the presence of N-ethyldiisopropylamine in DMSO to give a bridged bicyclic lactone: Heterocycles, 31, 987 (1990). For Pd catalyzed lactonization in the presence of oxygen, giving a mixture of [3.2.1] and [2.2.2] bicyclic unsaturated lactones, see: J. Org. Chem., 60, 5298 (1995).
