All compounds except trans—trans iridodial have been described previously (11, 21).5 The identity and purity of compounds were verified based on NMR spectra recorded on a Bruker 400-MHz/54-mm UltraShield Plus long hold time automated spectrometer at 400 MHz (1H NMR) and 100 MHz (13C NMR). The residual solvent peak of chloroform was adjusted to δ 7.26 (1H NMR) and 77.16 (13C NMR). Assignment of peaks was aided by two-dimensional 1H-COSY and 1H-13C-HSQC data (supplemental information).