To do this, authentic standards of the side products needed to be prepared. Mass spectrometry data strongly suggested that the minor products of the CrISY reaction were alternative stereoisomers of nepetalactol and iridodial. Standards of 7S-nepetalactol isomers can be obtained via diisobutylaluminum hydride (DIBAL-H) reduction of the cis–cis, cis–trans, trans–cis, and trans—trans nepetalactone isomers (Fig. 3a) (11, 21–23).5 However, the trans–trans isomer could not be isolated in sufficient quantities from plants and was instead generated by base-catalyzed isomerization of the cis–cis isomer, an inefficient uphill process with only 10% yield (21). Both nepetalactones with the ring fusion in trans configuration open directly to the corresponding iridodials (21) because of instability of the strained ring. Iridodials in cis–cis and cis–trans configuration were obtained by incubating the respective nepetalactols in 100 mm HCl overnight. The stereocenter at C1 in nepetalactol, which equilibrates in aqueous solution (21), and the stereocenter forming at C4 upon conversion to iridodial were not resolved. Each of these standards could be separated on achiral and chiral GC-MS columns.