Trans—trans nepetalactone was reduced to trans—trans iridodial ([1R,2S,5S]-2-methyl-5-[1-oxopropan-2-yl]cyclopentane-1-carbaldehyde) following the procedure described for the cis—cis isomer. Only the major stereoisomer at C7 (approximately 90%) could be assigned. 1H NMR: δ 9.63 (1H, d, J = 2.1 Hz, C6), 9.59 (1H, d, J = 3.6 Hz, C9), 2.59 (1H, dddd, all J≈8 Hz, C5), 2.40 (1H, ddq, J = 2.1/7.3/7.3 Hz, C7), 2.18–2.13 (1H, m, C2), 2.16–2.08 (1H, m, C1), 1.99–1.91 (1H, m, C4), 1.95–1.86 (1H, m, C3), 1.57–1.49 (1H, m, C4), 1.39–1.33 (1H, m, C3), 1.082 (3H, d, J = 7.2 Hz, C8), 1.078 (3H, d, J = 6.4 Hz, C10). 13C-NMR: δ 204.08 (C6 or C9), 203.46 (C6 or C9), 63.48 (C1), 50.86 (C7), 41.26 (C5), 37.18 (C2), 34.00 (C3), 29.58 (C4), 19.34 (C10), 12.37 (C8). Acid opening of cis–cis and cis—trans nepetalactol was achieved by treatment with 100 mm hydrochloric acid as described for cis—trans nepetalactol.5