AbstractShort‐path thermolysis of (+)‐isopinocampheol (1) at about 330° in the gas phase yields mainly (—)‐(3 S, 4 S)‐3, 7‐dimethyl‐octa‐1,6‐dien‐4‐ol (2). Longer heating of 2 at about 290–330° yields as main products the diastereoisomeric hydroxy‐Δ8‐iridenes 3, 4 and 5 in ratios dependent on temperature. Above 400°, formation of 4‐methylpent‐3‐en‐1‐al (7) and 2‐butene (8) predominates. Compounds 7 and 8 also appear as the stable final thermolysis products of 3, 4 and 5 above 500°. Small quantities of (+)‐iso‐dihydrocarveol (6) always occur as by‐product in the thermolysis of 1.Short‐path thermolysis of (—)‐isopinocamphone (13) at about 430° leads, with slight epimerisation, to the three diastereoisomeric oxo‐Δ8‐iridenes 15, 18 and 17 via (+)‐(3 S)‐3, 7‐dimethylocta‐1, 6‐dien‐4‐one (14). Structure and stereochemistry of all reaction products are established spectroscopically and chemically.