Thermische Umlagerungen von (+)‐Isopinocampheol und (−)‐Isopinocamphon

Short‐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‐Δ 8 ‐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‐Δ 8 ‐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.