1. Formation of cyclic diterpenoids Acyclic diterpenoids are characterized by six methyl group equivalents including 5 2ndry, 1 primary methyl groups. Labdanes are characterized by six methyl group equivalents including 3 3ry, 2 2ndry, 1 primary methyl groups. Pimaranes and abietanes are characterized by five methyl group equivalents including 4 3ry and a vinyl group in pimaranes, 3 3ry and an isopropyl group in abietanes. Kauranes are characterized by four methyl group equivalents including 3 3ry and 1 2ndry methyl groups.

2. Labdane

4. Abietane

5. Kaurane

6. Clerodane