Short and Versatile Two-Carbon Ring Expansion Reactions by Thermo-Isomerization: Novel Straightforward Synthesis of (±)-Muscone, Nor- and Homomuscones, and Further Macrocyclic Ketones

Thermo-isomerization of 1-vinyl substituted medium-and large-ring cycloalkanol derivatives in a flow reactor system at temperatures of 600 °C to about 650 °C leads directly to the ring-expanded macrocyclic ketones. Alkyl substituents at the vinylic moiety are transferred locospecifically to the ring-expanded ketone as corresponding α-, and β-substituents, respectively. This novel thermal 1,3-C shift reaction therefore provides a new access to short syntheses of many alkyl-substituted macrocyclic ketone derivatives [e.g. (′)-muscone and analogues] in a systematic manner.