Cleavage of a chiral auxiliary using RCM on an especially sterically crowded alkene: Syntheses of chiral carbo- and heterocycles

Chiral 1,5-, 1,6-, and 1,7-dienes generated in 3–4 steps from chiral auxiliary p-menthane-3-carboxaldehyde undergo RCM with notable discrepancies in reactivity depending on the nature and number of substituents flanking the central double bond. The chiral auxiliary is thus cleaved releasing a carbo- or heterocycle in the process. Special features concerning the RCM on these especially crowded systems are discussed.