Dynamic diastereoselectivity during Fe(CO) 3promoted [6 + 2] ene spirocyclization of amide complexes, having a chiral center on the pendant side chain, was investigated to show that the introduction of chirality can dictate the stereochemistry of the cyclization products by strong steric hindrance effect in reaction intermediates. One substrate underwent diastereoselective cyclization to afford two high optical purity products, which might be possible important intermediates for total synthesis of the natural product 18-deoxycytochalasin H. Furthermore, a stepwise second cyclization and a tandem double cyclization mediated by the Fe(CO) 3moiety was investigated.
An intramolecular iron tricarbonyl promoted aldehyde-diene coupling reaction was discovered and investigated to provide spirocyclic or bicyclic products. The ability to stereospecifically build new chiral centers, introduce a functionalizable hydroxyl group and avoid isomerization of products significantly expands the scope of our previously reported [6+2] ene type of spirocyclization and tandem double cyclization.
An all-carbon double cyclization reaction was also investigated, but it could not proceed to give the anticipated cyclized products due to the difficulty in cyclohexadiene double bond migration before the cyclization step. An alternative strategy was designed and is still under investigation.