Organocatalysed pericyclic reactions: Combining old and new chemistry producing a powerful tool (New)
The goal of this research project is to develop new methodologies that will enable the synthesis of functionalised and optically active building-blocks through unprecedented organocatalysed pericyclic processes. The main transformations to be studied are: sigmatropic rearrangements, electrocyclic rearrangements, cheleotropic additions, and ene reactions. In all cases, the proposed methodology will enable the formation of multiple controlled stereocenters from simple and easily accessible starting materials.
The first example of this methodology will be performed using [3,3]-sigmatropic rearrangements. Starting with a substituted .,d-enone, a [3,3]-sigmatropic rearrangement initiated by a chiral amine catalyst (such as a proline type catalyst) would generate a new ketone, possessing two new chiral centers, through an enamine intermediate. With an oxygen atom correctly positioned, a new carbonyl could be formed. An intramolecular addition of a chiral enamine onto this newly formed carbonyl would generate a cyclised a,ß-unsaturated ketone through an intramolecular aldol condensation. In the latter case, the cyclic, substituted and optically active enone would be formed from an acyclic precursor generating up to three new stereocenters.
Extending this idea further would enable the formation of substituted and optically active cyclopentenones. To do so, the use of a keto-ether is envisioned. Chiral amine could catalyse a [3,3]-sigmatropic rearrangement of the keto-ether. This would generate the carbonyl intermediate. Condensation of the chiral enamine on the newly formed carbonyl, followed by loss of a water molecule, would then generate the desired 5-membered ring.
I also would like to investigate the organocatalysed electrocyclisation of substituted dienones. An enamine generated from a chiral amine catalyst and a dienone could rearrange to a 6-membered ring from which a ketone could be formed by a-alkylation of the intermediate enamine. This methodology would enable the formation of optically active 6-membered rings, with up to three new stereocenters, from acyclic and achiral precursors in a single step.
Overall, this methodology has great potential for the synthesis of optically active 5 and 6-membered rings. The proposed organocatalytic methodology will give access to highly useful building blocks in one step from simple and achiral starting materials. Moreover, the formation of up to three contiguous and controlled stereocenters will be possible.
