Calcium-Catalyzed Formal [2+2+2] Cycloaddition

• Published in: Chemistry : a European journal 2015-04, Vol.21 (17), p.6371-6374
• Main Authors: Meyer, Vera J., Ascheberg, Christoph, Niggemann, Meike
• Format: Article
• Language: English
• Subjects: Aldehydes; allenes; Assembly; Calcium; calcium catalysis; carbocations; Catalysts; Chemistry; Cycloaddition; cycloisomerization; enynes; Gold; Precursors; Proposals
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201500181

A formal intermolecular [2+2+2] cycloaddition reaction of enynes to aldehydes is presented, which can be realized in the presence of a simple and benign calcium catalyst. The reaction proceeds with excellent chemo, regio‐ and diastereoselectivity and leads to a one‐step assembly of highly interesting bicyclic building blocks containing up to three stereocenters from simple precursors via a new type of skeletal rearrangement of enynes. The observed diastereoselectivity is accounted for by two different mechanistic proposals. The first one engages mechanistic prospects arising from a gold catalyzed reaction in the absence of the stabilizing gold substituent. The second proposal involves an unprecedented cyclization–carbonyl allene ene reaction–hydroalkoxylation cascade. A simple catalyst for a complex task: A formal intermolecular [2+2+2] cycloaddition reaction of enynes to aldehydes was realized in the presence of a simple and benign calcium catalyst (see scheme). The reaction proceeds with excellent chemo‐, regio‐, and diastereoselectivity and leads to a one‐step assembly of highly interesting bicyclic building blocks containing up to three stereocenters from simple precursors via a new type of skeletal rearrangement of enynes.