Calcium‐Catalyzed Formal [2+2+2] Cycloaddition |
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Authors: | Dr Vera J Meyer Christoph Ascheberg Prof Meike Niggemann |
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Institution: | Institute of Organic Chemistry, RWTH Aachen University, Landoltweg 1, 52074 Aachen (Germany) |
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Abstract: | 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. |
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Keywords: | allenes calcium catalysis carbocations cycloaddition cycloisomerization enynes |
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