title: Calcium-catalyzed formal [2+2+2] cycloaddition.
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.
authors: Institute of Organic Chemistry, RWTH Aachen University, Landoltweg 1, 52074 Aachen (Germany).
authors: Vera J
authors: VJ
authors: Meyer
authors: Christoph
authors: C
authors: Ascheberg
authors: Meike
authors: M
authors: Niggemann
keywords: allenes; calcium catalysis; carbocations; cycloaddition; cycloisomerization; enynes