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.

Synthesis of Functionalized Isoindolinones via Calcium Catalyzed Generation and Trapping of N-Acyliminium Ions

“…Our group has a growing interest in developing methodology to catalytically generate reactive intermediates and in particular using calcium complexes to mediate these processes. , Calcium represents a relatively underexplored metal in catalysis; however, over the past decade, there has been an increase in interest in exploring the reactivity of calcium, which has resulted in a wealth of innovative uses for this abundant element. − We, and others, have recently reported the use of Ca­(NTf 2 ) 2 as an excellent catalyst to produce N -acyliminium ions from readily available 3-hydroxyisoindolinones. Due to the importance of these scaffolds in both total synthesis − and medicinal chemistry, we wanted to explore this reaction further.…”

Carbon–Carbon and Carbon–Heteroatom Bond-Forming Transformations Catalyzed by Calcium(II) Triflimide

“…33 In the same vein, the Niggemann group could imitate typical transition-metal-catalyzed [2+2+2] cycloadditions 34 with Ca(NTf 2 ) 2 (Scheme 15). 35 Dihydropyrans were obtained in good yields and a complete control of the diastereoselectivity from enynols and aldehydes. The reaction proceeds at room temperature and proved to be compatible with a large scope of aldehydes, but not with ketones.…”