Which are ubiquitous structural motifs found in bioactive terpenoidsĪnd pharmaceuticals (Figure (Figure1a). Salts as dienophiles, we targeted the synthesis of cis- and trans-fused bicyclic γ- and δ-lactones To test the reactivity of α,β-unsaturated Might emulate the electronic properties of activated dienophiles. The reactivity of α,β-unsaturated acylammonium saltsĪs dienophiles in DA reactions anticipating that these intermediates 8d Inspired by these studies, we sought to explore 8a Building on thisĮarly work, Smith recently employed mixed anhydrides as α,β-unsaturatedĪcylammonium precursors for the direct synthesis of dihydropyranonesĭemonstrated the full potential of chiral, triply reactive, α,β-unsaturatedĪcylammonium salts for the rapid assembly of complex cyclopentanes 8c and optically active γ-lactams and piperidones. Herein, we report the first enantioselective organocatalyticĭA reactions with α,β-unsaturated acid chlorides activated in situ by a chiral isothiourea catalyst.Ĭatalysis was first realized by Fu in asymmetric, net annulations Surprisingly, however, simple acidĬhlorides have yet to be successfully employed in organocatalyzedĭA reactions. Iminium-activated chiral dienophiles, whereas α,β-unsaturatedĪldehydes 7b and indolinones 7c were activated through hydrogen-bonding catalysisīy Rawal and Barbas, respectively. 7 MacMillan and co-workers employedīoth α,β-unsaturated aldehydes 4a and ketones 4b in cycloadditions through 3 Furthermore, enantioselective organocatalyticĭA variants have recently been established using iminium, 4 enamine, 5 bifunctionalĪcid–base catalysis, 6 and hydrogen-bondingĬatalysis. Heterocycles and carbocycles from simple achiral substrates. Generate optically active, architecturally complex, and densely functionalized 2 In particular, catalytic asymmetricĭA reactions are unparalleled in their ability to rapidly and efficiently Is arguably the most versatile and powerful transformation in chemical 1 In this regard, the Diels–Alder (DA) cycloaddition Generate complex and structurally diverse molecular architecturesĪre essential components of modern organic chemistry.
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