Abstract:Asymmetric catalysis is a challenge for chemists: How can we design catalysts to achieve the goal of forming optically active compounds? This review provides the reader with an overview of the development of catalytic asymmetric hetero‐Diels–Alder reactions of carbonyl compounds and imines. Since its discovery, the Diels–Alder reaction has undergone intensive development and is of fundamental importance for synthetic, physical, and theoretical chemists. The Diels–Alder reaction has been through different stage… Show more
“…Since Danishefsky's initial report of cyclo-addition reactions with 1-methoxy-3-[(trimethylsilyl)oxy]-butadiene (''Danishefsky's diene''), this transformation has been a standard for evaluation of enantiocontrol with chiral Lewis acid catalysts (7)(8)(9)(10)(11)(12)(13). Although high selectivity has often been achieved, a high catalyst loading (TON Յ50) is required in virtually all cases (14). As a Lewis acid, the catalyst activates the aldehyde by coordination with a lone pair of electrons on the carbonyl oxygen (15,16).…”
Chiral dirhodium(II) carboxamidates are highly efficient catalysts for reactions between a variety of aldehydes and activated dienes. Catalyst loadings as low at 0.01 mol % have been realized with enantioselectivities up to 97%. Kinetic investigations reveal a pronounced electronic influence on the rate of the hetero-DielsAlder reaction with a Hammett value of ؉1.9 (versus ؉ ). Inhibition of the catalyst by reactant aldehyde is apparent, but reactions show first-order dependence on aldehyde and diene, and there is a variable dependence on catalyst.
“…Since Danishefsky's initial report of cyclo-addition reactions with 1-methoxy-3-[(trimethylsilyl)oxy]-butadiene (''Danishefsky's diene''), this transformation has been a standard for evaluation of enantiocontrol with chiral Lewis acid catalysts (7)(8)(9)(10)(11)(12)(13). Although high selectivity has often been achieved, a high catalyst loading (TON Յ50) is required in virtually all cases (14). As a Lewis acid, the catalyst activates the aldehyde by coordination with a lone pair of electrons on the carbonyl oxygen (15,16).…”
Chiral dirhodium(II) carboxamidates are highly efficient catalysts for reactions between a variety of aldehydes and activated dienes. Catalyst loadings as low at 0.01 mol % have been realized with enantioselectivities up to 97%. Kinetic investigations reveal a pronounced electronic influence on the rate of the hetero-DielsAlder reaction with a Hammett value of ؉1.9 (versus ؉ ). Inhibition of the catalyst by reactant aldehyde is apparent, but reactions show first-order dependence on aldehyde and diene, and there is a variable dependence on catalyst.
“…[1][2][3] The extraordinary range of applications of enantio-pure hetero-Diels-Alder (HDA) adducts has stimulated the search for efficient chiral catalysts for cycloadditions between dienes and carbonyl dienophiles. Many catalysts, including chiral aluminium, boron, titanium, chromium, europium, or ytterbium complexes, can accelerate the reaction of unactivated aldehydes with activated dienes to generate high yields with excellent stereochemical control.…”
A practical and environmentally friendly organocatalytic one-pot strategy designed to furnish the hetero-Diels-Alder products was shown to be effective in the preparation of disubstituted tetrahydropyranones in a highly selective manner. (S)-1-(2-pyrrolidinylmethyl)pyrrolidine catalyzed an asymmetric assembly reaction involving a hetero-Diels-Alder reaction between alkylidene-and arylidene-acetones generated in situ from Wittig reactions with diethyl ketomalonate to furnish the substituted tetrahydropyranones in moderate to very good yields with moderate enantioselectivity.
“…By contrast to the typical Diels-Alder reaction, at least one of the six reacting carbons is replaced by a heteroatom (mainly oxygen, nitrogen or sulfur) [2]. Among these reactions, HDA reactions of nitroso compounds have been studied as an entry towards aza-heterocycles [2,3].…”
a b s t r a c tThe hetero Diels-Alder (HDA) reactions of 1-diethoxyphosphonyl-1,3-butadiene with various nitroso dienophiles have been studied at the B3LYP/6-31G** level. Structural, energetic and electronic properties are discussed. These cycloadditions with nitroso dienophiles are characterized by a total proximal regioselectivity and an endo selectivity. The influence of the nitroso substitution on the activation barrier and the regiochemistry of the reaction is presented. The analysis of the chemical rearrangement along the intrinsic reaction pathway (IRC), based on bond order and on natural bond orbital (NBO) calculations, emphasizes the polar nature of these cycloadditions. Despite the early and the cyclic nature of the corresponding transition states, a two-center interaction governs this mechanism: these cycloadditions are Polar Diels-Alder reactions (P-DA).
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