Catalytic Asymmetric Hetero-Diels–Alder Reactions of Carbonyl Compounds and Imines

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 stages of development, and at the beginning of the 21st century catalytic Diels–Alder reactions are one of the main areas of focus. The preparation of numerous compounds of importance for our society is based on cycloaddition reactions to carbonyl compounds and imines. There are several parallels between the reactions of carbonyl compounds and those of imines, which, however, begin to vanish on entering the field of catalytic reactions. Why? From a mechanistic point of view some similarities can be drawn, but the synthetic development of catalytic enantioselective hetero‐Diels–Alder reactions of imines are several years behind those of the carbonyl compounds. For hetero‐Diels–Alder reactions of carbonyl compounds there a number of different chiral catalysts, and great progress has been achieved in developing enantioselective reactions for unactivated and activated carbonyl compounds. In contrast the development of catalytic enantioselective hetero‐Diels–Alder reactions of imines is in its infancy and only few catalytic reactions have been published. This review will focus on the most important developments, and discuss the synthetic and mechanistic aspects of enantioselective hetero‐Diels–Alder reactions of carbonyl compounds catalyzed by chiral Lewis acids. For the hetero‐Diels–Alder reactions of imines, the diastereoselective reactions of optically substrates catalyzed by Lewis acids will be presented first, followed by the catalytic enantioselective reactions.

Asymmetric hetero-Diels–Alder reaction catalyzed by dirhodium(II) carboxamidates

“…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).…”

Direct organocatalytic Wittig/Hetero-Diels-Alder reactions in one-pot: synthesis of highly-substituted tetrahydropyranones

“…[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.…”

“…(CDCl 3 , DEPT) δ 195.9 (C, C=O), 169.4 (2 × C, O=C-O), 142.6 (CH, olefinic-CH), 132.9 (C, C-Br), 132.2 (2 × CH, Ph-CH), 129.7 (2 × CH, Ph-CH), 126.2 (CH, olefinic-CH), 125.1 (C), 76.7 (C, C-OH), 62.6 (2 × CH 2 …”

HDA cycloadditions of 1-diethoxyphosphonyl-1,3-butadiene with nitroso heterodienophiles: A computational investigation

“…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].…”