Conjugate addition cycloadditions

Keywords Aminocatalysis Conjugate addition Cycloaddition Ttninintn ion Organocatalysis... 

The conjugate addition/cycloaddition manifold is highly influenced by a number of factors, including the pyrrole complex, electrophile, solvent, temperature, and, in some cases, concentration. The key for predicting the course of the reaction between the olefin and an Ti2-pyrrole complex is the coordination site of the metal at the time of electrophilic attack (Figure 19). Although the intermediate azomethine ylide, where... 

Methacryhc acid and its ester derivatives are Ctfjy -unsaturated carbonyl compounds and exhibit the reactivity typical of this class of compounds, ie, Michael and Michael-type conjugate addition reactions and a variety of cycloaddition and related reactions. Although less reactive than the corresponding acrylates as the result of the electron-donating effect and the steric hindrance of the a-methyl group, methacrylates readily undergo a wide variety of reactions and are valuable intermediates in many synthetic procedures. 

Chiral Cu(ll)-complexes ofbis-oxazolines as Lewis acids for catalyzed cycloaddition, carbonyl addition, and conjugate addition reactions 99PAC1407. 

Gothelf presents in Chapter 6 a comprehensive review of metal-catalyzed 1,3-di-polar cycloaddition reactions, with the focus on the properties of different chiral Lewis-acid complexes. The general properties of a chiral aqua complex are presented in the next chapter by Kanamasa, who focuses on 1,3-dipolar cycloaddition reactions of nitrones, nitronates, and diazo compounds. The use of this complex as a highly efficient catalyst for carbo-Diels-Alder reactions and conjugate additions is also described. 

Introduction of an additional methyl group on the donor atom of TMM moiety gives a low 33% yield of the perhydroindans (49, X=H2) and (50, X=H2) with substantial production of the diene by-products [24]. However, it is still remarkable that the reaction works at all since the corresponding intermolecular cycloaddition failed. Incorporation of a carbonyl moiety adjacent to the donor carbon atom doubles the yield of the cycloadducts to 66% (Scheme 2.15). This so-called acyl effect works by making the donor carbon of the TMM unit "softer," thus facilitating the initial step of the conjugate addition, as well as inhibiting base-induced side reactions [22]. 

In numerous synthetic studies,9" 6 100 it has been demonstrated that porphyrins react at the chromophore periphery in cycloaddition reactions, rearrangements, conjugative additions and substitution reactions to yield interesting porphyrin derivatives. Thus, metal-free protoporphyrin IX dimethyl ester reacts in Diels-Alder reactions108a b with dienophilcs like ethenetetra-carbonitrile and acetylenedicarboxylates at the diene structural parts to yield, according to the reaction conditions, the corresponding monoadducts 2 and 3 (see also Section 1.2.) and bisadducts 1 (see also Section 1.4.), respectively. 

Cyclopropane-fused chlorins derived from tetraphenylporphyrins can be prepared by the aforementioned carbene cycloaddition route, e.g. conjugative addition of nialonate to nickel(II) nitrotetraphenylporphyrin 14 (M = Ni) yields the cyclopropane-fused chlorin 15.22... 

Conjugate addition, 34-5, 51-2,53, 132, 133 Conjugate hydroxymethylation, 59-60 Copper(n) bromide, 54 Copper([) chloride, 120 Copper(n) chloride, 120 Copper(i) cyanide, 7,52, 53 Copper(i) iodide, 54 Corey s internal quench, 104 Cyanohydrin trimethylsilyl ether, 137 Cycloaddition. 34,112 Cydobutane-l,2-dione, 135 Cyclohept-2-dione, 135 Cyclohex-2-enone, 52,123 Cyclohcxa-1,3-diene, 26 Cyclohexane carboxaldehyde, 22-3,69 73,78... 

The stereoselectivity of conjugate addition and cyclopropanation of the chiral nitrovinyldioxolanes 17 can be effectively controlled <96TL6307>, and good selectivity is observed in the ultrasound-promoted cycloaddition of nitrile oxides to alkenyldioxolanes 18 <95MI877,95JOC7701 >. Asymmetric Simmons-Smith cyclopropanation of 19 proceeds with... 

Since aromatic substitutions, aliphatic substitutions, additions and conjugate additions to carbonyl compounds, cycloadditions, and ring expansion reactions catalyzed by Fe salts have recently been summarized [17], this section will focus on reactions in which iron salts produce a critical activation on unsaturated functional groups provided by the Lewis-acid character of these salts. 

When ene-nitrile oxidoisoquinolium betaine 131 was heated as a dilute solution in toluene to 120 °C (Scheme 1.15), near quantitative conversion to the cycloadduct 133, resulting from the undesired regioselectivity, was observed. While the near complete conversion to cycloadduct 133 of oxidoisoquinolinium betaine 131 indeed demonstrated complete avoidance of the conjugate addition pathway in favor of cycloaddition, initial production of undesired isomeric cycloadduct 133 (instead of 136) was disappointing. Notably, cycloadduct 133 is expected to be less kinetically favored based on frontier molecular orbital (FMO) analysis (assuming dipole HOMO-controlled cycloaddition) of the putative transition state. This result stands in contrast to the cycloaddition of nitroalkene oxidoisoquinolinium betaine... 

The sequential intramolecular conjugate addition of the oxime followed by intramolecular dipolar cycloaddition of the intermediate nitrone affords a... 

Intramolecular nitrile oxide cycloaddition. The conjugate addition of t-butyl isocyanide to a nitroalkene can generate a nitrile oxide, which can be trapped intramolecularly by a double bond to form an isoxazoline. 

This chapter will begin with a discussion of the role of chiral copper(I) and (II) complexes in group-transfer processes with an emphasis on alkene cyclo-propanation and aziridination. This discussion will be followed by a survey of enantioselective variants of the Kharasch-Sosnovsky reaction, an allylic oxidation process. Section II will review the extensive efforts that have been directed toward the development of enantioselective, Cu(I) catalyzed conjugate addition reactions and related processes. The discussion will finish with a survey of the recent advances that have been achieved by the use of cationic, chiral Cu(II) complexes as chiral Lewis acids for the catalysis of cycloaddition, aldol, Michael, and ene reactions. 

In order to study the reactivity of the nitrogen atom in saccharidic OZT moieties Rollin and co-workers13,55 explored some standard reactions IV-acylation, IV-sulfonylation, IV-vinylsulfonylation by Michael addition, reductive elimination, conjugated addition and cycloaddition. 

The chemical behavior of heteroatom-substituted vinylcarbene complexes is similar to that of a,(3-unsaturated carbonyl compounds (Figure 2.17) [206]. It is possible to perform Michael additions [217,230], 1,4-addition of cuprates [151], additions of nucleophilic radicals [231], 1,3-dipolar cycloadditions [232,233], inter-[234-241] or intramolecular [220,242] Diels-Alder reactions, as well as Simmons-Smith- [243], sulfur ylide- [244] or diazomethane-mediated [151] cyclopropanati-ons of the vinylcarbene C-C double bond. The treatment of arylcarbene complexes with organolithium reagents ean lead via conjugate addition to substituted 1,4-cyclohexadien-6-ylidene complexes [245]. 

The elfectiveness of imidazolidinone of type 11 was confirmed by successful application to a broad range of chemical transformations, including cycloadditions, conjugate additions, Friedel-Crafts alkylations, Mukaiyama-Michael additions, hydrogenations, cyclopropanations, and epoxidations. A summary of these enantio-selective iminium catalyzed processes is provided by reaction subclass. 

The proposed catalytic cycles for the iminium ion catalysed Diels-Alder cycloaddition and conjugate addition reactions are outlined in Fig. 2. The general principles of these catalytic cycles can be used to understand each of the reactions described within this review which all follow a similar mechanistic pathway. The catalytic cycle consists of three principle steps ... 

Step 2 Key bond forming reaction (i.e. cycloaddition or conjugate addition)... 

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