Catalysis of the Diels-Alder reaction

In the previous section efficient catalysis of the Diels-Alder reaction by copper(II)nitrate was encountered. Likewise, other bivalent metal ions that share the same row in the periodic system show catalytic activity. The effects of cobalt(II)nitrate, nickel(II)nitrate, copper(II)nitrate and zinc(ll)nitrate... 

Fortunately, in the presence of excess copper(II)nitrate, the elimination reaction is an order of magnitude slower than the desired Diels-Alder reaction with cyclopentadiene, so that upon addition of an excess of cyclopentadiene and copper(II)nitrate, 4.51 is converted smoothly into copper complex 4.53. Removal of the copper ions by treatment with an aqueous EDTA solution afforded in 71% yield crude Diels-Alder adduct 4.54. Catalysis of the Diels-Alder reaction by nickel(II)nitrate is also... 

With the aim of catalysis of the Diels-Alder reaction of 5.1 with 5.2 by metallo micelles, preliminary studies have been performed using the surfactants 5.5a-c and 5.6 (Scheme 5.2). Unfortunately, the limited solubility of these surfactants in the pH region that allows Lewis-acid catalysis of the Diels-... 

Several aluminum- and titanium-based compounds have been supported on silica and alumina [53]. Although silica and alumina themselves catalyze cycloaddition reactions, their catalytic activity is greatly increased when they complex a Lewis acid. Some of these catalysts are among the most active described to date for heterogeneous catalysis of the Diels-Alder reactions of carbonyl-containing dienophiles. The Si02-Et2AlCl catalyst is the most efficient and can be... 

Saha AK, Hossain MM (1993) Synthesis of a polymer-bound iron Lewis acid and its utilization in Diels-Alder reactions. Tetrahedron Lett 34 3833-3836 Olson AS, Seitz WJ, Hossain MM (1991) Transition metal catalysis of the Diels-Alder reaction. Tetrahedron Lett 32 5299-5302... 

Lewis Acid Catalysis of the Diels-Alder Reaction... 

While the ambiguity of the catalysis of the Diels-Alder reaction needs to be carefully elucidated, the application of the ferrocenyl carbocations in the Mukaiyama aldolization turned out evidently to be unrealisable due to their interaction with the TMS enol ether that produces TMSOTf, which proved readily to catalyze the aldolization [154]. 

An interpretation of the results and a hypothesis on potential intermediates was difficult at this stage, since no defined complexes could be obtained. The first identification of species present in solution during the catalysis of the Diels-Alder reaction was achieved in a collaboration between our group and three physical chemists, Bertagnolli, Gescheidt, and Schweiger [64]. Using various techniques... 

Measurements of molar rotation showed that this parameter is almost proportional to the number of chiral binaphthyl units and the molar rotation per binaphthyl unit varies only slightly. On catalysis of the Diels-Alder reaction of cyclopentadiene with 3-[(E)-but-2-enoyl]oxazolidin-2-one the branched catalysts 7 and 8 showed an approximately 25% higher reactivity than the monofunctional catalyst 6 however, the former led to just a slight improvement of ee and endo-selectivity compared to 6. It is thus inappropriate to speak of a dendritic effect on catalysis, although one does indeed exist in relation to the chiroptical properties. 

One aspect of antibody catalysis that tmly ignites the imagination of the chemical biologist is that these biocatalysts are not limited to reactions that have a natural enzymatic equivalent. The Diels-Alder reaction has immense synthetic utility however, this chemical transformation is extremely rare in nature. Furthermore, the reaction proceeds via an entropicaUy disfavored, highly organized pericyclic transition state (78). The programmability of a catalytic antibody has enabled the catalysis of the Diels-Alder reaction previously considered beyond the realm of possibility with a protein (79-84). 

Janda KD. Anti-metallocene antibodies a new approach to enan- 100. tioselective catalysis of the Diels-Alder reaction. J. Am. Chem. 

Like alumina, SiO2 also shows catalytic efficiency for organic reactions under solvent-free conditions. A good example is catalysis of the Diels-Alder reaction (Scheme 5.34) by silica gel with high regio- and stereoselectivity. 

Enzymic catalysis of the Diels-Alder reaction in the biosynthesis of natural... 

Roussel C, Lid n A, Chanon M, Metzger J, Sandstrbm J (1976) J Am Chem Soc 98 2847 Honda Y, Date T, Hiramatsu H,Yamauchi M (1997) Chem Commun 1411 For a more in-depth discussion of this observation, see Yamauchi M, Honda Y, Matsuki N, Watanabe T, Date K, Hiramatsu H (1996) J Org Chem 61 2719 For a general reference on catalysis of the Diels-Alder reaction by achiral transition metal Lewis acids, see Bonnesen PV, Puckett CL, Honeychuck RV, Hersh WH (1989) J Am Chem Soc 111 6070... 

A. SURFACE AND AQUEOUS CATALYSIS OF THE DIELS-ALDER REACTION... 

Laszlo, P. and J. Lucchetti. 1984. Catalysis of the Diels-Alder reaction in the presence of clays. Tetrahedron Lett. 25 1567-1570. 

Otto and Engberts recently reported catalysis of the Diels-Alder reaction between cyclopentadiene (2.1) and the enone 2.48 by Lewis acids in water [29] ... 

Tan, B., Hernandez-Torres, G., Barbas HI, C. F. (2011). Highly efficient hydrogen-bonding catalysis of the Diels-Alder reaction of 3-vinylindoles and methyleneindohnones provides carbazolespirooxindole skeletons. Journal of the American Chemical Society, 133, 12354-12357. 

Although heterocycUc ortho-quinodimethanes (oQDMS) have been studied extensively to design Diels-Alder reactions for the synthesis of complex indole alkaloids for more than 30 years, asymmetric catalysis of the Diels-Alder reaction of nitroolefins 32 or methylene-indolinones 39 with in situ generated heterocyclic... 

Hydrogen-bonding catalysis of the Diels-Alder reaction of 2-vinylindoles 39 and methylene-indolinones 69 has been accomplished by the Barbas group using a C2-symmetric bis-thiourea organocatalyst [31]. This efficient transformation provided a powerful approach by which to construct carbazole-spirooxindole derivatives 71 extremely rapidly (less than 10 min) with excellent enantiopurity and structure diversity (Scheme 38.20). 

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