Catalyzed Cycloaddition Reactions

The enantioselective cycloaddition reaction catalyzed by chiral BOX-copper(II) complexes has been used for conjugated cyclic dienes, e.g. 1,3-cyclohexadiene 5c, as shown in Scheme 4.21 [9, 32]. This cycloaddition reaction is dependent on sol-... 

In the nitrone cycloaddition reactions catalyzed by the l ,J -DBFOX/Ph transition metal complexes also, the diastereo- and enantioselectivities were found to depend upon the presence of MS 4 A [71]. Thus, both the selectivities were much lowered in the iron(II) or nickel(II) complex-catalyzed reactions without MS 4 A,... 

Fiirstner A, Majima K, Martin R, Krause H, Kattnig E, Goddard R, Lehmann CW (2008) A cheap metal for a Noble task preparative and mechanistic aspects of cycloisomerization and cycloaddition reactions catalyzed by low-valent iron complexes. J Am Chem Soc 130 1992-2004... 

Jprgensen and co-workers (247) investigated the asymmetric 1,3-dipolar cycloaddition reaction catalyzed by bis(oxazoline)-copper(II) complexes. In the presence of 25 mol% 269c, nitrone (401) reacts with ethyl vinyl ether and methoxypropene to afford the [3 + 2] adducts in modest diastereoselectivity and high enantioselectivity, Eq. 217. Ethyl vinyl ether preferentially forms the exo adduct while methoxypropene prefers the endo mode for reasons that are unclear. 

Reactions by Other Nucleophiles As in the case of the formal cycloadditions of alkenes to allyl cations, the addition of alkenes to gold(I)-activated allenes generates intermediates that determine which cycloaduct formed. Based on this hypothesis, Toste et al. recently developed enantiorich bicycle-[3.2.0] structures by [2+2]-cycloaddition reaction catalyzed by chiral biarylphosphinegold(I) complexes [51]. 

A tetrahydrofuran fused with a seven-membered ring was obtained from an enyne through a [5+2] cycloaddition reaction catalyzed by [(C10H8)Rh(COD)]+ SbF6 complex <02AG(E)4550>. Rhodium-catalyzed carbonylative alkene-alkyne coupling reactions... 

Asymmetric Cycloaddition Reactions Catalyzed by Cinchona-Based Primary Amines 313... 

Cycloaddition. Many types of cycloaddition reactions catalyzed by PtCl2 have been discovered. Platinized carbonyl ylides formed in situ from 4-alkynones are intercepted by electron-rich aUcenes. ... 

Recent progress in the synthesis of heterocycles (pyridines, p3ridones, pyrans, pyrimidinediones, etc.) using [2 + 2 + 2] cycloaddition reactions catalyzed by transition metal complexes 06ASC2307. 

Bnimmond and Gao have demonstrated the use of a (2 + 2 +1) cycloaddition reaction catalyzed by Rh(II), usually called a Pauson-Khand reaction (PKR) when in the presence of carbon monoxide. This intramolecular version generates simultaneously both the five-membered ring of the PKR, as well as the seven-membered ring, thus furnishing the guanacastepene skeleton (Scheme 61) [99]. 

Scheme 10.2 [2+2+1] Cycloaddition reaction catalyzed by ruthenium and iron carbonyls (partially reproduced from Refs. [20] and [21]).

Until now, all cycloaddition reactions catalyzed by transition metals other than Cu are limited to organic solvents. We expect such cycloaddition reactions to be optimized to proceed in aqueous solution at room temperature in the fumre, which would significantly expand their applications in biological systems. 

Canales, E. Corey, E. J. Highly Enantioselective [2 -i- 2]-Cycloaddition Reactions Catalyzed by a Chiral Aluminum Bromide Complex.. Am. Chem. Soc. 2007,129,12686-12687. 

In practical terms, particularly important are the cycloaddition reactions catalyzed through the formation of cation-radicals. A theoretical analysis of the PES of these reactions [94] has helped to evolve some general notions concerning the mechanism of ionradical pericyclic transformations. 

Intermolecular cycloaddition reactions catalyzed by Cu(I) were studied by Salomon and Kochi, by Mackor and by others. The use of better soluble CuOTf instead of Cu-halides allowed reactions to be run more effectively and cleaner. Reactions studied are the 2 -t- 2 cycloaddition of norbomene giving the exo-trans-exo isomer exclusively (97 %), the analogous reaction with e d(9-dicyclopentadiene as substrate, the codimerization of norbomene with cyclooctene, the dimerization of cyclopentene, cyclohexene, cyclo-heptene and mixtures thereof. 

Asymmetric Catalytic [2+2] Cycloaddition Reaction Using a Chiral Aluminum Complex In 2007, Canales and Corey provided the first enantioselective [2+2] cycloadditions of sUyl enol ethers with a, 3-unsaturated esters by catalytic amounts of aluminum bromide complex [21]. Aluminum catalyst 18 is conveniently generated in situ by the addition of a commercially available solution of aluminum bromide in CH2Br2 to a solution of the known oxazaborohdine component [22,23]. The results of enantioselective [2+2] cycloaddition reaction catalyzed by aluminum complex are summarized in Table 4.6. 

A possible mechanism for the catalytic [2+2] cycloaddition reaction catalyzed by Tf2NH is depicted in Scheme 4.9. The Mukaiyama-type Michael addition of silyl enol ether to enoate catalyzed by silyl triflic imide aHbrds the corresponding silyl ketene acetal, and then it proceeds successively to the intramolecular silyl oxonium carbon to... 

In relation to this, Sapeta and Kerr also showed that the use of a chiral cyclopropane in both enantiomers was able to undergo the cycloaddition reaction catalyzed by the original Yb(OTf)3 Lewis acid. This resulted in the formation of both enantiomers of the oxazines with a high degree of diaster-eocontrol and excellent enantioselectivity with ee up to 95% was observed [27]. It was also noted that, as the reaction progressed, a racemization of the chiral cyclopropane took place and the ee of the oxazine diminished with time. 

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