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Selectivity in Diels-Alder reaction

Edman and Simmons [146] synthesized bicyclo[2.2.1]hepta-2,5-diene-2,3-dicar-boxylic anhydride 80 as a facially perturbed dienophile on the basis of the norbornadiene motif, and its top selectivity in Diels-Alder reactions with cyclopentadiene (top-exo top-endo = 60 70 1) was observed by Bartlett (Fig. 14) [147], The most preferred addition was top-exo addition, along with the minor addition modes, top-endo bottom-enrfo addition (Fig. 14). The addition of butadiene to this anhydride preferentially afforded the top-adduct (top bottom = 6 1). In the addition of anthracene, a top-adduct was formed exclusively. [Pg.162]

It becomes intriguing to inquire what leads to the observed contrasteric reactivity. Intensive studies to disclose the origin of Tt-facial selectivity examined various dienes having unsymmetrical 7t-plane, since their reactions potentially generate five or more consecutive stereocenters with one operation. In this chapter, we review the theories to disclose the origin of 7t-facial selectivity in Diels-Alder reactions of the substrates having unsymmetrical 7t-planes. Recent works are discussed. [Pg.185]

Overman, Hehre and coworkers reported anti rr-fadal selectivity in Diels-Alder reactions of vinylcyclopenten 73, 74 and 4,5-dihydro-3-etliynylthiophen S-oxide 75 [38] (Scheme 31). These results are not in agreement with the Cieplak effect, at least in Diels-Alder reactions of the dienes having unsymmetrical rr-plane. Yadav and coworkers reported that the reactions between the vinylcyclohexene 76 and dienophiles favor the reactions syn to oxygen, while 77 and 78 favor the reaction anti to oxygen substituents [39], They discuss the Cieplak effect but the reactions are not suitable. [Pg.203]

Kahn and Hehre straightforwardly extended this idea to the description of Jt-facial selectivity in Diels Alder reactions. They simply stated cycloaddition involving electron-rich dienes and electron-poor dienophiles should occur preferentially onto the diene face which is the more nucleophilic and onto the diene face which exhibits the greater electrophihcity (Scheme 40) [49],... [Pg.208]

Overman, Hehre and coworkers also reported anti tt-facial selectivity in Diels-Alder reactions of the vinylcyclopentenes 73,74 and 4,5-dihydro-3-ethynylthiophen 5 -oxide 75. They attributed the selectivity to destabilizing electronic interaction between the allylic heteroatom and dienophile in the syn attack transition state (Scheme 43) [38],... [Pg.210]

C. Bumouf, J. C. Lopez, F. G. Calvo-Flores, M. D. Laborde, A. Olesker, and G. Lukacs, ir-Facial selectivity in Diels-Alder reactions of 2-C-vinylglycals. Stereocontrolled route to annulted C-glycopyranosides, J. Chem. Soc. Chem. Commun. p. 823 (1990). [Pg.592]

Asymmetric Diels-Alder reactions. Chiral a,p-unsaturated N-acyl oxazolidones exhibit high diastereoface selection in Diels-Alder reactions, particularly those conducted in the presence of diethylaluminum chloride (1.2 equiv.). [Pg.360]

Conversion of —Si (013)3 to —OH. Searle chemists have used this transformation in a synthesis of 4-demethoxydaunomycinone (6). Thus aryl-trimethylsilanes were known to be converted into aryl trifluoroacetates by lead tetrakistrifluoroacetate (4, 282-283) the Searle chemists found that this trifluoroacetoxylation was also applicable to benzyltrimethylsilane. With this information and knowing that 1,3-butadienes substituted by trimethylsilyl groups show selectivity in Diels-Alder reactions, they then devised the route shown in the formulation. The first step involved a Diels-Alder reaction to give 3. This product... [Pg.439]

In an effort to develop enantioselective methods for azirine cycloadditions, azirine 87 was added to chiral diene 99 <1998TL7579, 2003TL6561>. Diene 99 has previously shown facial selectivity in Diels-Alder reactions with a number of dienophiles. Reaction of Z equiv of azirine 87 with 99 provides aziridine 100 in excellent yield as a single isomer (Equation 24). [Pg.123]

Silvero, G., Lucero, M. J., Winterfeldt, E., Houk, K. N. Theoretical study of the facial selectivity in Diels-Alder reactions of 4,4-disubstituted cyclohexadienones. Tetrahedron 1998, 54, 7293-7300. [Pg.576]

Bachmann, C., Boeker, N., Mondon, M., Gesson, J.-P. Density Functional Study of -Facial Selectivity in Diels-Alder Reactions. J. Org. Chem. 2000, 65, 8089-8092. [Pg.576]

Wiberg reported the Diels-Alder reaction of butadiene and cyclopropene [53] and Baldwin estimated from the reaction between cyclopropene and 1-deuteriobutadiene at 0°C that 99.4% of the formed cycloadduct was the endo isomer [54], There are many suggestions which attempt to explain endo selectivity in Diels-Alder reactions (Alder s rule [55]), but none are firmly established. According to Woodward and Hoffmann [56], the preference is the result of favorable Secondary Orbital Interactions (SOI) or secondary orbital overlap [57-59] between the diene and dienophile in the corresponding transition state structure. One can also find an explanation for the reaction preference in the difference between primary overlap [60], volumes of activation [61], and the polarity of the transition states [62]. Secondary orbital overlap between the diene and the dienophile does not lead to bonds in the adduct, but primary orbital overlaps do. [Pg.102]

Table 11.5. endo/exo Selectivity in Diels-Alder Reactions of Cyclopentadiene... [Pg.940]

It has been reported that Cplex-isoelectronic theory predicts endo selectivity in Diels-Alder reactions. Phosphorylated nitroso alkenes react with cycUc dienes to give hetero Diels-Alder-type cycloadducts and subsequent aza-Cope rearrangement gives 5,6-dihydro-4H-l,2-oxazines (Scheme 20). ... [Pg.485]

All these results came to light in the midst of our ongoing interest in the E-facial selectivity in Diels-Alder reactions of homochiral dienes bearing an allylic stereogenic... [Pg.43]

Water as solvent is shown to enhance both the rate and the selectivity in Diels-Alder reactions using several water-soluble trans buta-l,3-dienyl derivatives of carbohydrates from the simplest one with only one asymmetric center, derived from D-glyceraldehyde to partially protected buta-l,3-dienyl glucosides. In each case, virtually complete endo selectivity was observed, and it is shown that the facial stereoselectivity can be modulated through chemical manipulation of the sugar moiety. It is also shown that the rate enhancement in such aqueous cycloadditions has an entropic origin. [Pg.147]

Lubineau, A. Auge, J. Lubin, N., Aqueous cycloaddition using glyco-organic substrates. Facial selectivity in Diels-Alder reactions of a chiral diene derived from D-glyceraldehyde,... [Pg.45]

Facial selectivity in Diels-Alder reactions has also been studied using theoretical methods. Poirier et al. have studied reactions of ethylene with 5-substituted cyclopenta-dienes (12) and have shown that the major factor responsible for determining the facial selectivity is the deformation of the addends at the transition states, and not the direct interaction between the diene and the dienophile. For reactions between cyclopentadiene and chiral butenolides (13) the most favorable diastereoisomer corresponds to the attack of the diene at the less sterically hindered face of the lactone. Steric interaction between the addends is also reflected in geometry distortions at the transition states. [Pg.2034]


See other pages where Selectivity in Diels-Alder reaction is mentioned: [Pg.66]    [Pg.46]    [Pg.100]    [Pg.343]    [Pg.469]    [Pg.33]    [Pg.59]    [Pg.780]    [Pg.207]    [Pg.46]    [Pg.343]    [Pg.375]    [Pg.343]    [Pg.810]    [Pg.177]    [Pg.1581]    [Pg.64]    [Pg.40]    [Pg.1249]   
See also in sourсe #XX -- [ Pg.333 , Pg.334 ]




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