Reactivity and Regioselectivity

The catalyst [Ir(COD)Cl]2/P(OPh)3 was highly effecHve also for allyhc airuna-Hons. Branched monoallylahon products were mainly obtained with primary amines as nucleophiles and Hnear fE)-allylic substrates. In contrast, mixtures of Hnear mono- and disubsHtuHon products are usually produced with Pd-catalysts. Many types of amine could be used, for example benzylairune, piperidine and anihne [14]. In terms of allyhc substrates, carbonates were more suitable than acetates. With regards to the solvent, the best results were obtained with ethanol, with complete conversion typicaUy being achieved after a reacHon time of 3 h at 50°C. The reacHons of (Z)-aUylic carbonates to give Hnear fZj-propenylamines proceeded with perfect stereospecificity. 

P(OPh)3 leads to the coordinatively saturated complex K2 [15], As complex K2 is coordinatively saturated, P(OPh)3 must dissociate in order to obtain a catalytically active 16-VE d -Ir complex. Similar C—H activation was later found for (phosphoramidite)Ir complexes. 

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Cycloadditions ot diazomethane with fluonnated cyclobutenes provide insight into those factors that govern the reactivity and regioselectivity of such reactions Although 3,3,4,4-tetrafluorocyclobutene undergoes reactions at ambient temperature in 5 min [77, 72], complete reaction with the less reactive perfluorocyclobutene requires 14 days [7J] (equation 8). Note also the regioselectivity observed in the reaction of diazomethane with 3,3-difluorocyclobutene [14] (equation 9)... 

The reactivity and regioselectivity of the cycloadditions of the 2-vinylindoles are markedly dependent on the substitution pattern as shown by the calculated HOMO energies and coefficients [85a]. 

The cleavage of epoxides by water is a classical reaction. Such epoxide cleavage can be catalyzed by both acids and bases in aqueous media. In the presence of other nucleophiles, the corresponding nucleophilic ringopening products are obtained with the nucleophiles being incorporated into the products.68 Examples include azides, iodides, and thiols in the presence or absence of metal salts in aqueous media. The pH of the reaction medium controls the reactivity and regioselectivity of the... 

Amination of heterocyclic nitro compounds such as nitroquinolines, nitroisoquinolines, or nitropyridines can be carried out by means of a liquid ammonia-KMn04 system, which has been studied by Wozniak and coworkers (Eq. 9.44). Frontier molecular orbital calculation can predict the reactivity and regioselectivity of this amination.75 In a similar way, nitroquinolines are methylaminated with a liquid methylamine solution of KMn04.76... 

Houk, K.N., Williams Jr., J.C., Mitchell, P.A. and Yamaguchi, K. (1981). Conformational control of reactivity and regioselectivity in singlet oxygen ene reactions Relationship to the rotational barriers of acyclic alkylethylenes. J. Am. Chem. Soc. 103, 949-951... 

The reactivity and regioselectivity in the first and second substitutions steps were studied by Ibata s group141 in the reactions of 24 with 6.0 molar equivalent of morpholine and pyrrolidine, monitoring the kinetics of formation of the reaction products by NMR measurements. In the reactions with morpholine (Figure 8), the yields of 25a, 26a and 27a increased monotonously during the initial 20 h, while 1 decreases monotonously to zero recovery. The amount of 26a decreases slowly after 20 h this indicates that the second attack of morpholine proceeds slowly to give 28a and 29a, in contrast to no attack on 27a. 

The reactivity and regioselectivity of the cycloaddition of l-(A-phenacylidene)amino-1,2,3-triazoles with diphenyl nitrilimine (see Section 4.01.7.4) are examined on the basis of CNDO/2 calculations. The cycloaddition regioselectivity is HOMOjdipoie) controlled. The predominant orbital interaction shown in Figure 1 rationalizes the regioselective formation of 277-1,2,3-triazoles... 

Because the addition steps are generally fast and consequently exothermic chain steps, their transition states should occur early on the reaction coordinate and therefore resemble the starting alkene. This was recently confirmed by ab initio calculations for the attack at ethylene by methyl radicals and fluorene atoms. The relative stability of the adduct radicals therefore should have little influence on reacti-vity 2 ). The analysis of reactivity and regioselectivity for radical addition reactions, however, is even more complex, because polar effects seem to have an important influence. It has been known for some time that electronegative radicals X-prefer to react with ordinary alkenes while nucleophilic alkyl or acyl radicals rather attack electron deficient olefins e.g., cyano or carbonyl substituted olefins The best known example for this behavior is copolymerization This view was supported by different MO-calculation procedures and in particular by the successful FMO-treatment of the regioselectivity and relative reactivity of additions of radicals to a series of alkenes An excellent review of most of the more recent experimental data and their interpretation was published recently by Tedder and... 

Many examples of the influence of steric effects on reactivity and regioselectivity in free radical additions are known. The anti-Markownikoff regioselectivity apparently is smalier than originally assumed and frequently dependent on... 

Similar reactivity and regioselectivity is observed with the parent system, 1,2,4-triazine (eq 2) Reduction of this process to a catalytic Diels-Alder reaction with in situ generation of the pyrrolidine enamine does... 

The highly effective desilylation routes to nonstabihzed azomethine ylides have provided the basis for much of this chemistry. Thus, the reaction of A-(silylmethyl)-thioimidates (30) with AgF in the presence of a range of dipolarophiles (electron-deficient alkenes and alkynes, and aldehydes) led to the isolation of nitrile ylide adducts in generally high yields (20,21). Differences in reactivity and regioselectivity... 

The reactivity and regioselectivity of 1,3-dipolar cycloadditions have been discussed in terms of the frontier orbitals [271]. Most of the features may be understood on the basis of simple Hfickel MO theory. The HOMO and LUMO n orbitals and n orbital energies for all 18 combinations of the parent dipoles are shown in Figure 12.8. The frontier orbitals of many of the 1,3-dipoles have previously been derived by CNDO/2 and extended Hfickel theory [272]. The first six structures, all of 16-electron type, are shown in greater detail ... 

The reactivity and regioselectivity of 1-azidoadamantane (See Scheme 18), a bridgehead azide, have been investigated with electron-poor olefins.155 The reaction with ethyl acrylate proceeds smoothly at 25°C to afford exclusively the 4-substituted triazoline in good yield the regiochemistry is supported by 13C- and H-NMR spectral data. /S-Nitrostyrene and nitroethylene give only triazoles. 

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