Allyl system tests

Another example was the transformation of the aza-allylic system of N-ben-zylimine 33, which resulted in the formation of the N-benzylidene derivatives 34 as outlined in Scheme 5 [37]. Upon hydrolysis, the chiral amine 35 was produced. The chiral bases 36,37, and 38 (Fig. 2) were tested as the catalysts. Presumably, the bulkiness of the base controlled the reaction selectivities. 

Oxidation of sulfides in the presence of electron-rich double bonds is problematic with many of the traditional oxidants such as MCPBA, NaI04, and oxone because of interference with double bond oxidation (e.g., epoxidation). Koo and coworkers [40] addressed this problem and studied the selective oxidation of allylic sulfides having multiple alkyl substituents. They tested various stoichiometric oxidants and a number of catalytic reactions with 30% aqueous H2O2 as the oxidant. Of all the oxidation systems tested for the sulfoxidation, they found that the use of LiNbMoOg as catalyst with H2O2 as the oxidant gave the best result. With this system no epoxidation took place and a reasonably good selectivity for sulfoxide over sulfone was obtained (Table 8.2). 

The system provides an opportunity to test our method for finding the conical intersection and the stabilized ground-state structures that are formed by the distortion. Recall that we focus on the distinction between spin-paired structures, rather than true minima. A natural choice for anchors are the two C2v stmctures having A2 and B, symmetry shown in Figures 21 and 22 In principle, each set can serve as the anchors. The reaction converting one type-I structirre to another is phase inverting, since it transforms one allyl structure to another (Fig. 12). 

The activity of the FePeCli6-S/tert-butyl hydroperoxide (TBHP) catalytic system was studied under mild reaction conditions for the synthesis of three a,p-unsaturated ketones 2-cyclohexen-l-one, carvone and veibenone by allylic oxidation of cyclohexene, hmonene, and a-pinene, respectively. Substrate conversions were higher than 80% and ketone yields decreased in the following order cyclohexen-1-one (47%), verbenone (22%), and carvone (12%). The large amount of oxidized sites of monoterpenes, especially limonene, may be the reason for the lower ketone yield obtained with this substrate. Additional tests snggested that molecular oxygen can act as co-oxidant and alcohol oxidation is an intermediate step in ketone formation. 

The supported aqueous phase methodology was applied to the system Pd(OAc)2/5 TPPTS, a catalytic precursor for the Trost-Tsuji reaction. The characterization of the solid by 31P MAS NMR confirms the presence of Pd°(TPPTS)3 as the main surface species. The catalytic properties of the solid were tested for the allylic substitution of E-cinnamylethylcarbonate by different nucleophiles such as ethyl acetoacetate, dimethyl malonate, morpholine, phenol, and 2-mercapto-pyridine. The absence of palladium leaching was demonstrated, and having solved the problem of water leaching from the solid to the organic phase, the SAP-Pd catalyst was successfully recycled several times without loss in its activity. It was used in a continuous flow experiment which... 

The chiral nonracemic bis-benzothiazine ligand 75 has been screened for activity in asymmetric Pd-catalyzed allylic alkylation reactions (Scheme 42) <20010L3321>. The test system chosen for this ligand was the reaction of 1,3-diphenylallyl acetate 301 with dimethyl malonate 302. A stochiometric amount of bis(trimethylsilyl)acetamide (BSA) and a catalytic amount of KOAc were added to the reaction mixture. A catalytic amount of chiral ligand 75 along with a variety of Pd-sources afforded up to 90% yield and 82% ee s of diester 303. Since both enantiomers of the chiral ligand are available, both R- and -configurations of the alkylation product 303 can be obtained. The best results in terms of yield and stereoselectivity were obtained in nonpolar solvents, such as benzene. The allylic alkylation of racemic cyclohexenyl acetate with dimethyl malonate was performed but with lower yields (up to 53%) and only modest enantioselectivity (60% ee). 

All the other cycloadditions, such as the [4+2] cycloadditions of allyl cations and anions, and the [8+2] and [6+4] cycloadditions of longer conjugated systems, have also been found to be suprafacial on both components, wherever it has been possible to test them. Thus the trans phenyl groups on the cyclopentene 2.65 show that the two new bonds were formed suprafacially on the rrans-stilbene. The tricyclic adducts 2.61, 2.77, 2.79, and 2.83, and the tetracyclic adduct 2.82, show that both components in each case have reacted suprafacially, although only suprafacial reactions are possible in cases like these, since the products from antarafacial attack on either component would have been prohibitively strained. Nevertheless, the fact that they have undergone cycloaddition is important, for it is the failure of thermal [2+2], [4+4] and [6+6], and photochemical [4+2], [8+2] and [6+4] pericyclic cycloadditions to take place, even when all-suprafacial options are open to them, that is significant. 

This screening concept was also applied to liquid/liquid systems. As a test reaction, the isomerization of allylic alcohols to carbonyls with water-soluble catalysts in a biphasic heptane/water system was chosen [109,113]. The catalysts (metal precursor, Rh, Ru, Pd, Ni ligands, sulfonated phosphane or disphosphane ligands) were injected the liquid carrier 2 (water). The substrates (different allylic alcohols) were injected into liquid carrier 1 (heptane) ... 

It has to be mentioned that as early as in 1991 Porri et al. reported on the reaction of NdCl3 with Mg(C3H5)Cl in THF yielding an undefined Nd allyl compound which was successfully tested in diene polymerizations [141, 167,294]. For the polymerization experiments the cocatalysts TIBA, TMA, TIBAO and MAO were used and no halide donor was added. The undefined Nd allyl compound + TIBA yields a catalyst system that is reported to be at least three times more active than the system NdzO/TIBA/DEAC. The application of MAO with the Nd allyl compound increases catalytic activity 30-fold. 

If proton transfer from appropriate substrates leads to stabilized Nd allyl or Nd benzyl species allyl or benzyl proton donors allow for the control of molar mass (Sect. 2.2.8). On the basis of this consideration hexane, toluene and terf-butylbenzene (TBB) were comparatively tested in the polymerization of BD. In this study the catalyst system NdV/DIBAH/EASC was used. The rate of polymerization decreases in the order hexane > TBB > toluene. Only in hexane does the monomer conversion proceed to full completion (Fig. 6) [422]. 

Presently, the importance of Nd allyl compounds as intermediates in Nd carboxylate- and other Nd-based catalyst systems is widely accepted. As various Nd allyl compounds have been synthesized, characterized and successfully tested as polymerization catalysts this view is supported by solid experimental evidence (Sect. 2.1.1.5 and the references therein). Selected Nd allyl compounds exhibit significant polymerization activities without the addition of cocatalysts. In these cases the active species is neutral. But also cationic active Nd species are taken into consideration (Sect. 2.1.1.5) [288,291]. Cationic species also prevail in the presence of non-coordinating anions. 

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