G-allylation

Dramatic rate accelerations of [4 + 2]cycloadditions were observed in an inert, extremely polar solvent, namely in5 M solutions oflithium perchlorate in diethyl ether(s 532 g LiC104 per litre ). Diels-Alder additions requiring several days, 10—20 kbar of pressure, and/ or elevated temperatures in apolar solvents are achieved in high yields in some hours at ambient pressure and temperature in this solvent (P.A. Grieco, 1990). Also several other reactions, e.g, allylic rearrangements and Michael additions, can be drastically accelerated by this magic solvent. The diastereoselectivities of the reactions in apolar solvents and in LiClO EtjO are often different or even complementary and become thus steerable. 

Radicals with adjacent Jt-bonds [e.g. allyl radicals (7), cyclohexadienyl radicals (8), acyl radicals (9) and cyanoalkyl radicals (10)] have a delocalized structure. They may be depicted as a hybrid of several resonance forms. In a chemical reaction they may, in principle, react through any of the sites on which the spin can be located. The preferred site of reaction is dictated by spin density, steric, polar and perhaps other factors. Maximum orbital overlap requires that the atoms contained in the delocalized system are coplanar. 

In the HMO or extended Hiickel approach, the individual ionization potentials should be set equal to orbital energies. The inadequacy of the HMO treatment is apparent with odd alternant hydrocarbons (e.g., allyl, benzyl), where a constant value is obtained, in disagreement with the experiment. Streitwieser and Nair (105) showed, however, that reasonable results can be obtained with the co technique. 

The possibility of reticulating the materials by carefully introducing additional substituent groups in the polymer during the synthetic process (1-2% or less), prone to undergo selected reactions (e.g. allylic double bonds [576-579]), and/or by addition of appropriate external additives (e.g. sulfur [578] or hydroperoxides [531,576-578,580]) to these polymers... 

The presence of V does not diminish the activity of a grafted Ti-Si02 catalyst for olefin epoxidation. However, activity towards simple olefins such as cyclohexene is not enhanced. Since homogeneous V catalysts are known to catalyze the epoxidation of functionalized olefins (e.g., allylic alcohols), the ability of a mixed V-Ti/Si02 catalyst to achieve such transformations will be the next focus of our investigations. 

There are more interesting rearrangement possibilities inherent in delocalised cations, e.g. allylic rearrangements. 

M of the substituted benzene and 32.4 g dry FeCl3. Cool to -21° in an ice-salt bath and add dropwise with stirring over two hours, 76.5 g allyl-CI and continue stirring three hours. Add about 2 lbs. crushed ice and 100 ml concentrated HCI. Agitate and separate the organic layer and wash with dilute HCI, then water and filter, dry and evaporate in vacuum (or distill 100-115/10 with Claisen flask, etc.) to get the substituted-l-phenyl-2-Cl-propane (I). Dissolve 0.16 M (about 27 g) (I) in 450 ml ethanol saturated with NH3 (125 g/L, seal in an iron pipe in autoclave and agitate and heat about nine hours at 160°. Cool and filter and evaporate in vacuum to get the amphetamine in about 20% yield. 

In a reaction vessel equipped with mechanic propeller stirrer, argon inlet, and reflux condenser an emulsion is prepared of distilled water (300 g), methyl methacrylate (MMA 9.5 g),allyl methacrylate (ALMA 0.5 g) and sodium dodecyl sulfate (5D5 ... 

Thienyl sulfides with the 2-position of the thiophene ring blocked, e.g., allyl 2-methyl-3-thienyl sulfide (51), also undergo sigmatropic rearrangement when heated in quinoline [Eq. (23)]. 2,6-Dimethyl-2,3-dihydro-thieno[3,4-Z ]thiophene (52) is formed, together with other products. 

C-Glycoside synthesis may be achieved in twro ways. Intermolecular radical addition reactions are observed with (i) polarized, electron-deficient alkenes, (ii) alkenes that provide a high level of stabilization to the initial radical adduct and (in) substrates that undergo a facile fragmentation (e.g. allyl stannanes). Additions to less reactive substrates, though not favored for intermolecular processes, are observed if the two components are tethered in an intramolecular array. 

Examination of the observed and predicted values for log (I/D50) in Table 5 reveals that there are at least four types of compounds that are apparently not well-described by equation 4. These include compounds with hydroxy groups (e.g. compounds 20, 21, 22), compounds with chemically reactive a-hydrogens (e.g., allylic or benzylic systems, No s 9, 14), and compounds with extensive branching at the a-carbon (No s 4, 11). Acyclic nitro-samines, with one or two apparent exceptions (12), appear to constitute a separate reaction series (29). 

In 1994, Buzek et al. (109) reported that the allyl cation could be prepared from a variety of halide precursors, e.g., allyl chloride or cyclopropyl bromide, on SbF5 at cryogenic temperature, based on the infrared spectrum of the products. Those workers challenged BGW s claim of the persistent allyl cation based on the discrepancy between the isotropic 13C shift in the zeolite and that calculated at MP2/6-31G. This was one of the first examples of the use of chemical shift calculations to interpret (and in this case challenge) an NMR study of a species on a solid acid. 

SYNTHESIS To a solution of 43.2 g KOH pellets in 250 boiling EtOH there was added 96 g 4-methoxyphenol followed by the slow addition of 131.2 g allyl bromide, and the mixture was held under refluxing conditions for 16 h. After cooling, the reaction was added to 1.6 L H20, and made strongly basic with 25% NaOH. This was extracted with 3x100 mL CH,C1, the extracts pooled, washed once with dilute NaOH and then once with dilute HC1. Removal of the solvent under vacuum gave 93.8 g of 4-allyloxyanisole as a pale amber oil, which was used in the following reaction without further purification,... 

SYNTHESIS A solution of 268 g 2,6-dimethoxyphenol and 212 g allyl bromide in 700 mL dry acetone was treated with 315 g anhydrous K2C03 and held at reflux for 16 h. The solvent was removed under vacuum, and the residue dissolved inH20 and extracted with 3x100 mL CR,C1,. The pooled extracts were washed with 5% NaOH, then with H20, and the solvent removed under vacuum. The residue, which weighed245 g, was stirred and heated in an oil bath to 230 °C at which point an exothermic reaction set in. The heating was maintained at 230 °C for 0.5 h, and then the reaction mixture distilled. There was obtained a total of 127 g of 5-allyl-... 

Although this catalytic reaction appeared to be of synthetic interest, it has since then neither been applied in synthesis nor further developed. This might be attributed in part to problems with reproducibility and catalyst stability under the reaction conditions, although the Hieber complex was used in a stoichiometric manner for the preparation of a variety of 7i-allyl-Fe complexes. These latter compounds served as starting materials for a plethora of subsequent reactions [34]. The results obtained by Nakanishi and coworkers on the stability and reactivity of n-allyl-Fe-nitrosyl complexes proved such intermediates to be reactive towards a variety of nucleophiles however, the Fe complexes formed upon nucleophilic substitution were catalytically inactive. Hence, in order to maintain the catalytic activity, the formation of intermediate 7i-allyl-Fe complexes had to be circumvented. About 3 years ago we started our research in this field and envisioned the use of a monodentate ligand to be a suitable way to stabilize the proposed catalytically active G-allyl complex. The replacement of one CO by a non-volatile basic ligand was thought to prevent the formation of the catalytically inactive 7t-allyl-Fe complex (Scheme 7.21). 

Pegolotti, J. A. Young, W. G. Allylic rearrangements. LI. Displacement reactions in trifluoro-methylallyl systems./. Am. Chem. Soc. 1961,... 

Overman, L. E. Zipp, G. G. Allylic transposition of alcohol and amine functionality by thermal or Pd(II)-catalyzed rearrangements of allylic N-benzoylbenzimidates. J. Org. Chem. 1997, 62, 2288-2291. 

Acetamido-2-hydroxyacetophenone (19.3 g), allyl bromide (12.1 ml) and hydrous potassium carbonate (21.5 g) were stirred in dry dimethylformamide (250 ml) at room temperature for 24 hours. The reaction mixture was poured into water and the product was extracted with ethyl acetate. The organic solution was then washed well with water dried over magnesium sulphate and evaporated to dryness. The sub-title product was obtained as buff coloured solid (20.5 g). The structure of the product was confirmed by NMR and mass spectroscopy. 

SAD Spin-alternant determinant. The VB determinant with one electron per site and with alternating spins. Other terms describing the same determinant are the quasiclassical (QC) state, and the antiferromagnetic (AF) state. In nonalternant hydrocarbons, where compete spin alternation is impossible, the determinant is called MS AD, namely, the maximum spin-alternating determinant. The SAD MSAD are the leading terms in the wave function of molecules with one electron per site, for example, conjugated hydrocarbons. In radicals (e.g., allyl radical) the SAD is the root cause of spin polarization (i.e., negative spin densities flanked by positive ones). See Chapters 7 and 8. 

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