Anisyl groups

Dove et al. designed and synthesized unsymmetrically substituted /3-diketimininate ligands 97, bearing bulky diisopropylphenyl and Lewis-basic anisyl groups for the purpose of lowering the Lewis acidity of their zinc complexes.155 In both solution phase and the solid state, however, the oxygen atom does not seem to interact sufficiently with the zinc atom to have a noticeable effect on the Lewis acidity of the metal center. 

In a related study involving structurally similar chiral methylzinc anisyl fencholates, both chiral amplification and depletion were observed in the catalytic alkylations of benzaldehyde.209 Thus, methylzinc anisyl fencholates, bearing sterically small substituents in the ortho-position of the anisyl group, crystallized preferentially as homochiral dimers, as shown for the methyl-substituted anisyl group in Scheme 91. Because of the greater stability of the homochiral dimers, scalemic mixtures of both enantiomers of the ligand showed a chiral depletion of the benzyl alcohol. 

Similarly, the benzannulated enyne-allenes 172 and 173 were prepared from the propargylic acetates 171 by cuprate addition or by Pd-catalyzed addition of arylzinc chloride (Scheme 20.35) [49]. The presence of a butyl group and a p-anisyl group at the allenic terminus of 173a and 173b permits competition between a formal ene reaction and a formal Diels-Alder reaction leading to 174 and 175, respectively. 

Explain why the migratory aptitude of the o-anisyl group is only 0.3 in the pinacol rearrangement. 

The Cjg—Si bond fragmentation in cation 401 occurs already at temperatures where the corresponding 1-mesityl-, l-(p-tolyl)- and 1 -phenylvinyl-/l-(tri isopropyl Jsi lyl-substi tutcd vinyl cations 375, 389a and 393 are stable. The facile formation of the 1 (p-anisyl)vinyl cation 403 can be ascribed to a second protonation of 401 at the oxygen of the anisyl group. 

The fact that pyrylium salts easily form anhydrobases in water over a large range of pH values, and pseudobases at pH >5, makes such salts incompatible with biomedical applications, but the highly fluorescent 2,4,6-triarylpyrylium salts with phenyl or para-anisyl groups have various applications in reprographic industries. On the other hand, chalcogenopyrylium cations with other atoms (S, Se, Te) are less... 

The different electronic nature of the two substituents may provide another reason why the unsymmetrically substituted cyclopropane (32) rearranges more readily. If the anisyl group preferentially delocalizes the positive charge, whereas the allyl moiety stabilizes the spin, the remaining bond between the two centers may be somewhat weaker than in the more symmetrically delocalized diphenylcy-clopropane radical cations. 

Solvolysis of trianisylvinyl bromide (229, X = Br) is only 1 7 times faster than that of a-bromo-p-methoxystyrene (Rappoport and Gal, 1968). The participation of the neighbouring /1-anisyl groups in the solvolysis, if any, is small, probably because the groups are held too far... 

The relative reactivities of aryl-tin bonds in (< -An)2SnPh2 (290) and (o-Tol)2SnPh2 toward iodine were determined686. The lower [o-AnI]/PhI value (5.2 1) compared to the [o-TolI]/PhI ratio (68 5.1) is considered to indicate an enhanced reactivity of the Ph—Sn bond in 290, arising from the nucleophilic assistance by an o-anisyl group during the Ph—Sn bond cleavage. 

The remarkable reactivity of trianisyl derivatives is certainly due to the a-anisyl group and not to the j8-groups. The rate of compound 138 relative to 139 in buffered acetone-water 7 3 at 120° is 830 whereas... 

This preorganization principle not only affects the thermodynamic stability of the complex but also has a pronounced effect on the kinetic stability of the alkali complexes of the spherands. The anisyl groups in the spherands provide the preorganized ligating donor sites, and they shield the cavity from solvent molecules. As a result, the rates of complexation by the spherands are decreased and the rates of decomplexation are decreased even more when compared with related flexible crown ethers. 

Scheme 6. Regioselective cleavage of />-anisyl groups from peri-substituted naphthalenes...

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