Xylyl groups

Corey and colleagues studied the chiral induction of various analogs of 406 in which the phenyl groups on the tertiary carbinol unit were replaced by other aromatic groups. The use of 3,5-xylyl groups (catalyst 412) gave the best results. Cycloadduct 413, for example, was obtained with 95% ee in the presence of this catalyst255. 

These y and 8 will be the effect of the aryl group on the hydrogenolytic behavior. For example, 2,5,2 -TrMeDPM will be constituted from 2-MeDPM and 2,5-DMeDPM. When the value for the phenyl side is taken as 1, the value of the tolyl side becomes 4.88 (y), using the value obtained experimentally. In the same manner, that of a xylyl group becomes 7.33 ( ). 

Martell et al. (33g) while studying the complex equilibria of a new octaaza macrobicyclic cryptand, (MX)3(tren)2 (containing two tren moieties and three m-xylyl groups) reported the synthesis and... 

Assembling [2] rotaxanes (wheel and axle) can involve three basic processes (Scheme 13). One of these (93CC1269) involves slippage, in which the axle (115) is linked by a 4,4 -bipyridine, and the wheel (116) is a bisparaphenylene-34-crown-10 ether. Heating the two components in acetonitrile at 60°C yields the rotaxane, which can be characterized by FABMS and H and l3C NMR, but extrusion of the wheel occurs at 100°C. In other developments (94NAT(369)133), the pyridine component may be incorporated in the wheel, as in structure (117), where two bipyridinium units are connected by p-xylyl groups, and here the rotaxane acts as molecular switch. At room temperature in acetonitrile the wheel... 

Figure 5 Molecular structure of [TpPd( j.-CNXyl)]2 (510) with Xylyl groups and hydrogen atoms omitted for clarity.

In an approach towards a photochemically bistable molecular rotor, the synthesis of the sterically overcrowded isomeric alkenes cis-20a and trarcs-20b, functionalized with an o-xylyl group as a rotor, has been described (Eq. (55)) [87]. The key step in the synthesis was a Suzuki coupling to attach the xylyl moiety. 

Surprisingly, when the phenyl group of 1 is replaced by a 2,6-xylyl group, the same reduction results in an (R)-allylic alcohol, but usually in lower optical yield. 

The crystal structure of [(p-r-butylphenyl)2Mg]2(l,3,16,18-dixylyl-30-crown-8) [Compound 49] indicates that this crown ether has greater flexibility, giving rise to unique coordination environments around Mg [47]. The two diarylmagnesium units bond to the crown ether on either side of the two xylyl groups. The same geometry is observed in the crystal structure of (p-t-butylphenyOjMgldiglyme) [Compound 50], which is pentacoordinate with Mg and O in one plane [47]. The (p-r-butylphenyl)2Mg(tetraglyme)... 

Carboxylate and Related Complexes. The FTIR spectrum of M(Nap)3 (phen), where M = Y, La, Eu, Tb or Dy HNap = a-naphthoic acid, includes bands from bidentate carboxylates.348 IR and Raman data for [Ln(2,6-dhb)5(H20)2]2, where Ln = Sm, Tb Hdhb = 2,6-dihydroxybenzoic acid, also reveal vC02 bands from bidentate carboxylates.349 vC=0 bands for homo-binuclear Ln3+ complexes of (65) linked by p-xylyl groups are seen in the range 1580-1600 cm-1, compared to 1690 cm-1 for the free ligand (Ln = Eu, Tb, Yb).350... 

Yamamoto and cowoikers have recently found a chiral aluminum catalyst (79) that catalyzes the hetero cyclocondensation reaction (Scheme 28). In the reaction of benzaldehyde with diene (14) an enantiofacial selectivity of up to 95% ee was observed. A summary of substituted aldehydes and dienes used in this study is given in Table 20. As with the Eu(hfc)3 catalyst, the more substituted dienes give higher enantiofacial selectivity. Aromatic aldehydes are the best substrates and xylyl groups give the most efficient catalysts. The aluminum catalyst has also been extended to other simple aldehydes (Table 21) and has recently been used for the resolution of racemic dienophiles. ... 

The family of bis(cyclam macrocycles) represented by 32, in which the cyclam subunits are linked through nitrogen atoms by — (CH2) — (n = 2-4), m-xylyl, or p-xylyl groups, has been synthesized (58). The di-Ni(II) and di-Cu(II) complexes of these bis(macrocycles) have been used in an investigation of the effects of mutual electrostatic interaction on the redox behavior of the respective metal centers. 

Recently, a bis intercalating derivative of daunomycin has been studied [97]. In this compound the amino groups are joined by a xylyl group. This daunomy-... 

When the m-xylyl group is replaced by pyridine in these mixed amine/amide maaocycles, 21b, folded structures normally ensue as seen in the perrhenate structure (Figure 9b). In this case, the two secondary amines of the macrocycle are protonated, resulting in a host with charge complementarity for a dianionic guest. A similar structure is seen for dichromate as well. Protonation of the tertiary amines appears to be common in the pyridine series, potentially assisting in the... 

The self-assembly of an optically active [2]catenane involved the incoiporation of a chiral hydrobenzoin unit into one of its component rings one of the p-xylyl groups in the tetracationic cyclophane may be substituted by a flexible CH2CX H2CH20CH2CH2 chain without impeding catenane formation (Scheme 18). However, when both the p-xylyl units are replaced, the tetracationic cyclophane loses its ability to complex with Tc-electron rich aromatic substrates. This achievement has implications for the design of chiral solid-state devices and the construction of asymmetric catalysts. 

Previous to this study, the Tolman group had also reported on complexes similar to the XYL-H model system which employ dinucleating triazacyclononane moieties linked by m- orp-xylyl groups. These systems form either (i-T) T] -peroxodicopper(II) complexes or bis-ji-oxo-dicopper(III) complexes, depending on conditions such as solvent, temperature, and concentration. Based on this report, the p.-Ti iri -peroxodicopper(II) complex leads to arene hydroxylation, similar to the XYL-H system, whereas the bis-ji-oxo-dicopper(IH) complex favors monooxygenation leading to N-dealkylation. 

The 2,6-xylyl group (C(31)-C(38)) is twisted 62.5° out the metal iminoacyl plane to diminish steric interactions with the THF molecule. The THF ring is twisted 20.2° out the same plane in the same direction [146]. 

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