TBPS protection with

Ethyl L-lactate can be protected with a TBPS group by reaction with rer -butyldiphenylsilyl chloride and imidazole in either tetrahydrofuran [134] or DMF [135]. Alternatively, using DBU as the base in methylene chloride furnishes 427 in 100% yield [140]. 

Acetylenic diols, potential building blocks for the synthesis of L-hexoses and L-pentoses, are available with either syn or anti configuration using TBPS-protected L-lactic acid derivatives as the chiral source (Scheme 108). 

The chromium(II)-mediated addition (Hiyama reaction) of chiral allylic bromide 835 to lactaldehyde 831 proceeds with high Felkin—Anh selectivity to furnish exclusively adduct 836 [230]. In addition to the Felkin model, the high stereoselectivity is also explained by the effect of matched pairing of the two reaction partners. If the corresponding R-enantiomer of THP-lactaldehyde 831 is employed ( mismatched pair ), a mixture of three diastereomers (3 1 1) is produced. The THP group of 836 can be removed in the presence of the TBPS protecting group by treatment with PPTS in methanol (54% yield). 

The correct stereochemistry of the C-1 hydroxyl is introduced by reducing the carbonyl group of 527 with L-Selectride. Acylation of the alcohol with ( S)-a-methylbutyric anhydride, oxidation of the TBPS-protected primary alcohol to an aldehyde, and acetonide cleavage affords the penultimate lactol 528. Oxidation of this lactol with Fetizon s reagent (Ag2C03/Celite) gives ( + )-compactin (97) or ( + )-mevinolin (98). 

The nature of the diluent has an important role on the degradation rate of calix-arene (see Table 8.7). In dodecane, the loss of calixarene was very high, compared with measurements in the aromatic NPOE diluent. As already mentioned with other ligands (like TBP), aromatic diluents had a protective effect, explained by a lower ionization potential. However, serious radiolytic damage (e.g., a considerable rise in viscosity) has been observed with NPOE alone (68). Therefore, authors, such as Lamouroux, have suggested the use of a mixture NPOE-dodecane (72). 

To limit the radiolytic degradation of extractants, the influences of free-radical inhibitors have been measured. The addition of dimethoxybenzaldehydes (DMBA), particularly 3,5- and 3,4-DMBA, to the PUREX solvent could improve its stability and decrease its contamination (307). DMBA has a double effect, including a protective effect for the excited molecules of TBP (because of its low ionization potential), and the aldehyde radiolysis products could react with the HDBP present and therefore inhibit its complexing properties. 

In solution, phase amino acid derived methyl ester N-Fmoc-Tyr-OMe 4 was successfully condensed under Mitsunobu conditions with 2,3,4,6-tetra-Oacetyl-D-glucose 2 to afford the fully protected glucosylamine 5. The reaction provides products of analytical purity and predictable stero-chemistry, as confirmed by H/ C NMR. Synthetic conditions and protective groups for glycopeptides synthesis have been investigated. Mitsunobu conditions employed in solution phase are based on the improved redox system l,l -azodicarbonyldipiperidine (ADDP)—tributylphosphine (TBP) in... 

Fig. 7.9. Efficiency data for two test cells (active area 4 cm2) exposed to outdoor conditions for 1 year. The efficiencies of the cells were measured from time to time with an indoor solar simulator. The dye used is Ru(NCS)2(2,2 -bipyridyl-4,4 -dicarboxylate)2 (N719). 0.6 M hexylmethylimidazolium iodide (HMII), 0.1 M Lil, 0.05 M I2, 0.5 M tert-butylpyridin (TBP) in propionitril was used as the electrolyte. Surlyn 1702 (Dupont) was used as the sealant. The cells were placed under a window to protect them from rain. Test location INAP, Gelsenkirchen, Germany...

Several points are worth mentioning about the TBP family of compounds. First, the structure with axial Mn(lll) ions was obtained only in combination with equatorial Mn(II) ions, which can be explained by redox processes that take place when Mn(lII) is combined with other divalent metal ions, as well as the instability of the [Mn° CN)6] building block in the presence of protic solvents and the absence of free CN. A similar situation is observed in the case of equatorial Cr(II) ions that remain stable in the TBP cluster only when combined with axial Cr(III) ions. The only other complex with Cr(ll) was obtained in combination with [Ru (CN)5] , but the final product, [Cr (tmphen)2][Cr (tmphen)2]2[Ru (CN)6l2, contains both Cr(II) and Cr(lll) in the equatorial positions due to the reduction of axial Ru(lll) to Ru(ll) ions. Second, compounds [M(tmphen)2l3[M (CN)6l2, where M = Ru or Os, are the only structurally characterized complexes of hexacyanoruthenate(ni) and hexacyanoosmate(III) reported to date (178). Finally, the use of 7i-accepting tmphen ligands to protect the equatorial positions of the TBP cluster allows for stabilization of oxidation states that are not possible in the traditional extended structures of PB type. In the early literature, there were... 

The compound [Mn°(bpy)2]4[Mo (CN)g]2] (194), with an octahedral cyanide-bridged core, can be considered as an extension of the pentanuclear TBP clusters described in Section II. D. The equatorial plane of the SBP (octahedron) is formed by four Mn(II) ions, each of which has four out of six coordination sites protected by two bidentate bpy ligands (Fig. 41). The other two sites are coordinated by bridging CN hgands provided by [Mo (CN)g] ions that occupy axial positions of the SBP. The formation of the SBP instead of the TBP stmcmre is explained by the presence of octacyanometalate fragments in the axial positions and the sufficiently low steric constraints of the bpy ligands that cap the equatorial metal sites. 

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