TBPS group

The enhanced stability of the TBPS group relative to the TMS or TBS groups, in addition to its steric bulk, makes this protecting group extremely versatile to the organic chemist. 

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]. 

In both cases the TBPS group is removed with fluoride to afford the corresponding diols, R=TMS (90% overall yield) and R=CH(OEt)2 (70% overall yield) [225]. 

Epoxide 303 has been used an an enantioselective synthesis of the methylenecyclopropa-neacetic acid (514a) portion of (methylenecyclopropyl)acetyl-CoA (514b), a mammalian metabolite of hypoglycines A and B. Addition of the anion derived from phenyl 2-(tri-methylsilyl)ethyl sulfone to 303 produces a 3 1 mixture of threo and erythro diastereomers 509. Either diastereomer cyclizes to the same cyclopropane 511 upon treatment with LDA, which suggests that epimerization at C-5 must be occurring prior to cyclization. Selective removal of the TBPS group followed by oxidation of the alcohol to an acid and elimination affords the desired product 514a (Scheme 73) [126,127]. 

Recently we developed catalyst systems, a combination of the Ti complexes having 2,2 -thiobis(4-methyl-6- t-butyl-phenoxy) (TBP) group and MAO, which are specifically active toward styrene, giving syndiotactic polymer and also active toward olefins. In the present work we found that these catalyst systems can copolymerize styrene with ethylene, giving highly alternating ethylene-styrene (ES) copolymer. This paper deals with the results of styrene... 

The only sequence-specific hydrogen bonds between TBP side chains and the bases in the minor groove occur at the very center of the TATA box (Figure 9.7). The amide groups of two asparagine side chains donate four hydrogen bonds, two each to adjacent bases on the same DNA strand (Asn 69... 

TFIIA and TFIIB are two basal transcription factors that are involved in the nucleation stages of the preinitiation complex by binding to the TBP-TATA box complex. Crystal structures of the ternary complex TFIIA-TBP-TATA box have been determined by the groups of Paul Sigler, Yale University, and Timothy Richmond, ETH, Zurich, and that of the TFIIB-TBP-TATA box by Stephen Burley and collaborators. The TBP-DNA interactions and the distortions of the DNA structure are essentially the same in these ternary complexes as in the binary TBP-TATA complex. 

Ru04 , which is believed to be tetrahedral in solution, is formed from Ru04 and excess concentrated aqueous KOH, isolable as black crystals of K2Ru04.H20, which is actually K2[Ru03(0H)2]. The anion has a tbp structure with axial OH groups (Ru=0 1.741-1.763 A, Ru—OH 2.028-2.040 A) [55],... 

On the other hand, the [Bu2Sn(lV)] complexes of the O analogs of the above-mentioned ligands are linear oligomers. The FT-IR and Raman spectroscopic data indicated the presence of bidentate and/or monodentate -COO groups, nonlinear C-Sn-C bonds, and Sn-O bonds within the complexes. The results of Mossbauer spectroscopic measurements showed a Tbp arrangement around the central Sn atom in addition to the and structures. ... 

The FT-IR spectroscopic measurements shown that in most cases the -COO or -0 groups formed a bridge between two Sn central atom, and polymerization occurred. The pqs approximations proved the formation of complexes with Oh, Tbp, and structures. H NMR measurements performed in DMSO solution have shown that the polymeric structure of the complexes does not persist in solution, and depolymerization occurs.. ... 

Diphenic acid (H2A) also forms diorganotin(IV) complexes, which are with two monodentate -COO groups. On the other hand, soluble dinuclear triorganotin(IV) complexes (where the organo moieties are Me and Ph) contain symmetrically bound carboxylates, while the less-soluble compound (cHexsSn) has two asymmetrically bonded carboxylates. All have Tbp structures with [RsSnirV)] units remote from each other. °... 

R3Sn(IV)]4H2TPPS, (R = Me, Bu, Ph), respectively, in the solid state, are maintained in solution. Pentacoordination, in a Tbp configuration, eq-Rs, has been proposed for RsSnflV) derivatives of L-homocysteic acid on the basis of IR and Mossbauer spectroscopy The SO3 and NH3 groups of L-homocysteic acid are not involved in the coordination. 

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