Ligands tricyclic

The Rh2(DOSP)4 catalysts (6b) of Davies have proven to be remarkably effective for highly enantioselective cydopropanation reactions of aryl- and vinyl-diazoacetates [2]. The discovery that enantiocontrol could be enhanced when reactions were performed in pentane [35] added advantages that could be attributed to the solvent-directed orientation of chiral attachments of the ligand carboxylates [59]. In addition to the synthesis of (+)-sertraline (1) [6], the uses of this methodology have been extended to the construction of cyclopropane amino acids (Eq. 3) [35], the synthesis of tricyclic systems such as 22 (Eq. 4) [60], and, as an example of tandem cyclopropanation-Cope rearrangement, an efficient asymmetric synthesis of epi-tremulane 23 (Eq. 5) [61]. 

Fig. 7.4. Tricyclic transition structures for aminoalcohol catalysts syn and anti refer to the relationship between the transferring group and the bidentate ligand cis and trans refer to the relationship between the aldehyde substituent and the coordinating zinc. Reproduced from J. Am. Chem. Soc., 125, 5130 (2003), by permission of the American Chemical Society.

The susceptibility of phosphites to hydrolysis limits their application as ligands for homogeneous catalysis. The fused tricyclic monophosphites derived from ca 1 i x[4]arenes260-262 form coordination complexes with palladium.263... 

Asymmetric synthesis of tricyclic nitro ergoline synthon (up to 70% ee) is accomplished by intramolecular cyclization of nitro compound Pd(0)-catalyzed complexes with classical C2 symmetry diphosphanes.94 Palladium complexes of 4,5-dihydrooxazoles are better chiral ligands to promote asymmetric allylic alkylation than classical catalysts. For example, allylic substitution with nitromethane gives enantioselectivity exceeding 99% ee (Eq. 5.62).95 Phosphi-noxazolines can induce very high enatioselectivity in other transition metal-catalyzed reactions.96 Diastereo- and enantioselective allylation of substituted nitroalkanes has also been reported.9513... 

Erker and Trinkl synthesized the tricycles 177 as novel GABA-A/benzodiazepine receptor ligands via synthesis of enol phosphates such as 175 and reaction with isocyanides 176 (Scheme 13) <2001H1963>. 

To illustrate the multifaceted chemistry of nitrones and their application in synthesis, let us consider the synthetic scheme of bicyclic and tricyclic chiral ligands (Scheme 2.1) (7) as well as diastereo- and enantiostereoselective syntheses of alkaloids (Scheme 2.2) (8). 

A unique tricyclic bisphospholane ligand, C5-Tricyclophos (34), has been described in a patent by Zhang [57]. Derived from resolved bicyclopentyl-2,2 -diol (originally used in the preparation of the chiral diphosphine, B1CP [58]), this li-... 

Tricresyl phosphate, 11 493, 494 Tricyanocuprate(I), 7 578t Tricyanovinyl dyes, 9 258 Tricyclic encapsulating ligand, tetraprotonated form of, 24 44 cis,lrares-Tricyclodecanediamine physical properties of, 2 500t Tricyclohexyl citrate... 

These findings imply that, in the case of secondary radicals, the trapping with a second equivalent of Cp2TiCl can compete with tetrahydrofuran formation, and that -hydride elimination can kinetically compete with protonation of Ti - C bonds under our protic conditions [65,66,73,74], It remains to be seen how the reaction can be completely driven toward the tricyclic system 60 by ligand variation of the catalyst. 

In the case of ligands E, F and H the chelate/cryptate nature of the complexes will depend on whether or not the cation is contained between a branch and a ring or between two rings, or included inside a ring. Of course, in such cases, the above definitions, which concern the limiting cases, are less clear and classification may have to await a crystal structure determination. Finally, complexes formed by inclusion of a cation in a cavity delimited by a monocyclic, bicyclic or tricyclic structure may... 

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