40335-59-9Relevant academic research and scientific papers
Preparation and Structural Analysis of Several New α,α,α',α'-Tetraaryl-1,3-dioxolane-4,5-dimethanols (TADDOL's) and TADDOL Analogs, Their Evaluation as Titanium Ligands in the Enantioselective Addition of Methyltitanium and Diethylzinc Reagents to Benzaldehyde, and Refinement of ...
Ito, Yoshio N.,Ariza, Xavier,Beck, Albert K.,Bohac, Andrej,Ganter, Camille,et al.
, p. 2071 - 2110 (2007/10/02)
Preparation and screening of twenty new ligands, all analogs of α,α,α',α'-tetraaryl-1,3-dioxolane-4,5-dimethanol (TADDOL), for the Ti-catalyzed asymmetric addition of methyltri(isopropoxy)titanium and diethylzinc to benzaldehyde are described.These ligands have the dioxolane ring of the TADDOL's replaced by cyclobutane, cyclopentane, cyclohexene, cyclohexane, bicycloheptene and -heptane and bicyclooctene and -octane moieties; several have H-atoms or alkyl groups in place of the aryl groups, and nine of them have C2 symmetry.X-Ray crystallography and molecular mechanics are used to analyze the structure of the ligands, and two structural features appear to correlate with selectivity: i) the torsion angle for the chelating O-atom and the ortho-C-atom of the axial Ph group (a small, ca. 19 deg, angle is optimum, Fig. 8) and ii) the "degree of perpendicularity" of the axial Ph group (Fig. 9).Competition experiments indicate that TADDOL 1a catalyzes both the methyltitanium and diethylzinc additions >/= 50 times faster than the related dioxolane analogs 12a, 12c, and 12e (Scheme 7), indicating that both axial and equatorial aryl groups (see Footnote 6) are necessary for ligand-accelerated catalysis of these reactions.A refined mechanistic hypotesis is presented (Fig. 10) to explain the selectivities observed for these new ligands.Our analysis suggests that a combination of structural features appear necessary for good catalytic efficiency and high selectivity.These features, especially the rather subtle conformational effects, appear to be optimized (among the ligands tested) in the TADDOL's.
Enzymatic optical resolution of norbornanecarboxylic esters using Pig Liver Esterase
Gastel, F. J. C. van,Klunder, A. J. H.,Zwanenburg, B.
, p. 175 - 184 (2007/10/02)
The hydrolysis of a series of norbornane-type carboxylic esters catalyzed by pig liver esterase (PLE) has been investigated.It was found that an exo-ester function (syn to the C7 methylene group) is hydrolyzed with high preference.Enantioselective hydrolysis can be accomplished when a vicinal carbonyl-containing function (ester, formyl, acetyl) is present in a trans position with respect to the exo ester.The regiospecifity of the enzymatic hydrolysis has been used for the separation of exo/endo mixtures of the cycloadducts derived from cyclopentadiene and alkene esters.The regiospecifity and enantioselectivity of the enzymatic hydrolysis of norbornane-type esters were analyzed in terms of Tamm's substrate model and also by Griengl's method.
Deuterium Kinetic Isotope Effects in the 1,4-Dimethylenecyclohexane Boat Cope Rearrangement
Gajewski, Joseph J.,Jimenez, Jose Leonardo
, p. 468 - 474 (2007/10/02)
In order to examine the extent of bond making in the boat-like 3,3-sigmatropic shift transition states, trans-2,3-dimethyl-1,4-dimethylenecyclohexane (T) and its exomethylene tetradeuteria derivative (TXD) were prepared.The 3,3-shift of TXD at 305 deg C r
Derivatives of Bicyclooctane-2,6:3,5-dicarbolactone
Carman, Raymond M.,Smith, Stephanie S.
, p. 1285 - 1294 (2007/10/02)
The reactions of the title dilactone with both acid and base are discussed.Evidence is presented for stable γ-lactones in the bicyclooctane-2,6-carbolactone series.Epimerization α to hindered acid groups occurs under acetylating conditions to relieve steric strain in this system.
