88586-06-5Relevant academic research and scientific papers
Nonreductive enantioselective ring opening of N-(methylsulfonyl)dicarboximides with diisopropoxytitanium α,α,α′,α′-tetraaryl-1,3-dioxolane-4,5- dimethanolate
Ramon, Diego J.,Guillena, Gabriela,Seebach, Dieter
, p. 875 - 894 (2007/10/03)
The bicyclic and tricyclic meso-N-(methylsulfonyl)dicarboximides 1a-f are converted enantioselectively to isopropyl [(sulfonamido)carbonyl]-carboxylates 2a-f by diisopropoxytitanium TADDOLate (75-92% yield; see Scheme 3). The enantiomer ratios of the products are between 86:14 and 97:3, and recrystallization from CH2Cl2/hexane leads to enantiomerically pure sulfonamido esters 2 (Scheme 3). The enantioselectivity shows a linear relationship with the enantiomer excess of the TADDOL employed (Fig. 3). Reduction of the ester and carboxamide groups (LiAlH4) and additional reductive cleavage of the sulfonamido group (Red-Al) in the products 2 of imide-ring opening gives hydroxy-sulfonamides 3 and amino alcohols 4, respectively (Scheme 4). The absolute configuration of the sulfonamido esters 2 is determined by chemical correlation (with 2a, b; Scheme 6), by the X-ray analysis of the camphanate of 3e (Fig. I), and by comparative 19F-NMR analysis of the Mosher esters of the hydroxy-sulfonamides 3 (Table I). A general proposal for the assignment of the absolute configuration of primary alcohols and amines of Formula HXCH2CHR1R2, X = O, NH, is suggested (see 11 in Table I). It follows from the assignment of configuration of 2 that the Re carbonyl group of the original imide 1 is converted to an isopropyl ester group. This result is compatible with a rule previously put forward for the stereochemical course of reactions involving titanium TADDOLate activated chelating electrophiles (12 in Scheme 7). A tentative mechanistic model is proposed (13 and 14 in Scheme 7).
Enzymes in organic synthesis 49. Resolutions of racemic monocyclic esters with pig liver esterase
Toone,Jones
, p. 207 - 222 (2007/10/02)
Pig liver esterase (PLE)- catalyzed hydrolyses of the racemic methyl esters of cyclobutane-, cyclohexane-, and cyclohex-4-ene-carboxylic acids bearing cis-2-methyl or cis-2-bromomethyl substituents are highly stereoselective, giving the corresponding acid products of ≥ 97% ee. The stereoselectivity of the enzyme exhibits the expected reversal for such compounds, with the absolute configurations of the cyclobutane and cyclohexame acids being of the opposite absolute configuration type, and cyclopentane substrates such as cis-1-carbomethoxy-2-methylcyclopentane representing the change-over structures and giving products of only 22%ee. This stereoselectivtiy reversal, and the absolute configurations preferred, are as predicted by the recently proposed active site model for the enzyme.
ENZYMATIC RESOLUTION OF RACEMIC BICYCLIC LACTONES BY HORSE LIVER ESTREASE
Guibe-Jampel, E.,Rousseau, G.,Blanco, L.
, p. 67 - 68 (2007/10/02)
Optically active lactones were prepared by Horse Liver esterase catalyzed hydrolysis of bicyclic γ-butyrolactones.
ENZYMATIC RESOLUTION OF RACEMIC LACTONES
Blanco, L.,Guibe-Jampel, E.,Rousseau, G.
, p. 1915 - 1918 (2007/10/02)
PPL, HLE or PLE enzymatic resolution of racemic γ, δ and ε-lactones gives optically active lactones (ee: 60 to 90percent).
Enzyme-catalysed Asymmetric Synthesis, IV. - Synthesis of Homochiral Building Blocks for the Enantioselective Total Synthesis of Cyclopentanoids with an Esterase-catalysed Asymmetric Reaction as Key Step
Gais, Hans-Joachim,Lukas, Karl L.,Ball, Walter A.,Braun, Siegmar,Lindner, Hans J.
, p. 687 - 716 (2007/10/02)
An efficient synthesis of the homochiral building blocks 2a and ent-2a based on the "enantiotopos-enzyme concept" for the total synthesis of cyclopentanoids is described.Key steps thereof are the almost quantitative PLE-catalysed asymmetric hydrolysis of the meso-diester 8 to the homochiral hemiester 9, whose absolute configuration was determined by crystal structure analysis of the (-)-ephedrine salt 12, the preparation of optically pure 9 and ent-9 by a racemate resolution of rac-9 using (+)- and (-)-ephedrine, the enantiodivergent synthesis of the lactones 18 and ent-18 from 9, as well as the enantioconvergent synthesis of 18 or ent-18 from 9 and ent-9 by optional chemoselective reduction of the ester and carboxy group, and finally the regioselective Dieckmann cyclisation of the isomeric diesters 23b/24b and ent-23b/ent-24b, respectively, to give the cyclopentanoid target compounds 2a and ent-2a.The structures of 23b, 24b, rac-2b, and rac-29 were determined by INADEQUATE-13C-NMR experiments.Dieckmann cyclisation of the trans-diester rac-31 also leads to rac-2a and rac-26a.
