88586-06-5Relevant articles and documents
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 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).
