Stereochemistry of the reduction step mediated by recombinant 1-deoxy-D-xylulose 5-phosphate isomeroreductase

[formula: see text] The stereochemistry of the 1-deoxy-D-xylulose 5-phosphate (DXP) isomeroreductase reduction step has been examined using the recombinant enzyme from Synechocystis sp. PCC6803. Using [3-2H]DXP and [4S-2H]NADPH, it has been determined that the C1 pro-S hydrogen in the 2-C-methyl-D-erythritol 4-phosphate product derives from C3 of DXP, indicating that hydride attack occurs on the re face of the intermediate aldehyde. The 4S-hydride from NADPH is delivered, assigning this enzyme as a class B dehydrogenase.     

Stereochemistry in the synthesis and reaction of exo-glycals

Two general methods are explored for the stereoselective synthesis of exo-glycals. One method utilizes a nucleophilic addition of fully protected sugar lactones of gluco-, galacto-, and manno-types, followed by the subsequent dehydration, to give the desired exo-glycals with (Z)-configuration. The other method proceeds with selenylation of C-glycosides in a stereoselective manner. The subsequent selenoxide elimination also provides (Z)-exo-glycals. The prepared exo-glycal conjugated esters of either gluco- or manno-type react with allyl alcohol to give exclusively alpha-anomers.     

Stereochemistry of the glyoxylate N-sulfonylimine ene reaction

Ene reactions of sulfonylimine $\text{1b}$ with cyclohexane and $\text{trans}$-2-butene are highly stereoselective, affording products $\text{4}$ and $\text{10}$, respectively.     

Thiourea dioxide catalyzed multi-component coupling reaction for the one step synthesis of naphthopyran derivatives

An aqueous solution of thiourea dioxide was used to catalyze a one-pot three-component coupling reaction of an aromatic aldehyde, malononitrile, and α- or β-naphthol for the synthesis of various naphthopyran derivatives in excellent yields. At the end of the reaction, the product was isolated by filtration or extraction and the remaining aqueous solution of thiourea dioxide was reused as such for several subsequent runs.     

Stereochemistry of the aza-Michael reaction with natural alantolactones

Hydrogenated 3-aminomethylnaphtho[2,3-b]furan-2-ones were synthesized by the reaction of natural alantolactones with pharmacophoric amines. Determination of the newly formed asymmetric center configuration by two-dimensional NMR data is presented. The structure of the obtained compounds was proved by X-ray structural analysis.     

Stereochemistry in the reaction of alkylsulfinyl phenylmethyl carbanion with electrophiles

Stereochemistry of the reactions of methyl-, ethyl-, 2-propyl-, and 1,1-dimethylethylsulfinyl phenylmethyl carbanions with deuterium oxide and methyl iodide in tetrahydrofuran have been studied. The 2-propylsulfinyl phenylmethyl carbanion exerts abnormal behavior in the sense that the alkyl substituent herein has no ability to freeze the conformation of the carbanion. The results are interpreted in terms of hard and soft interactions. ⁷Li and ¹⁷O nuclear magnetic resonance (NMR) spectroscopy revealed that the carbanions derived from these sulfoxides behave as the oxylate form.     

Stereochemistry of reaction paths at carbonyl centres

Results of recent experimental and theoretical studies of nucleophilic addition to carbonyl groups are described. The reaction paths found by different methods for different nucleophiles show some striking similarities that appear to be characteristic for the reaction type.     

Stereochemistry of the vinylogous sN2′ reaction

Theoretical treatment indicates that the stereochemistry of both the vinylogous S_N2′ and 1,6- conjugate elimination reaction will be opposite to that of the S_N2′ and 1,4-conjugate elimination reaction.     

Stereochemistry at titanium in the sulfur dioxide insertion reaction of titanocene compounds

The insertion reaction of SO₂ has been studied for the two diastereoisomeric forms of η⁵-C₅H₅-η⁵-C₅H₄ CHMePhTi(C₆F₅)CH₃. The reaction is regioselective and stereospecific. Arguments that it involves a retention at the titanium atom are given.     

Stereochemistry as a probe for photochemical reaction mechanisms

In this publication we have reviewed examples derived from our photochemical investigations where stereochemistry provides information allowing elucidation of the mechanistic details of electronically excited state transformations. The reactions discussed include unimolecular rearrangements of both singlet and triplet excited state species.