Marija Baranac

Stereo- and regiocontrol of electrophile-initiated rearrangement of push–pull 5-substituted 4-oxothiazolidine derivatives

Abstract Regioselective α-bromination of ( Z )-5-substituted-2-alkylidene-4-oxothiazolidine derivatives affords, under mild experimental conditions, vinyl bromides 3 in good yields. They undergo rearrangement providing a highly efficient route to the stereodefined 4-oxothiazolidine derivatives possessing two fully delocalized exocyclic double bonds at C(2) and C(5) positions. A mechanism of this novel rearrangement reaction via base-promoted proton transfer from one carbanionic site to another, followed by the bromination–dehydrobromination sequence, is proposed.

High regioselectivity in the heterocyclization of β-oxonitriles to 4-oxothiazolidines: X-ray structure proof

Base-catalyzed reactions of β-oxonitriles 1 with diethyl mercaptosuccinate favour heterocyclization to afford 2-alkylidene-4-oxothiazolidines 3, rather than 2-alkylidene-4-oxo-1,3-thiazinanes 4. The observed regioselectivity is based on spectroscopic and experimental evidence, including a single-crystal X-ray structure determination.

A novel and efficient 4-oxothiazolidine-1,2-dithiole rearrangement induced by Lawesson's reagent

Abstract Functionalized 1,2-dithioles have been synthesized by a ring opening–closing process of 5-substituted- and 5-unsubstituted-2-alkylidene-4-oxothiazolidines with Lawessons reagent. The 13 C NMR data confirmed the meso -ionic structure of these aromatic-type 1,2-dithioles.

Stereocontrolled synthesis of new tetrahydrofuro[2,3-d]thiazole derivatives via activated vinylogous iminium ions

Heterocyclization of (Z)-5-(2-hydroxyethyl)-3-methyl-4-oxothiazolidines, bearing electron-withdrawing groups conjugated to an exocyclic double bond at C(2)-position, afforded under reductive conditions, cis-tetrahydroftiro[2,3- d]thiazole derivatives. The reactions of these functionalized push-pull beta-enamines occur in a stereocontrolled fashion via activated vinylogous N-methyliminium ions, which are trapped by an internal hydroxyethyl group

Sequential Bromination-Rearrangement of Push-Pull Thiazolidines Induced by Pyridinium Hydrobromide Perbromide under Homogenous Reaction Conditions

Regiospecific bromination-rearrangement of the 5-substituted 2-alkylidene-4-oxothiazolidine derivatives induced by pyridinium hydrobromide perbromide (PHBP) provides a new synthetic approach to the corresponding push-pullthiazolidines with two exocyclic double bonds. In comparison to a heterogenous alternative, this conversion, taking place in acetonitrile under homogenous reaction conditions, has the advantage of almost quantitative yields and a substantial rate enhancement.

Nucleophilic Functionalization of 2-Alkylidene-4-Oxothiazolidines at C(5)-Position Induced by Formation of Novel Pyridinium Salt

Abstract The synthesis of unsubstituted pyridinium salt containing the 4-oxothiazolidine moiety bondedviaC(5) to the N position of the pyridine nucleus is reported. The nucleophilic displacement of pyridine from pyridinium salt by the selected nucleophiles leads to the formation of new 5-substituted 4-oxothiazolidines in good yields.

Mechanism of stereoselective synthesis of push-pull (Z)-4-oxothiazolidine derivatives containing an exocyclic double bond. A MNDO-PM3 Study

Calculations using the MNDO-PM3 method were performed to elucidate the mechanism of stereoselective base-catalyzed reaction affording exclusively (Z)-2-alkylidene-4-oxothiazolidine push-pull derivatives from the corresponding α-mercapto esters and activated β-oxonitriles in ethanol as a solvent.