Efikasno premeštanje push-pull 5-supstituisanih 4-oksotiazolidina indukovano piridinijum-hidrobromid-perbromidom pod homogenim reakcionim uslovima

Pyridinium hydrobromide perbromide (PHBP) is a highly efficient reagent for the conversion of 5-substituted-2-alkylidene-4-oxothiazolidine derivatives to the corresponding thiazolidines with two fully delocalized exocyclic double bonds at the C(2) and C(5) positions. This conversion as a two-step bromination-rearrangement process occurs in acetonitrile under homogeneous reaction conditions.Piridinijum-hidrobromid-perbromid (PHBP) je veoma efikasan reagens za konverziju 5-supstituisanih-2-alkiliden-4-oksotiazolidinskih derivata u odgovarajuće tiazolidine sa dve potpuno delokalizovane egzociklične dvogube veze u položajima C(2) i C(5). Ova konverzija je dvofazni proces bromovanja i premeštanja koji se odvija u acetonitrilu pod homogenim reakcionim uslovima

Vodonična veza u push-pull 5-supstituisanim 2-alkiliden-4-oksotiazolidinima: 1H-NMR spektroskopsko proučavanje

Application of dynamic H-1-NMR spectroscopy added to the understanding of the hydrogen bonds existing in the structurally related 5-substituted-2-alklidene-4-oxothiazolidines in polar and apolar solvents. The equilibrated mixtures of these topical push-pull alkenes in CDCl3 consist of the intramolecularly H-bonded (E)-isomer and intermolecularly H-bonded (Z)-isomer in varying proportions which depend on the solvent polarity. For the representative of the series. (Z)-2-(5-ethoxycarbonylmethyl-4-oxothiazolidin-2-ylidene)-1-phenylethanone, a concentration effect on the degree of intermolecular hydrogen bonding in apolar CDCl3 has been studied.Primenom dinamičke 1H-NMR spektroskopije došlo se do boljeg razumevanja o vrsti vodoničnih veza koje postoje u strukturno sličnim 5-supstituisanim 2-alkiliden-4-oksotiazolidinima u polarnim i apolarnim rastvaračima. Uravnotežene smese ovih tipičnih push-pull alkena u CDCl3 sadrže (E)-izomer vezan intramolekulskom vodoničnom vezom kao i intermolekulski vodoničnom vezom vezan (Z)-izomer u različitim odnosima, koji zavise od polarnosti rastvarača. U slučaju tipičnog predstavnika serije (Z)-2-(5-etoksikarbonilmetil-4-oksotiazolidin- 2-iliden)-1-feniletanona uticaj koncentracije na stepen stvaranja intermolekulske vodonične veze u apolarnom CDCl3 je takođe proučavan

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-pull thiazolidines 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

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

Regioselective a-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-oxo-thiazolidine 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. (C) 2001 Elsevier Science Ltd. All rights reserved

Regioselective synthesis of a stereodefined heterocyclic push-pull alkene - H-1 NMR studies and two-dimensional TLC illustrating Z/E isomerization

Introducing students to the regioselective synthesis of a stereodefined push-pull alkene from inexpensive chemicals can be facilicated through experiment. In the experiment, preparation of the precursor, such as diethyl mercaptosuccinate from mercaptosuccinic acid and ethanol in toluene as a cosolvent, demonstrates the educational significance of binary and tertiary azeotropes in practical organic synthesis. The utility of 1H NMR spectroscopy is illustrated as a tool to identify the configurational isomers and to study the stereodynamic behavior of the isolated heterocyclic product

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

Base-catalyzed reactions of beta-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. (C) 2003 Elsevier Ltd. All rights reserved

Kinetics and mechanism of structural transformations of 2-(5-ethoxycarbonylmethyl-4-oxothiazolidin-2-ylidene)-N-(2-phenylethyl)-ethanamide during heating

The kinetics and mechanism of the structural transformation of 2-(5-ethoxycarbonylmethyl-4-oxothiazolidin-2-ylidene)-N-(2-phenylethyl)-ethanamide in non-isothermal conditions were studied by using isoconversion as well as non-isoconversion techniques. It was shown that the crystal, Z-form of compound, was stable in the temperature range from room temperature to melting point, when E-form of compound was formed. This process involves the breaking of crystal structure and the forming of glass material as a new phase, which by cooling forms crystal of the E-form of compound very slowly. The dependences of kinetic parameters on fractional extent conversion were determined indicating a very complex process which involves more than one elementary step, as can be expected for most solid state reactions. The possible mechanism of the process was discussed according to the algorithm concerning the form of these dependences. The evaluation of kinetics parameters and isokinetic relationships were done by combination of model fitting and model-free approach