The Equilibrium Between 2-Lithium-Oxazole(-Thiazole, -Imidazole) Derivatives and Their Acyclic Isomers - A Structural InvestigationDedicated to Professor Dr. D. Seebach on the occasion of his 60th birthday.
2-Metallated oxazoles, thiazoles and imidazoles are of interest for the preparation of derivatives of the respective heterocycles, and - especially in the case of metallated thiazoles - as acyllithium equivalents in organic syntheses. Metallation at C2 of these compounds, however, often leads (more so with Li-oxazoles than with Li-thiazoles and Li-imidazoles) to products derived from the acyclic isomers of the metallated heterocycles. In order to obtain more information on the positions of the relevant equilibria, we have carried out a 13C-NMR study of substituted li- and ZnCl-oxazoles, Li-thiazoles and Li-imidazoles. In the case of Li-oxazoles, the equilibrium is completely on the side of the acyclic isomers. Addition of ZnCl2, however, leads to ring-closure, and, even in the case of 2-ZnCl-substituted benzoxazole, only the ring-closed isomer is observed. This demonstrates a dramatic gegenion effect on the equilibrium between two isomeric anions. In the case of Li-thiazoles, depending on the substitution pattern, either solely the ring-closed or an equilibrium with the ringopened isomer is observed. In the series of Li-imidazoles, only the 2-lithiated benzimidazole is in equilibrium with its ring-opened isomer. The tendency of these compounds to undergo ring-opening parallels the leaving group properties of the various subunits [OLi > SLi > R2NLi, and phenyl-O(S, NR)Li > vinyl-O(S, NR)Li]. The difference between the effects of Li+ vs. ZnCl+ in the (benz)oxazole series is in agreement with results of solid-state structure investigations of 2-lithiated and a 2-zincated thiazole: in the Li compound the C-S bond is 2.9 pm longer than in the ZnCl species, indicating a more facile C-S bond cleavage with Li+ as the gegenion..
| Medienart: |
E-Artikel |
|---|
| Erscheinungsjahr: |
1997 |
|---|---|
| Erschienen: |
1997 |
| Reproduktion: |
Wiley InterScience Backfile Collection 1832-2000 |
|---|---|
| Enthalten in: |
Zur Gesamtaufnahme - volume:130 |
| Enthalten in: |
Berichte der deutschen chemischen Gesellschaft - 130(1997) vom: Sept., Seite 1213-1221 |
| Sprache: |
Deutsch |
|---|
| Beteiligte Personen: |
Hilf, Christoff [Sonstige Person] |
|---|
| Links: |
dx.doi.org [Deutschlandweit zugänglich] |
|---|
| Umfang: |
9 |
|---|
| Förderinstitution / Projekttitel: |
|
|---|
| PPN (Katalog-ID): |
NLEJ161578888 |
|---|
| LEADER | 01000caa a22002652 4500 | ||
|---|---|---|---|
| 001 | NLEJ161578888 | ||
| 003 | DE-627 | ||
| 005 | 20230506163746.0 | ||
| 007 | cr uuu---uuuuu | ||
| 008 | 070201s1997 xx |||||o 00| ||ger c | ||
| 035 | |a (DE-627)NLEJ161578888 | ||
| 040 | |a DE-627 |b ger |c DE-627 |e rakwb | ||
| 041 | |a ger | ||
| 245 | 1 | 0 | |a The Equilibrium Between 2-Lithium-Oxazole(-Thiazole, -Imidazole) Derivatives and Their Acyclic Isomers - A Structural InvestigationDedicated to Professor Dr. D. Seebach on the occasion of his 60th birthday. |
| 264 | 1 | |c 1997 | |
| 300 | |a 9 | ||
| 336 | |a nicht spezifiziert |b zzz |2 rdacontent | ||
| 337 | |a nicht spezifiziert |b z |2 rdamedia | ||
| 338 | |a nicht spezifiziert |b zu |2 rdacarrier | ||
| 520 | |a 2-Metallated oxazoles, thiazoles and imidazoles are of interest for the preparation of derivatives of the respective heterocycles, and - especially in the case of metallated thiazoles - as acyllithium equivalents in organic syntheses. Metallation at C2 of these compounds, however, often leads (more so with Li-oxazoles than with Li-thiazoles and Li-imidazoles) to products derived from the acyclic isomers of the metallated heterocycles. In order to obtain more information on the positions of the relevant equilibria, we have carried out a 13C-NMR study of substituted li- and ZnCl-oxazoles, Li-thiazoles and Li-imidazoles. In the case of Li-oxazoles, the equilibrium is completely on the side of the acyclic isomers. Addition of ZnCl2, however, leads to ring-closure, and, even in the case of 2-ZnCl-substituted benzoxazole, only the ring-closed isomer is observed. This demonstrates a dramatic gegenion effect on the equilibrium between two isomeric anions. In the case of Li-thiazoles, depending on the substitution pattern, either solely the ring-closed or an equilibrium with the ringopened isomer is observed. In the series of Li-imidazoles, only the 2-lithiated benzimidazole is in equilibrium with its ring-opened isomer. The tendency of these compounds to undergo ring-opening parallels the leaving group properties of the various subunits [OLi > SLi > R2NLi, and phenyl-O(S, NR)Li > vinyl-O(S, NR)Li]. The difference between the effects of Li+ vs. ZnCl+ in the (benz)oxazole series is in agreement with results of solid-state structure investigations of 2-lithiated and a 2-zincated thiazole: in the Li compound the C-S bond is 2.9 pm longer than in the ZnCl species, indicating a more facile C-S bond cleavage with Li+ as the gegenion. | ||
| 533 | |f Wiley InterScience Backfile Collection 1832-2000 | ||
| 700 | 1 | |a Hilf, Christoff |4 oth | |
| 700 | 1 | |a Bosold, Ferdinand |4 oth | |
| 700 | 1 | |a Harms, Klaus |4 oth | |
| 700 | 1 | |a Marsch, Michael |4 oth | |
| 700 | 1 | |a Boche, Gernot |4 oth | |
| 773 | 0 | 8 | |i in |t Berichte der deutschen chemischen Gesellschaft |d Weinheim : Wiley-VCH |g 130(1997) vom: Sept., Seite 1213-1221 |w (DE-627)NLEJ159071097 |x 0365-9496 |7 nnns |
| 773 | 1 | 8 | |g volume:130 |g year:1997 |g month:09 |g pages:1213-1221 |g extent:9 |
| 856 | 4 | 0 | |u http://dx.doi.org/10.1002/cber.19971300908 |q text/html |z Deutschlandweit zugänglich |
| 912 | |a GBV_USEFLAG_U | ||
| 912 | |a ZDB-1-WIS | ||
| 912 | |a GBV_NL_ARTICLE | ||
| 951 | |a AR | ||
| 952 | |d 130 |j 1997 |c 9 |h 1213-1221 |g 9 | ||