Thiophenes formation

Novel compounds for use in liquid crystal displays have been prepared via the Stetter procedure followed by Paal thiophene formation with Lawesson s reagent. Thus... 

This reaction can also be catalyzed by rhodium [85JOM(293)C15]. Systematic studies have revealed that the catalytic thiophene formation is sensitive to the controlling system Y at the cobalt (83MI2) (Scheme 5). 

A comparison of the TON in Scheme 5 shows that the catalytic activities of the YCo(cod) complexes in the thiophene formation increase with increasing electron-donating ability of the ligand Y. The borininato-cobalt core shows the least activity, which is in contrast to the results found in the pyridine synthesis. 

Thiomethyl iminoether formation, 289 Thiophene formation, cycloaddition, thioglycolate, 583 Thiophenodiazepine formation, 622 Thiophenol formation, 527 sulfonyl chloride, 527 Thiourea formation... 

Figure 15.6. Mechanisms of thiophene formation by the Thorpe-Ziegler and Gewald reactions. X leaving group Z electron-withdrawing group.

The catalytic properties of unsupported transition metal sulphides have been examined for the reaction of dehydrogenation of tetrahydrothiophene. This study has shown that a selectivity higher than 90% for thiophene formation can be obtained for the most active catalysts, essentially the second row sulphide catalysts. The comparison between the catalytic activities in both dehydrogenation of tetrahydrothiophene and... 

The selectivity towards thiophene formation, defined by the ratio S=thiophene/(E products) is represented in Fig.3. These results show that except the Zn, Fe, Mn and Co sulphides which are among the less active solids, selectivities higher than 90% are usually observed. 

In one case, formation of the thiophene from sulfur and dimethyl acetylenedicarboxylate, a viable catalytic procedure was optimized (75% yield) by using CpCo(COD) and elemental selenium, which promotes thiophene formation in refluxing toluene. The role of the Se is not known, and the implications of these results have not been explored. ... 

There can now be little doubt that the reaction of singlet carbenes and car-benoids with thiophene proceeds by attack of the carbene at the ring sulfur atom to generate the S,C-ylid. However, only in the special cases indicated above do these ylids enjoy any real stability. In the majority of cases, other products usually result from rearrangement of the intermediate ylids and the nature of the products formed is remarkably sensitive to both steric and electronic effects. Broadly speaking, six major reaction pathways have been observed (1) 2-substituted thiophene formation, (2) 2H-thiopyran formation, (3) formation of derivatives of 2-thiabicyclo[3.1.0]hex-3-ene, (4) 3-substituted thiophene formation, (5) oxathiocin formation, and (6) carbenic fragmentation. 

Abdelrehim IM, Thornburg NA, Sloan JT, Land DP (1993) Benzene and thiophene formation from acetylene on sulfided Pd(lll) studied by LITD FTMS. Surf Sci 298 L169... 

Formation of a Five>membered Ring I. Pyrrole Pyrazole Imidazole Furan Thiophene Formation of a Six-membered Ring I. Pyridine Pyridin-4-one Pyridazine Pyrazin-2-one 1,2,4-Triazine Pyran-2-onc... 

It is significant that, unlike oxidative dehydrogenation, there has been no serious amount of attention given to sulfoxidation as a process to produce four carbon or higher olefins and diolefins. The reason is that thiophene formation occurs. For example ... 

An extremely interesting example of electrocyclic thiophene formation is the intramolecular closure of a tropolone to form a thieno-fused bicyclic derivative this compound may be induced to undergo photochemical isomerization to produce a novel thienopyridine derivative (Scheme 6)... 

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