Diels-Alder reagent

In view of the remarkable effects that water can exert on the uncatalysed Diels-Alder reaction, there might well be a similar effect on the rate and the selectivity of the Lewis-acid catalysed process. At the same time, coordination of a Lewis-acid to a Diels-Alder reagent is likely to overcome the... 

Thiete sulfones show an irregular behavior pattern when involved in cycloaddition reactions. With 1,3-dienes, dienamines, enamines, ynamines, diazoalkenes, cyclopropadiene, and its substitution products, furan, and anthracene, the addition proceeds in the normal fashion. With certain Diels-Alder reagents such as tetraphenylcyclopentadienone (tetracycloneX however, the cyclic sulfones react anomalously. The Diels-Alder adducts undergo decomposition with SO 2 and CO extrusion to a seven-membered ring, the tetraphenylcycloheptatriene 223. Bicyclic octadienone is produced as well (Eq. 62). The mechanism of this unusual reaction is proposed by... 

Both 1-methyl-pyrrole and -indole react under mild conditions with the reactive cheletropic Diels-Alder reagent, tetrachlorothiophene 1,1-dioxide, to produce, after the extrusion of sulfur dioxide, an octachlorotetrahydrocarbazole and tetrachlordihydrocar-bazole, respectively (80JOC856). 

Tetrachlorothiophene 1,1-dioxide (523) has been proved to be an extremely versatile, reactive but stable, cheletropic Diels-Alder reagent (80JOC856, 81H(16)ll45>. It undergoes [4 + 2] cycloaddition with a variety of unactivated double bonds, followed by extrusion of... 

The reaction with acrylic acid deserves special attention, because acrylic acid is not usually a good Diels-Alder reagent. That the reaction proceeds catalytically and with high ee indicates the facile exchange of the (acyloxy)borane of the cycloadduct with the carboxylic group of unreacted acrylic acid, whereas the monoacrylated tartaric acid remains bound to boron (Fig. 1). 

Keywords solid-solid reaction, pyrocatechol, hydroquinone, o-benzoquinone, p-benzoquinone, DDQ, DDQH, Diels-Alder reagent... 

In summary, the results of the modification reactions indicate that polyacetylene may be chemically modified via the Diels-Alder reaction. A broad range of dienophiles may be employed, but the use of common Diels-Alder reagents provides only modest conversions [15a, Chapter 6c]. 

Diels-Alder cycloadditons have been explored on solid supports, and Winkler and Kwak have demonstrated a chemoselective variant that affords a single reaction of a dienophile containing two reactive double bonds with a bis-diene. Utilizing bis-reactive Diels-Alder reagents in the absence of a solid support is problematic as competing oligomerization can occur. Thus, a dienophile was immobilized as 8 and reacted with the... 

Figure 6.8. An SAM end-functionalized with an electrochemically active quinone as a Diels-Alder reagent for coupling activated dienes. Biotin can be incorporated via this method by the use of a PEG-modified diene (adapted from ref. (22))...

---