“…We were unable to evaluate the combined effect of Lewis acid catalysis and a C5 nitrile (entry 2). Though we have found ZnCl 2 to be an effective catalyst in the Diels−Alder reactions of the cyano derivative 1b ,1b in the present application, only trace amounts of the desired cycloadduct could be isolated due to decomposition of this product under the conditions of the reaction.…”
mentioning
confidence: 73%
“…A variety of Lewis acids (e.g. TiCl 4 , EtAlCl 2 , Et 2 AlCl, BF 3 ·OEt 2 , ZnCl 2 ) were screened in this application 1b. Optimized conditions are used in the present studies.…”
Section: Referencesmentioning
confidence: 99%
“…We recently reported the Diels−Alder reaction of substituted 2,3-dihydro-4-pyrones (e.g. 1 ) with electron-rich dienes (Scheme ) . Application of this method allows for the facile preparation of highly functionalized 1-oxadecalin derivatives 3 , which can serve as potential intermediates for the synthesis of a variety of complex natural products.…”
The Diels−Alder reaction of activated dihydropyrones with electron-rich dienes proceeds with synthetically useful levels of diastereoselectivity.
Product ratios vary with the nature and location of substituents on diene and dienophile, as well as with reaction conditions. Lewis acid
catalyzed reactions of related pyrone and benzopyrone dienophiles are also diastereoselective.
“…We were unable to evaluate the combined effect of Lewis acid catalysis and a C5 nitrile (entry 2). Though we have found ZnCl 2 to be an effective catalyst in the Diels−Alder reactions of the cyano derivative 1b ,1b in the present application, only trace amounts of the desired cycloadduct could be isolated due to decomposition of this product under the conditions of the reaction.…”
mentioning
confidence: 73%
“…A variety of Lewis acids (e.g. TiCl 4 , EtAlCl 2 , Et 2 AlCl, BF 3 ·OEt 2 , ZnCl 2 ) were screened in this application 1b. Optimized conditions are used in the present studies.…”
Section: Referencesmentioning
confidence: 99%
“…We recently reported the Diels−Alder reaction of substituted 2,3-dihydro-4-pyrones (e.g. 1 ) with electron-rich dienes (Scheme ) . Application of this method allows for the facile preparation of highly functionalized 1-oxadecalin derivatives 3 , which can serve as potential intermediates for the synthesis of a variety of complex natural products.…”
The Diels−Alder reaction of activated dihydropyrones with electron-rich dienes proceeds with synthetically useful levels of diastereoselectivity.
Product ratios vary with the nature and location of substituents on diene and dienophile, as well as with reaction conditions. Lewis acid
catalyzed reactions of related pyrone and benzopyrone dienophiles are also diastereoselective.
“…The preparation of 1-oxadecalines via Diels-Alder reaction of 2,3-dihydro-4H-pyran-4-ones with electron-rich dienes has been reported, mainly by the group of Totah. [7][8][9][10][11] Although useful levels of diastereoselectivity can be achieved, the enantioselective version of this strategy has yet to be developed. Moreover, the corresponding Diels-Alder reaction of pyranyl-based dienes with electron-deficient alkenes is limited to highly electrophilic dienophiles, such as maleimides or maleic anhydride, most likely due to the poor reactivity associated with these types of dienes under thermal conditions.…”
TpMo(CO) 2 (5-alkenyl-η-2,3,4-pyranyl) diene complexes function as excellent chiral scaffolds for the efficient regio-and enantiocontrolled synthesis of highly functionalized 1-oxadecaline derivatives through a novel transition metal-mediated Diels-Alder reaction. Very good to excellent yields and excellent levels of endo-selectivity are obtained and the reaction gives products with complete retention of enantiomeric purity when carried out with chiral, non-racemic scaffolds. A subtle structural modification on the diene (replacement of an H by a trans-CH 3 group) leads to a complete change of regiochemistry, which is discussed from a mechanistic point of view. The role of the η 3 -coordinated TpMo(CO) 2 moiety is also critical to the further functionalization of the [4+2] cycloadducts, as illustrated by the preparation of 20 variously functionalized 1-oxadecaline derivatives (>98% ee when carried out with high enantiopurity scaffolds).
“…Our interest in natural products containing the oxadecalin structural unit has led us to investigate [4 + 2] cycloaddition reactions involving 4-pyrones as dienophiles ( 1 → 2 in Figure ). − Such a strategy should serve as a highly convergent approach to the synthesis of natural products such as arisugacin ( 3 in Figure ), ,− pyripyropenes, and forskolin . However, at this point, a strong electron-withdrawing group has proven to be essential for rendering the electron-rich 4-pyrones as reactive dienophiles in these cycloadditions under thermal or Lewis acidic conditions. 3b,5a Although this specific necessity could hinder the synthetic scope of this strategy, given the scarce studies of reactions using 4-pyrones as dienophiles, these initial endeavors have yielded interesting synthetic structures that could serve as entries to unique natural products and their analogues. 1 …”
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
