Abstract:Catalytic enantioselective tandem oxidopyrylium formation -intramolecular 1,3-dipolar cycloaddition reactions of phthalic anhydride-derived unsaturated diazocarbonyl compounds in up to 19% ee are described.
“…[13] The same group made further efforts to extend this chemistry to other types of substrates with different chiral dirhodium complexes for related tandem oxidopyrylium formation -intramolecular 1,3-dipolar cycloaddition reactions, however in all cases very poor enantioselectivities were obtained (<20% ee; Scheme 7, bottom). [14] Despite the moderate chiral inductions within these initial reports, a chiral rhodium(ii)-bounded ylide-type was then proposed as key intermediate, which was crucial for the later development of further methodologies. [13,15] As a result, the enantioselective rhodium-catalyzed generation of carbonyl ylides and their study in cycloaddition reactions has become a vast and rapidly growing field.…”
The use of (benzo)pyrylium salts as versatile synthetic building blocks has become an attractive platform for the preparation of valuable heterocyclic compounds. Besides other numerous direct applications of (benzo)pyryliums, the intrinsic electrophilic nature of these species or the
dipole character of the related oxidopyrylium derivatives have been exploited towards the development of enantioselective transformations such as nucleophilic dearomatization and cycloaddition reactions. This review aims at providing an overview on the relevant catalytic enantioselective methodologies
developed in the past years, which are presented considering the involved metal- and/or organic catalytic system, as well as the type of reaction.
“…[13] The same group made further efforts to extend this chemistry to other types of substrates with different chiral dirhodium complexes for related tandem oxidopyrylium formation -intramolecular 1,3-dipolar cycloaddition reactions, however in all cases very poor enantioselectivities were obtained (<20% ee; Scheme 7, bottom). [14] Despite the moderate chiral inductions within these initial reports, a chiral rhodium(ii)-bounded ylide-type was then proposed as key intermediate, which was crucial for the later development of further methodologies. [13,15] As a result, the enantioselective rhodium-catalyzed generation of carbonyl ylides and their study in cycloaddition reactions has become a vast and rapidly growing field.…”
The use of (benzo)pyrylium salts as versatile synthetic building blocks has become an attractive platform for the preparation of valuable heterocyclic compounds. Besides other numerous direct applications of (benzo)pyryliums, the intrinsic electrophilic nature of these species or the
dipole character of the related oxidopyrylium derivatives have been exploited towards the development of enantioselective transformations such as nucleophilic dearomatization and cycloaddition reactions. This review aims at providing an overview on the relevant catalytic enantioselective methodologies
developed in the past years, which are presented considering the involved metal- and/or organic catalytic system, as well as the type of reaction.
“…Enantioselective carbonyl ylide type cycloadditions of (aromatic) oxidopyryliums have also been studied. Although only low ee values have been observed so far in intramolecular cycloadditions of oxidopyryliums (up to 19% ee), for the intermolecular process up to 93% ee using DMAD and catalyst 5 has been recorded and up to 98% ee has been reported using a 3-acryloyl-2-oxazolidinone dipolarophile with a chiral Lewis acid−Rh catalyst combination 1 Tandem Catalyzed Carbonyl Ylide Formation−Cycloaddition 1 Chiral rhodium catalysts. …”
Catalytic enantioselective tandem carbonyl ylide formation-intramolecular 1,3-dipolar cycloaddition reactions of 2-diazo-3,6-diketoesters show promising scope in terms of asymmetric induction as the tethered alkene/alkyne dipolarophile component is varied. Cycloadditions were found to occur in moderate to very good yields, with a difference in ee exhibited by the electronically different 2-diazo-3,6-diketoesters 1, 25 and 33, 34. Values for ee of up to 90% for alkene dipolarophiles and up to 86% for alkyne dipolarophiles were obtained.
[3 + 2] cycloadditions of carbonyl ylides with dipolarophiles provides a synthetically powerful way to make a variety of 5‐membered oxacycles. One of the best ways to generate carbonyl ylide intermediates is by transition metal‐catalyzed loss of nitrogen from diazocarbonyl compounds and trapping of the resultant metallocarbenes by a carbonyl group.
This chapter covers the metal‐catalyzed intra‐ and intermolecular cycloadditions of carbonyl ylides derived from diazocarbonyl compounds with various dipolarophiles. The literature up to the end of 2011 is covered.
A comprehensive discussion is provided of mechanism and stereochemistry, regioselectivity, stereoselectivity, and asymmetric cycloadditions. The structural scope at the diazo group, of the carbonyl group forming the ylide, and of the dipolarophile is delineated. A systematic analysis is presented of the scope and limitations of intra‐ and intermolecular cycloadditions of cyclic diazocarbonyl‐derived carbonyl ylides from ketones, esters, amides or imides, including cycloadditions of aromatic pyrylium and isomünchnone ylides. The generation of acyclic carbonyl ylides from aldehydes, ketones, or imides and their cycloadditions is also reviewed. Finally, important applications to the total synthesis of natural products and a critical comparison with other methods for carbonyl ylide generation‐cycloaddition are presented.
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