Cycloadditions of Cyclic Carbonyl Ylides

A review of the methods for the generation of cyclic carbonyl ylides from intramolecular carbene additions has recently appeared [64]. This intermediate was first exploited as the An component for cycloaddition reactions by Ibata [65]. ort/io-Disubstituted carboalkoxy aryl diazoketones such as 54 were decomposed by copper complexes, generating six-membered ring carbonyl ylides. These transient intermediates underwent subsequent intermolecular cycloadditions in the presence of ethylenic and acetylenic reagents to give predominantly exo products containing the oxabicyclo[3.2.1] nucleus, Eq. 38. 

Padwa subsequently described some intramolecular versions of this reaction. A structurally similar aryl ester, 55, a tethered to a terminal olefin was subjected to rhodium-catalyzed diazo decomposition. Carbonyl ylide formation followed by intramolecular cycloaddition resulted in tricyclic product 56 a, Eq. 39 [66 - 69]. Cycloaddition also occurred with the amide analogue 55 b. 

Carbonyl ylide formation in the aliphatic ketoester 57 a was complicated due to competing reaction processes however, the diketone 57 b underwent cycloaddition at room temperature to give 58, Eq. 40 [70]. 

Another example of an intramolecular cycloaddition was reported by Dau-ben, in which both isomers 59 a and 59 b of the substrate underwent tandem car-bene-cyclization and intramolecular cycloaddition to give pentacyclic adducts 60a and 60b, Eq. 41. The stereochemistry of the newly constructed bonds was directed by the distal cyclopropane and was independent of the stereocenters at C4, C10 or Q 2- 

The phorbol skeleton to yield 61 was also assembled in one step via rhodium catalyzed carbenoid formation, Eq. 42 [71]. 

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SCHEME IJS Asymmetric cycloadditions of cyclic carbonyl ylides by monoactivation and dual activation approaches. 

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