Cycloaddition reactions carbonyl ylides

Synthetic Aspects of Carbonyl Ylide Cycloaddition Reactions. 

SYNTHETIC ASPECTS OF CARBONYL YLIDE CYCLOADDITION REACTIONS... 

Reactions of the same carbonyl ylide intermediate with aldehydes are even more fruitful. The Rh2(OAc)2 catalyzed reaction proceeds at room temperature in the presence of 2 mol% of the catalyst, but the diastereoselectivity is disappointingly low (endo/exo = 49 51, Scheme 11.56). However, when 10 mol% of the cocatalyst Yb(OTf)3 is added, the reaction becomes highly exo-selective (endo/ exo = 3 97) (198). Suga has extended this Lewis acid catalyzed carbonyl ylide cycloaddition reaction to catalyzed asymmetric versions. The chiral cocatalyst employed is ytterbium(III) tris(5)-1,1 -binaphthyl-2,2 -diyl phosphonate, Yb[(S) BNP]3 (10 mol%). In the reaction of methyl o-(diazoacetyl)benzoate with benzyloxyacetaldehyde in the presence of Rh2(OAc)2 (2 mol%) at room temperature with the chiral Yb catalyst, the diastereoselectivity is low (endo/exo = 57 43) and the enantiopurity of the endo-cycloadduct is 52% ee. 

The tandem carbonyl ylide/cycloaddition reaction is also observed when crotonaldehyde or acetone is used instead of benzaldehyde (dimethyl fumarate as dipolarophile), whereas with cyclohexanone, an enol ether derived from the carbonyl ylide is isolated [19] (Scheme 9). 

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