Carbonyl Ylide Cycloadditions to C,C‐Double Bonds of Methylenecyclopropanes

The carbonyl ylide 1,3‐dipoles generated by dirhodium tetraacetate‐catalyzed decomposition from 1‐diazo‐5‐phenylpentane‐2,5‐dione ( 4 ) and 1‐(1‐acetylcyclopropyl)‐2‐diazo‐ethanone ( 5 ) cycloadd to substituted methylenecyclopropanes 2a – e and bicyclopropylidene ( 3 ) to give substituted mono‐, di‐, and trispirocyclopropanated 8‐oxabicyclo[3.2.1]octan‐2‐ones 7 , 8 , and 11 and 7‐oxabicyclo[2.2.1]heptan‐2‐ones 10 and 12 in 6–75 % yields with different regio‐ and stereoselectivities. The structures of the two isomeric cycloadducts endo ‐ and exo ‐ 10d formed from the carbonyl ylide derived from 5 and methyl 2‐chloro‐2‐(cyclopropylidene)acetate ( 2d ) were confirmed by X‐ray crystal structure analyses. (Diphenylmethylene)cyclopropane and trans ‐3‐methylenecyclopropane‐1,2‐dicarboxylate (diethyl ester of Feist’s acid) did not undergo such cycloadditions, while methylenecyclobutane ( 13 ) afforded a mixture of [3+2] and [2+1] cycloadducts 14 and 15 in 28 and 29 % yields, respectively. The scope and limitations of these cycloadditions as well as the influence of different factors upon their regio‐ and stereoselectivities are discussed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)