188. P. Müller, S. Chappellet,
     “Asymmetric 1,3-Dipolar Cycloadditions of 2-Diazo-cyclohexane-1,3-diones and Diazopyruvate Esters”
     Helv. Chim. Acta 2005, 88, 1010-1021.

The 1,3-dipolar cycloaddition reactions of 2-diazocyclohexane-1,3-dione (7a; Table 1) and of alkyl diazopyruvates (11a-e; Table 3) to 2,3-dihydrofuran and other enol ethers have been investigated in the presence of chiral transition metal catalysts. With Rh^II catalysts, the cycloadditions were not enantioselective, but those catalyzed by [Ru^IICl₂(1a)] and [Ru^IICl₂(1b)] proceeded with enantioselectivities of up to 58% and 74% ee, respectively, when diazopyruvates 11 were used as substrates. The phenyliodonium ylide 7c yielded the adduct 8a in lower yield and poorer selectivity than the corresponding diazo precursor 7a (Table 2) upon decomposition with [Ru(pybox)] catalysts. This suggests that ylide decomposition by Ru^II catalysts, contrary to that of the corresponding diazo precursors, does not lead to Ru-carbene complexes as reactive intermediates. Our method represents the first reproducible, enantioselective 1,3-cycloaddition of these types of substrates.

DOI : 10.1002/hlca.200590071 

archive ouverte unige:7836