The cyclopropanation of styrene with (silanyloxyvinyl)diazoacetates proceeds with exceptional diastereo- and enantioselectivity in the presence of chiral Rh(II) catalysts. 1,8-Naphthoyl-protected amino acids are the most effective Rh(II) ligands for these transformations. [reaction--see text]

The cyclopropanation of olefins with 2-diazodimedone 1a and the corresponding phenyliodonium ylide 1b in the presence of selected chiral Cu(I)-and Rh(II)-catalysts proceeds without significant enantioselectivity. Contrary to previous reports in the literature, the cyclopropanation of styrene with 1a in the presence of [Cu{(+)-facam} 2 ] is not enantioselective. While the transition metal catalyzed 1,3-dipolar cycloaddition of 2-diazodimedone (1a) to furan and dihydrofuran is equally non-selective, the introduction of heteroatoms and/or unsaturation in the carbene precursor results in slightly enhanced enantioselectivity.

A s y m m e t r i c S y n t h e s i s o f D i h y d r o f u r a n s Abstract: The cyclopropanation of dihydrofuran and dihydropyran with methyl 1-(silanyloxy)vinyl diazoacetates in the presence of chiral Rh(II)-catalysts affords cyclopropanes with high diastereoand enantioselectivitiy. The cyclopropanes, in turn, rearrange to dihydrofurans upon desilylation with TBAF.

No abstract

The cyclopropanation of dihydrofuran and dihydropyran with title compound (I) in the presence of chiral Rh-catalysts affords cyclopropanes with high diastereo-and enantioselectivity. The cyclopropanes, in turn, rearrange to dihydrofurans upon desilylation with TBAF. -(MUELLER, P.; BERNARDINELLI, G.; ALLENBACH, Y. F.; FERRI, M.; GRASS, S.; Synlett 2005, 9, 1397-1400; Dep. Org. Chem., Univ. Geneva, CH-1211 Geneva 4, Switz.; Eng.) -M. Paetzel 41-106