Modulable and Highly Diastereoselective Carbometalations of Cyclopropenes

The copper‐catalyzed carbomagnesiation reaction of cyclopropenyl esters 1 leads to various substituted cyclopropanes species 3 in good yields with very high diastereoselectivities. The reaction proceeds through a syn‐chelated carbomagnesiation reaction and could be extended to various cyclopropenylmethyl ester derivatives 5 . The potential of this approach was illustrated by the preparation of two consecutive all‐carbon quaternary stereocenters. However, the carbometalation reaction needs to be performed at temperature ranging from ?35 to ?20 °C to avoid subsequent fragmentation reaction into stereodefined β,γ‐nonconjugated unsaturated esters 4 . Alternatively, the carbocupration reaction with organocopper species could also be performed to leads to configurationally stable cyclopropyl copper species 2[Cu] . Additionally, when the Lewis acid character of the copper center is decreased (i.e., RCuCNLi), the reaction proceed with an anti‐selectivity. The diastereodivergent behavior of these organometallic species is of synthetic interest, since both diastereomers syn‐ 3 and anti‐ 3 can be obtained, at will, from the same precursor cyclopropenyl esters 1 .     

Cover Picture: Chem. Eur. J. 2/2003

The cover picture conveys the concise message that a fixed element of axial chirality residing in one ring of a catenane can induce chirality of a helical nature within a dynamic setting in the other (interlocked) ring. The overwhelming preference for one enantiomeric pair within a bipartite set of diastereoisomers relating to the particular [2]catenane, presented as its X‐ray crystal structure in the circular inset, becomes more and more pronounced as its 1,4‐dioxybenzene units are replaced, one at a time, by 1,5‐dioxynaphthalene ones, with their concomitant planar chiralities. The very high levels of induction of dynamic helical and planar chiralities by a fixed source of axial chirality in a simple catenane conjures up a number of scenarios where this approximately cubic nanometer of programmable information might be put to good use. For more details concerning these tiny stereochemical wonders with no stereogenic center in sight, see the article on p. 543 ff by J. F. Stoddart and D. J. Williams and the wizards that work their magic for them.