[5] The configuration of the olefin is retained throughout the process;[6] however, metal carbenes with heterotopic faces may generate a mixture of diastereomers, as shown at the right of Eq.
[10] (4)Cyclopropanation of olefins with diazocarbonyl compounds is commonly accomplished using rhodium carboxylate complexes, although copper was originally used.
This section describes the various classes of diazocarbonyl compounds that react with olefins under rhodium catalysis to afford cyclopropanes.
Diazoacetates that possess a single carbonyl substituent attached to the diazo carbon, have been used for the cyclopropanation of a wide array of olefins.
In addition, adding electron density to the catalyst (for instance by replacing acetate ligands with acetamide, acam) increases the diastereoselectivity of the reaction.
[15] (5)Diazocarbonyl compounds substituted with two electron-withdrawing groups, such as diazomalonates, are prone to experience side reactions under cyclopropanation conditions.
[20] (8)(9)Furans react similarly with vinyl diazoacetates, although the intermediate cyclopropane may transform either into the Cope rearrangement product or an opened unsaturated carbonyl compound.
The use of methyl lactate as a chiral auxiliary on the vinyl diazoacetate led to moderate diastereoselectivity in the tandem cyclopropanation/Cope rearrangement of Boc-protected pyrrole.
[26] (13)Substituted zinc carbenoids can be prepared from the corresponding ketones or aldehydes through a sequence analogous to the mechanism of the Clemmensen reduction.