IODOTRIMETHYLSILANE-PROMOTED ADDITIONS OF MONOORGANOCOPPER COMPOUNDS TO ALPHA,BETA-UNSATURATED KETONES, ESTERS, AND LACTONES

Conjugate additions with the efficient monoorganocopper-iodotrimethylsilane combination, exemplified plified mainly with methylcopper, butylcopper, and tert-butylcopper, proceed cleanly, smoothly, and rapidly to a variety of alpha,beta-unsaturated carbonyl compounds; cyclic and acyclic enones, beta-alkoxy enones, enoates and lactones in ether, THF, and dichloromethane, often at -78-degrees-C. The RCu-(LiI)-TMSI reagent gives a good economy of group transfer with good to excellent yields of conjugate adducts. Lithium iodide, present from preparation of the organocopper compounds, increases the rate of the reactions and is a favorable component. Additions are faster, but somewhat less selective, in THF than in ether. Careful workup after addition of triethylamine or pyridine at low temperature permits isolation of TMS enol ethers and TMS ketene acetals. Acyclic enones preferentially give the Z-silyl enol ethers. The RCu(LiI)-TMSI system is a most useful alternative to the conventional lithium diorganocuprates in conjugate additions.