Preparation and reactivity of functionalized alkenyl-zinc, -copper, and -chromium organometallics

Abstract

β-Halogeno-α,β-unsaturated carbonyl derivatives were converted to the corresponding zinc organometallics 2a under mild conditions inTHF (Zn dust, 25–45°C, 1ϵ4h). These functionalized alkenylzinc iodides react with a variety of alkenyl and aromatic iodides affording the desired coupling products in 40–97% yield. The addition of a THF solution of CuCN·2LiCl to 2a affords the corresponding organocopper derivatives 2b which react with electrophiles, such as alkynyl and allylic halides, nitro olefins, enones, and chlorotrimethylstannane providing polyfunctional unsaturated carbonyl compounds in 71–95% yield. The insertion of chromium (II) chloride to β-iodo and to some β-(p-tosyl)enones in DMF furnishes new functionalized chromium (III) organometallics 2c which react with aldehydes providing γ--hydroxy unsaturated carbonyl derivatives in 40–91% yield. The synthetic scope and the limitations of this methodology are discussed.