DIASTEREOSELECTIVE REACTIONS OF TUNGSTEN ETA-2-PROPARGYL COMPLEXES WITH ALKYL-HALIDES AND ALDEHYDES

Deprotonation of the alkyne methyl group in Tp'(CO)(I)W (PhC = CCH3) [Tp' = hydridotris(3,5-dimethyl-pyrazolyl)borate] borate] produces a nucleophilic propargyl synthon. Reaction of the complex anion with MeI or PhCH2Br yields an elaborated alkyne and avoids the propargyl/allenyl regiochemical control problem. Deprotonation of Tp'(CO)(I)W(PhC = CCH2Me) followed by benzylation produces a single diastereomer as determined by H-1 NMR, while methylation of the anion formed from Tp'(CO)(I)W(PhC = CCH2Bz) yields the opposite diastereomer. Pivaldehyde or benzaldehyde adds to the coordinated eta-2-propargyl carbanion, Li[Tp'(CO)(I)W(eta-2-PhC = C = CHMe)], to form alcohol products. Conversion to a coordinated enyne was achieved for the benzaldehyde adduct by first forming the mesyl derivative and then eliminating HOSO2Me to yield Tp'(CO)(I)W(PhC = CCMe = CHPh).