Copper-catalyzed reactions of organotitanium reagents. Highly selective SN2′-allylation and conjugate addition

Article abstract of DOI:10.1016/0040-4020(92)80022-8

In the presence of a catalytic amount of CuI·ILiCl, alkyltitanium (RTi(O-I-Pr)₃) and titanate reagents (R_nTi(O-i-Pr)_5-nLi) undergo highly selective S_N2′-alkylation reactions with allylic chlorides and allylic diethylphosphates in high yields. The regioselectivity of the reaction is as high as 99.8%. The reaction proceeds with excellent anti-stereoselectivity with respect to the nucleophile and the leaving group, and exhibits high 1,2-anti-diastereoselectivity with a δ-chiral allylic chloride. The catalytic copper reagent is also a mild agent to transfer an alkyl group to an enone in the presence of Me₃SiCl. The alkyltitanium-based catalytic reagent selectively reacts with an allylic phosphate rather than with an enone, while in the presence of a silicon activator, it reacts preferentially with the enone rather than with the phosphate. ¹H NMR studies on a mixture of Me₂CuLi and TiCl(O-i-Pr)₃ provided information on reagent composition.