Activation of Low-Valent Titanium Reagents with Iodine: Facile Low-Temperature McMurry Reaction and N/O-Debenzylation/Deallylation

A highly reactive, low-valent titanium (LVT) reagent has been prepared by the addition of substoichiometric amounts of iodine to the LVT species generated by Rieke's method (TiCl3−Li−THF). While the conventional McMurry reaction requires high temperatures and prolonged reaction times for the generation of olefins, the present activated LVT reagent is able to effect the reductive coupling of aliphatic as well as aromatic carbonyls to the corresponding olefins at lower temperatures and much reduced reaction times. The protocol is also useful for the intramolecular coupling reactions leading to the one-step synthesis of heterocycles. The temperature-controlled McMurry reaction provides enhanced diastereoselectivity and features an excellent chemoselectivity. In addition to the McMurry reaction, other SET-induced carbon−heteroatom (O, N) bond cleavages can also be carried out with the activated reagent at a fast rate and at a low temperature in high yields.