Cr(II)-Mediated Cascade Reactions of tert-Trihalomethylcarbinols

Significance

Trihalocarbinols are a readily available class of functionalized alcohols. Herein, a very interesting transformation of these compounds with a one-carbon homologation into α,β-enones, induced by Cr(II), is described. It affords, starting from cyclic ketones, an elegant synthetic approach to the ring-expanded exocyclic enones. This is a rather unusual low-valent metal-induced reaction, with good perspectives for the following study. Rather expensive CrCl₂ can be used in smaller amounts if Mn powder is added to the reaction mixture. Possibly, further work will allow to decrease its quantity further to substoichiometric or catalytic amounts.