Highly Efficient Ring Closure of Aromatic Dialdehydes to Macrocyclic Allenes

The one-pot double deoxygenation of simple alkyl- and polyether-tethered aromatic dialdehydes to give macrocyclic allenes has been accomplished in extraordinarily high yield without the need for slow-addition techniques, using a Ti(IV)-substituted ylide reagent and bis(trimethylsilyl)amide bases. Diastereoselective allene formation occurs when a binaphthyl unit is present in the substrate backbone, and the resulting cyclic allene is characterized by X-ray diffraction. Highly efficient cyclization is proposed to be the result of a combination of preorganization about the amide base counterion and a low concentration of the immediate precursor to Wittig-style olefination ring closure.