Solvent-Controlled Switching of Cycloisomerization to Transposition in the Ag/Cu-Promoted Reaction of Terminal α-Allenols

In recent years, allenes (1,2-dienes) have evolved from a laboratory curiosity to a versatile and uniquely reactive functional group, allowing chemists to prepare a variety of compounds of chemical and biological interest.

Transition-metal catalyzed nucleophile addition to allenes is a very powerful tool for the synthesis of functionalized molecules containing heteroatoms in an atom efficient manner. The reaction on allenic systems has a benefit as the regiochemistry can be controlled by using different metals or by changing the substituents or the length of the chain between the allene and the heteroatom in the intramolecular case.

On the other hand, both non-aromatic oxacycles and quaternary α-substituted aldehydes are structural units that are extensively encountered in a number of biologically active natural products and functional molecules, and therefore their stereocontrolled synthesis remains an intensive research area.

We wish to report herein a study on the Ag/Cu-catalyzed reactivity of α-allenols. The focus was the development of new methodologies for cyclization and/or transposition of this moiety. By simple solvent switch, the divergent preparation of dihydrofurans and 3-halo-3-alkenals in a controlled manner has been reached.