Regio- and Enantioselective Cobalt-Catalyzed Reductive [3+2] Cycloaddition Reaction of Alkynes with Cyclic Enonesi A Route to Bicyclic Tertiary Alcohols

摘要

Cycloaddition reactions are among the most powerful and widely applied methods for the synthesis of carbo- and heterocycles in organic synthesis. Transition-metal-catalyzed cycloaddition reactions are particularly attractive because they can provide new opportunities for the synthesis of various cyclic molecules in one pot. These reactions become possible as the complexation of substrates to metal temporarily polarizes and activates otherwise unreactive species. Some recent developments in this field are metal-catalyzed reductive [3+2] cycloaddition reactions utilizing a,|3-unsaturated carbonyl compounds as the three-carbon unit. Sato et al. reported a stoichiometric titanium-promoted addition of tethered alkynes and enoates to synthesize bicyclic ketones. The work of Montgomery and co-workers on stoichiometric nickel-promoted addition of tethered alkynes and enals showed that the [3+2] cyclization can also be achieved using enolate metallacycles. Later, they disclosed a catalytic intermolecular version of the cycloaddition of alkynes and enals to synthesize cyclopentenols and cyclo-pentenones using triethylborane as the reducing agent. In 2007, we reported a cobalt-catalyzed diastereoselective reductive [3+2] cycloaddition of allenes and enones affording 3-methylene cyclopentanol derivatives. Subsequently, Urabe and co-workers described an iron-mediated intramolecular reductive cyclization of dienedioates to synthesize bicyclic ketoesters. Very recently, Ogoshi and Ohashi developed a unique Ni~0-catalyzed [3+2] cycloaddition reaction of α,β-unsaturated phenyl esters with alkynes in i'PrOH to yield cyclopentenone derivatives.