Aryne Annulation Reactions Toward the Synthesis of Heterocyclic Molecules

Abstract

The last decade has seen an outgrowth in the development of synthetic methodologies exploiting benzyne. The unique ability of this reactive intermediate to directly furnish ortho-difuntionalized aromatic systems first stoked interest in this research group as a possible partner in asymmetric arylation reactions. Since our initial forays, we have expanded our synthetic strategies to include bond insertions, cycloadditions, condensations, and multicomponent reactions. The first project discussed in this volume is the development of an aryne annulation strategy for constructing common, synthetically useful heterocyclic structures in a convergent manner. We have developed a convergent approach to indoles and indolines. Likewise, through an orthogonal functional group intallation upon an enamine substrate, isoquinolines, quinolines, and isoquinolones can all be accessed as well. In this manner, we have been able to generate an array of functionalized heterocycles, including some that are prohibited by traditional means of synthesis. We have also begun to understand some of the reactivity trends in this context for the elusive aryne reaction partner. The development of the aryne annulation strategy for the synthesis of isoquinolines directly led to the shortest reported total synthesis of the opiate alkaloid papaverine, and the tetrahydroisoquinoline anticancer antibiotic quinocarcin. Our more recent, ongoing efforts toward the synthesis of the bis-tetrahydroisoquinoline antitumor molecule jorumycin and its many structural relatives are detailed herein. Jorumycin has been targeted through a combination of aryne annulation and acyl-alkylation/condensation methodologies aimed at the synthesis of a functionalized bis-isoquinoline intermediate. Reduction of this key bis-isoquinoline to a bis-tetrahydroisoquinoline and subsequent lactamization will provide the pentacyclic core of jorumycin and related natural products in only three steps from simple isoquinoline building blocks. The final project described is the development of several different aryne multicomponent reactions to form novel carbo- and heterocyclic scaffolds, including iminoisobenzfurans, iminoindenones, dibenzoketocaprolactams, and 2-quinolones.