Stereoselective synthesis of benzannulated spiroketals: influence of the aromatic ring on reactivity and conformation.

Overview

A systematic stereocontrolled synthesis of benzannulated spiroketals has been developed, using kinetic spirocyclization reactions of glycal epoxides, leading to a new AcOH-induced cyclization and valuable insights into the reactivity and conformations of these systems. One stereochemical series accommodates axial positioning of the aromatic ring while another adopts an alternative (1)C(4) chair conformation to avoid it. Equatorial aromatic rings also participate in nonobvious steric interactions that impact thermodynamic stability. A discovery library of 68 benzannulated spiroketals with systematic variations in stereochemistry, ring size, and positioning of the aromatic substituent has been synthesized for broad biological evaluation.