Total Syntheses of Herqulines B and C.

An approach for the syntheses of herqulines B and C is reported that takes advantage of an l-tyrosine-derived diketopiperazine, a mycocyclosin analogue, as a synthetic precursor. The strategy relies on a series of consecutive reductions to adjust the mycocyclosin oxidation state to that observed in the herquline class of natural products. The strained and distorted l-tyrosine-based biaryl system characteristic for mycocyclosin is selectively converted to the 1,4-diketone structural motif common to the herqulines via initial hypervalent iodine-mediated dearomatization and a subsequent directed Birch reduction, enabled by an intramolecular H-source. Additionally, the piperazine oxidation state is accessible via an iron-catalyzed reduction of a diketopiperazine intermediate.