Tandem Sequence of Phenol Oxidation and Intramolecular Addition as a Method in Building Heterocycles

A tandem phenol oxidation-Michael addition furnishing oxo- and -aza-heterocycles has been developed. Dirhodium caprolactamate [Rh-2(cap)(4)] catalyzed oxidation by T-HYDRO of phenols with alcohols, ketones, amides, carboxylic acids, and N-Boc protected amines tethered to their 4-position afforded 4-(tert-butylperoxy)cyclohexa-2,5-dienones that undergo Bronsted acid catalyzed intramolecular Michael addition in one-pot to produce oxo- and -aza-heterocycles in moderate to good yields. The scope of the developed methodology includes dipeptides Boc-Tyr-Gly-OEt and Boc-Tyr-Phe-Me and provides a pathway for understanding the possible transformations arising from oxidative stress of tyrosine residues. A novel method of selective cleavage of O-O bond in hindered internal peroxide using TiCl4 has been discovered in efforts directed to the construction of cleroindicin F, whose synthesis was completed in 50% yield over just 3 steps from tyrosol using the developed methodology.