ortho-Selective Dearomative [2π+2σ] Photocycloadditions of Bicyclic Aza-Arenes

Kleinmans, Roman; Dutta, Subhabrata; Ozols, Kristers; Shao, Huiling; Schafer, Felix; Thielemann, Rebecca E.; Chan, Hok Tsun; Daniliuc, Constantin G.; Houk, Kendall N.; Glorius, Frank

Abstract

Dearomative photocycloadditions are valuable chemical transformations, serving as an efficient platform to create three-dimensional molecular complexity. However, the photolability of the original addition product especially within the context of ortho cycloadditions often causes undesired consecutive rearrangements, rendering these ortho cycloadducts elusive. Herein, we report an ortho-selective intermolecular photocycloaddition of bicyclic aza-arenes including (iso)quinolines, quinazolines, and quinoxalines by utilizing a strain-release approach. With bicyclo[1.1.0]butanes as coupling partners, this dearomative [2π + 2σ] cycloaddition enables the straightforward construction of C(sp3)-rich bicyclo[2.1.1]hexanes directly connected to N-heteroarenes. Photophysical experiments and DFT calculations revealed the origin of the [2π + 2σ] selectivity and indicate that, in addition to the originally proposed energy transfer or direct excitation pathways, a chain reaction mechanism is operative depending on the reaction conditions.