Sensitized photooxygenations of .DELTA.2-oxazolin-5-ones and related studies

An umpolung strategy for chemoselective metal-free [4 + 2] annulation of azlactones: access to tetrahydro-β-carbolin 1,3-diketone frameworks

“…Acidic additives, such as phosphoric acid, were unable to increase the reaction efficiency (entry 9). The efficiency of the process was then further optimized by screening several solvents, such as dichloromethane (DCM), chloroform (CHCl 3 ), toluene, tetrahydrofuran (THF), and acetonitrile (MeCN) (entries [10][11][12][13][14]. Fortunately, DCM proved to be the best reaction medium, giving product 3a in a yield of 68%.…”

“…Initially, the focus centered on investigating the action of the oxidant, and it was observed that the reaction of DDQ alone with 2b resulted in the formation of the coupling product INT1. 10,11 Subsequently, the isolated coupling product INT1 was subjected to reactions with 1a, both in the presence and absence of DDQ. Notably, it was discerned that the desired product 3g could only be obtained when DDQ was added albeit with reduced yield compared with that of the one-pot process, thus indicating the imperative role of the oxidant in the isomerization stage of the coupling product (Scheme 4-i).…”