Trapping of 1,8-Biradical Intermediates by Molecular Oxygen in Photocycloaddition of Naphthyl-N-(naphthylcarbonyl)carboxamides; Formation of Novel 1,8-Epidioxides and Evidence of Stepwise Aromatic Cycloaddition

Abstract

The photocycloaddition reaction of naphthyl-N-(naphthylcarbonyl)carboxamides (1) was examined under argon and oxygen atmospheres. In addition to the [2 + 2] and [4 + 4] cycloadducts, 3 and 4, respectively, novel 1,8-epidioxides (5) were formed under oxygen atmosphere. The transient absorption at lambda max of 360 nm with the lifetime of 360 ns was observed by laser flash photolysis of 1c and was interpreted as the absorption of biradical intermediate 2. On the basis of the anti stereochemistry of 5, which was different from that of the major [4 + 4] cycloadducts, syn-4, it was deduced that equilibrium between biradical intermediates syn-2 and anti-2 would exist. Retro [2 + 2] cycloaddition of 3 was responsible for the efficient trapping of the biradical intermediate with molecular oxygen. The photocycloaddition of the anthryl derivatives, 9-anthryl-N-(methylethyl)-N-(naphthylcarbonyl)carboxamides (7), afforded the [4 + 4] cycloadducts (8) exclusively in a quantitative yield even under oxygen atmosphere. The absence of trapping with molecular oxygen was interpreted to be due to the lack of retro [4 + 4] cycloaddition of 8.

Optical switches with biplanemers obtained by intramolecular photocycloaddition reactions of tethered arenes

“…37 In the case of the tethers 20d-g, the [2 + 2] cycloadducts 23 are the sole or at least the major products and the [4 + 4] cycloadducts the minor products. 33 In the presence of oxygen, the epidioxides 24 were obtained. 33 A consecutive Cope rearrangement can generate cyclobutane derivatives (21a,c -25a,c).…”

“…30,31 The reaction mechanism ranges from a concerted process to a stepwise process via an intermediate diradical DR. A reliable proof for the participation of diradicals is given when epidioxides are formed in the presence of oxygen (trapping of 1,8-biradicals). 33 Fig. 2 visualizes intramolecular excimers/exciplexes E*, pericyclic minima PM* for a concerted reaction and diradicals DR, which may have zwitterionic character.…”

Photo-Induced Cycloaddition Reactions of α-Diketones and Transformations of the Photocycloadducts

“…Photoinduced [4 + 4] reactions represent the highest order photocycoadditions of α-diketone known up to now. [4 + 4] Photocycloadditions have been found in some photoreactions of excited aromatic compounds with dienes [51,52,53,54,55,56,57]. In an isolated example, excited 1,2-naphthoquinone was reported to react with cycloheptatriene to give the [4 + 4] product as minor products [58].…”

Photochemistry of Nitrogen-Bridged Cyclophanes: 2,11-Diaza[32]anthracenoparacyclophane and 2,11-Diaza[32]paracyclophane Systems

“…On exposure to 254-nm light, they afforded cage molecules 27 and 28 in 7 and 4.5% yield, respectively (Scheme 8). 56 Photoproducts 27 and 28 have a common pentacyclo[6.3.0.1 4,11 .0 2,6 .0 5,10 ]dodecane framework, which is known as one of the members of the C 12 H 16 hydrocarbon family 57 and was first constructed in one step by photoreactions. 56…”

“…In contrast to the broad studies on such bridged chromophores, there have only been a few investigations into the photochemistry of cyclophanes or linked aromatics possessing nitrogen-containing bridges. 10,20 Since the carbon-nitrogen single bond is generally shorter than carbon-carbon, carbon-sulfur, or carbon-silicon s-bonds, 21 it is expected that cyclophanes possessing carbon-nitrogen bond(s) in their bridge chains will display more significant interactions between their aromatic nuclei than the corresponding cyclophanes with carbon-carbon, carbon-sulfur, or carbon-silicon bridges, thus enhancing their photoreactivity.…”