Irradiation norbornadiene derivatives

Norbornadiene derivative 123, on either direct or sensitized irradiation in solution, gives quadricyclene 124 (Equation 9). On the other hand, photochemical reaction of 125 in acetone at room temperature is very rapid and the product 126 is obtained in high yield (Equation 10) <1998HCA828>. 

The incorporation of sulphonyl groups does not inhibit the cyclization process as demonstrated by Gleiter and Ohlbach133, who have reported the efficient synthesis of the quadricyclane 252 by irradiation of the norbornadiene derivatives 253. A study has also been made of the sulphonyl-substituted norbornadiene derivatives 254134 135. 

The irradiation of the norbornadiene derivatives (148) yields the quadricyclanes (149). These quadricyclanes can be reconverted to the starting material by treatment with silver ion. The norbornadienes (150) photochemically ring close to the quadricyclanes (151). Both direct and sensitized irradiation were used but the direct irradiation afforded a mixture of products. The reactions were much cleaner using benzophenone as the sensitizer. Irradiation of the norbornadiene derivative (152) affords the quadricyclane (153). Paquette and Racherla - have synthesized the norbornadiene (154) in which it is claimed that homoconjugation is high. This is borne out on acetophenone-sensitized irradiation in pentane when it is converted to the quadricyclane (155). Prinzbach and his coworkers have reported on the photochemical (2+2)-cycloadditive behaviour of adducts of the type represented by (156). The acetone-sensitized irradiation of this compound brings about (2 + 2)-cycloaddition to afford a 2 1 mixture of the adducts (157) and (158). Direct irradiation, however, follows a different path to yield a mixture of the (2+2)-adduct (157) as... 

Both the acid induced and the photochemical rearrangement of the norbornaidiene derivative (146) affords the hydroxynaphthalene (147). The photo-process is not affected by triethylamine and it is thought to involve benzy lie-ally lie C-O bond cleavage. No evidence was put forward for the intermediacy of a quadricyclane. Prinzbach smd his coworkers have reported the synthesis of the oxanorbornadienes (148) and their photoconversion into the corresponding oxaquadricyclane derivatives (149) on irradiation. The azaquadricyclanes (150) have been prepared by the irradiation of the corresponding norbornadiene derivatives (151). ... 

Investigations have also examined the photochemical outcome of the inclusion of other aromatic substituents onto the norbornadienes. Examples of this are the direct and sensitized irradiation of the naphthyl-substituted derivatives 249 that brings about cyclization to 250. Sensitization of the cyclization with ketones such as benzophenone leads to a much cleaner reaction. Biacetyl has also been used as the sensitizer130,131. Cyclization also occurs with the norbornadiene 251132. 

Like the cyclization of the parent system, the photocyclization of hetero analogues of norbornadiene was reported many years ago. Recent interest in this area will serve to illustrate the potential of the conversions. Thus the irradiation of the oxanorbomadiene system 259 brings about conversion to the oxepine 260138. The formation of 260 presumably arises by quadricyclane 261 formation, followed by secondary photolytic ring-opening. Other research has shown that irradiation of the oxanorbomadiene 262 follows the same reaction mode and it undergoes (2 + 2)-cycloaddition to the quadricyclane derivative 263. Apparently, in this instance, cycloreversion affords the ylide 264 that can be trapped by suitable addends, giving the adducts illustrated in Scheme 3139. 

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