Oxanorbornadiene derivatives

Unlike the ROMP of 190a, that of 200 catalyzed by RuCls in PhCI proceeds without an induction period. In the series of esters, 200-202, the rate declines with increasing bulk of the ester group while the cis content of the polymer goes up from 15% to 22% to 26%. The presence of the 7-oxa group enhances the reactivity (Monakov 1992). 

Competition experiments have shown that 203 reacts more than 50 times faster with Mo(=CHCMe2Ph)(=NAr)(OCMe3)2 than does its norbomadiene analogue (139). The oxygen in the 7-position enhances the activity, presumably by assisting the initial coordination of the monomer to the molybdenum centre, although it is released once the metallacycle has formed. The comparative stability of the metallacycles formed from the 7-oxanorbomadiene derivatives is not the result of any direct interaction between the oxygen and the metal, and must therefore be due to inductive effects. Further competition experiments have shown that 203 also reacts about 30 times faster than norbomene with this initiator, but that when 

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More recently, a Pd(II) salt was shown to catalyze the 1,2-insertion polymerization of a 7-oxanorbornadiene derivative (Fig. 10-16) [50]. The resulting saturated polymer, when heated, gives polyacetylene via a retro-Diels-Alder reaction. (This reaction is reminiscent of the Durham route to polyacetylene discussed below). One advantage of this technique over other routes is that it employs a late transition metal polymerization catalyst. Catalysts using later transition metals tend to be less oxophilic than the d° early transition metal complexes typically used for alkene and alkyne polymerizations [109,110]. Whereas tungsten alkylidene catalysts must be handled under dry anaerobic conditions, the Pd(II)-catalyzed reaction of water-insoluble monomers may be run as an aqueous emulson polymerization. 

Even azide moieties are capable of entering DA cycloaddition reactions with oxanorbornadiene derivatives, yielding triazole products. For example, the tandem [3 + 2]/Diels-Alder cycloreversion (CrDA) was used for the PEGyZatzon of an N-terminally azido functionalized peptide (GGRGDG). Furthermore, labeling of oxanorbornadiene-modified hen egg-white lysozyme with fluorescent coumarine was demonstrated. The release of furan... 

Oligomers Oppolzer s camphor sultam (see also camphor derivatives) Organometallics Organosilicon Organosulfur Organozirconocenes Orthoquinodimethanes Oxabutadienes Oxanorbornadiene(s) Oxazinolactams Oxazinones Oxazoles... 

Arene oxides 42 and 49 were obtained as minor products by an unusual thermal isomerization of the photooxide of 3-diphenylisobenzofuran. Although the thermal isomerization reaction of 3-oxaquadricyclane has been used in the synthesis of benzene oxide 1, this route to benzene oxides was initially limited to specifically substituted derivatives owing to the unavailability of the unsubstituted 7-oxanorbornadiene. Thus most of the substituted arene oxides prepared by this route contained electron-withdrawing substituents X [X = —CF3 (77), —COaMe (76, 86, 88-92, 94), and —C02Et (93)] which increased their thermal stability. 

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 oxanorbornadiene system 259 brings about conversion to the oxepine 260. The formation of 260 presumably arises by quadricyclane 261 formation, followed by secondary photolytic ring-opening. Other research has shown that irradiation of the oxanorbornadiene 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 3. ... 

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). ... 

Two intramolecular [2 + 2] photocycloadditions of note have been reported. The quantitative conversion of 7-oxanorbornadiene to the corresponding oxaquadri-cyclane has now been achieved despite many earlier efforts. Few syntheses of prismane derivatives can match the efficiency displayed in the cyclization to afford (45) which results from cycloaddition across the 1,4-diene system of the bicyclo-hexadiene, being best effected with light of wavelength 350 nm, which the product... 

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