Oxanorbomene

There are a few communications concerning cycloadditions of nitrile oxides to unsaturated oxa and aza cage systems. Benzo- and mesitonitrile oxides RCNO give, with five substituted 7-oxanorbomenes 106, mixtures of the corresponding exo-adducts 107 and 108 in nearly quantitative yields. No traces of compounds resulting from the endo-face attack was detected (274). Substituents at positions 5 and 6 of 106 render the process highly regioselective. 

In 1988 Novak and Grubbs reexamined the ruthenium catalysed ROMP in protic media with 7-oxanorbomene as the substrate [26], As catalysts they used... 

Hoping to improve or to shorten our total synthesis of L-daunosamine, we explored the following reactions with 112 and 113, the adducts of the racemic 7-oxanorbomene derivative 47 + 48 to PhSeCl and PhSCl, respectively. Saponification of 112 and 113, followed by treatment with formalin, afforded ketones 114 and 115, respectively. Treatment of with tributyltin hydride in toluene/benzene (AIBN 1 - 2%, 80 °C) gave the key intermediate ( )-I03 in 69 % yield. Under the same conditions, 115 was reduced to ( )-I03 in 40 - 45 % yield. Raney nickel reduction of 115 afforded ( )-103 in 50 % yield together with 40 % of ( )-7-oxabicyclo[2.2.1]heptan-2-one. However, we found the multistep procedure 32 100 101 102 103 easier to scale up. Several intermediates in our synthesis do not have to be isolated. For instance, transfomation of 32 into 102 can be carried out in the same pot in 94 % yield. 

Ikoma M, Oikawa M, Sasaki M (2009) Chemospecific allylation and domino metathesis of 7-oxanorbomenes for skeletal and appendage diversity. Eur J Org Chem 72-84... 

Although the alkylidene complexes initiate the ROMP of functionalized norbomenes and 7-oxanorbomenes in aqueous solution quickly and completely in the absence of acid, the propagating species in these reactions often decompose before the polymerization reaction is complete. For example, in the ROMP of the water-soluble... 

One example of oxetane formation proceeding by an intramolecular syn addition of a sulfenate ester intermediate has been reported (equation 5).16 This mode of cyclofunctionalization appears to fail unless the substrate enforces the correct alignment of the sulfenate ester.16b However, related 7-oxanorbomen-2-ols give oxetane products with an exo phenylsulfenyl group.17... 

Scheme 3 Preparation of spirocyclic 7-oxanorbomene-P-lactam 9 through Staudinger reaction...

These highly activated aqueous ROMP catalysts can be applied to the polymerization of monomers hitherto reluctant to polymerize in aqueous solution. This can be illustrated with the following example. When either 7-oxanorbomene-2,3-dicarboxylic acid, 46, or its dipotassium salt, which posses both the 1,4-bridging epoxide and the dicarboxylate moieties, is allowed to react with a wide range of metathesis catalysts, only catalyst deactivation is observed, Eq. (48) [79]. 

The Ni(dppe)Br2-catalyzed condensation of oxabenzonorbomadienes with either p-iodo-(Z)-propenoates or o-iodobenzoate provided a new synthesis of aimulated coumarins. As shown below, this reaction was also found to be regioselective <030L4903>. The same group also reported the reductive coupling of oxabenzonorbomadienes and 7-oxanorbomenes with various propiolates under similar Ni-catalyzed conditions at room temperature <03CEJ3165>. 

In addition to those listed in Tables 1 and 2, many more active catalyst systems have been reported, including W-carbyne complexes [68], and metallacycles such as Ti or Ta cyclobutanes [8, 69], which are initiators for ROMP. The ROMP of functionalized monomers such as 7-oxanorbomene derivatives can also be performed successfully using certain Ru initiators, affording polymers with a high molecular weight (eq. (18)) [70]. Moreover, in water alone, polymerization proceeds very rapidly in nearly quantitative yields in the presence of Ru catalysts under an atmosphere of air [71] (cf. Section 3.3.10.1). 

The observation that these polymerizations proceeded in alcoholic solution led to the discovery that selected Ru and Ru " complexes catalyze the ROMP of these 7-oxanorbomene derivatives in water alone to provide quantitative yields of the desired ring-opened polymer (eq. (6)) [29]. 

Further studies of the regioselective tandem ring opening/cross metathesis of 2-emlo-substituted 7-oxanorbomenes with electron-rich olefins, a process first described in 2004, were reported. Reaction of the 2-exo isomer, like that of the 2-endo isomer, was also found to... 

The lessons learned from these complexes were eventually applied to the synthesis of well-defined ruthenium alkylidenes 8 and 9. Although they were insoluble in water, these alkylidenes could be used to initiate the living ROMP of functionalized norbornenes and 7-oxanorbomenes in aqueous emulsions. Substitution of the phosphine ligands in 9 for bulky, electron-rich, water-soluble phosphines produced water-soluble alkylidenes 10 and 11, which served as excellent initiators for the ROMP of water-soluble monomers in aqueous solution. These new ruthenium alkylidene complexes are powerful tools in the synthesis of highly functionalized polymers and organic molecules in both organic and aqueous environments. 

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