Addition oxanorbornene

Murakami [27] and Lautens [28] independently reported the rhodium-catalyzed addition of arylboronic acids to oxanorbornenes (Scheme 3.12). Murakami reported that the reaction of oxabenzonorbornadiene 37 a with phenylboronic acid 2m, in the presence of a rhodium-P(OEt)3 catalyst in MeOH at reflux, gave an 86% yield of the ring-opened alcohol 38 am. Lautens reported the asymmetric version of the reaction, where high enantioselectivity was observed with chiral ferrocenylbisphosphine hgand 39 in a... 

Scheme 3.12 Rhodium-catalyzed asymmetric addition of phenylboronic acid to oxanorbornenes [27, 28].

Scheme 7.18 Fe-catalyzed conjugate addition—ring opening of oxanorbornenes.

Using catalysis by palladium systems, allylic halides show little tendency to add. However, with nickel(O) catalysts [e.g., Ni(cod)2] allylic halides add to norbornene. in contrast to vinyl and aryl halides9. The palladium system also catalyzes the coaddition of alkynes and benzylic halides to strained bicyclic alkenes10- u. Thus, addition of methyl 2-[3-(chloromethyl)phenoxy]acetate and optically pure (S)-l-octyn-3-ol to norbornene, norbornadiene or 7-oxanorbornene 4 leads to diastereomeric adducts 5, used as precursors of interphenylene prostaglandin endoperoxides, in 34-58% yield. No diastereomeric ratios were reported. 

Additional well-defined side-chain liquid crystalline polymers should be synthesized by controlled polymerizations of mesogen-ic acrylates (anionic or free radical polymerizations), styrenes (anionic, cationic or free radical), vinyl pyridines (anionic), various heterocyclic monomers (anionic, cationic and metalloporphyrin-initiated), cyclobutenes (ROMP), and 7-oxanorbornenes and 7-oxanorbornadienes (ROMP). Ideally, the kinetics of these living polymerizations will be determined by measuring the individual rate constants for termination and... 

A, A -dimethylpiperidinium)]" "Cl . These complexes initiate the ROMP of functionalized 7-oxanorbornenes in water and methanol as well as aqueous emulsions [88]. More recently the same authors made the remarkable discovery that in the first case the activity is greatly enhanced by the addition of an equivalent of DCl, the role of which is to remove one of the two phosphine ligands, so generating the more active monophosphine complex 15 eqn. (22). This rapidly brings about the living ROMP of monomers 16 or 17 at 45°C (My/M = 1.3), eqn. (23), and block copolymers can also be made from the two monomers [89]. 

Scheme4.2S Proposed catalytic cycle for the rhodium

Generally speaking, Schrock initiators are highly active in the ROMP of a vast variety of cyclic alkenes such as substituted NBEs, norbomadienes, 7-oxanorbornenes, cyclooctatetraenes (GOTs), 1,4-CODs, etc., or polycyclic alkenes such as certain quadricyclanes. In addition, they may be used for 1-alkyne polymerization and the cyclopolymerization of 1,6-hepta-diynes. Despite the fact that they are highly sensitive... 

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