Norbomen-2-ones regioselectivity

The regioselectivity and stereoselectivity of electrophilic additions to 2-benzyl-2-azabicyclo[2.2.1]hept-5-en-3-one are quite dependent on the specific electrophile. Discuss the factors which could influence the differing selectivity patterns and compare this system to norbomene. 

Electronic effects on alkene regioselectivity in the Pauson-Khand reaction have also been observed. The regioselectivity observed in cycloadditions of norbomen-2-ones has been interpreted as arising from an electronic preference for attachment of the 5 C-S of the alkene to an alkyne carbon rather than cobalt in the bond-forming insertion step (equation 13). In these systems electronic and steric effects have been separated by carrying out identical reactions with the corresponding norbomen-2-ols, in which the... 

Aromatic alkylation and Suzuki or Heck coupling are combined in one operation by proper design of a catalytic system. Norbomene acts as a platform for regioselective o-alkylation. 

One may, by careful choice of monomer, study the potential of different catalysts to behave in a stereoselective or regioselective manner. Thus, with a symmetrical monomer such as norbomene [58], norbomadiene [59] or their 5,6 [60] or 7-substituted derivatives [61,62] we have obtained polymers with a variety of cis main chain double bond contents and distributions. In a number of the 7-substituted examples, fine structure on certain NMR resonances is observed which is attributable to tacticity effects. Conversely, one may use the unsymmetrical monomers such as 1-substituted derivatives [63] and delineate the propensity of the different catalysts to regioselectivity, which manifests itself as head-tail bias in the polymer. 

The addition of resolved P-chiral hydrogen phosphinates to alkenes has been accomplished without significant loss of the stereochemistry at phosphorus (Scheme 4.84) [124]. This reaction was achieved with the use of a radical initiator. One of the attractive aspects of this chemistry was that it proceeded under solvent-free conditions. The reaction was regioselective for the anti-Markovnikov product, and fair to moderate yields of the alkyl-phosphinate were obtained. Generally, high yields of the alkylphosphinate were obtained for a host of terminal alkenes as well as strained internal alkenes such as norbomene. Internal alkenes were significantly less reactive and satisfactory conversions were only... 

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