Intramolecular cycloaddition polymerization

A second class of activated alkenes capable of undergoing intramolecular cycloadditions contains crotonate moieties from a topological point of view and thus exhibits enhanced stability with respect to polymerization. Additionally, the spacer between the methylenecyclopropane and the alkene only consists of s p -hybridized atoms in the case of substrates 8 and 11 so that the whole side chain should behave less rigidly than that of 3. In accordance with these predictions, moderate to high yields of the cycloaddition products, methyl c 5-3-melhylene-octahydropentalene-l-carboxylate (9) and methyl 3-methylenehexahydroindan-l-carboxylate (12), are obtained. From 8, however, a product 10 of a formal alkylation reaction is additionally formed. ... 

The length of the tether is crucial for a successful macrocycle formation. When 51 was attached to acryUc acid through a three carbon linker, no intramolecular cycloaddition was observed to compete with the thermal polymerization of the diene (for other examples of macrocyclic formation through intramolecular Diels-Alder addition, see e.g., [195-200]). 

In an approach to a dihydrooritidine analogue, the intermolecular [2 + 2]-photo-cycloaddition of 2, 3 -0-isopropylideneuridine to chiral and achiral acrylates was found to be unsatisfactory both with respect to regio- and diastereoselectivity. The intramolecular approach was more successful, and uridine 143 produced selectively the single diastereomerically pure product 144. Due to concurrent photodimerization and polymerization reactions, however, the yield was only moderate (Scheme 6.50) [136]. 

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