Spiro oligomerization reaction

FIGURE 6.30 a,cu-Bis(tocopheryl)alkanes (36) and other a, >-bis(hydroxyphenyl)-alkanes (37-40) as starting materials for the spiro oligomerization/spiro polymerization reaction. 

There have been attempts to optimize the selectivity of the di- and oligomerization reactions by using various nickel(O) catalysts with spiro[2.3]hex-l -ene (9) as substrate. Being more reactive than 3,3-dimethylcyclopropene, 9 must be used as a diluted solution (< 1 mol/L), which remains unchanged for more than one month at 20 C. There is a clean and complete cyclodimerization within 10 minutes at 60-80 °C. On treatment with the catalyst, the cyclodimer is formed together with trimers and oligomers. Especially remarkable is the high activity and selectivity of bro-motris(triphenylphosphane)nickel. 

FIGURE 6.28 Influence of the reaction of the first o-QM (to a pyrano or spiro structure) on the reactivity of the second o-QM from 33 according to computations only spiro/pyrano, but no pyrano/pyrano or spiro/spiro pairs are formed in the oligomeric products.56... 

Methylenecyclopropanes, although usually stable at ambient temperature, do undergo efficient oligomerization and polymerization when heated to form a variety of linear and cyclic products. From transition metal catalyzed reactions of this kind, the spiro-fused di- and trimerization products are most remarkable and useful from a synthetic point of view. 

Cyclization, Isomerization, and Coupling Reactions. Inter-(eq 42) and intramolecular (eq 43) cyclotrimerizations of alkynes are mediated by Wilkinson s catalyst. This is an extremely efQcient route to ring fused systems. Similarly, Diels-Alder-Uke [4 + 2] cyclization processes are promoted by RhCljPPhsjs dienophile components in these reactions need not be electron deficient, and they can be an alkene or alkyne (eqs 44 and 45) AUenes oligomerize in pathways determined by their substituents For instance, four molecules of aUene combine to give a spiro-cyclic system (eq 46), but tetraphenylallene isomerizes to give an indene (eq 47). ... 

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