Rearrangements prototropic, base-catalysed

The stereochemistry of dienes has been found to have a pronounced effect in the concerted cyclo-additions with benzyne 64>65h A concerted disrotatory cyclo-addition of tetrafluorobenzyne, leading for example with trans- (3-methylstyrene to (63, R = Me), is likely and in accord with the conservation of orbital symmetry 68>. However while the electro-cyclic rearrangement of (63, R = H) to (65, R = H) is not allowed, base catalysed prototropic rearrangement is possible. A carbanion (64, R = H) cannot have more than a transient existence in the reaction of tetrafluorobenzyne with styrene because no deuterium incorporation in (65) was detected when either the reaction mixture was quenched with deuterium oxide or when the reaction was conducted in the presence of a ten molar excess of deuteriopentafluorobenzene. 

Matsson (1985) determined the secondary /3-deuterium KIE for the base-catalysed stereospecific 1,3-prototropic rearrangement (37) of 1-methylindene... 

Base-catalysed prototropic rearrangements of cyclic polyacetylenes have often been used to synthesize annulene and dehydroannulene systems. In such reactions, transannular carbon-carbon bond formation between proximate triple bonds occasionally takes place to give polycyclic compounds. Treatment with a base of cyclic polyacetylenes 57 and 59 gave benzenoid aromatic compounds 58 and 61, with the desired dehydro[16] and [I8]annulenes, respectively. ... 

Results of a theoretical study of 1,3-prototropic rearrangement of 1-methylindene, catalysed by ammonia and MesN in water and in cyclohexane, have confirmed earlier predictions that the proton moves freely over the indene ring once it has been abstracted by the base. The relative rates of deprotonation, ion-pair collapse and ion-pair rearrangement have been estimated and discussed in each case. 

Trans-to-cis photoisomerization of unsymmetrical 4,4/-disubstituted trans-1,3-diphenyltriazenes gives a non-equilibrium mixture of two isomeric cis pairs, which, as in the case of symmetrical 1,3-diphenyltriazenes, undergo thermal cis-to-trans isomerization by means of 1,3-prototropic rearrangements catalysed by general acids and general bases (Scheme 124).187... 

---