Cycloadditions giving fluorinated derivatives

The thermal reaction between two molecules of olefin to give cyclobutane derivatives (a 2 + 2 cycloaddition) can be carried out where the olefins are the same or different, but the reaction is not a general one for olefins.921 Dimerization of like olefins occurs with the following compounds F2C=CX2 (X = F or Cl) and certain other fluorinated alkenes (though not F2C=CH2), allenes (to give derivatives of 97),922 benzynes (to give biphenylene deriv-... 

Fluorinated alkenes have been reported to give cyclobutane derivatives by thermal additions to other alkenes. Olefins in their ground electronic states have not been observed to give stereospecific cycloaddition one with another whereas a carbon-carbon double bond which is part of an allene or keten will undergo stereospecific concerted cycloadditions. The separate reactions of tetrafluoroethylene with cis- and trans-[l,2- H2]ethylene, which should not be subject to an adverse steric effect, have been studied to establish whether these reactions are stereospecific. Identical mixtures of products were obtained from both reactions, as expected if they proceed through the... 

The 1,3-dipolar cycloadditions offluonnatedallenes provide a rich and varied chemistry Allenes, such as 1,1-difluoroallene and fluoroallene, that have fluorine substitution on only one of their two cumulated double bonds are very reactive toward 1,3-dipoles Such activation derives from the electron attracting inductive and hyperconjugative effects of the allylic fluorine substituent(s) that give nse to a considerable lowering of the energy of the LUMO of the C(2)-C(3) n bond [27]... 

X = F.H). The fluorine-substituted derivative underwent cycloaddition with RCH CHC02Me (R = H, C02Me) to give pyrazolines (14). ... 

Fluorinated pyrroles have been studied intensively in recent years. As a resnlt, a significant number of synthetic approaches to these compounds was elaborated. The most general methods involve direct fluorination/trifluoromethylation of the parent pyrroles, both the [3 -1- 2]- and the [4H-2]-cycloaddition reactions, the applications of carbonyl compounds as well as TOSMIC and isocyanoacetates. Thongh variety of methods are already known, the elaboration of novel preparative pathways towards fluorinated pyrrole derivatives is still ongoing, which is due to the manifold of biological activities of this structural motive and the use as precursors for porphyrins synthesis. It is no doubt, that this branch of synthetic organic chemistry will enjoy a much attention, giving rise to sustainable flow of novel convenient pathways to the synthesis of fluorinated pyrroles. 

Fluorinated thiophene derivatives have found a broad application as biologically intriguing molecules and especially as modem organic materials. However, methods for their synthesis are still limited. The direct fluorination or trifluoromethylation of thiophene is either not selective or proceeds in low yields. The most convenient approach to fluorothiophenes and their benzoanalogues involves Uthiation-fluorination reactions. Other common methods are based on heterocycUzations with participation of methyl thioglycolate, or cycloaddition reactions. The scarce methods for fluorinated thiophenes synthesis give a chance for synthetic chemists to elaborate new, better pathways to these intriguing and useful compounds. 

---