Vinylcyclopropane radical

Roth et aJ [10] have used CIDNP to study the structures of vinylcyclopropane radical cations fomied from precursors such as sabinene (1). 

As a consequence of the above observations, the intramolecular capture of the vinylcyclopropane radical cation was attempted next. Thereby, chrysanthemol and homochrysanthemol both yielded the expected cyclization products (Scheme 35) [55],... 

Scheme 35 Cyclization by intramolecular capture of vinylcyclopropane radical cations.

Figure 7. Calculated bond lengths (pm) and hyperfine couplings (G) for the syn- and ant/-conformers of vinylcyclopropane radical cationic states (MP4SDQ/6-31G )." ...

On the other hand, the CIDNP approach and recent ab initio calculations have provided what we consider unambiguous evidence for the nature of the vinylcyclo-propane radical cation as well as for some simple derivatives. We have carried out ab initio calculations on the prototype 19 and several simple derivatives, and probed by CIDNP the structures of three simple vinylcyclopropane radical cations in which the two functionalities are locked in a syn configuration. 

Actually, the earliest derivative of a vinylcyclopropane radical cation was a serendipitous discovery. It was formed by an unusual hydrogen shift upon photo-induced electron transfer oxidation of tricyclo[4.1.0.0 ]heptane (26). This result has been questioned on the grounds that the same rearrangement was not observed in a Freon matrix. However, there is no basis for the assumption that radical cation reactions in frozen matrices at cryogenic temperatures should follow the same course as those at room temperature in fluid solution and in the presence of a radical anion, which is potentially a strong base. In several cases, matrix reactions have taken a decidedly different course from those in solution. For example, radiolysis of 8 in a Freon matrix generated the bicyclo[3.2.0]hepta-2,6-diene radical cation (27 ), or caused retro-Diels-Alder cleavage yet, the... 

The nature of vinylcyclopropane radical cations was elucidated via the electron transfer induced photochemistry of a simple vinylcyclopropane system, in which the two functionalities are locked in the anri-configuration, viz., 4-methylene-l-isopropylbicyclo[3.1.0]hexane (sabinene, 39). Substrates, 39 and 47 are related, except for the orientation of the olefinic group relative to the cyclopropane function trans for 39 versus cis for 47. The product distribution and stereochemistry obtained from 39 elucidate various facets of the mechanism and reveal details of the reactivity and structure of the vinylcyclopropane radical cation 19 . 

Phenylcyclopropane radical cation (9 ) has divergent hyperfine coupling constants for the secondary cyclopropane protons (aptrans = 0.78 mT upcis = 0.07 mT CIDNP, B3LYP/6-31G calculations), apparently because the cis protons are located in a nodal plane. " Similarly, vinylcyclopropane radical cation is... 

The vinylcyclopropane radical cation, generated at 77 K by X-irradiation of (139) in a Freon-113 matrix, was shown to rearrange at 105-110 K to afford two ring-opened distonic radical cationic species.300 The rearrangement reactions of the radical cations of 1,3- and 1,4-pentadiene and cyclopentene and the formation of spin adducts with 2.4.6-tri-/-butylnitrosobenzene (BNB) are discussed. The pulse radiolysis of 1,1 -binaphthyl-2,2,-diyl hydrogenphosphate (BiNPCUH) (140) in deaerated f-butanol at... 

The vinylcyclopropane radical cation, is another radical cation of structure type B, which is stabilized by conjugation. Its proposed structure was based exclusively on ab initio calculations (B3LYP/6-31G ) because the electron-transfer photochemistry of this species failed to provide clear-cut CIDNP effects [128], In this context it is worth noting that product studies cannot, in principle, establish the cyclopropane radical cation structure type. Irrespective of the structure, nucleophilic capture is expected to result in the cleavage of the strained ring. 

Methylene-l-isopropylbicyclo[3.1.0]hexane (sabinene, 34) contains an alkene and a cyclopropane function locked in the anti orientation. CIDNP effects for 34 support a radical cation, in which the electron spin is delocalized between the olefinic 7t-system and the internal cyclopropane bond. The results are compatible with a vinylcyclopropane radical cation, 34 , with one weakened cyclopropane bond, which has retained the steric integrity of the parent molecule [219]. 

Oxgaard, J., Wiest, O. The Vinylcyclopropane Radical Cation Rearrangement and Related Reactions on the C5H8.bul.+ Hypersurface. J. Am. Chem. Soc. 1999,121,11531-11537. 

Oxgaard, J., Wiest, O. Substituent effects in the vinylcyclopropane radical cation rearrangement A computational road to a new synthetic tool. Eur. J. Org. Chem. 2003,1454-1462. 

Irradiation (s.a. under 1,4-Dicyanonaphthalene) 3-Ethylene-5-sulfonylselenides from vinylcyclopropanes Radical homoconjugate selenosulfonation... 

Roth HD and Herbertz T (1993) The structure of simple vinylcyclopropane radical cations. Evidence for conjugation between alkene and cyclopropane group. Journal of the American Chemical Society 115 9804-9805. 

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