2.2- Diaryl-1 -methylenecyclopropanes

Reaction of diaryl diselenides with methylenecyclopropanes in the presence of PhI(OAc)2 (2.2equiv.) results in ring expansion to afford 1,2-diselenylcyclobutenes (Scheme 41).206... 

At least one of the hexadiene radical cations (20 +) can be viewed as a species containing spin and charge in two separate (though equivalent) molecular fragments. This separation can be enforced in systems of lower symmetry in this context, we mention two radical cations derived from l,l-diaryl-2-methylenecyclopropane (23), and 6-methoxy-l,2,3,4,6-pentamethyl-5-methylenebicyclo [2.2.0]hex-2-ene (25). 

In some cases, the structures of oxygenation products have been crucial for assigning the structures of unusual radical cations. Eor example, the endo-peroxides (83 and 85) support the structures assigned to radical cations (24 and 84 ) derived from l,l-diaryl-2-methylenecyclopropane (23) and 2,5-diaryl-l,5-hexadiene, respectively.Time-resolved spectroscopic data suggest that 83 is generated by coupling of triplet biradical (24 ) with (triplet) molecular oxygen. 

Reactions of 2-phenyl- 1-methylenecyclopropane and of 2,2-diaryl-1-methylene-cyclopropane with hydrido complexes of Rh and Ir causes C-C bond cleavage of the three-membered ring (Scheme 87).130 The bond cleavage occurs via /3-alkyl... 

Intuitively, suitable substituents will favor placing the spin on one set and the charge on the other. Indeed, solution phase, chemi-ionization via a photoexcited quinone of gem-diaryl-substituted methylenecyclopropane results in two, non-interconverting, different radical cations. For the 2,2-derivatives (11) the electron is lost from the ring. This results in... 

Although SET photochemistry is often a practical method to promote cation radical reactions, such a variant had not been probed until we recently discovered the SET-photoinduced degenerate methylenecyclopropane rearrangement of 2,2-diaryl-1-methylenecyclo-propanes." Below, we describe in detail the results of our studies of this process including the chemical and spectroscopic identification... 

Photoexcitation of the EDA complexes of methylenecyclopropanes and TCNE is a convenient procedure to generate trimethylenemethane cation radical intermediates. 2,2-Diaryl-l-methylenecyclopropanes (77a-c) form colored EDA complexes when mixed with TCNE in dichloromethane. Irradiation (A, > 390 nm) of an oxygen-saturated dichloromethane solution (X max = 370 and 568 nm) of 77a ( ° = +1.35 V vs. SCE) and TCNE, leads to formation of dioxolanes 78a and 79a and the TCNE adducts 80a and 81a in respective yields of42and54%. 

Diaryl-2-isopropylidene-3-methylenecyclopropanes react with C,iV-diarylnitrones to give 2,2-dimethyl-l,6-diaryl-3-(diarylmethylene)piperidin -ones and 5-methyl-l-aryl-l-(arylamino)-4-(diarylmethylene)hex-5-en-3-ones (Scheme 75). ... 

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