Rearrangement four electron cyclic

As in Explanation 27, sulfur of sulfur trioxide becomes attached to the more electronegative (electrophilic) carbon of the double bond of perflu-oroisobutylene. The electron density of the central carbon is increased by back-donation of electrons of the difluoromethylene group, and by electron withdrawal of the two trifluoromethyl groups. The intermediate four-membered cyclic sulfate rearranges to 2,2-bis(trifluoromethyl)-l-fluoroethenyl fluorosulfate 46. ... 

A new entiy to the total synthesis of isocryptolepine (cryptosanguinolentine), isolated from Cryptolepis sanguinolenta, was achieved by constructing a tetracyclic ring system through a microwave-assisted tandem Curtius rearrangement and electro-cyclic reaction of an aza 67c-electron system (Hayashi et al., 2012). The tetracyclic lactam was further converted to isocryptolepine in a four-step sequence. The acid is simply reacted with DPPA in toluene under microwave irradiation to dehver the desired fused lactam in 97% yield. 

Mass spectrometry was applied in conjunction with thermolysis studies leading mainly to sulfines and rearranged products with four-membered sulfoxides and to a loss of sulfur dioxide with sulfones The fragmentation pattern of thietes under electron impact can be explained by the sequential loss of the elements of sulfur monoxide and oxygen from an intervening cyclic sulfmate intermediate . ... 

On the basis of mechanistic studies, mainly on these isolable cyclic four-membered peroxides (1 and 2), two main efficient chemiexcitation mechanisms can be defined in organic peroxide decomposition (i) the unimolecular decomposition or rearrangement of high-energy compounds leading to the formation of excited-state products, exemplified here in the case of the thermal decomposition of 1,2-dioxetane (equation l)11-15-19 and (ii) the decomposition of a peroxide, catalyzed by the interaction with a second compound, which is ultimately formed in its electronically excited state. 

T electrons with one si inversion (Mdbius-like). A Mobius array in the ground state is antiaromatic with six electrons but is aromatic and stable in the excited state. °> Thus the di-ir-methane rearrangement via transition state (3) is photoallowed. The orbital scheme (4) involves a cyclic array of four 17- electrons with no sign inversions (Hiickel-like). Again the ground state is antiaromatic but it is aromatic in the excited state and the reaction is photochemically allowed. 

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