Pericyclic reaction atom transfer

Paquette has reported the most detailed investigation of this sort, of the relationship between (crystal) structure and reactivity for a series of compounds [78] (Paquette et al., 1990). These undergo a thermal pericyclic reaction in which two hydrogen atoms are transferred between alkene and alkane C-C bonds across a gap whose dimensions can be accurately measured, and can be varied by varying the group X bridging the central... 

The ene reaction is another pericyclic reaction which involves the combination of an alkene with an allylic system and a hydrogen atom transfer (Scheme 3.20). 

Bicyclo[4.4.1]undec-l(ll)-ene (28), however, exhibits different behavior, for it dimerizes in 95% yield to form structure (29). Whether this process involves hydrogen atom transfer from a tetra-methylene diradical, or an unusual pericyclic reaction reminiscent of an ene reaction, remains unclear. 

The stereochemical and kinetic data for the thermal ring contraction which proceeds with inversion of configuration at the halogen-receiving carbon atom are consistent with an intermolecular halogen transfer and exclude the occurrence of a thermally allowed pericyclic reaction ... 

The Alder ene reaction is like a Diels Alder reaction in which one Jt-bond in the diene has been replaced by a C-H bond 121. It does not therefore form a ring and does not fit easily into any of the three classes of pericyclic reaction (cycloaddition, electrocyclic, and sigmatropic). Since a hydrogen atom is transferred from one component to the other it is best described as a group transfer reaction.21 The regioselectivity is determined by the interaction 123 with the Jt-bond of the ene (the HOMO) with the LUMO of the enophile. ... 

Nj. Ab initio SCF calculations at various levels were performed on the symmetric dihydrogen transfer reaction c/s-N2H2 N2 a pericyclic transition structure with synchronous motion of the transferring hydrogen atoms was derived [9]. 

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