Through-bond interactions electrophilic additions

According to the transition state proposed by Nagasawa et al., the catalyst forms a complex with the Z-enolate of Schiffs base through ionic and hydrogen-bonding interactions. In addition, the methyl groups on the spiro ether ring controls the electrophile approach. 

The addition of alkyl radicals to alkenes is important for C-C bond formation. A tert-butyl radical, a typical nucleophilic radical, reacts with acrylonitrile taking a rate constant of 2.4 X 106 M-1 s-1 (27 °C), through a SOMO-LUMO interaction. However, it reacts with 1-methylcyclohexene, an electron-rich alkene, taking a rate constant of 7.4 X 102M-1 s-1 (21 °C). On the other hand, the diethyl malonyl radical, a typical electrophilic radical, shows the opposite reactivity [66-71]. Similarly, the rate constant for the reaction of nucleophilic C2H5 and cyclohexene is2X 102 M 1 s 1, while that of electrophilic C3F7 with cyclohexene is 6.2 X 105 M-1 s 1. 

Pericyclic reactions, such as the addition of a carbene to an alkene and the Diels-Alder cycloaddition (Review Table 1, reactions Ih and li), involve neither radicals nor nucleophile-electrophile interactions. Rather, these processes take place in a single step by a reorganization of bonding electrons through a cyclic transition state. We ll look at these reactions mate closely in Chapter 30. 

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