Sustmann type II addition

Sustmann type II additions occur whenever both terms of Equation 15.8 contribute to a similar (and small) extent to the stabilization of the transition state of 1,3-cycloadditions (Figure 15.38, column 3). These reactions correspondingly represent a reactivity minimum. 

Some 1,3-dipoles possess HOMO and LUMO energies that allow for fast Sustmann type I additions with electron-poor dipolarophiles and for fast Sustmann type III additions with electron-rich dipolarophiles. In reactions with dipolarophiles with intermediate electron density, such dipoles merely are substrates of the much slower Sustmann type II additions. A plot of the rate constants of the 1,3-dipolar cycloadditions of such dipoles as a function of the HOMO energy of the dipolarophiles—or as a function of their LUMO energy that varies with the same trend—then has a U-shape. One such plot is shown in Figure 15.39 for 1,3-dipolar cycloadditions of diazomalonates. 

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See also in sourсe #XX -- [ ]

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