Effect of Sensitizers and Solvents on Chemoselectivity

In addition to the steric issues in chemoselectivity, which are intrinsic to the reaction of a given set of substrates, solvent and sensitizer effects are of importance for a direct control on selectivity because they can be controlled. The reaction of 8a and 13c catalyzed by sensitizer 6 shows an overall increase in cross-product formation with increasing solvent polarity. Entries 4 and 5 in Table 4.1 demonstrate that use of 3a reduces the formation of cross-products in polar solvents. This difference can be rationalized by the fact that after ET by 6, a strongly complexed ion pair is formed, whereas in the case of 3a, the sensitizer is neutral and can dissociate more easily from the radical cation formed. 

Entry Concentration (M) Sensitizer Solvent Cross-Product/18 Dimer 

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