Paternò–Büchi reaction

The Paternò - Büchi reaction is named after Emanuele Paternò and George Hermann Büchi photochemical [2 2 ] cycloaddition to form four-membered oxetane rings of a carbonyl moiety and an alkene.

Overview reaction

Example acetone reacts with 2,3- dimethylbut -2-ene under the influence of light to Hexamethyloxetan (1):

The substituents on the alkene and the carbonyl determine the stereochemistry of the products so formed in the reaction of benzaldehyde (Ph = phenyl ) with 2-methyl, a mixture of two structurally isomeric oxetanes 2a and 2b:

Mechanism

The reaction is initiated by irradiation with long-wave UV light, which excites only the carbonyl compound. The carbonyl compound (aldehyde or ketone ) reacts with the alkene concerted or a diradical stage. Olefins with electron-withdrawing substituents favor a concerted mechanism, while donor substituents favor a free-radical mechanism, the diradicals can be detected by trapping.

Application

The reaction is used in the synthesis of natural products, but has only limited because of the often low selectivity industrial importance.