Paternò–Büchi reaction

The Paternò–Büchi reaction, named after Emanuele Paternò and George Büchi who established its basic utility and form, is a that forms four-membered oxetane rings from a carbonyl and an alkene.

With substrates benzaldehyde and 2-methyl-2-butene the reaction product is a mixture of structural isomers:

Another substrate set is benzaldehyde and furan