The Nazarov cyclization reaction ( often referred to as simply the Nazarov cyclization ) is a chemical reaction used in organic chemistry for the synthesis of cyclopentenones . The reaction is typically divided into classical and modern variants , depending on the reagents and substrates employed . It was originally discovered by Ivan Nikolaevich Nazarov ( 1906 – 1957 ) in 1941 while studying the rearrangements of allyl vinyl ketones .