Nazarov Cyclization

In 1941, the Russian chemist Ivan Nikolaevich Nazarov extensively studied the cyclization reactions of allyl vinyl ketones to the corresponding 2-cyclopentanones. Although cyclizations following this general procedure had been observed before Nazarov's work, it was his study of the rearrangements of allyl vinyl ketones that marked the first close examination of this process. Nazarov correctly reasoned that the allylic olefin isomerized in situ to form a divinyl ketone before ring closure to the cyclopentenone product. Subsequently, the protic or Lewis acid-catalyzed ring closure of divinyl ketones through formation of the corresponding pentadienylic cations became known as the Nazarov cyclization.

This reaction became useful in organic synthesis due to the frequent appearance of the cyclopentanone ring in natural products and in the formation of synthetic intermediates in total synthesis campaigns. For example, in the synthesis of (±)-trichodiene by K.E. Harding and colleagues, the Nazarov cyclization was employed as a key ring-forming step to control the stereochemistry.