Synthesis of heterocyclic chromenes via Buchwald C–N coupling and the substituent effect on their photochromic properties

Synthesis of series of new heterocyclic [2]H- and [3]H-chromenes via Buchwald C–N coupling is described. Introduction of heterocyclic substituent to 6-position of benzopyrans and in 8-position of naphthopyrans led to significant bathochromic shift (up to 154 nm) in the spectra of their open forms. Substituted benzopyrans display high colorability values along with acceptable resistance to fatigue. By using judicious substituents, the absorption range of this type of pyrans can be tuned according to the nature of the heterocyclic unit, and the photochromic properties of pyrans could be adjusted to desired values.