Intramolecular cyclisation of photolabile thienylchromenones : synthesis of angular tetracyclic compounds

Department of Chemistry, Kurukshetra University, Kurukshetra-136 119, Haryana, India E-mail : rckamboj@rediffmail.com Fax: 91-1744-238277 Manuscript received 12 May 2011, revised 20 March 2012, accepted 07 June 2012 Photo-irradiation of 3-alkoxy-2-(thiophen-2-yI)-4H-chromen-4-ones in methanol with Pyrex filtered UV-Iight lead to the formation of interesting angular tetracyclic compounds. In the present study, we demonstrate the formation and distribution of the photoproducts which depends upon the stability of in situ generated 1,4-biradicals (through type II process)