Substituted 2,4,4,6-tetraphenyl-4H-selenopyrans: preparation, photocolouration and 4H-selenopyran ring geometry; an X-ray and DFT calculation study

Abstract

1,5-Diaryl-3,3-diphenylpentane-1,5-diones 3a–d react with Al₂Se₃–HCl–AcOH reagent to give the 2,6-diaryl-4,4-diphenyl-4H-selenopyrans 4a–d in satisfactory yields while the same procedure starting from 1,5-diketone 5 affords small amounts of spiroheterocycle 6. 2,4,4,6-Tetraphenyl-4H-selenopyran 4a can be brominated or nitrated at positions 3 and 5 to give substituted derivatives 7–9. Dibromo derivatives 4c and 7 were converted with copper(I) cyanide to dicyano derivatives 4e and 10,11, respectively. Similarly to 4H-pyrans 1 and 4H-thiopyrans 2, the 1-selena analogues 4a–d and 8 exhibit solid state photocolouration which was investigated in terms of dispersive first-order reaction kinetics. The influence of selenium heteroatom on the geometry of the heterocyclic ring of molecules 4a,c and 6 is discussed on the basis of X-ray structure determinations, quantum DFT and semiempirical PM3 calculations.