Benzopentalenonaphthalenones from the intramolecular capture of a merocyanine derived from a naphthopyran.

Novel, highly coloured benzopentalenonaphthalenones result from a cascade process initiated by the thermally-induced ring-opening of diarylmethanol substituted 2H-naphtho[1,2-b]pyrans in the presence of acid.

The influence of a 1,1-diarylvinyl moiety on the photochromism of naphthopyrans.

1,1,3-Triarylpent-4-en-1-yn-3-ols, efficiently obtained in two steps from 1,1,3-triarylprop-2-yn-1-ols by a Meyer-Schuster rearrangement and subsequent addition of lithium trimethylsilylacetylide, react with either a 1- or 2- naphthol to afford photochromic 1,1-diarylvinyl substituted naphtho[1,2-b]- or naphtho[2,1-b]-pyrans respectively. Irradiation of solutions of these naphthopyrans results in reversible electrocyclic ring-opening to afford photomerocyanines which possess an extended conjugated system and show a bathochromically-shifted λ(max) relative to the non-vinyl substituted analogues.

Ring contraction during the 6pi-electrocyclisation of naphthopyran valence tautomers.

The thermal and photochemical ring-opening of spiro(3H-naphtho[2,1-b]pyran-3,9'-thioxanthene-10,10-dioxide) results in the facile ring-contraction to 9-(naphtho[2,1-b]furan-2-yl)-9H-thioxanthene-10,10-dioxide . Similar behaviour is displayed by the isomeric spiro(2H-naphtho[1,2-b]pyran-2,9'-thioxanthene-10,10-dioxide) affording 9-(naphtho[1,2-b]furan-2-yl)-9H-thioxanthene-10,10-dioxide , though more severe reaction conditions were required. The comparative ease of this rearrangement for the isomers and was rationalised on the basis of the relative isomer populations of the ring-opened naphthopyrans.