Observations on the synthesis of photochromic naphthopyrans

Christopher D. Gabbutt, B. Mark Heron, Alicia C. Instone, David A. Thomas, Steven M. Partington, Michael B. Hursthouse, Thomas Gelbrich

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Abstract

1-Naphthol reacts with 1,1-diarylprop-2-yn-1-ols 5a,b, under alumina catalysis, by two pathways to give the photochromic naphtho[1,2-b]pyrans 6a,b, together with the propenylidenenaphthalenones 7a,b, representatives of a new class of merocyanine dyes. With 2-methyl-1-naphthol, formation of the photochrome is suppressed; the only products are merocyanines 7c,d. The cyclocondensation of 2-naphthol with 5a,b proceeds much more efficiently, to give the naphtho[2,1-b]pyrans 14a,b. Pyran formation is not suppressed from either 1-bromo- or 1-(4 -methoxyphenyl)-2-naphthol; reaction with 5a,b merely results in expulsion of the C-1 substituent. An alternative pathway supervenes in the reaction of 1-methyl-2-naphthol with 5a to give the benz[e]indanone 17, the constitution of which was determined by X-ray crystallography. Reaction of the 1,3,3-triarylpropynols 19a,b with 1-naphthol affords the naphthopyrans 20 together with merocyanines 21, whilst the isomeric pyrans 23 are efficiently produced from 2-naphthol. The configuration of merocyanines 7a and 21a was unequivocally established by X-ray crystallography.

Original languageEnglish
Pages (from-to)1220-1230
Number of pages11
JournalEuropean Journal of Organic Chemistry
Volume2003
Issue number7
DOIs
Publication statusPublished - 1 Mar 2003
Externally publishedYes

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    Gabbutt, C. D., Heron, B. M., Instone, A. C., Thomas, D. A., Partington, S. M., Hursthouse, M. B., & Gelbrich, T. (2003). Observations on the synthesis of photochromic naphthopyrans. European Journal of Organic Chemistry, 2003(7), 1220-1230. https://doi.org/10.1002/ejoc.200390176