Synthesis and photochromic properties of 2H,9H-indeno[1,2-f]- and 3H,7H-indeno[2,1-i]-naphtho[2,1-b]pyrans

Article abstract of DOI:10.1080/15421400590946334

Expedient syntheses of the 3-hydroxy- and 6-hydroxy- derivatives of 11H-benzo[a]-fluoren-11-one, obtained via Suzuki-Miyaura couplings are described. Reactions of these phenols with 1,1-diarylprop-2-yn-1-ols give indeno[2,1-i]- and indeno[1,2-f]-naphtho[2

Full text of DOI:10.1080/15421400590946334

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Synthesis and Photochromic
Properties of 2H,9H-
Indeno[1,2-f]- and 3H,7H-
Indeno[2,1-i]- naphtho[2,1-
b]pyrans
Christopher D. Gabbutt a , B. Mark Heron a , Craig A.
Mars a & Steven M. Partington b
a Department of Colour & Polymer Chemistry,
University of Leeds, Leeds, UK
b James Robinson Ltd., Huddersfield, UK
Version of record first published: 31 Aug 2006.
To cite this article: Christopher D. Gabbutt, B. Mark Heron, Craig A. Mars & Steven M.
Partington (2005): Synthesis and Photochromic Properties of 2H,9H-Indeno[1,2-f]- and
3H,7H-Indeno[2,1-i]- naphtho[2,1-b]pyrans, Molecular Crystals and Liquid Crystals,
430:1, 167-172
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Mol. Cryst. Liq. Cryst., Vol. 430, pp. 167–172, 2005
Copyright # Taylor & Francis Inc.
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400590946334
Synthesis and Photochromic Properties of
2H,9H-Indeno[1,2-f]- and 3H,7H-Indeno[2,1-i]-
naphtho[2,1-b]pyrans
Christopher D. Gabbutt
B. Mark Heron
Craig A. Mars
Department of Colour & Polymer Chemistry,
University of Leeds, Leeds, UK
Steven M. Partington
James Robinson Ltd., Huddersfield, UK
Expedient syntheses of the 3-hydroxy- and 6-hydroxy- derivatives of 11H-benzo[a]-
fluoren-11-one, obtained via Suzuki-Miyaura couplings are described. Reactions of
these phenols with 1,1-diarylprop-2-yn-1-ols give indeno[2,1-i]- and indeno[1,2-f]-
naphtho[2,1-b]pyranones respectively. The photochromic properties of these and
the reduced derivatives are reported. A rationale for the pronounced hypsochromic
shift in kmax of the photomerocyanine from a 2H,9H-indeno[1,2-f]naphtho[2,1-
b]pyran is presented.
Keywords: indenonaphthopyran; naphthopyran; photomerocyanine; Suzuki coupling
INTRODUCTION
The isomeric naphthopyrans 1 and 2 are currently the most commer-
cially important class of photochrome and are extensively employed in
a variety of variable transmission devices. Both 1 and 2 exhibit T-type
(thermally reversible) photochromism [1], due to electrocyclic ring
opening to a merocyanine valence tautomer 3 (Scheme 1).
The photomerocyanines from 1 exhibit slower fading kinetics, greater
colourability and have kmax bathochromically shifted compared to those
from 2 (i.e. 3). Much work has centred on efforts to improve the fading
We are grateful to Professor J. Griffiths for helpful discussions.
Address correspondence to Christopher D. Gabbutt, Department of Colour & Polymer
Chemistry, University of Leeds, Leeds, LS2 9JT, UK. E-mail: c.d.gabbutt@leeds.ac.uk
167

168
C. D. Gabbutt et al.
SCHEME 1
kinetics of 1 and enhance the colourability of 2. In particular, a consi-
derable number of fused-ring naphthopyrans has been obtained. Thus,
the indenonaphthopyrans 4 [2] (R1 ¼ H, alkyl, R2 ¼ H, alkyl, aryl;
R1 ¼ R2 ¼ NR2) containing an embedded naphtho[1,2-b]pyran core have
been obtained. The isomeric systems 5 have also been described [3].
The pyran moiety in 5 can be reconfigured to give an alternative series
of indenonaphthopyrans exemplified by 6 [3], 7 [4a] and 8 [4b]. Hetero-
cyclic analogues of 8 have recently been reported [4c].
RESULTS AND DISCUSSION
The indeno[1,2-f]naphtho[2,1-b]pyran 8 has been obtained via acyla-
tion of 2-indanone with 3,4-dimethoxyphenylacetyl chloride [4b]. We

Synthesis and Photochromic Properties of Indenonaphtho pyrans
169
now report an alternative route to indeno systems (cf. 8) which offers
greater flexibility in terms of accessibility of starting materials and
substitution patterns which may be achieved. The requisite starting
material, 6-hydroxy-11H-benzo[a]fluoren-11-one is obtained via
Suzuki-Miyaura coupling of methyl 2-bromobenzoate to the readily
available boronic acid 9. Subsequent intramolecular Friedel-Crafts
acylation provides 11 and thus 12 in high yield (Scheme 2). This
approach to 11 represents an alternative to the current literature pro-
cedure, which utilises the directed remote metallation of an analogue
of 10 in which the CO2Me function is replaced by CONPri2 [5].
Acid catalysed condensation of 12 with 1,1-di(4-methoxyphenyl)-
prop-2-yn-1-ol gave the 2H,9H-indeno[1,2-f]naphtho[2,1-b]pyran-9-
one 13 [6] in moderate yield.
The reduced system 14 could be efficiently obtained by reduction
and demethylation of 11 to give 6-hydroxy-11H-benzo[a]fluorene and
subsequent reaction with the propynol.
Electron donating substituents at C-8 in naphtho[2,1-b]pyrans
induce bathochromic shifts in kmax of the photomerocyanine valence
isomer [1,7]. The route outlined in Scheme 2 provides an efficient
SCHEME 2

170
C. D. Gabbutt et al.
entry to the hitherto inaccessible compounds 13 and 14. With access to
these systems it was of interest to extend this approach to the
synthesis of indeno[2,1-i][2,1-b]napthopyrans, conformationally rigid
analogues of 8-phenylnaphtho[2,1-b]pyrans.
The required starting materials, 3-(alk)oxy-11H-benzo[a]fluorenes
15 and 16 were obtained via Suzuki methodology from 6-bromo-2-
methoxynaphthalene (Scheme 3) and subsequently converted to the
fluorenones 17a [8] and 17b, fluorenol 18 and the fluorene derivative 19.
SCHEME 3

Synthesis and Photochromic Properties of Indenonaphtho pyrans
171
Attempts to obtain 9-dialkylamino derivatives of e.g. 17 or 19, could
not be realised owing to the reluctance of the ester 20, or its deriva-
tives to cyclise. Further studies in this area are in progress.
PHOTOCHROMIC PROPERTIES
Surprisingly, the indenonaphthopyranone 13 did not exhibit any
observable photochromic response at ambient temperature, the com-
pound was strongly coloured and gave a yellow-orange solution
[kmax(PhMe) ¼ 443 nm]. In contrast, the fluorene 14 exhibited colour-
less ! orange photochromism (kmax ¼ 461 nm, t1=2 ¼ 2 s). In the case
of the indeno[2,1-i]-naphthopyranones 17a and 17b, the former exhib-
ited a very weak photochromic response (kmax ¼ 463 and 584 nm,
t1=2 ¼ 50 s), whereas the latter provided only an orange solution
(kmax ¼ 457 nm). The reduced derivatives 18 (kmax ¼ 492 nm, t1=2 ¼ ca.
1.5 s) and 19 (kmax ¼ 495 nm, t1=2 ¼ ca. 1.5 s) exhibit identical proper-
ties to the 3,3-dianisyl-8-phenylnaphtho[2,1-b]pyran (vide supra).
The effective absence of a photochromic response in the fluorenones
13 and 17a,b is remarkable and merits further investigation. The pro-
nounced hypsochromic shift of kmax of the photomerocyanine 13A pre-
sumably stems from steric destabilisation arising from interaction of
O-1 with H-13.
REFERENCES
[1] Hepworth, J. D., Gabbutt C. D., & Heron, B. M. (1999). Colour Science ‘98, Volume 1:
Dye and Pigment Chemistry, Griffiths, J. (Ed.), 161; Van Gemert, B. (1998).
In: Organic Photochromic and Thermochromic Compounds, Volume 1; Main Photo-
chromic Families, Crano, J. C. & Guglielmetti, R. J. (Eds.), Plenum Press: New York,
p. 111.

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C. D. Gabbutt et al.
[2] Nelson, C. M., Chopra, A., Petrovskaia, O. G., Knowles, D. B., Van Gemert, B., &
Kumar, A. (2001). PCT WO, 01=19813; Van Gemert, B., Chopra, A., & Kumar, A.
(2000). U. S. Patent, 6113814.
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(c) Mann, C., Melzig, M., & Weigand, U. (2004). U. S. Pat. Appl., 0092743A1.
[5] Laufer, R. S. & Dmitrienko, G. I. (2002). J. Am. Chem. Soc., 124, 1854.
[6] 1H NMR data for 2,2-di(4-methoxyphenyl)-2H,9H-indeno[1,2-f]naphtho [2,1-b]
pyran-9-one 13, dH(DMSO-d6, 400 MHz) 8.65 (1H, m, H-8), 8.04 (1H, m, H-5), 7.82
(1H, br.d, H-10), 7.55–7.45 (3H, m, Ar-H), 7.43–7.35 (2H, m, Ar-H), 7.32–7.23 (5H,
m, 1 ꢀ Ar-H and 4 ꢀ C6H4OMe), 6.82, (4H, AA0BB0, Japp. ¼ 8.8 Hz, C6H4OMe), 6.64
(1H, d, J ¼ 10.0 Hz, H-3), 3.59 (6H, s, OMe).
[7] Aiken, S., Gabbutt C. D., & Heron, B. M. (2003). Abstracts, 19th International
Congress on Heterocyclic Chemistry, Fort Collins, USA, Elsevier: Oxford, 102; Aiken,
S., Gabbutt, C. D., Heron B. M., & Mars, C. A. Unpublished results.
[8] 1H NMR data for 3,3-di(4-methoxyphenyl)-3H,7H-indeno[2,1-i]naphtho[2,1-b]pyran-
7-one 17a, dH(CDCl3, 400 MHz) 8.82 (1H, d, J ¼ 9.2 Hz, H-6), 8.10 (1H, br.d, Ar-H),
7.62–7.54 (2H, m, Ar-H), 7.46–7.35 (6H, m, 2 ꢀ Ar-H and 4 ꢀ C6H4OMe), 7.29–7.19
(3H, m, Ar-H), 6.85 (4H, AA0BB0, Japp. ¼ 8.8 Hz, C6H4OMe), 6.24 (1H, d, J ¼ 10.0 Hz,
Hz, H-2).