Tetrahedron Letters 53 (2012) 2226–2230

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Tetrahedron Letters

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The 3-substitution of naphthalene-1,2-diones with boronic acids: a C–Hfunctionalization approach to novel spirooxazine photochromics

Mark YorkCSIRO Materials Science and Engineering, Bag 10, Clayton, Victoria 3169, AustraliaCooperative Research Centre for Polymers, 8 Redwood Drive, Notting Hill, Victoria 3168, AustraliaAdvanced Polymerik Pty Ltd, 8 Redwood Drive, Notting Hill, Victoria 3168, Australia

a r t i c l e i n f o

Article history:Received 10 November 2011Revised 7 February 2012Accepted 17 February 2012Available online 24 February 2012

Keywords:Boronic acidC–H functionalizationPhotochromicSpirooxazine

0040-4039/$ - see front matter Crown Copyright � 2doi:10.1016/j.tetlet.2012.02.082

E-mail address: Mark.York@csiro.au

a b s t r a c t

The addition of alkyl and aryl boronic acids to naphthalene-1,2-diones in the presence of an excess ofammonium persulfate and catalytic silver nitrate to yield 3-functionalized naphthalene-1,2-diones isreported. The products of these reactions were then further processed to yield the corresponding novelspirooxazine photochromic dyes.

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Scheme 1. Mechanics of photochromism of a spirooxazine.

Spirooxazines are a commercially important class of photochro-mic dyes, which upon irradiation with ultraviolet light undergo areversible colour change (Scheme 1) from the colourless spirocyclicform 1 to the coloured merocyanine form 2.1

During our research into the synthesis and applications of pho-tochromic compounds,2 we had reason to prepare a number ofnovel spirooxazine dyes based upon a 3-substituted naphtha-lene-1,2-dione core. A survey of the literature, however, found onlylimited methods for the preparation of such naphthoquinones.Thomson and co-workers reported a method for the formation of3-phenylnaphthalene-1,2-dione from naphthalene-1,2-dione andbenzene in the presence of stoichiometric palladium(II) acetate.3

This process appeared quite limited in terms of scope and was alsonot economically viable. Alternatively, the synthesis of 3-arylnaph-thalene-1,2-diones via the oxidation of the corresponding phenolhas been reported by Estevez and co-workers.4 Whilst this processwould furnish the desired compounds in a regioselective manner,it was not judged suitable for the synthesis of a large number ofanalogous 3-substituted naphthalene-1,2-dione compounds dueto the need for a separate, multi-step synthesis of each precursorphenol.

Baran and co-workers reported a C–H functionalization of 1,4-quinones with boronic acids.5 Within this study an example ofthe functionalization of naphthalene-1,2-dione with an arylboronicacid was provided with the corresponding 4-arylnaphthalene-1,2-dione being reported as the product. However, in our hands the

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reaction between naphthalene-1,2-dione and phenylboronic acidin the presence of ammonium persulfate and silver nitrate gave40% yield of 3-phenylnaphthalene-1,2-dione,6 with 10% of the4-phenyl compound (identified from a characteristic singlet atapproximately 6.5 ppm in the 1H NMR spectrum) formed as a minorproduct (Scheme 2, R = Ph). As this provided a rapid method for theformation of the desired 3-substituted naphthalene-1,2-dione pre-cursors 3, a number of such compounds were prepared (Table 1).

The substitution reaction gave similar yields of the desiredproduct when performed with either boronic acids (Table 1, entry1) or boronate esters (Table 1, entry 2), and was successful with

Scheme 2. Synthesis of 3-substituted naphthalene-1,2-diones.

ights reserved.

Table 1Synthesis of 3-substituted-naphthalene-1,2-diones

Entry Naphthalene-1,2-dione Boronic acid Product Yield (%)

1 40

10

2 44

3 39

4 25

5 52

6 21

7 0

8 50

10

9 0

M. York / Tetrahedron Letters 53 (2012) 2226–2230 2227

Scheme 3. Synthesis of novel spirooxazine photochromics.

Table 2Synthesis of novel spirooxazine photochromics

Entry Naphthalene-1,2-dione Product Yield (%)

1 48

2 61

3 29

4 67

5 48

6 72

7 62

2228 M. York / Tetrahedron Letters 53 (2012) 2226–2230

Figure 1. X-ray structure of novel spirooxazine 6f.

M. York / Tetrahedron Letters 53 (2012) 2226–2230 2229

arylboronic acids bearing either electron-donating or electron-withdrawing groups (Table 1, entries 3 and 4). A 4-substitutednaphthalene-1,2-dione was also a suitable substrate for the pro-cess, giving the corresponding 3,4-disubstituted naphthalene-1,2-dione in moderate yield (Table 1, entry 5). Alkylboronic acidsunderwent the reaction, but in this case the 3,4-dialkylatednaphthalene-1,2-dione was the major product (Table 1, entry 6).Despite this observation, attempts to functionalize 3-arylnaphtha-lene-1,2-dione in the 4-position with an alkylboronic acid gaveonly unreacted starting material (Table 1, entry 7). Aryl bromidesubstituents were tolerated (Table 1, entry 8) providing anotherpossible point of diversity via cross-coupling reactions. Reactionwith thiophene-3-boronic acid failed to give any of the expectedproduct, possibly as a result of the consumption of oxidants bythe in situ oxidation of the thiophene ring system (Table 1, entry9). In some cases isolation of the corresponding 4-substitutednaphthalene-1,2-dione minor product was possible (Table 1,entries 1 and 8, compounds 4a and 4b).

The substituted naphthalene-1,2-diones 3 were then treatedwith hydroxylamine hydrochloride to yield the corresponding ni-troso naphthol 5, which on heating with 1,3,3-trimethyl-2-methy-lene indoline gave the desired spirooxazine photochromics 6(Scheme 3 and Table 2).7

The 3-substituted naphthalene-1,2-diones (3a–e, g) gave thecorresponding spirooxazine compounds in moderate yields(Table 2, entries 1–6). The regiochemistry of both boronic acidaddition and subsequent oxime formation was confirmed byX-ray crystallography of crystalline spirooxazine 6f (Fig. 1).8 Whenisolated from the initial addition reaction, the 4-substituted

Figure 2. Novel spirooxazine compoun

naphthalene-1,2-dione side product could also be transformed intothe corresponding spirooxazine (Table 2, entry 7).

In order to perform a preliminary evaluation of the photochro-mic performance of the novel compounds 6a to 6f and 7, testlenses were prepared using a matrix composed of polyethylenegly-col 400 dimethacrylate and bisphenol A ethoxylate dimethacrylatein a 1:4 weight ratio with 0.4% AIBN by mass as initiator.1.2 � 10�6 mol of spirooxazine per gram of matrix was thoroughlymixed into the lens matrix and the lenses thermally cured beforeirradiation at 365 nm with a handheld UV source. The lenses afterirradiation can be seen in Figure 2.

The compounds display predominantly blue colouration ofvarying shades with photochromic 6d displaying green colourationin common with other known spirooxazines derived from 4-aryla-mino substituted naphthalene-1,2-diones.2d,9 Interestingly, dibutylspirooxazine 6e displayed purple colouration similar to that ob-served for spirooxazines derived from 4-amino substituted naph-thalene-1,2-diones.2a,10

In summary, the convenient one-step synthesis of a number of3-substituted naphthalene-1,2-diones is reported from the corre-sponding naphthalene-1,2-diones and boronic acids. These com-pounds were used to synthesize a range of novel spirooxazinephotochromic dyes with colours ranging from purple to green.

Acknowledgments

The author thanks the Co-operative Research Centre for Poly-mers, Advanced Polymerik Pty Ltd and CSIRO Materials Scienceand Engineering for their support.

Supplementary data

Supplementary data (experimental procedures and data for allnew compounds) associated with this article can be found, in theonline version, at doi:10.1016/j.tetlet.2012.02.082.

References and notes

1. (a) Lokshin, V.; Samat, A.; Metelitsa, A. V. Russ. Chem. Rev. 2002, 71, 893–916;(b) Bouas-Laurent, H.; Durr, H. Pure Appl. Chem. 2002, 73, 639–665.

2. (a) Evans, R. A.; York, M. Tetrahedron Lett. 2010, 51, 2195–2197; (b) Ali, A.;Campbell, J. A.; Evans, R. A.; Malic, N.; York, M. Macromolecules 2010, 43, 8488–8501; (c) Evans, R. A.; Hanley, T. L.; Skidmore, M. A.; Davis, T. P.; Such, G. K.;Yee, L. H.; Ball, G. E.; Lewis, D. A. Nat. Mater. 2005, 4, 249–253; (d) Evans, R. A.;York, M. Synth. Commun. 2010, 40, 3618–3628.

3. Mackenzie, N. E.; Surendrakumar, S.; Thomson, R. H.; Cowe, H. J.; Cox, P. J. J.Chem. Soc., Perkin Trans. 1 1986, 2233–2238.

4. Martínez, A.; Fernández, M.; Estévez, J. C.; Estévez, R. J.; Castedo, L. Tetrahedron2005, 61, 485–492.

5. Fujiwara, Y.; Domingo, V.; Seiple, I. B.; Giantassio, R.; Del Bel, M.; Baran, P. S. J.Am. Chem. Soc. 2011, 133, 3292–3295.

6. Experimental procedure: A mixture of naphthalene-1,2-dione (2.00 g,12.65 mmol), phenylboronic acid (2.31 g, 18.97 mmol), (NH4)2S2O8 (8.66 g,37.90 mmol) and AgNO3 (0.43 g, 2.53 mmol) in 1,2-dichloroethane (40 mL) andH2O (30 mL) was stirred in an open flask for 2.5 h. A further portion of AgNO3

(0.43 g, 2.53 mmol) was then added and the mixture stirred for a further 2.5 hbefore dilution with CH2Cl2 (100 mL) and H2O (100 mL). The organic phase wasseparated, washed with 10% w/v Na2CO3 solution (100 mL), filtered throughCelite, dried (MgSO4) and evaporated in vacuo. The residue was purified bycolumn chromatography eluting with 0–10% v/v EtOAc/petroleum ether to give3-phenylnaphthalene-1,2-dione (3a) as a red solid (1.18 g, 40%). Also present

ds 6a–f and 7 after UV irradiation.

2230 M. York / Tetrahedron Letters 53 (2012) 2226–2230

was 4-phenylnaphthalene-1,2-dione (4a) (0.30 g, 10%). The spectral data ofboth compounds were in accordance with those reported previously.3

7. Experimental procedure: A mixture of 3-phenylnaphthalene-1,2-dione (0.40 g,1.71 mmol) (3a) and hydroxylamine hydrochloride (0.24 g, 3.42 mmol) in EtOH(15 mL) was stirred at room temperature for 18 h. The mixture was thenevaporated in vacuo, suspended between CH2Cl2 (30 mL) and H2O (30 mL), theorganic phase separated, dried (MgSO4) and evaporated in vacuo. Theresidue was suspended in EtOH (10 mL), treated with 1,3,3-trimethyl-2-methyleneindoline (0.385 g, 2.22 mmol) and heated in a sealed tube at100 �C for 3 h. The mixture was evaporated in vacuo and the residue purifiedby column chromatography eluting with 0–10% v/v EtOAc/petroleum ether togive 1,3,3-trimethyl-50-phenylspiro[indolin-2,30-naphtho[2,1-b][1,4]oxazine](6a) as a green gum (0.33 g, 48%). 1H NMR (CDCl3, 400 MHz) d 8.60 (d,J = 9.5 Hz, 1H), 7.84–7.79 (m, 3H), 7.61 (t, J = 8.3 Hz, 1H), 7.49–7.43 (m, 3H),7.26–7.13 (m, 4H), 7.01 (d, J = 7.3 Hz, 1H), 6.86 (t, J = 7.4 Hz, 1H), 6.54 (d,J = 7.8 Hz, 1H), 2.75 (s, 3H), 1.28 (s, 3H), 1.26 (s, 3H); 13C NMR (CDCl3, 50 MHz)d 149.9, 147.2, 141.5, 136.5, 135.9, 130.2, 129.7, 129.2, 129.0, 127.8, 127.2,

127.0, 124.5, 121.5, 121.2, 119.7, 106.8, 98.1, 50.9, 29.7, 25.3, 21.2; HRMS (EI)calcd for C28H24N2O [M+]: 404.1888, found: 404.1888.

8. Crystallographic data (excluding structure factors) for 50-(4-bromophenyl)-1,3,3-trimethylspiro[indoline-2,30-naphtho[2,1-b][1,4]oxazine] (5f) have beendeposited with the Cambridge Crystallographic Data Centre as supplementarypublication no CCDC 850790. Copies of the data can be obtained, free of charge,on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK, (fax: +44(0)1223 336033 or email: deposit@ccdc.cam.ac.uk).

9. Clarke, D.; Heron, B. M.; Gabbut, C. D.; Hepworth, J. D.; Partington, S. M.; Corns,S. N. U.S. 6303,673; 2001, Chem. Abstr. 2003, 139, 296689.

10. (a) Rickwood, M.; Marsden, S. D.; Ormsby, M. E.; Staunton, A. L.; Wood, D. W.;Hepworth, J. D.; Gabburr, C. D. Mol. Cryst. Liq. Cryst. 1994, 246, 17–24; (b)Koshkin, A. V.; Lokshin, V.; Samat, A.; Gromov, S. P.; Fedorova, O. A. Synthesis2005, 1876–1880; (c) Koshkin, A. V.; Fedorova, O. A.; Lokshin, V.; Guglielmetti,R.; Hamelin, J.; Texier-Boullet, F.; Gromov, S. P. Synth. Commun. 2004, 34, 315–322; (d) Pang, M. L.; Zhang, H. J.; Liu, P. P.; Zou, Z. H.; Han, J.; Meng, J. B.Synthesis 2010, 20, 3418–3422.