Ring contraction during the 6π-electrocyclisation of naphthopyran valence tautomers

Article abstract of DOI:10.1039/b807744d

The thermal and photochemical ring-opening of spiro(3H-naphtho[2,1-b]pyran- 3,9′-thioxanthene-10,10-dioxide) 3 results in the facile ring-contraction to 9-(naphtho[2,1-b]furan-2-yl)-9H-thioxanthene-10,10-dioxide 6. Similar behaviour is displayed by the is

Full text of DOI:10.1039/b807744d

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www.rsc.org/obc | Organic & Biomolecular Chemistry
Ring contraction during the 6p-electrocyclisation of naphthopyran valence
tautomers†
Christopher D. Gabbutt,a B. Mark Heron,*a Suresh B. Kolla,a Colin Kilner,b Simon J. Coles,c Peter N. Hortonc
and Michael B. Hursthousec
Received 7th May 2008, Accepted 9th June 2008
First published as an Advance Article on the web 9th July 2008
DOI: 10.1039/b807744d
The thermal and photochemical ring-opening of spiro(3H-naphtho[2,1-b]pyran-3,9ꢀ-thioxanthene-10,
10-dioxide) 3 results in the facile ring-contraction to 9-(naphtho[2,1-b]furan-2-yl)-9H-thioxanthene-10,
10-dioxide 6. Similar behaviour is displayed by the isomeric spiro(2H-naphtho[1,2-b]pyran-2,9ꢀ-
thioxanthene-10,10-dioxide) 9 affording 9-(naphtho[1,2-b]furan-2-yl)-9H-thioxanthene-10,10-dioxide
12, though more severe reaction conditions were required. The comparative ease of this rearrangement
for the isomers 3 and 9 was rationalised on the basis of the relative isomer populations of the
ring-opened naphthopyrans. The rearrangement of simple mono- and bis-methylsulfonylphenyl
substituted photochromic naphthopyrans 18, 20 was examined; the former failed to rearrange
whereas the latter could be induced to rearrange only under prolonged UV irradiation. The
photochromism of diastereoisomerically pure sulfoxides derived from the oxidation of
spiro(3H-naphtho[2,1-b]pyran-3,9ꢀ-thioxanthene) 2a and spiro(2H-naphtho[1,2-b]pyran-2,9ꢀ-
thioxanthene) 2b resulted in conversion to the most thermodynamically stable trans-isomer in
each case.
Introduction
Results and discussion
The reversible 6p electrocyclic opening of the pyran ring has
attracted considerable attention particularly when the pyran
ring is fused to a naphthalene unit and where the photo-
chemical ring-opening–thermal ring-closing sequence is accom-
panied by a change in colour.1 There are numerous reports
concerning the influence of substituents on the photochromic
properties of diarylnaphthopyrans.2 However, none of these
accounts3 discusses the influence of a single strong conjugating
electron withdrawing substituent in one of the geminal aryl
rings upon the photochromism of the pyran unit since such
groups are difficult to incorporate using the standard Claisen
rearrangement route4 and suitable staring materials are not
readily available for the Ti(OEt)4 promoted route.5 We were
interested in investigating the synthesis of such substituted
naphthopyrans and thought that the use of electron donating
thioether substituents, which could be subsequently oxidised to
a sulfone unit, would be a convenient strategy to access such
compounds.
An obvious starting point was the preparation of the known
spirothioxanthene substituted compounds 2a, b6 (Scheme 1),
which could be readily oxidised in a later step.
Addition of lithium trimethylsilylacetylide (LiTMSA) to thiox-
anthone, followed by base-promoted unmasking of the terminal
acetylene unit, proceeded cleanly to afford propynol 1 in excellent
yield (94%). Heating a PhMe solution of 2-naphthol with 1 in
the presence of acidic alumina for 1 h afforded 2a in 55% yield
[d2-H = 6.18, d, d1-H = 7.03, d (J = 10.2 Hz)].6 Our attempts
to oxidise 2a with excess peracetic acid were unsuccessful, but
oxidation of a CH2Cl2 solution of 2a with 1.5 equivalents of m-
CPBA gave three new components, which were readily separated
by flash chromatography (Scheme 2). The use of greater amounts
of m-CPBA for the oxidation of 2a resulted in the formation of
trace amounts of by-products, which proved difficult to remove by
flash column chromatography.
The compounds resulting from the oxidation were characterised
as the sulfone 3 (17%) [d2-H = 6.36, d, d1-H = 7.08, d (J = 10.2 Hz)],
the cis-sulfoxide 4 (28%) [d2-H = 5.59, d, d1-H = 7.05, d (J = 10.0 Hz),
Fig. 1]7 and the trans-sulfoxide 5 (20%) [d2-H = 6.58, d, d1-H
=
7.78, d (J = 10.2 Hz), Fig. 2].8 The pronounced deshielding of
the alkene protons in the trans-sulfoxide 5 compared to the cis-
isomer 4 (Dd2-H = 0.99; Dd1-H = 0.73) presumably stems from their
aDepartment of Colour Science, School of Chemistry, University of Leeds,
Leeds, UK LS2 9JT. E-mail: b.m.heron@leeds.ac.uk; Fax: +44 (0)113
3432947; Tel: +44 (0)113 3432925
=
proximity to the anisotropic S O unit. It is also noteworthy that
bSchool of Chemistry, University of Leeds, Leeds, UK LS2 9JT
2-H in 4 resonates at an unusually high field position (d 5.59)
compared to those in 2a and 3 (d ∼ 6.2). A possible explanation
for this anomalous shift is provided by the X-ray crystal structure
(Fig. 1), which indicates that 2-H not only lies within a shielding
zone of one of the thioxanthene rings but also is in close proximity
to the sulfur lone pair of the sulfoxide unit.
cDepartment of Chemistry, University of Southampton, Highfield,
Southampton, UK SO17 1BJ
† Electronic supplementary information (ESI) available: 1H, 13C NMR
and UV–visible spectra for compounds. CCDC reference numbers 670085,
670086, 661552, 663292. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/b807744d
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Scheme 1 Preparation of spiro(naphthopyranthioxanthenes) 2a, b.
Scheme 2 Oxidation of spiro(3H-naphtho[2,1-b]pyran-3,9ꢀ-[9H]-thioxanthene) 2a.
Fig. 1 X-Ray crystal structure of compound 4.
Fig. 2 X-Ray crystal structure of compound 5.
and aromatisation to the naphtho[2,1-b]furan 611 [d(CDCl3)9-H
In both sulfoxide diastereoisomers 4 and 5 the sulfoxide oxygen
prefers a pseudo equatorial site with stereochemical differentiation
occurring through the arrangement of the pyran ring oxygen
and C-2 atoms about the spiro carbon (C-1, crystallographic
numbering). This preference for the equatorial orientation of the
sulfoxide oxygen atom in each of the isomers 4 and 5 precludes
the potential photochemical isomerisation of the sulfoxide group.9
The thioxanthene moiety adopts the typical boat conformation
leading to a ridge tile or ‘V-shaped’ arrangement.10
Attempts to obtain crystals of the sulfone 3 for a comparative
crystal study were unsuccessful due to the appreciable thermal
lability of this compound. Even brief heating during recrystalli-
sation (EtOAc–hexane) resulted in formation of a significant
quantity (TLC) of a new, non-photochromic product. Quantitative
conversion could be achieved by heating a solution of 3 in EtOAc–
hexane, 1 : 1 under reflux for 45 min. The instability of 3 stems
from its proclivity to undergo an irreversible ring contraction
=
ꢀ
5.92, s, d1 -H = 7.10, s], the constitution of which was established
by X-ray crystallography (Fig. 3).12
Each of the new naphthopyrans 3–5 displayed photochromism
and reversibly developed a yellow colour, with ca. kmax 426 nm,
on irradiation of a toluene solution with a TLC inspection lamp
(365 nm, 8 Watt); kmax is shifted hypsochromically relative to 2a
(481 nm) in keeping with the decrease in electron donating ability
of the S atom upon oxidation. Interestingly, the photochromism
of 3 was particularly short-lived with irradiation (TLC inspection
lamp, 365 nm) of a d8-toluene solution (ca. 20 mg/2.5 mL)
resulting in the complete loss of photochromism in less than
1
90 s (cf. Fig. 4). Examination of the H NMR spectrum of this
solution revealed that facile ring contraction had again occurred
to afford 6. Irradiation (365 nm, 180 s) of a d8-toluene solution
of 4 resulted in the complete isomerisation of 4 into 5, whereas
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Fig. 4 UV–Visible spectra of naphthopyran 3 in toluene at various
irradiation times.
electrocylisation sequence to generate the aromatic thiaanthracene
and thence the thioxanthene upon proton transfer.
The isomeric 2H-naphtho[1,2-b]pyran 2b [d3-H = 6.16, d, d4-H
=
Fig. 3 X-Ray crystal structure of compound 6.
6.43, d (J = 9.9 Hz)]6 was obtained from 1-naphthol and alkynol
1 in 45% yield. Oxidation of 2b with m-CPBA resulted in a similar
mixture of compounds, sulfone 9 (28%) [d3-H = 6.31, d, d4-H = 6.50,
d (J = 9.9 Hz)], cis-sulfoxide 10 (24%) [d3-H = 5.55, d, d4-H = 6.47,
similar treatment of 5 resulted in no change, which suggests that
the trans-diastereoisomer 5 is the more thermodynamically stable
of the pair.
A mechanism for the facile ring contraction of 3 to 6 is presented
in Scheme 3. Thermal and photochemical ring-opening of the
pyran unit affords the isomeric dienones 8a, b. The ratio of these
two isomers is presumed to favour the less sterically congested
isomer 8b and is supported by studies on the photochemical ring-
opening of 3H-naphtho[2,1-b]pyrans, which have established the
predominance of the trans,cis-isomer (TC) cf. 8b, using NMR
spectroscopy.13 The geometry of 8b favours the intervention of a
rapid 5-exo-trig ring closure over the usual isomerisation and 6p-
d (J = 9.7 Hz)] and trans-sulfoxide 11 (43%) [d3-H = 6.46, d, d4-H =
7.19, d (J = 10.0 Hz), Fig. 5]14 (Scheme 4). It is noteworthy that
again the cis-sulfoxide 10 exhibits anomalous shifts of the pyran
ring protons in accord with those of cis-isomer 4. UV irradiation
of a toluene solution of each of the new naphthopyrans resulted in
the reversible development of an orange-yellow colour (ca. kmax
=
470 nm), again shifted hypsochromically relative to the unoxidised
compound 2b (kmax = 503 nm). Interestingly, for the naphtho[1,2-
b]pyrans 9–11, the hypsochromic shift is ca. 30 nm, significantly
Scheme 3 Proposed mechanism for the ring contraction of naphthopyran 3 to naphthofuran 6.
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contraction to naphthofuran 12 (72%) [d(CDCl3)9-H = 5.93, s,
ꢀ
d1 -H = 6.77, s] (Scheme 5). A longer period of UV irradiation
(3600 s, 8 Watt TLC lamp) was also required to effect the efficient
contraction to 12.
The reluctance of 9, compared with isomer 3, to undergo ring
contraction may be explained by considering the likely geometry
and relative abundance of the ring-opened coloured forms 13a,
b (Scheme 5). Steady state spectroscopic investigations of 2H-
naphtho[1,2-b]pyrans have revealed that ring-opened species with
trans,trans- (TT) geometries corresponding to 13a are longer
lived (more stable) than their cis,trans- (CT) isomers cf. 13b.15
Isomer 13a does not posses the appropriate geometry for a
facile ring contraction, however, the relatively small proportion
of 13b under the applied irradiation conditions can undergo ring
contraction with the result that the isomer ratio gradually adjusts
to compensate for the removal of 13b, which is manifest in the
slow conversion of 9 into 12.
Fig. 5 X-Ray crystal structure of compound 11.
We were interested to explore whether this rearrangement was
a consequence solely of the thioxanthene dioxide unit or was
more general and would operate with simple electron withdraw-
ing methylsulfonyl groups. Thus the monomethylthio- and bis-
methylthio- naphtho[2,1-b]pyrans 16 and 17, respectively, were
obtained according to Scheme 6. (Methylthio)benzophenones 14a,
b were obtained by a standard Friedel–Crafts acylation procedure
smaller than that for the alternative series 2a, 3–5 of ca. 50 nm.
Irradiation of a d8-toluene solution of the sulfoxides 10 and 11
resulted in the complete isomerisation of the former into the most
stable diastereoisomer 11, whilst the trans-sulfoxide 11 remained
unchanged. Interestingly, for this naphtho[1,2-b]pyran isomer, the
sulfone 9 proved to be more resistant to ring contraction and
heating in toluene for 26 h was required in order to effect the
Scheme 4 Oxidation of spiro(2H-naphtho[1,2-b]pyran-2,9ꢀ-[9H]-thioxanthene) 2b.
Scheme 5 Proposed mechanism for the ring contraction of naphthopyran 9 to naphthofuran 12.
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Scheme 6 Preparation of intermediates and naphthopyrans 16, 17 and their oxidised analogues 18–22.
and were converted to propynols 15a, b in excellent yield using
the preferred method of addition of LiTMSA with subsequent
in situ base promoted desilylation.4 Propynols 15a, b were directly
converted into the naphthopyrans 16 and 17 respectively, upon
heating in toluene containing 2-naphthol and suspended acidic
alumina. Naphthopyran 17 has recently been prepared in 36%
yield through the addition of excess 4-methythiophenylmagnesium
bromide to 3H-naphtho[2,1-b]pyran-2-one,16 whilst 16 is surpris-
ingly unknown.
Scheme 7 Photochemical ring contraction of naphthopyran 20.
Oxidation of 16 gave the sulfone 18 [d2-H 6.25, d, J = 9.9 Hz, dMe
3.01] together with an inseparable mixture of diastereoisomeric
sulfoxides 19 [d2-H 6.25 and 6.26, d, J = 9.9 Hz, dSOMe 2.686 and
2.691]. Similarly, 17 gave the bis-sulfone 20 [d2-H 6.22, d, J = 9.9 Hz,
dMe 3.02], the diastereoisomeric mixed sulfoxide-sulfones 21 [d2-H
6.23 and 6.24, d, J = 9.9 Hz, dSOMe 2.70 and 2.71, dMe 3.02] and
the bis-sulfoxide 22 as an inseparable mixture of diastereoisomers
[d2-H 6.24 m, dSOMe 2.702 and 2.705]. The hypsochromic shifts
noted in kmax upon oxidation of the S-atom(s) were ca. 35 nm
and 60 nm respectively, for the series derived from 16 and 17.
This ca. 60 nm shift in kmax upon oxidation of bis-methylthio
substituted naphthopyran 17 confirms the approximate additive
effect of substituents in the geminal aryl rings.1
Heating a solution of 18 in toluene under reflux for either 24 h or
irradiation for 15 min in an immersion well photochemical reactor
(125 Watt, medium pressure Hg lamp) failed to effect the ring
contraction to the naphthofuran. However, similar irradiation of
bis-sulfone 20 resulted in the contraction to 23, though all attempts
to effect the thermal contraction failed (Scheme 7).
the geminal aryl rings are conformationally constrained in a
thioxanthene unit or the stabilising influence of the aromatic
thiaanthracene intermediate.
Conclusion
The synthesis of naphthopyrans bearing electron withdrawing
substituents can be conveniently accomplished by manipulation
of the oxidation state of thioether units. Oxidation of the
thioether unit of the spiro(naphthopyran–thioxanthenes) 2a, 2b
affords sulfones and separable mixtures of the respective dias-
teroisomeric sulfoxides. The former, 3 and 9, display only transient
photochromism (UV irradiation) before efficient ring contraction
supervenes in the normal cyclisation process and results in the
formation of a naphthofuran in each case. Thermally induced
ring contraction of these sulfones to the respective naphthofurans
was also facile. Differentiation between the 3H-naphtho[2,1-b]-
3 and 2H-naphtho[1,2-b]- 9 pyran systems was observed, with
the latter requiring longer irradiation/heating times for complete
ring contraction to be observed, a feature attributed to the
established valence isomer distribution under irradiation. The
sulfoxides derived from each naphthopyran isomer display good
photochromism with the reversible generation of yellow solutions.
The ring contraction of sulfones 3 and 9 that contain the
thioxanthene 10,10-dioxide moiety is far more facile than that
of 18 and 20. This may be a consequence of either a more
favourable cyclisation geometry for the 5-exo-trig closure when
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UV irradiation of the cis-isomer of each sulfoxide results in the
irreversible isomerisation to the more thermodynamically stable
trans-isomer. Different behaviour under UV irradiation was noted
for the mono- and bis-sulfones, 18 and 20 respectively, with 18
proving resistant to ring contraction under the applied conditions,
whereas 20 afforded naphthofuran 23 but only photochemically
and under more severe conditions.
1,1-Bis(4-methylthiophenyl)prop-2-yn-1-ol (15b)
(3.35 g, 93%) as colourless microcrystals, mp 75.0–77.0 ◦C, mmax
3453, 3246, 1594, 1488, 1432, 1396, 1090, 1061, 993 cm−1, dH 2.46
(6H, s, SMe), 2.76 (1H, s, alkyne-H), 2.87 (1H, s, OH), 7.20 (4H,
m, Ar–H), 7.49 (4H, m, Ar–H).
General method for the preparation of methylthio substituted
naphthopyrans (16) and (17)
Experimental
A stirred solution of 2-naphthol (1.89 g, 13.1 mmol) and the
prop-2-yn-1-ol (13.1 mmol) in toluene (60 mL) was warmed to
50 ◦C. Acidic alumina (2.0 g) was added and the mixture was
refluxed until TLC examination indicated that none of the prop-
2-yn-1-ol remained (ca. 1.5 h). The mixture was cooled to ∼50 ◦C,
filtered and the alumina was washed with hot toluene (2 × 30 mL).
Removal of the toluene from the combined washings and filtrate
gave a red gum that was eluted from silica (50% ethyl acetate in
hexane), followed by recrystallisation from MeOH to afford the
naphthopyran.
Unless otherwise stated, reagents were used as supplied. NMR
spectra were recorded on a 400 MHz spectrophotometer (1H NMR
400 MHz, 13C NMR 100 MHz) for sample solution in CDCl3
with tetramethylsilane as an internal reference. FT-IR spectra
were recorded on either a spectrophotometer system equipped
with a diamond probe ATR attachment (neat sample) or in KBr
discs. UV–visible spectra were recorded for spectroscopic grade
toluene solutions of the naphthopyrans (ca. 1 × 10−5mol dm−3)
using a diode array spectrophotometer with activating irradiation
provided by a TLC inspection lamp (Spectroline E Series 365 nm,
8 Watt). An immersion well photochemical reactor (Photochemi-
cal Reactors Ltd. UK) equipped with a 125 Watt, medium pressure
Hg lamp was used for the ring contraction of 20. Naphthopyrans
2a (mp 154–156 ◦C) and 2b (mp 161–163 ◦C) had physical and
spectroscopic data in good agreement with that reported by
Coelho et al.6 and methylthio substituted benzophenones 14a17
and 14b18 had similar good agreement with literature reported
data. All compounds were homogeneous by TLC using a range of
eluent systems of differing polarity.
3-(4-Methylthiophenyl)-3-phenyl-3H-naphtho[2,1-b]pyran (16)
(2.59 g, 52%) as off-white microcrystals, mp 120–121 ◦C,
kmax(PhMe) 464 nm, mmax 1634, 1489, 1223, 1090, 1079, 1002, 950,
812, 751, 736, 707, 696 cm−1, dH 2.44 (3H, s, SMe), 6.22 (1H, d, J =
9.8 Hz, 2-H), 7.19 (3H, m, Ar–H, 5-H), 7.25 (1-H, m, Ar–H), 7.33
(4H, m, Ar–H, 1-H), 7.39 (2H, m, Ar–H), 7.48 (3H, m, Ar–H),
7.65 (1H, d, J = 8.8 Hz, 6-H), 7.73 (1H, d, J = 8.8 Hz, 7-H),
7.95 (1H, d, J = 8.8 Hz, 10-H), dC 15.6, 82.3, 114.0, 118.3, 119.7,
121.3, 123.6, 126.0, 126.6, 126.9, 127.5, 127.6, 127.6, 128.1, 128.5,
129.3, 129.8, 129.9, 137.9, 138.1, 141.6, 144.7, 150.5. Found M+ =
380.1228. C26H20OS requires M+ = 380.1229.
General method for the preparation of prop-yn-1-ols (15a) (15b)
n-Butyllithium (1.6 M in hexanes) (9.4 mL, 15 mmol) was
added slowly via syringe to a cold (−10 ◦C), stirred solution of
trimethylsilylacetylene (2.12 mL, 15 mmol) in anhydrous tetrahy-
drofuran (60 mL) under a nitrogen atmosphere. On completion
of the addition (ca. 5 min) the cold solution was allowed to stir
for 1 h. The benzophenone 14a or 14b (12 mmol) was added in
a single portion and the mixture stirred until TLC examination
of the reaction mixture indicated that none of the benzophenone
remained (ca. 3 h). The reaction mixture was re-cooled to 0 ◦C and
a solution of methanolic potassium hydroxide (from potassium
hydroxide (1.74 g, 31 mmol) in methanol (20 mL)) was added
in a single portion. The cooling bath was then removed and
the mixture warmed to room temperature; after ca. 15 min,
TLC examination indicated that deprotection was complete. The
mixture was acidified to pH ∼ 7 using glacial acetic acid and then
poured into water (500 mL). The organic layer was separated and
the aqueous layer extracted with ethyl acetate (3 × 100 mL). The
organic phases were combined, washed with water (3 × 50 mL)
and dried (anhyd. Na2SO4). Removal of the solvent gave the prop-
2-yn-1-ol, which was used directly without further purification.
3,3-Bis(4-methylthiophenyl)-3H-naphtho[2,1-b]pyran (17)
(4.3 g, 77%) as colourless microcrystals, mp 171–173 ◦C (mp
apparatus, uncorrected), 174 ◦C (DSC) [lit. mp = 142–143 ◦C16],
kmax(PhMe) 478 nm, mmax 1627, 1486, 1093, 1082, 1002, 955, 820,
740 cm−1, dH 2.45 (6H, s, SMe), 6.18 (1H, d, J = 9.9 Hz, 2-H),
7.18 (5H, m, Ar–H, 5-H), 7.31 (2H, m, Ar–H, 1-H), 7.38 (4H,
m, Ar–H), 7.46 (1H, m, Ar–H), 7.65 (1H, d, J = 8.8 Hz, 6-H),
7.72 (1H, d, J = 8.1 Hz, 7-H), 7.94 (1H, d, J = 8.5 Hz, 10-H), dC
15.6, 82.0, 114.0, 118.3, 119.8, 121.3, 123.7, 126.0, 126.7, 127.3,
127.5, 128.5, 129.3, 129.7, 129.9, 137.9, 141.5, 150.4. Found M+ =
426.1112. C27H22OS2 requires M+ = 426.1107.
General method for the oxidation of thioether substituted
naphthopyrans (2a, 2b, 19, 20).
m-Chloroperoxybenzoic acid (1.34 g, 5.95 mmol, 77%,) was added
portionwise over 5 min to a cold (0 ◦C) stirred solution of the
photochromic thioether (3.97 mmol) in CH2Cl2 (25 mL). On
completion of the addition, the cooling bath was removed and
the solution was stirred until TLC examination of the reaction
mixture indicated that no further thioether remained (15 min). The
reaction mixture was poured into water (200 mL) and the organic
layer separated. The aqueous layer was extracted with CH2Cl2
(2 × 50 mL) and the combined CH2Cl2 layers were washed with
aqueous Na2SO3 solution (2 × 50 mL, 2 M), saturated NaHCO3
solution (2 × 50 mL) and water (50 mL). Removal of the dried
1-(4-Methylthiophenyl)-1-phenylprop-2-yn-1-ol (15a)
(2.20 g, 72%) as a pale yellow oil, mmax 3450, 3244, 1595, 1483, 1398,
995 cm−1, dH 2.45 (3H, s, SMe), 2.86 (1H, s, alkyne-H), 2.87 (1H,
bs, OH), 7.18 (2H, m, Ar–H), 7.29 (3H, m, Ar–H), 7.50 (2H, m,
Ar–H), 7.58 (2H, m, Ar–H).
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(anhydrous Na2SO4) CH2Cl2 gave the crude product, which was
purified by flash column chromatography.
Fraction 2: cis-spiro(2H-naphtho[1,2-b]pyran-2,9ꢀ-[9H]-thio-
xanthene-10-oxide) (10). (0.36 g, 24%) as pale yellow microcrys-
tals from EtOAc–hexane, mp 204–206 ◦C, kmax(PhMe) 471 nm, mmax
1651, 1617, 1568, 1442, 1392, 1265, 1206, 1108, 1087, 1070, 1040,
984, 817, 758, 733 cm−1, dH 5.54 (1H, d, J = 9.7 Hz, 3-H), 6.47 (1H,
d, J = 9.7 Hz, 4-H), 7.17 (1H, d, J = 8.3 Hz, 5-H), 7.53 (7H, m,
Ar–H), 7.78 (2H, dd, J = 7.8, 1.1 Hz, Ar–H), 7.89 (1H, m, Ar–H),
8.06 (2H, dd, J = 7.7, 1.1 Hz, Ar–H), 8.42 (1H, m, Ar–H), dC
79.5, 113.1, 121.4, 121.6, 122.3, 122.4, 123.5, 124.2, 124.7, 124.8,
126.4, 127.0, 128.1, 128.4, 130.7, 135.2, 137.7, 138.5, 147.9. Found
C, 78.7; H, 4.2; S, 8.2; M + H+ = 381.0939. C25H16O2S requires C,
78.9; H, 4.3; S, 8.4%; M + H+ = 381.0944.
From spiro(3H-naphtho[2,1-b]pyran-3,9ꢀ-[9H]-thioxanthene)
(2a) after elution with 25% EtOAc–hexane as three fractions:
Fraction
1:
spiro(3H-naphtho[2,1-b]pyran-3,9ꢀ-[9H]-thio-
xanthene-10,10-dioxide) (3). (0.27 g, 17%) as pale yellow
microcrystals, mp 209–210 ◦C, kmax(PhMe) 426 nm, mmax 1639,
1590, 1296, 1163, 1132, 1095, 1071, 1011, 806, 751 cm−1, dH 6.36
(1H, d, J = 10.2 Hz, 2-H), 7.08 (1H, d, J = 10.2 Hz, 1-H), 7.35
(1H, d, J = 8.8 Hz, 5-H), 7.41 (1H, m, Ar–H), 7.49 (1H, m,
Ar–H), 7.57 (4H, m, Ar–H), 7.85 (2H, m, Ar–H), 7.93 (3H, m,
10-H, Ar–H), 8.18 (2H, m, Ar–H), dC 78.1, 110.6, 116.4, 116.6,
121.1, 123.8, 124.2, 125.0, 126.5, 127.2, 128.7, 129.0, 129.7, 129.8,
130.8, 133.3, 133.9, 138.1, 143.3, 150.9. Found C, 75.6; H, 4.0; S,
8.0; M + Na+ = 419.0714. C25H16O3S requires C, 75.7; H, 4.1; S,
8.1%; M + Na+ = 419.0712.
Fraction 3: trans-spiro(2H-naphtho[1,2-b]pyran-2,9ꢀ-[9H]-thio-
xanthene-10-oxide) (11). (0.65 g, 43%) as pale yellow microcrys-
tals from EtOAc–hexane, mp 157–158 ◦C, kmax(PhMe) 473 nm, mmax
1650, 1619, 1444, 1374, 1264, 1168, 1094, 1054, 1036, 946, 924, 822,
770, 765, 754, 739, 659 cm−1, dH 6.46 (1H, d, J = 10.0 Hz, 3-H),
7.19 (1H, d, J = 10.0 Hz, 4-H), 7.22 (1H, d, J = 8.3, 5-H), 7.36
(3H, m, Ar–H), 7.50 (4H, m, Ar–H), 7.65 (1H, m, Ar–H), 7.76
(2H, dd, J = 7.6, 1.1 Hz, Ar–H), 8.05 (1H, m, Ar–H), 8.14 (2H,
dd, J = 7.6, 1.3 Hz, Ar–H), dC 78.4, 114.6, 119.4, 121.2, 122.2,
124.4, 124.5, 125.5, 125.9, 126.7, 127.2, 127.5, 128.5, 128.9, 130.0,
134.8, 136.0, 144.8, 147.2. Found M + H+ = 381.0941. C25H16O2S
requires M + H+ = 381.0944.
Fraction 2: cis-spiro(3H-naphtho[2,1-b]pyran-3,9ꢀ-[9H]-thio-
xanthene-10-oxide) (4). (0.42 g, 28%) as pale yellow microcrys-
tals from EtOAc–hexane, mp 205–206 ◦C, kmax(PhMe) 426 nm,
mmax 1632, 1588, 1239, 1204, 1098, 1045, 1011, 811, 749, 546 cm−1,
dH 5.59 (1H, d, J = 10.0 Hz, 2-H), 7.05 (1H, d, J = 10.0 Hz,
1-H), 7.40 (1H, m, Ar–H), 7.50 (4H, m, Ar–H), 7.57 (2H, m, Ar–
H), 7.86 (5H, m, Ar–H), 8.04 (2H, m, Ar–H), dC 78.8, 111.5,
116.9, 117.9, 121.2, 122.4, 124.18, 124.21, 124.7, 127.2, 128.4,
128.7, 129.7, 129.8, 130.5, 131.0, 137.5, 138.5, 151.1. Found M
+ H+ = 381.0942. C25H16O2S requires M + H+ = 381.0944.
From 3-(4-methylthiophenyl)-3-phenyl-3H-naphtho[2,1-b]py-
ran (16) after elution with 25% EtOAc–hexane as two fractions:
Fraction 1: 3-(4-methylsulfonylphenyl)-3-phenyl-3H-naphtho-
[2,1-b]pyran (18). (0.54 g, 33%) as colourless microcrystals from
EtOAc–hexane, mp 180–181 ◦C, kmax(PhMe) 425 nm, mmax 1631,
1587, 1513, 1489, 1310, 1295, 1246, 1217, 1148, 1089, 1081, 1008,
957, 821, 775, 756, 723, 711 cm−1, dH 3.01 (3H, s, SO2Me), 6.25
(1H, d, J = 9.9 Hz, 2-H), 7.21 (1H, d, J = 8.8, 5-H), 7.28 (1H,
m, Ar–H), 7.36 (3H, m, Ar–H), 7.38 (1H, d, J = 9.9 Hz, 1-H),
7.47 (3H, m, Ar–H), 7.68 (1H, d, J = 8.7 Hz, Ar–H), 7.72 (3H, m,
Ar–H), 7.87 (2H, m, Ar–H), 7.96 (1H, d, J = 8.6 Hz, 10-H),
dC 44.5, 82.0, 114.1, 118.1, 120.7, 121.3, 124.0, 126.6, 126.9,
Fraction 3: trans-spiro(3H-naphtho[2,1-b]pyran-3,9ꢀ-[9H]-thio-
xanthene-10-oxide) (5). (0.30 g, 20%) as pale yellow microcrys-
tals from EtOAc–hexane, mp 210–211 ◦C, kmax(PhMe) 427 nm, mmax
1632, 1587, 1510, 1445, 1239, 1219, 1082, 1059, 1035, 1000, 930,
807, 777, 751, 736 cm−1, dH 6.58 (1H, d, J = 10.2 Hz, 2-H), 6.90
(1H, d, J = 8.8 Hz, 5-H), 7.37 (1H, m, Ar–H), 7.45 (2H, m, Ar–H),
7.53 (3H, m, Ar–H), 7.59 (1H, d, J = 8.8 Hz, 6-H), 7.71 (1H, d,
J = 8.1 Hz, Ar–H), 7.76 (2H, dd, J = 7.6, 1.2 Hz, Ar–H), 7.78 (1H,
d, J = 10.2 Hz, 1-H), 8.05 (1H, d, J = 8.5 Hz, 10-H), 8.12 (2H,
dd, J = 7.6, 1.3 Hz, Ar–H), dC 77.8, 113.3, 117.5, 119.8, 121.1,
123.7, 124.1, 125.6, 127.03, 127.04, 128.7, 128.9, 129.6, 129.7,
130.0, 130.5, 135.8, 144.8, 149.9. Found M + H+ = 381.0943.
C25H16O2S requires M + H+ = 381.0944.
126.9, 127.3, 127.9, 128.1, 128.4, 128.6, 129.5, 129.7, 130.3, 139.5,
+
143.7, 150.2, 151.0. Found C, 75.5; H, 4.8; S, 7.7; M + NH4
430.1473. C26H20O3S requires C, 75.7; H, 4.9; S, 7.8%; M + NH4
430.1471.
=
+
=
From spiro(2H-naphtho[1,2-b]pyran-2,9ꢀ-[9H]-thioxanthene)
(2b) after elution with 25% EtOAc–hexane as three fractions:
Fraction 2: 3-(4-methylsulfinylphenyl)-3-phenyl-3H-naphtho[2,1-
b]pyran (19). As an inseparable mixture of two diastereoisomers
(1.03 g, 65%) as colourless microcrystals from EtOAc–hexane, mp
195–197 ◦C, kmax(PhMe) 429 nm, mmax 1629, 1586, 1447, 1394, 1243,
1220, 1079, 1048, 1007, 957, 819, 762, 751, 744, 734, 697 cm−1, dH
all signals, 2.686 (3H, s, SOMe), 2.691 (3H, s, SOMe), 6.25 (1H, d,
J = 9.9 Hz, 2-H), 6.26 (1H, d, J = 9.9 Hz, 2-H), 7.20 (1H, d, J =
8.8 Hz, 5-H), 7.21 (1H, d, J = 9.1 Hz, 5-H), 7.27 (1H, m, Ar–H),
7.33 (4H, m, Ar–H, 1-H), 7.46 (3H, m, Ar–H), 7.59 (2H, m, Ar–
H), 7.67 (3H, m, Ar–H), 7.72 (1H, d, J = 8.3 Hz, Ar–H), 7.96 (1H,
d, J = 8.5 Hz, 10-H), dC all signals, 43.8, 82.1, 114.0, 118.2, 120.3,
121.3, 123.5, 123.8, 126.8, 126.9, 127.0, 127.9, 128.0, 128.3, 128.6,
129.4, 129.7, 130.1, 138.1, 144.1, 144.1, 144.7, 148.2, 150.3. Found
C, 78.6; H, 5.0, S, 8.1; M + H+ = 397.1258. C26H20O2S requires C,
78.7; H, 5.1; S, 8.1%; M + H+ = 397.1257.
Fraction
1:
spiro(2H-naphtho[1,2-b]pyran-2,9ꢀ-[9H]-thio-
xanthene-10,10-dioxide) (9). (0.42 g, 28%) as pale yellow
microcrystals, mp 198–199 ◦C, kmax(PhMe) 472 nm, mmax 1646,
1569, 1466, 1440, 1393, 1295, 1264, 1164, 1147, 1134, 1104, 1068,
974, 920, 809, 765, 755, 723 cm−1, dH 6.31 (1H, d, J = 9.9 Hz,
3-H), 6.50 (1H, d, J = 9.9 Hz, 4-H), 7.20 (1H, d, J = 8.3 Hz,
5-H), 7.55 (7H, m, Ar–H), 7.86 (3H, m, Ar–H), 8.20 (2H, m, 4ꢀ,
5ꢀ-H), 8.27 (1H, m, Ar–H), dC 78.7, 112.4, 121.2, 121.3, 121.6,
123.3, 123.8, 124.8, 124.8, 126.3, 126.7, 126.9, 128.0, 128.9, 133.4,
134.0, 135.1, 143.5, 147.6. Found C, 75.7; H, 4.0; S, 7.8; M+
396.0817. C25H16O3S requires C, 75.7; H, 4.1; S, 8.1%; M+
396.0815.
=
=
3102 | Org. Biomol. Chem., 2008, 6, 3096–3104
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From
3,3-bis(4-methylthiophenyl)-3H-naphtho[2,1-b]pyran
8.07 (1H, d, J = 8.2 Hz, Ar–H), 8.21 (2H, m, Ar–H), dC 43.5,
106.4, 112.2, 123.4, 123.5, 124.1, 124.7, 125.5, 126.5, 127.6, 128.4,
128.7, 129.3, 130.3, 132.7, 137.3, 138.0, 152.7, 153.1. Found M +
NH4 = 414.1158. C25H16O3S requires M + NH4 = 414.1158.
(17) after elution with 25% EtOAc–hexane as three fractions:
Fraction 1: 3,3-bis(4-methylsulfonylphenyl)-3H-naphtho[2,1-
b]pyran (20). (0.66 g, 34%) as colourless microcrystals from
EtOAc–hexane, mp 171–172 ◦C, kmax(PhMe) 415 nm, mmax 1633,
1588, 1395, 1311, 1291, 1146, 1086, 1007, 952, 769 cm−1, dH 3.02
(6H, s, SO2Me), 6.22 (1H, d, J = 9.9 Hz, 2-H), 7.22 (1H, d, J =
8.8 Hz, 5-H), 7.37 (1H, m, Ar–H), 7.45 (1H, d, J = 9.9 Hz, 1-H),
7.52 (1H, m, Ar–H), 7.70 (6H, m, Ar–H), 7.92 (4H, m, Ar–H), 7.97
(1H, d, J = 8.4 Hz, 10-H), dC 44.4, 81.5, 114.2, 117.9, 121.3, 121.8,
+
+
Procedure for the thermal rearrangement of spiro(2H-
naphtho[1,2-b]pyran-2,9ꢀ-thioxanthene-10,10-dioxide (9)
A solution of naphthopyran (9) (0.25 g, 0.63 mmol) in toluene
(75 mL) was heated under reflux until TLC examination of the
mixture indicated that no reactant remained (ca. 26 h). Removal
of the solvent gave:
124.3, 125.4, 127.2, 127.6, 127.8, 128.7, 129.6, 129.7, 130.8, 138.1,
140.1, 149.7, 149.8. Found C, 66.1; H, 4.5; S, 13.0; M + NH4
+
=
9-(naphtho[1,2-b]furan-2-yl)-9H-thioxanthene-10,10-dioxide (12).
508.1249. C27H22O5S2 requires C, 66.1; H, 4.5; S, 13.1%; M +
+
(0.18 g, 72%) as pale brown plates upon recrystallisation from
NH4 = 508.1247.
◦
PhMe, mp 243–244 C, mmax 1581, 1570, 1472, 1445, 1385, 1290,
1273, 1158, 1142, 1124, 1056, 962, 807, 760, 745, 734, 680 cm−1,
dH 5.93 (1H, s, 9-H), 6.77 (1H, s, 3ꢀ-H), 7.42 (3H, m, Ar–H), 7.50
(1H, m, Ar–H), 7.56 (5H, m, Ar–H), 7.66 (1H, d, J = 8.3, Ar–H),
7.91 (1H, d, J = 8.1, Ar–H), 8.21 (3H, m, Ar–H), dC 43.5, 108.4,
119.7, 119.9, 121.2. 123.6, 123.8, 124.1, 125.3, 126.4, 128.4, 128.4,
129.2, 131.5, 132.7, 137.3, 138.1, 150.9, 153.0. Found C, 75.7; H,
4.0; S, 7.9; M+ = 396.0817. C25H16O3S requires C, 75.7; H, 4.1; S,
8.1%; M+ = 396.0815.
Fraction 2: 3-(4-methylsulfinylphenyl)-3-(4-methylsulfonyl-
phenyl)-3H-naphtho[2,1-b]pyran (21). As an inseparable mixture
of two diastereoisomers (0.86 g, 46%) as colourless microcrystals
from EtOAc–hexane, mp 207.0–209.0 ◦C, kmax(PhMe) 423 nm,
mmax 1633, 1394, 1307, 1293, 1147, 1084, 1047, 1006, 951, 827, 812,
774 cm−1, dH all signals 2.704 (3H, s, SOMe), 2.706 (3H, s, SOMe),
3.02 (3H, s, SO2Me), 6.23 (1H, d, J = 9.9 Hz, 2-H), 6.24 (1H, d,
J = 9.9 Hz, 2-H), 7.21 (1H, d, J = 8.8 Hz, 5-H), 7.22 (1H, d, J =
8.9 Hz, 5-H), 7.37 (1H, m, 8-H), 7.43 (1H, d, J = 9.9 Hz, 1-H),
7.51 (1H, m, 9-H), 7.63 (4H, m, Ar–H), 7.72 (3H, m, Ar–H), 7.74
(1H, d, J = 8.1 Hz, Ar–H), 7.90 (2H, m, Ar–H), 7.97 (1H, d, J =
8.6 Hz, 10-H), dC all signals 43.8, 44.4, 81.6, 114.1, 118.0, 121.3,
121.4, 123.8, 124.2, 125.8, 127.1, 127.5, 127.9, 128.0, 128.6, 129.6,
129.7, 130.6, 139.9, 145.5, 146.9, 149.9, 150.2. Found C, 68.1; H,
4.6, S, 13.5; M+ = 474.0952. C27H22O4S2 requires C, 68.3; H, 4.7;
S, 13.5%; M+ = 474.0954.
Photochemical rearrangement of (20)
A stirred solution of naphthopyran (20) (0.40 g, 0.81 mmol) in
toluene (100 mL) in an immersion well photochemical reactor
was degassed with nitrogen and irradiated until TLC examination
of the reaction mixture indicated that no further change in the
composition of the reaction mixture had occurred (ca. 15 min).
The toluene was removed and the crude product was recrystallised
from EtOAc and hexane to afford:
Fraction 3: 3,3-bis(4-methylsulfinylphenyl)-3H-naphtho[2,1-
b]pyran (22). As an inseparable mixture of diastereoisomers
(0.32 g, 18%) as colourless microcrystals from EtOAc–hexane,
mp 191–193 ◦C, kmax(PhMe) 426 nm, mmax 1629, 1214, 1084, 1044,
1006, 950, 813, 741 cm−1, dH all signals 2.702 (3H, s, SOMe),
2.705 (3H, s, SOMe), 6.24 (1H, m, 2-H), 7.20 (1H, d, J = 8.7 Hz,
Ar–H), 7.36 (1H, m, Ar–H), 7.41 (1H, d, J = 9.6 Hz, 1-H), 7.50
(1H, m, Ar–H), 7.62 (8H, m, Ar–H), 7.70 (1H, d, J = 9.2 Hz,
Ar–H), 7.74 (1H, d, J = 8.0 Hz, Ar–H), 7.97 (1H, d, J = 8.4 Hz,
10-H), dC all signals 43.8, 43.8, 81.8, 114.1, 118.1, 121.0, 121.3,
123.7, 124.1, 126.2, 127.0, 127.9, 128.6, 129.5, 129.7, 130.4, 145.3,
147.4, 150.0. Found M+ = 458.1006. C27H22O3S2 requires M+ =
458.1005.
2 - [1,1 - bis(4 - methylsulfonylphenyl)methyl]naphtho[2,1 - b]furan
(23). (0.34 g, 85%) as colourless microcrystals from PhMe, mp
235–237 ◦C, mmax 1593, 1302, 1144, 1089, 954, 805, 762 cm−1, dH 3.09
(6H, s, SO2Me), 5.86 (1H, s, methine), 6.84 (1H, s, 1-H), 7.47 (5H,
m, Ar–H), 7.57 (1H, m. Ar–H), 7.59 (1H, d, J = 9.2, 5-H), 7.73
(1H, d, J = 9.0, Ar–H), 7.95 (5H, m, Ar–H), 8.03 (1H, d, J = 8.0,
9-H), dC 44.5, 50.9, 105.7, 112.1, 123.1, 123.3, 124.8, 125.6, 126.6,
127.4, 128.1, 128.8, 129.9, 130.3, 139.8, 146.1, 152.8, 155.6. Found
+
C, 65.9; H, 4.5; S, 12.9; HM + NH4 = 508.1253. C27H22O5S2
+
requires C, 66.1; H, 4.5; S, 13.1%; M + NH4 = 508.1247.
Acknowledgements
Procedure for the thermal rearrangement of spiro(3H-
naphtho[2,1-b]pyran-3,9ꢀ-thioxanthene-10,10-dioxide (3)
The authors thank Yorkshire Forward and James Robinson Ltd.
(Huddersfield, UK) for a research studentship to SBK and the
EPSRC for access to the National Mass Spectrometry Service
(Swansea) and the National X-Ray Crystallography Service
(Southampton, UK). The Clothworkersꢀ of the City of London
are thanked for a millennium grant for the purchase of a Bruker
Avance NMR spectrophotometer.
A solution of naphthopyran (3) (0.25 g, 0.63 mmol) in EtOAc
(30 mL) and hexane (30 mL) was heated under reflux until TLC
examination of the mixture indicated that no reactant remained
(ca. 45 min). Removal of the solvent gave:
9-(naphtho[2,1-b]furan-2-yl)-9H-thioxanthene-10,10-dioxide (6).
(0.25 g, 100%) as pale brown plates from EtOAc–hexane, mp 239–
241 ◦C, mmax 1566, 1445, 1385, 1293, 1270, 1163, 1143, 1129, 797,
740, 726, 578, 567, 499 cm−1, dH 5.92 (1H, s, 9-H), 7.10 (1H, s, 1ꢀ-
H), 7.42 (2H, m, Ar–H), 7.48 (1H, m, Ar–H), 7.58 (6H, m, Ar–H),
7.73 (1H, d, J = 8.9 Hz, Ar–H), 7.93 (1H, d, J = 8.1 Hz, Ar–H),
References
1 For recent reviews see: J. D. Hepworth and B. M. Heron, in Functional
Dyes, ed. S.-H. Kim, Elsevier, Amsterdam, 2006, pp. 85–135 and B.
Van Gemert, in Organic Thermochromic and Photochromic Compounds,
This journal is
The Royal Society of Chemistry 2008
Org. Biomol. Chem., 2008, 6, 3096–3104 | 3103
©

View Article Online
Volume 1 Main Photochromic Families, ed. J. C. Crano and R. J. Gugliel-
metti, Plenum Press, New York, 1999, pp. 111–140.
9 For examples of photochemical isomerisation of sulfoxides see: A. A.
Rachford and J. J. Rack, J. Am. Chem. Soc., 2006, 128, 14318; T. Fujita,
H. Kamiyama, Y. Osawa, H. Kawaguchi, B. J. Kim, A. Tatami, W.
Kawashima, T. Maeda, A. Nakanishi and H. Morita, Tetrahedron,
2007, 63, 7708.
2 P. J. Coelho, M. A. Salvador, B. M. Heron and L. M. Carvalho,
Tetrahedron, 2005, 61, 11730; C. D. Gabbutt, B. M. Heron and A. C.
Instone, Tetrahedron, 2006, 62, 737; S. Delbaere, G. Vermeersch, M.
Frigoli and G. H. Mehl, Org. Lett., 2006, 8, 4931; J. N. Moorthy,
P. Venkatakrishnan, S. Sengupta and M. Baidya, Org. Lett., 2006, 8,
4891; W. Zhao and E. M. Carreira, Chem.–Eur. J., 2007, 13, 2671; E. A.
Shilova, V. P. Perevalov, A. Samat and C. Moustrou, Tetrahedron Lett.,
2007, 48, 4127.
3 Examples of the Claisen route to naphthopyrans are known, however,
in these instances, the electron withdrawing aryl group is partnered
with an electron rich aryl unit to improve reactivity e.g. J. Momoda,
S. Matsuoka, H. Nagou, PCT WO 2000075238 (2000); J. Momota,
T. Hara, Japanese Patent, JP 09124645 (1997).
10 J. A. Gillean III, D. W. Phelps and A. W. Cordes, Acta Crystallogr.,
Sect. B, 1973, 29, 2296.
11 Crystallographic data for compound 6 (CCDC661552): formula
˚
C25H16O3S; formula weight = 396.44; T = 150(2) K; k = 0.71073 A
[Mo-Ka]; crystal system = monoclinic; space group = P21/n; unit
◦
˚
˚
cell dimensions, a = 7.97170(10) A, a = ◦90 ; b = 20.6854(3) A, b =
◦
3
˚
˚
101.1430(7) ; c = 11.1804(2) A, c = 90 ; volume = 1808.87(5) A ;
Z = 4; density (calculated) = 1.456 Mg m−3; absorption coefficient =
0.205 mm−1; F(000) = 824; crystal = pale brown plate; crystal size =
0.31 × 0.20 × 0.08 mm; h range for data collection = 2.71 ≤ h ≤ 26◦;
index ranges = −9 ≤ h ≤9, −25 ≤ k ≤ 25, −13 ≤ l ≤ 13; reflections
collected = 34563; independent reflections = 3553 [R(int) = 0.084];
absorption correction = none; refinement method = full-matrix least-
squares on F2; data/restraints/parameters = 3553/0/262; goodness-
of-fit = 1.058; Final R indices [I > 2r(I)] = R1 = 0.0396, wR2 = 0.1011;
R indices (all data) = R1 = 0.0483, wR2 = 0.1084; largest diff. peak and
4 C. D. Gabbutt, B. M. Heron, A. C. Instone, D. A. Thomas, S. M.
Partington, M. B. Hursthouse and T. Gelbrich, Eur. J. Org. Chem.,
2003, 1220.
5 J.-L. Pozzo, V. A. Lokshin and R. Guglielmetti, J. Chem. Soc., Perkin
Trans. 1, 1994, 2591.
6 P. Coelho, L. M. Carvalho, S. Abrantes, M. M. Oliveira, A. M. F.
Oliveira-Campos, A. Samat and R. Guglielmetti, Tetrahedron, 2002,
58, 9505; A. Mustafa, J. Chem. Soc., 1949, 2295.
−3
˚
hole = 0.298 and −0.545 e A
.
12 There is only one previous report describing the contraction of
8-ethenyl-3,3-diphenyl-3H-naphtho[2,1-b]pyran, which was accom-
plished under prolonged intense irradiation in either cyclohexane
or ethanol leading to a dihydronaphthofuran, which was accom-
panied by benzophenone: S. Coen, N. Lehadus, C. Moustrou,
A. Samat and R. Guglielmetti, Heterocycl. Commun., 2002, 8,
27.
7 Crystallographic data for compound 4 (CCDC670085): formula
˚
C25H16O2S; formula weight, 380.44; T = 120(2) K; k = 0.71073 A;
crystal system = monoclinic; space group, P21/n; unit cell dimensions,
◦
◦
˚
˚
a = 11.1939(5) A, a = 90 ; b = 14.0344(4) A, b = 101.498(2) ; c =
◦
3
˚
˚
11.7187(5) A, c = 90 ; volume = 1804.06(12) A ; Z = 4; density
(calculated) = 1.401 Mg m−3; absorption coefficient = 0.198 mm−1
;
F(000) = 792; crystal, shard; colourless; crystal size = 0.08 ×
0.07 × 0.04 mm3 h range for data collection = 3.16–27.48◦; index
ranges = −14 ≤ h ≤ 14, −18 ≤ k ≤ 16, −15 ≤ l ≤ 15; reflections
collected = 21913; independent reflections = 4135 [Rint = 0.0999];
completeness to h = 27.48◦ = 99.8%; absorption correction = semi-
empirical from equivalents; max. and min. transmission = 0.9921
and 0.9843; refinement method = full-matrix least-squares on F2;
13 S. Delbaere, B. Luccioni-Houze, C. Bochu, Y. Teral, M. Campredon and
G. Vermeersch, J. Chem. Soc., Perkin Trans. 2, 1998, 1153; X. Sallenave,
S. Delbaere, G. Vermeersch, A. Saleh and J.-L. Pozzo, Tetrahedron
Lett., 2005, 46, 3257; M. Frigoli and G. H. Mehl, Chem. Commun.,
2004, 2040.
14 Crystallographic data for trans-sulfoxide 11 (CCDC663292): formula
˚
C25H16O2S; formula weight = 380.44; T = 150 K; k = 0.71073 A
data/restraints/parameters = 4135/0/253; goodness-of-fit on F2
=
[Mo-Ka]; crystal system = monoclinic; space group = C2/; unit cell
◦
1.065; final R indices [F2 > 2r(F2)] = R1 = 0.0671, wR2 = 0.1124; R
dimensions, a = 19.3719(8) A, a = 90 ; b = 11.5100(5) A, b =
˚
˚
◦
◦
3
˚
˚
indices (all data) = R1 = 0.1094, wR2 = 0.1255; largest diff. peak and
99.926(2) ; c = 16.4409(6) A, c = 90 ; volume = 3611.0(3) A ; Z = 8;
−3
hole = 0.369 and −0.361 e A
.
density (calculated) = 1.4 Mg m−3; absorption coefficient = 0.198 mm−1
;
˚
8 Crystallographic data for compound 5 (CCDC670086): formula
F(000) = 1584; crystal = pale brown fragment; crystal size 0.29 ×
0.26 × 0.21 mm; h range for data collection = 2.32 ≤ h ≤ 28.3◦; index
ranges = −25 ≤ h ≤25, −15 ≤ k ≤ 15, −18 ≤ l ≤ 21; reflections
collected = 29976; independent reflections = 4465 [R(int) = 0.0437];
absorption correction = none; refinement method = full-matrix least-
squares on F2; Data/restraints/parameters = 4465/0/253; Goodness-
of-fit = 1.025; Final R indices [I >2r(I)] = R1 = 0.0370, wR2 = 0.0875;
R indices (all data) = R1 = 0.0486, wR2 = 0.0936; largest diff. peak and
˚
C25H16O2S; formula weight = 380.44; T = 120(2) K; k = 0.71073 A;
crystal system = monoclinic;◦space group = P21/n; unit cell dimension◦s,
˚
˚
a = 11.3454(2) A, a = 90 ; b = 13.4896(2) A, b = 96.3650(10) ;
◦
3
˚
˚
c = 11.5736(3) A, c = 90 ; volume = 1760.36(6) A ; Z = 4; density
(calculated) = 1.435 Mg m−3; absorption coefficient = 0.203 mm−1
;
F(000) = 792; crystal = prism; colourless; crystal size = 0.30 ×
0.30 × 0.20 mm3 h range for data collection = 3.02–27.49◦; index
ranges = −14 ≤ h ≤ 14, −17 ≤ k ≤ 17, −15 ≤ l ≤ 14; reflections
collected = 22230; independent reflections = 4007 [Rint = 0.0303];
completeness to h = 27.49◦ = 99.3%; absorption correction = semi-
empirical from equivalents; max. and min. transmission = 0.9605
and 0.9415; refinement method = full-matrix least-squares on F2;
−3
˚
hole = 0.309 and −0.541 e A
.
15 S. Jockusch, N. J. Turro and F. R. Blackburn, J. Phys. Chem. A, 2002,
106, 9236.
16 T.-F. Tan, J. Han, M.-L. Pang, Y.-F. Fu, H. Ma, Y.-X. Ma and J.-B.
Meng, Tetrahedron, 2006, 62, 4900.
17 L. C. Schmidt, V. Rey and A. B. Pen˜e´n˜ory, Eur. J. Org. Chem., 2006,
2210.
data/restraints/parameters = 4007/0/253; goodness-of-fit on F2
=
1.059; Final R indices [F2 > 2r(F2)] = R1 = 0.0364, wR2 = 0.0930; R
indices (all data) = R1 = 0.0389, wR2 = 0.0948; largest diff. peak and
18 P. Lucas, N. El Mehdi, H. A. Ho, D. Be´langer and L. Breau, Synthesis,
−3
˚
hole = 0.360 and −0.470 e A
.
2000, 1253.
3104 | Org. Biomol. Chem., 2008, 6, 3096–3104
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The Royal Society of Chemistry 2008
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