Condensations of benzil with phenols and aryl ethers mediated by tin(IV) chloride pentahydrate

Article abstract of DOI:10.1016/S0040-4020(02)00357-5

The reaction of benzil with phenol at 180°C in the presence of SnCl₄·5H₂O produces a benzofuran, a benzofuranol, a benzodifuran, and a benzofuranone. Anhydrous tin(IV) chloride also gives a benzofuranofuranone. Other phenols and their methyl ethers yield related products. The good yields of the benzo- and naphtho-furanones make the method an attractive alternative to the benzilic acid route to such compounds.

Full text of DOI:10.1016/S0040-4020(02)00357-5

TETRAHEDRON
Pergamon
Tetrahedron 58 ,2002) 4255±4260
Condensations of benzil with phenols and aryl ethers mediated by
tinꢀIV) chloride pentahydrate
Brian J. Morrison and Oliver C. Musgravep
Department of Chemistry, The University, Old Aberdeen, Scotland AB24 3UE, UK
Received 14 January 2002; revised 4 March 2002; accepted 28 March 2002
AbstractÐThe reaction of benzil with phenol at 1808C in the presence of SnCl4´5H2O produces a benzofuran, a benzofuranol, a benzo-
difuran, and a benzofuranone. Anhydrous tin,IV) chloride also gives a benzofuranofuranone. Other phenols and their methyl ethers yield
related products. The good yields of the benzo- and naphtho-furanones make the method an attractive alternative to the benzilic acid route to
such compounds. q 2002 Elsevier Science Ltd. All rights reserved.
1. Introduction
we chose to employ the hydrated form which behaves as
both a Lewis and a protic acid and which is handled more
easily than is the anhydrous compound. Repetition of the
reaction between benzil 2, phenol 3, and SnCl4´5H2O using
Liebig's conditions and subsequent separation of the
products by PLC gave the lactone 4 and the benzofuranol
5 together with smaller amounts of the benzofuran 6 and the
benzodifuran 7 but the lactone 1 was not present
,Scheme 1).The yields are given in Table 1. Both the use
of a lower temperature ,1308C) and the substitution of
anhydrous zinc chloride in place of SnCl4´5H2O gave gener-
ally similar results but anhydrous aluminium chloride
provided a signi®cantly larger ,59%) yield of the lactone
4. In contrast polyphosphoric acid gave mainly the benzo-
furanol 5 even after prolonged heating. Finally the use of
anhydrous tin,IV) chloride produced a substance C34H22O3,
mp 235±2368C, which we believe to be the compound
with the same molecular formula, mp 2398C, reported by
Liebig and thought by him to be the lactone 1. We formulate
the substance as the benzofuran lactone 8. It shows the
characteristic behaviour of a g-lactone, absorbing strongly
Hans von Liebig reported1 in 1908 that benzil reacted with
phenol at 1808C in the presence of `Zinnchlorid' to give the
polycyclic lactone 1. His explanation for its formation
assumed an acid-catalysed benzil±benzilic acid rearrange-
ment and a novel anthracene synthesis. We found his argu-
ments unconvincing and have reinvestigated this reaction;
we have also extended it by the use of other phenols and
their methyl ethers.
2. Results and discussion
Liebig did not specify the type of tin,IV) chloride used and
Scheme 1.
Keywords: benzofurans; diones; furanones; phenols.
Corresponding author. Fax: 101224-272921; e-mail: o.c.musgrave@abdn.ac.uk
p
0040±4020/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020,02)00357-5

4256
B. J. Morrison, O. C. Musgrave / Tetrahedron 58 +2002) 4255±4260
Table 1. Products ,%) from benzil±phenol reactions ,8 h at 1808C)
Lewis/protic acid
Benzofuran 6
Benzodifuran 7
Lactone 4
Benzofuranol 5
Benzofuran lactone 8
SnCl4´5H2O
4
3
4
5
1
1
6
6
6
4
1
1
23
17
29
59
0
29
41
31
13
36
40
35
0
0
0
0
0
SnCl4´5H2O ,1308C)
ZnCl2 ,anhydrous)
AlCl3 ,anhydrous)
Polyphosphoric acid
Polyphosphoric acid ,24 h)
SnCl4 ,anhydrous)
2
16
2
0
0
25
Scheme 2.
Scheme 3.
in the IR at 1797 cm21 and losing carbon monoxide
followed by a hydrogen atom in the mass spectrometer to
give, as the base peak, an ion which may be written as the
pyrylium ion 9. Its UV absorption resembles that of the
benzofuranol 5; all its 1H NMR signals are those of aromatic
protons.
The same cation 13 may also participate in the formation of
the lactone 4, addition of the hydroxy group to the carbonyl
group of 13 being accompanied by migration of a phenyl
group to the electron-de®cient site but a synchronous
mechanism, as in structure 15, would seem to be more
appropriate ,Scheme 4). This 1,2-shift of a phenyl group
bears some resemblance to the benzpinacol±benzpinacone
rearrangement;3 it is favoured energetically by the stability
of the resulting g-lactone system. A similar rearrangement
has been postulated4 to account for the formation of the
lactone 4 ,in 17% yield) during the anodic oxidation of
the benzofuran 6. The tricyclic products 7 and 8 clearly
result from further reactions of the benzofuranol 5 with
benzil.
The formation of the benzofuranol 5 in which a second
oxygen function has been introduced meta to the original
hydroxy group appears to involve the reaction of one of the
benzil carbonyl groups at the para position of phenol to give
the hydroxyketol 10 ,Scheme 2) followed by acid-induced
dehydration to give the protonated p-quinonemethide 11
and subsequent cyclisation to form the furan ring. The
formation of the minor product, the benzofuran 6, requires
ortho alkylation of the phenol and this would be favoured by
the coordination of the oxygen atoms of both reactants with
the Lewis acid used. Before the furan ring can be formed the
arylbenzoin intermediate must undergo reduction presum-
ably via the a-ketocarbocation 132 ,Scheme 3). The redu-
cing agent would appear to be phenol two molecules of
which, probably coordinated with the Lewis acid, would
provide the necessary hydrogen producing a dihydroxybi-
phenyl in the process. This explanation receives support
from the corresponding reaction with 1-naphthol which
gave as a minor product the difuran 34. The latter clearly
results from the reaction of the intermediate dihydroxybi-
naphthyl 32 with benzil.
The replacement of phenol in the benzil±SnCl4´5H2O reac-
tion by other phenols and their methyl ethers resulted in the
formation of analogous products. In particular p-cresol 16
and m-cresol 17 gave good yields of the corresponding
lactones 18 ,65%) and 19 ,91%) together with small
amounts of the related benzofurans 20 and 21. In contrast
the less reactive methyl ethers anisole 22 and m-dimethoxy-
benzene 23 afforded only the methoxybenzofurans 24 and
25, respectively ,Scheme 5). 2-Naphthol 26 and 1-naphthol
Scheme 4.

B. J. Morrison, O. C. Musgrave / Tetrahedron 58 +2002) 4255±4260
4257
Scheme 5.
Scheme 6.
27 provided the naphthofurans 28 and 29 and the related
naphthofuranones 30 and 31, respectively, the latter again in
good yields ,70 and 65%) ,Scheme 6).
C34H20O2, which gave mass and UV spectra typical of a
polycyclic aromatic structure. Its molecular formula shows
it to be composed of two molecules of 1-naphthol plus one
of benzil less two molecules of water and two atoms of
hydrogen. We suggest that two molecules of 1-naphthol
The reaction with 1-naphthol also afforded a minor product,
Scheme 7.

4258
B. J. Morrison, O. C. Musgrave / Tetrahedron 58 +2002) 4255±4260
Scheme 8.
27, coordinated to tin,IV), couple to give 2,21-binaphthyl-
1,11-diol 32 ,and in so doing provide the hydrogen needed
for the formation of the naphthofuran 29). The diol then
reacts with benzil to form the protonated quinonemethide
33 which cyclises as in structure 11; elimination of water
from the two phenolic hydroxy groups gives the dinaphtho-
difuran 34 ,Scheme 7). The proton NMR spectrum supports
this formulation. The peri protons at C-1 and -13 appear as a
multiplet at d 8.50±8.60, similar to that at d 8.30±8.45
shown by the peri proton in the naphthofuran 29 while the
AB quartet centred at d 7.86 and 8.35 can be assigned to H-9
and -8 the low-®eld shift of the latter proton being a conse-
quence of the proximity of the oxygen at position 7. The
multiplet at d 7.97±8.05 corresponds to H-10; similar peri
protons in the dinaphthofuran 38 resonate at d 8.00.
the fraction bp 60±808C. All the products are colourless
solids. Their yields are based on the initial weights of benzil
used, no account being taken of the varying amounts of
starting materials that were recovered from all the
reactions.
3.1.1. Reactions of benzil with benzene derivatives.
+a) With phenol using SnCl4´5H2O.
A mixture of benzil ,5.0 g, 23.8 mmol), phenol ,5.0 g,
53.2 mmol), and SnCl4´5H2O ,5.0 g, 14.2 mmol) was heated
at 1808C for 8 h, cooled, diluted with chloroform ,75 ml),
and washed with water ,800 ml). Evaporation of the solvent
gave an oil which was separated by PLC using light
petroleum±chloroform ,1:1) followed in the case of the
less polar constituents by light petroleum into four fractions.
The fastest-moving component crystallised from ether±
light petroleum to give 2,3-diphenylbenzofuran 6 ,4%) as
needles mp 119±1208C ,lit.,6 1208C) ,Found: M1,
270.1039. Calcd for C20H14O: M, 270.1045); m/z 270
,100%, M1), 268 ,11, M22H), 241 ,18, M2CHO), and
239 ,18, 2682CHO); lmax ,nm) 238 ,log 1 4.27), 273in¯
,3.95), 305 ,4.29) and 313in¯ ,4.25); nmax ,cm21) 1600
,aromatic CvC), 764 ,4 adjacent ArH), 748 and 694 ,5
adjacent ArH); dH 7.17±7.80 ,14H, m, ArH). Next came
2-Methoxynaphthalene 35 underwent cleavage of the
methoxy group during reaction with benzil and SnCl4´5H2O
giving the same compounds as were obtained from
2-naphthol together with a minor product, C34H20O2,
isomeric with the dinaphthodifuran 34 and having generally
similar spectroscopic properties. A mechanistic argument
similar to that proposed above when applied to 2-naphthol
leads via the binaphthyldiol 36 to the structure 37 which
receives support from the proton NMR spectrum
,Scheme 8). Of the four low-®eld signals those at d 9.11
and 8.89 can be assigned to H-1 and -14 which are in close
proximity; the corresponding signals for the dinaphthofuran
38 appear as a broad doublet at d 9.12. The signal at d 8.54
can be attributed to H-4 being similar to that ,at d,8.37) of
H-9 of the naphthofuran 29. The signal at d 8.01 can be
assigned to H-11 as the corresponding proton of the
dinaphthofuran 38 resonates at d 8.00. Finally its UV
absorption shows a marked resemblance to that5 of the latter
compound.
2,3,5,6-tetraphenylbenzo[1,2-b:5,4-b1]difuran
7
,6%)
which crystallised from ether-light petroleum as needles,
mp 220±221.58C ,lit.,7 221±2228C) identical ,IR, UV,
mixed mp) with an authentic specimen ,Found: M1,
462.1622. Calcd for C34H22O2: M, 462.1620; m/z 462
,100%, M1) and 231 ,13, M21); lmax ,nm) 231 ,log 1
4.48), 245 ,4.49), 300 ,4.48), 331in¯ ,4.55), 339 ,4.60),
and 349in¯ ,4.50); nmax ,cm21) l600 ,aromatic CvC),
890 ,isolated ArH), 762 and 693 ,5 adjacent ArH); dH
7.15±7.83 ,22H, m, ArH). The third component crystallised
from chloroform±light petroleum to give 3,3-diphenyl-
2,3H)-benzofuranone 4 ,23%) as plates, mp 119±1208C
,lit.,1 1208C) ,Found: M1, 286.0996. Calcd for C20H14O2:
M, 286.0994); m/z 286 ,45%, M1), 258 ,52, M2CO), 257
,100, 2582H), 242 ,8, M2CO2), 241 ,10, M2CHO2) and
181 ,44, M2PhCO); lmax ,nm) 260 ,log 1 3.15), 266.5
,3.19), 272 ,3.24), and 280 ,3.18); nmax ,cm21) 1795
,g-lactone CvO), 1590 ,aromatic CvC), 763 ,4 adjacent
ArH), 749 and 695 ,5 adjacent ArH); dH 7.13±7.48 ,14H, m,
ArH). The slowest-moving component crystallised from
ether±light petroleum to give 2,3-diphenylbenzofuran-6-ol
5 ,29%) as needles, mp 117±1198C ,lit.,7 118±1208C)
,Found: M1, 286.0998. Calcd for C20H14O2: M,
286.0994); m/z 286 ,100%, M1), and 257 ,16, M2CHO);
lmax ,nm) 236 ,log 1 4.25), 320 ,4.31), and 347in¯ ,3.74);
nmax ,cm21) 3300 ,phenolic OH), 1622, 1600 ,aromatic
CvC), 795 ,2 adjacent ArH), 761 and 689 ,5 adjacent
3. Experimental
3.1. General
IR spectra were measured for KBr discs, and UV absorp-
1
tions for methanolic solutions. H and 13C NMR spectra
were recorded for CDCl3 solutions at 220 and 20 MHz,
respectively, using Me4Si as internal standard. Mass spectra
were obtained using EI at 70 eV. `Light petroleum' refers to

B. J. Morrison, O. C. Musgrave / Tetrahedron 58 +2002) 4255±4260
4259
ArH); dH 5.02 ,1H, s, 6-OH), 6.84 ,1H, dd, Jˆ1 and 9 Hz,
H-5), 7.10 ,1H, d, Jˆ1 Hz, H-7) and 7.29±7.72 ,11H, m,
ArH).
as plates mp 122±1248C ,lit.,9 1258C) ,Found: M1,
300.1156. Calcd for C21H16O2: M, 300.1150); m/z 300
,32%, M1), 272 ,51, M2CO), 271 ,100, M2CHO), 255
,6, M2CO22H), 241 ,12, 2712CO±Me), and 195
,M2Ph±CO); lmax ,nm) 235 ,log 1 4.13), 267 ,3.17), 275
,3.20), and 282 ,3.24); nmax ,cm21) 1796 ,g-lactone CvO),
1620, 1595 ,aromatic CvC), 817 ,2 adjacent ArH), 767,
752, and 698 ,5 adjacent ArH); dH 2.34 ,3H, s, Me), 6.98
,1H, br.s, H-7), 7.11 ,1H, br.d, Jˆ8 Hz, H-5), and 7.17±7.45
,11H, m, ArH); dC 21.6 ,q), 61.2 ,s), 111.7, 125.3, 125.8 ,all
d), 126.9 ,s), 127.7, 128.1, 128.7 ,all d), 139.7, 140.9, 152.7,
and 177.1 ,all s).
+b) With phenol using anhydrous SnCl4.
A similar reaction in a sealed ampoule using anhydrous
SnCl4 ,5.0 g, 19.2 mmol) in place of the hydrate gave, in
addition to the above benzofurans, 3,3,5,6-tetraphenyl-
2+3H)benzo [1,2-b:5,4-b1]furanofuranone 8 ,25%) which
crystallised from ethanol, mp 235±2368C ,Found: M1,
478.1568. C34H22O3 requires: M, 478.1569); m/z 478
,61%, M1), 450 ,56, M2CO), 449 ,100, 4502H), 373
,28, 4502C6H5), 105 ,17, PhCO) and 77 ,19, C6H5); lmax
,nm) 304in¯ ,log 1 4.03), 317 ,4.14), and 324in¯ ,4.11);
nmax ,cm21) 1797 ,g-lactone CvO), 1600 ,aromatic
CvC), 903 ,isolated ArH), 763, 752 and 695 ,5 adjacent
ArH); dH 7.08±7.65 ,22H, m, ArH).
+e) With anisole.
A similar reaction between benzil ,5.0 g, 23.8 mmol),
anisole ,5.0 g, 46.3 mmol) and SnCl4´5H2O ,5.0 g,
14.2 mmol) gave 6-methoxy-2,3-diphenylbenzo[b]furan 24
,29%) which crystallised from light petroleum as needles,
mp 121±1228C ,lit.,10 120±1218C) ,Found: C, 84.00; H,
5.40%; M1, 300.1152. Calcd for C21H16O2: C, 83.98; H,
5.37%; M, 300.1150); m/z 300 ,100%, M1), 285 ,71,
M2Me), 228 ,3, 2852CHO±CO) and 150 ,3, M21); lmax
,nm) 230 ,log 1 4.26), 316 ,4.40), and 350in¯ ,3.26); nmax
,cm21) 1610 ,aromatic CvC), 820 ,2 adjacent ArH), 765
and 700 ,5 adjacent ArH); dH 3.81 ,3H, s, MeOAr), 6.85
,1H, dd, Jˆ2 and 8 Hz, H-5), 7.05 ,1H, d, Jˆ2 Hz, H-7),
and 7.13±7.75 ,11H, m, ArH).
+c) With p-cresol using SnCl4´5H2O.
A similar reaction between benzil ,5.0 g, 23.8 mmol),
p-cresol ,5.0 g, 46.3 mmol) and SnCl4´5H2O ,5.0 g,
14.2 mmol) provided two products. The faster-moving
component gave 2,3-diphenyl-5-methylbenzofuran 20
,3.5%) which crystallised from chloroform as needles mp
112±1138C ,lit.,6 1148C) ,Found: M1, 284.1201. Calcd for
C21H16O: M, 284.1201); m/z 284 ,100%, M1), 282 ,9,
M22H), 255 ,8, M2CHO), and 239 ,8, M2CO±Me);
lmax ,nm) 237 ,log 1 4.19), 288in¯ ,4.09), 299in¯ ,4.18),
305 ,4.22), and 315 ,4.15); nmax ,cm21) 1599 ,aromatic
CvC), 797 ,2 adjacent ArH), 759 and 692 ,5 adjacent
ArH); dH 2.42 ,3H, s, Me) and 7.16±7.75 ,13H, m, ArH).
The slower-moving component was 3,3-diphenyl-5-methyl-
2,3)-benzofuranone 18 ,65%) which crystallised from
chloroform as plates mp 128±1298C ,lit.,8 1308C) ,Found:
M1, 300.1158. Calcd for C21H16O2: M, 300.1150); m/z 300
,20%, M1), 272 ,49, M2CO), 271 ,100, M2CHO), 255 ,7,
M2CO2±H), 241 ,8, M2CO2±Me), 228 ,7, 2712CO±
Me), and 195 ,35, M2CO±Ph); lmax ,nm) 233 ,log 1
4.14), 258in¯ ,3.17), 266in¯ ,3.13), 271in¯ ,3.18), 279
,3.29) and 288 ,3.22); nmax ,cm21) 1801 ,g-lactone
CvO), 1614, 1593 ,aromatic CvC), 809 ,4 adjacent
ArH), 770, 749, 738, and 699 ,5 adjacent ArH); dH 2.30
,3H, s, Me), 7.04±7.41 ,13H, m, ArH); dC 21.2 ,q), 61.5
,s), 110.7, 126.6, 127.8, 128.2, 128.6 and 129.7 ,all d),
131.0, 134.2, 140.9, 150.5, and 177.1 ,all s).
+f) With m-dimethoxybenzene.
A similar reaction with m-dimethoxybenzene ,5.0 g,
36.2 mmol) in place of anisole gave 4,6-dimethoxy-2,3-
diphenylbenzo[b]furan 25 ,23%) which crystallised from
benzene-light petroleum in needles mp 129±1308C
,Found: M1, 330.1258. C22H18O3 requires: M, 330.1255);
m/z 330 ,100%, M1), 315 ,70, M2Me), 299 ,3, M2MeO)
and 287 ,6, 3152CO); lmax ,nm) 246 ,log 1 4.24) and 324
,4.26); nmax ,cm21) 1602 ,aromatic CvC), 755 and 690 ,5
adjacent ArH); dH 3.60 and 3.82 ,each 3H, s, MeO at C-4
and -6), 6.25 ,1H, d, Jˆ2 Hz, H-5), 6.67 ,1H, d, Jˆ2 Hz,
H-7), and 6.91±7.60 ,10H, m, ArH).
3.1.2. Reactions of benzil with naphthalene derivatives.
+a) With 1-naphthol.
A mixture of benzil ,5.2 g, 24.8 mmol), 1-naphthol ,3.6 g,
25.0 mmol) and SnCl4´5H2O ,5.0 g, 14.2 mmol) after treat-
ment as in ,a) above gave three products. The fastest-
moving material crystallised from acetone±ethanol to give
2,3-diphenylnaphtho[1,2-b]furan 29 ,13%) as needles, mp
99±1008C ,lit.,11 1008C) ,Found: M1, 320.1206. Calcd for
C24H16O: M, 320.1201); m/z 320 ,100%, M1), 291 ,9,
M2CHO), 289 ,13, 29122H), 215 ,7, M2PhCO), and
160 ,7, M21); lmax ,nm) 252 ,log 1 4.52), 265in¯ ,4.46),
279in¯ ,4.36), 316 ,4.26), 325in¯ ,4.21), 333in¯ ,4.09) and
349 ,3.76); nmax ,cm21) 1595 ,aromatic CvC), 817 ,2
adjacent ArH), 770 ,4 adjacent ArH), 741 and 699 ,5
adjacent ArH); dH 7.17±7.95 ,15H, m, ArH) and 8.30±
8.45 ,1H, m, H-9). Next came 5,6-diphenylnaphtho[11,21-
b]naphtho[1,2-b:3,4-b1]difuran 34 ,2%) which crystallised
from acetone±methanol in needles, mp 171±1738C ,Found:
+d) With m-cresol.
A similar reaction with m-cresol ,5.0 g, 46.3 mmol) gave
two products. The faster-moving component was 2,3-
diphenyl-6-methylbenzofuran 21 ,2%) which crystallised
from chloroform±light petroleum in needles mp 87±888C
,lit.,6 898C) ,Found: M1, 284.1200, Calcd for C21H16O: M,
284.1201); m/z 284 ,100%, M1), 255 ,15, M2CHO) and
239 ,19, M2CO±Me); lmax ,nm) 239 ,log 1 4.30), 301in¯
,4.28), 309 ,4.32), and 328in¯. ,4.26); nmax ,cm21) 1602
,aromatic CvC), 818 ,2 adjacent ArH), 764 and 695 ,5
adjacent ArH); dH 2.46 ,3H, s, Me), 7.04 ,1H, dd, Jˆ9
and 1 Hz, H-5). and 7.20±7.75 ,12H, m, ArH). The
slower-moving component crystallised from chloroform to
give 3,3-diphenyl-6-methyl-2,3H)-benzofuranone 19 ,91%)

4260
B. J. Morrison, O. C. Musgrave / Tetrahedron 58 +2002) 4255±4260
M1, 460.1473. C34 H20 O2 requires: M, 460.1463); m/z 460
,100%, M1), and 230 ,5, M21); lmax ,nm) 236 ,log 1 4.56),
267in¯ ,4.61), 273 ,4.63), 300 ,4.57), 308in¯ ,4.53), 335
,4.32), 343in¯ ,4.25), and 362 ,3.96); nmax ,cm21) 1600
,aromatic CvC), 805 ,2 adjacent ArH), 764 ,4 adjacent
ArH), 755 and 701 ,5 adjacent ArH); dH 7.21±7.45 ,5H,
m, ArH), 7.48±7.72 ,10H, m, ArH), 7.86 ,1H, d, Jˆ8 Hz,
H-9), 7.97±8.05 ,1H, m, H-10), 8.35 ,1H, d, Jˆ8 Hz, H-8)
and 8.50±8.60 ,2H, m, H-1 and -13). The slowest-moving
material was 3,3-diphenyl-2,3H)-naphtho[1,2-b]furanone
31 ,65%) which crystallised from chloroform±light
petroleum as needles, mp 188±1898C ,lit.,12 1908C)
,Found: M1, 336.1147. Calcd for C24H16O2: M,
336.1150); m/z 336 ,24%, M1), 308 ,49, M2CO), 307
,100%, 308-H), 278 ,6, 3072CHO), 231 ,42, 3082C6H5),
202 ,16, 2312CHO), and 154 ,12, 30821); lmax ,nm) 239
,log 1 4.67), 286 ,3.78), 296in¯ ,3.73), 311 ,3.48), 318
,3.34), and 325 ,3.50); nmax ,cm21) 1800 ,g-lactone
CvO), 1596 ,aromatic CvC), 806 ,2 adjacent ArH), 766
,4 adjacent ArH), 749 and 699 ,5 adjacent ArH); dH 7.20±
7.73 ,14H, m, ArH), 7.83±7.91 ,1H, m, ArH) and 8.06±8.15
,1H, m, ArH).
+c) With 2-methoxynaphthalene.
A similar reaction between benzil ,4.2 g, 20.0 mmol),
2-methoxynaphthalene ,3.l6 g, 20.0 mmol) and SnCl4´5H2O
,5.0 g, 14.2 mmol) gave three products. The fastest-moving
material, the naphthofuran 28 ,4%) was followed by 6,7-
diphenylnaphtho[21,11-g]naphtho[1,2-b:3,4-b1]difuran 37
,4%) which crystallised from acetone as needles, mp 190±
1928C ,Found: M1, 460.1455. C34H20O2 requires: M,
460.1463); m/z 460 ,100%, M1), and 230 ,11, M21); lmax
,nm) 263.5 ,log 1 4.42), 293 ,4.45), 303 ,4.44), 313in¯
,4.36), 327 ,4.32), 343 ,4.27), 360 ,4.30), and 378 ,4.27);
nmax ,cm21) 1599 ,aromatic CvC), 798 ,2 adjacent ArH),
745 and 692 ,5 adjacent ArH); dH 7.29±7.94 ,16H, m, ArH),
8.01 ,1H, br.d, Jˆ7.5 Hz, H-11), 8.54 ,1H, br.d, Jˆ8 Hz,
H-4), 8.89 ,1H, br.d, Jˆ8 Hz, H-1), and 9.11 ,1H, br.d,
Jˆ7.5 Hz, H-14). The ®nal product was the naphthofura-
none 30 ,74%).
Acknowledgements
We are indebted to Drs R. J. Napier and I. Torto for
experimental assistance.
+b) With 2-naphthol.
A similar reaction using 2-naphthol ,5.0 g, 34.7 mmol) gave
two products. The faster-moving material crystallised from
chloroform±light petroleum to give 2,3-diphenyl-
naphtho[2,1-b]furan 28 ,6%) as needles mp 105±1068C
,lit.,13 1068C) ,Found: M1, 320.1198. Calcd for C24H16O:
M, 320.1201); m/z 320 ,100%, M1), 291 ,7, M2CHO), 289
,15, 29122H), 215 ,7, M2PhCO), 160 ,5, M21), and 105
,PhCO); lmax ,nm) 251in¯ ,log 1 4.13), 301in¯ ,4.15), 309
References
1. von Liebig, H. Liebig's Ann. Chem. 1908, 360, 199.
2. Begue, J.-P.; Charpentier-Morize, M. Acc. Chem. Res. 1980,
13, 207.
3. Harper, S. H. 2nd ed., Chemistry of Carbon Compounds;
Coffey, S., Ed.; Elsevier: Amsterdam, 1974; Vol. IIIF, p 310.
4. Cariou, M.; Simonet, J. Tetrahedron Lett. 1991, 32, 4913.
5. Cameron, D. W.; Sidell, M. D. Aust. J. Chem. 1978, 31, 1323.
6. Perrot, C.; Cerutti, E. Bull. Soc. Chim. Fr. 1974, 2225.
7. Dischendorfer, O. Monatsh. Chem. 1933, 62, 263.
8. Bistrzycki, A.; Nowakowski, L. Ber. 1901, 34, 3063.
9. Oeltmann, T. N.; Kramer, D. N.; Webber, J.; Daasch, L.
Spectrosc. Lett. 1970, 3, 43.
,4.17), 315 ,4.16), 329 ,4.28), and 344 ,4.35); nmax ,cm21
)
1594 ,aromatic CvC), 803 ,2 adjacent ArH), 765 ,4
adjacent ArH), 755 and 701 ,5 adjacent ArH); dH 7.17±
7.90 ,16H, m, ArH). The slower-moving material crystal-
lised from chloroform-light petroleum to give 3,3-diphenyl-
2,3H)-naphtho[2,1-b]furanone 30 ,70%) as plates, mp 182±
1838C ,lit.,9 1838C) ,Found: M1, 336.1152. Calcd for
C24H16O2: M, 336.1150); m/z 336 ,96%, M1), 308 ,53,
M2CO), 307 ,100, 3082H), 292 ,11, M2CO2), 291 ,8,
2922H), and 231 ,37, 3082C6H5); lmax ,nm) 233 ,log 1
4.57), 265 ,3.53), 271 ,3.55), 282 ,3.66), 295 ,3.66), 316
,3.27), 324 ,3.20), and 330 ,3.34); nmax ,cm21) 1805
,g-lactone CvO), 1627 and 1580 ,aromatic CvC), 809
,2 adjacent ArH), 766 ,4 adjacent ArH). 741 and 691 ,5
adjacent ArH); dH 7.19±7.65 ,14H, m, ArH), and 7.79±
7.97 ,2H, m, 8- and 9-H).
10. Brady, W. T.; Giang, Y. F.; Marchand, A. P.; Wu, A. J. Org.
Chem. 1987, 52, 3457.
11. Dischendorfer, O.; Hinrichs, H.; Schewtschenjo, J. Monatsh.
Chem. 1944, 75, 31.
12. Geipert, R. Ber. 1904, 37, 664.
13. Dischendorfer, O.; Ofenheimer, E. Monatsh. Chem. 1943, 74,
135.