The silver nitrate oxidation of 2,2,4,6,7-pentamethylcoumaran-5-ol

Article abstract of DOI:10.1016/S0040-4020(02)00465-9

The silver nitrate oxidation of 2,2,4,6,7-pentamethylcoumaran-5-ol (1) was investigated. The complex mixture of products received is in partial disagreement with the mechanisms supposed so far and proposes a less strong Mills-Nixon effect than assumed until now. Consecutive reactions of 2,2,4,7-tetramethylcoumaran-5,6-dione (2), which was received as main product, were examined.

Full text of DOI:10.1016/S0040-4020(02)00465-9

TETRAHEDRON
Pergamon
Tetrahedron 58 02002) 5081±5086
The silver nitrate oxidation of
2,2,4,6,7-pentamethylcoumaran-5-ol
²
Uta Schadel, Margit Gruner and Wolf D. Habicher
p
È
Institute of Organic Chemistry, Dresden University of Technology, Mommsenstrasse 13, 01069 Dresden, Germany
Received 12 February2002; revised 26 April 2002; accepted 30 April 2002
AbstractÐThe silver nitrate oxidation of 2,2,4,6,7-pentamethylcoumaran-5-ol 01) was investigated. The complex mixture of products
received is in partial disagreement with the mechanisms supposed so far and proposes a less strong Mills±Nixon effect than assumed
until now. Consecutive reactions of 2,2,4,7-tetramethylcoumaran-5,6-dione 02), which was received as main product, were examined.
q 2002 Elsevier Science Ltd. All rights reserved.
1. Introduction
formation of 2,2,4,7-tetramethylcoumaran-5,6-dione 02) as
a result of the oxidation of 1 with silver nitrate 0Scheme 1).
Compound 1 has often been looked at as being the coumaran
analog of the a-tocopherol model compound 2,2,5,7,8-
pentamethylchroman-6-ol exceeding the latter in anti-
oxidant activity.2
We recentlyreported on the oxidation reactions of 2,2,4,6,7-
pentamethylcoumaran-5-ol 01),1 where we mentioned the
The further investigation of the above-mentioned reaction is
caused bytwo ongoing discussions. So, the directing ability
of the dihydrofuran ring leading to reactions in 6-position3,4
of the aromatic ring exclusively and the dihydropyran ring
leading to reactions in 5-position5 has been widelyand
controversiallydiscussed as Mills±Nixon effect. Moreover,
Scheme 1.
Scheme 2.
Keywords: silver nitrate; oxidation; coumaran derivatives; o-quinone; phosphole.
Corresponding author. Tel./fax: 149-351-4633-4093; e-mail: wolf.habicher@chemie.tu-dresden.de
Á
Present address: Dipartimento di Chimica Organica e Industriale dell'Universita, Parco Area delle Scienze 17/A, 43100 Parma, Italy.
p
²
0040±4020/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020002)00465-9

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U. Schadel et al. / Tetrahedron 58 )2002) 5081±5086
5082
Scheme 3.
there have been contradictoryopinions concerning the
mechanism of the oxidation of a-tocopherol and 2,2,5,7,8-
pentamethylchroman-6-ol to the corresponding o-quinones.
Southwell-Keelyet al. plead for a wayinvolving the forma-
tion of an o-quinone methide with subsequent addition of
water and release of formaldehyde.6,7 Rosenau et al. suggest
the formation of a p-quinoid structure the isomeric form of
which does add the solvent alcohol in 5-position.8 After
elimination of methanol and further oxidation the formation
of the o-quinone is observed. The silver nitrate oxidation of
coumaran-5-ols has not been dealt with so far.9
2. Results and discussion
In the reaction of 1 with silver nitrate 2 is formed and could
be isolated as red needles in 40% yield.1 The remaining oil
was shown to consist of six major fractions along with some
minor fractions which could not yet be identi®ed. The upper
four major fractions were found to be compounds 3±8
0Scheme 2). The lower two were a mixture of several
dimeric and trimeric compounds. The pattern of their
mass spectra were consistent with those given byDean
and Orabi3 for the oxidation of 1 with potassium

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U. Schadel et al. / Tetrahedron 58 )2002) 5081±5086
5083
Scheme 4. 0a) 2, Zn-powder, glacial acetic acid, 908C, 10 min; 0b) 2, acetic anhydride, sodium acetate, 84% 0overall yield); 0c) 2, triethyl phosphite, THFdry
,
r.t., Ar, 4 h, 8 8%, 21 82%; 0d) 2, tris0diethyl)aminophosphine, THFdry, r.t., Ar, 4 h, 8 25%, 24 35%, 25 35%; 0e) 2, dimethyl acetylenedicarboxylate, r.t., 3 d,
16%; 0f) 2, methanol/glacial acetic acid 03:1), malononitrile, Et2NH, r.t., 2 d, 22%; 0g) 2, o-phenylendiamine, glacial acetic acid, 908C, 2 h, 89%.
hexacyanoferrate in toluene and those found by us for the
oxidation of 1 with silver oxide in n-hexane. Rf-values and
HPLC data were the same as well.
add further o-quinone methide to give the observed dimers
and trimers in a Diels±Alder reaction, the solvent ethanol to
form the 4- and the 6-ethoxymethyl compounds 5 and 6,
water to yield the 6-hydroxymethyl compound 12 or a
proton to give mesomer 15. The latter can either react
with water to yield the p-quinone 71 by a-cleavage or add
ethanol to form the cyclohexadienon 17. The latter can
eliminate the 4a-methyl group as methanol, for instance
after protonation of the carbonyl group and nucleophilic
attack of water at C-4a, thus forming the pyrocatechol
derivative 16. This reaction could well be driven bythe
possibilityof rearomatization. Compound 16 should ®nally
be oxidized with excess silver nitrate to o-quinone 2. Alde-
hyde 4 could be formed byoxidation of 12. Compounds 3
and 8 are obviouslysecondaryproducts. Compound 3 will
be derived from either 5 or 6 or both through oxidation to
the o-quinone methides 10 and 11 and subsequent addition
of ethanol. Isomer 8 is quantitativelyreceived if 2 is treated
with traces of base and is formed in traces if 2 is left stand-
ing in air.
To investigate the oxidation in more detail the reaction was
then carried out in n-butanol 0n-butanol proved to be inert
under the reaction conditions applied and was considered
prior to ethanol with regard to purityand detectibilityof the
expected products) and the evolving gases were passed into
CDCl3. When analyzed by NMR and MS spectroscopy the
formation of methanol could be shown while none of the
other products discussed in the literature 0formaldehyde,
formic acid, CO2) were found. With GC-MS a product
was detected the mass spectra of which {[m/z, 0%)]: 265
02, M1), 264 019, M), 218 0100), 138 043), 109 010), 59
020)} could give evidence for the existence of 6-butoxy-
2,2,4,7-tetramethylcoumaran-5-ol 09, Scheme 2). Further-
more, we recorded pH-values during the reaction course.
Immediatelyafter the addition of silver nitrate to the
ethanolic solution of 1 the pH-value drops below 2 and
stays at this level during the whole reaction. As the evolu-
tion of nitric gases was observed after some time it can be
anticipated that with traces of water 0the solvent was used
without drying) nitric acid is formed. The reaction of 1 with
Ag1-ions to the radical cation which can deliver a proton as
The action of a Mills±Nixon effect can be supported to the
point that a clear preference as to substitution in 6-position
is perceivable but the reaction does not take place in this
³
position exclusively. A problem still remaining is the role
of the NO32 without which the reaction does not proceed in
this way.
7
proposed bySuarna et al. could contribute as well to the
sudden decrease of the pH-value.
If we assume that the mechanism will not differ in principal
in the oxidation of the coumaran-5-ol and the chroman-6-ol
system our data raise some questions. The existence of
compounds 3±6 as well as the formation of the dimers
and trimers can hardlybe explained without anticipating
an intermediate o-quinone methide. On the other hand the
occurrence of methanol and of compounds 7 and 9 cannot be
coped with in this way. We would suggest the reaction to
proceed in the following way0Scheme 3). In the ®rst step
the two o-quinone methides 13 and 14 are formed. Theycan
o-Quinone 2 can undergo a varietyof further reactions. In
the presence of bases 2 is converted into the isomer 8. So 8 is
formed quantitativelywhen 2 is stirred in chloroform with
catalytic amounts of N-methylpiperidine while 2 remains
unchanged if stirred in ethanol.
³
A similar behaviour with less strict Mills±Nixon effects was observed for
reactions of 2-methyl-3-phenyl-4,6,7-trimethylcoumaran-5-ol and
2,5,7,8-tetramethylchroman-6-ol-2-carboxylic acid 0unpublished results,
in preparation).

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U. Schadel et al. / Tetrahedron 58 )2002) 5081±5086
5084
The reduction of 2 to the pyrocatechol 18 is fullyreversible
in air and 18 can be trapped with acetic anhydride to give
the diacetate 19 0Scheme 4). The reaction of 2 with
o-phenylenediamine in acetic acid gives the phenazine 20
in good yield. The cycloaddition of 2 with dimethyl
acetylenedicarboxylate forms the adduct 23.
The major bands listed in order of appearance could be
identi®ed, as the following products 0the substitution pattern
of all compounds was determined with 2D NMR spectro-
scopy0NOESY, COSY, HSQC, HMBC)).
3.1.2. 5-Hydroxy-2,2,4,7-tetramethylcoumaran-5-ol-6-
carbaldehyde +4). Rf-value 0.69; bright yellow needles
1
from n-pentane; yield 0.06 g 06%); mp 858C; H NMR
While 2 under basic conditions in most cases forms 8 as the
main product there are some exceptions. In the reaction of 2
with triethyl phosphite benzodioxaphosphole 21 is obtained
in 82% yield§ along with 8% of isomer 8 only. The 31P NMR
signal has quite a large up®eld shift 0248.6) which in other
cases was attributed to the in¯uence of the phosphole
ring.10,11 Reaction of 2 with tris0diethyl)aminophosphine
gives a 1:1 mixture of the diastereomers 24 and 25§ and
the isomer 8. Obviously, compounds 24 and 25 were not
formed from the o-quinone 2 directlybut via the isomer 8.
Reaction of 2 with malononitrile forms the benzofuran 22 in
rather poor yield.
0CDCl3, 500.13 MHz): dˆ1.45 0s, 6H), 2.09 0s, 3H), 2.37
0s, 3H), 2.94 0s, 2H), 10.16 0s, 1H), 12.12 0s, 1H); 13C NMR
0CDCl3, 125.8 MHz): dˆ10.0; 11.7; 28.3; 43.3; 85.5; 116.6;
116.8; 120.4; 137.9; 149.4; 156.9; 194.6; NOESY spectra:
strong cross coupling between aldehyde-H and H-7a
protons; UV 0methanol) lmax 390 nm; IR 0KBr) n 3430,
Ä
2959, 1638, 1455, 1265 cm21; Anal. calcd for C13H16O3:
C, 70.89; H, 7.32. Found C, 70.75; H, 7.28.
From the fraction containing compounds 4 and 6 0equal Rf-
values) the latter one precipitated after evaporating the
major part of the solvent, while the former one remained
in solution giving an oil after complete evaporation of the
solvent.
3. Experimental
3.1.3. 6-Ethoxymethyl-2,2,4,7-tetramethylcoumaran-5-
ol +6). Rf-value 0.51; light yellow solid from n-pentane/
3.1. General methods
1
ethyl acetate 3:1; yield 0.34 g 028%); mp 568C; H NMR
Melting points were received with a Ko¯er±Boetius
apparatus and are corrected. 1H NMR, 13C NMR, 31P
NMR, and 2D NMR spectra 0NOESY, COSY, HSQC,
HMBC) were recorded either on a Bruker AC-200P or on
a Bruker DRX-500 spectrometer. Spectra were taken in
CDCl3 and are reported in parts per million down®eld
from TMS as internal standard. IR spectra were determined
on a Nicolet 205 and UV spectra on a Varian cary3 spectro-
meter. Electron impact mass spectra were done at 70 eV on
a Hewlett±Packard 589/II spectrometer, for GC-MS a
Hewlett±Packard device 0GC: HP 5890/II, capillaryDB-5
MS, helium 00.75 mL min21), injection on column; MS: HP
5972, EI, 70 eV) was used. Elemental analysis was deter-
mined on a CHN-S analyser 0Carlo Erba). Analytical TLC
was performed using Merck prepared plates 0silica gel 60
F-254 on aluminium). Merck silica gel 063±200 mm) was
used for chromatography.
0CDCl3, 500.13 MHz): dˆ1.27 0t, 3H, Jˆ7.0 Hz), 1.44 0s,
6H), 2.08 0s, 3H), 2.09 0s, 3H), 2.91 0s, 2H), 3.60 0q, 2H,
Jˆ7.0 Hz), 4.70 0s, 2H), 7.63 0s, 1H); 13C NMR 0CDCl3,
125.8 MHz): dˆ11.3; 12.4; 15.1; 28.4; 42.8; 66.2; 68.2; 85.2;
113.6; 119.0; 119.3; 125.9; 148.2; 150.3; NOESY spectra:
cross coupling between H-6a and H-7a; Anal. calcd for
C15H22O3: C, 71.97; H, 8.86. Found C, 72.14; H, 8.90.
3.1.4. 4-Ethoxymethyl-2,2,6,7-tetramethylcoumaran-5-
ol +5). Rf-value 0.51; light brown oil; yield 0.10 g 08%);
1H NMR 0CDCl3, 500.13 MHz): dˆ1.27 0t, 3H,
Jˆ7.0 Hz), 1.44 0s, 6H), 2.08 0s, 3H), 2.13 0s, 3H), 2.88
0s, 2H), 3.59 0q, 2H, Jˆ6.9 Hz), 4.58 0s, 2H), 7.34 0s, 1H);
13C NMR 0CDCl3, 125.8 MHz): dˆ11.5; 12.2; 15.8; 28.4;
42.2; 66.2; 69.3; 85.1; 115.5; 118.5; 120.7; 123.2; 147.6;
150.5; NOESY spectra: cross coupling between H-3 and
H-4a; Anal. calcd for C15H22O3: C, 71.97; H, 8.86. Found
C, 72.14; H, 8.90.
3.1.1. Oxidation of 1. Compound 1 01.00 g, 4.85 mmol)
was heated in absolute ethanol 050 mL) to 708C and was
treated under stirring with carefullypulverized AgNO
3.1.5. 4,6-Diethoxymethyl-2,2,7-trimethylcoumaran-5-ol
+3). Rf-value 0.39; yellow-brown oil; yield 0.04 g 03%); H
3
1
03.8 g, 22.0 mmol). The reaction mixture was heated
under re¯ux for 20 min during which time the colour of
the solution changed to blood red, silver precipitated and
the evolution of nitric gases was observed. After cooling and
®ltering water 030 mL) was added to the ®ltrate and the
mixture was extracted with CH2Cl2 03£30 mL). The organic
layer was washed twice with little cold water and dried
0Na2SO4). After evaporation of the solvent there remained
a red oil from which 0.40 g 040%) 2,2,4,7-tetramethyl-
coumaran-5,6-dione 02) precipitated as purple needles.
Theywere ®ltrated and washed with little cold ether. The
washings were evaporated and together with the remaining
oil chromatographed on silica gel 0n-pentane/ethyl acetate
10:1).
NMR 0CDCl3, 300.13 MHz): dˆ1.23 0t, 6H, Jˆ7.1 Hz),
1.42 0s, 6H), 2.13 0s, 3H), 2.94 0s, 2H), 3.56 0q, 4H,
Jˆ7.1 Hz), 4.54 0s, 2H), 4.62 0s, 2H), 7.67 0s, 1H); 13C
NMR 0CDCl3, 75.5 MHz): dˆ11.6; 15.1; 15.2; 28.3; 42.4;
65.7; 65.8; 65.9; 67.2; 85.3; 117.6; 118.3; 121.3; 125.2;
148.6; 150.7; Anal. calcd for C17H26O4: C, 69.36; H, 8.90.
Found C, 69.62; H, 8.83.
3.1.6. 5-Hydroxy-2,2,4,7-tetramethyl-2H-benzofuran-6-
one +8). Rf-value 0.36; bright yellow needles from
n-pentane/ethyl acetate 5:1; yield 0.03 g 03%); mp 1228C;
1H NMR 0CDCl3, 500.13 MHz): dˆ1.47 0s, 6H), 1.86 0s,
3H), 2.00 0s, 3H), 6.81 0s, 1H), 7.32 0s, 1H); 13C NMR
0CDCl3, 125.8 MHz): dˆ7.4; 10.5; 25.4; 94.0; 104.0;
105.2; 131.4; 144.5; 146.8; 169.6; 181.5; NOESY spectra:
strong cross coupling between H-3 and H-2a protons, weak
§
Estimated byNMR, compounds are not stable to puri®cation and were
analyzed via 2D NMR only.

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U. Schadel et al. / Tetrahedron 58 )2002) 5081±5086
5085
cross coupling between H-3 and H-4a signals; UV 0metha-
nol) lmax 314, 385 nm; IR 0KBr) n 3420, 2930, 1610 cm21
Anal. calcd for C13H18O2: C, 69.88; H, 6.85. Found C,
70.06; H, 6.90.
2,2,4,7-tetramethylcoumaran-5,6-dione 02) were dissolved
in 30 mL of a 3:1 mixture of methanol and glacial acetic
acid. Then 0.20 g 03.00 mmol) malononitrile and ®nallyten
drops of diethyl amine were added. The reaction mixture
was stirred for two days at room temperature. Reaction was
quenched with 30 mL of water and extracted three times
with methylene chloride. The combined organic phases
were washed with water twice and dried 0Na2SO4). The
major part of the solvent was evaporated in vacuo and
the precipitating crystals were ®ltrated. After evaporation
of the ®ltrate a dark brown oil remained. It was chromato-
graphed on silica gel 0n-pentane/ethyl acetate 4:1). The ®rst
fraction contains unreacted malononitrile, from the second
fraction 26 crystallizes; colourless crystals; yield 0.07 g
022%); mp 2008C; 1H NMR 0CDCl3, 500.13 MHz):
dˆ1.46 0s, 6H), 2.18 0s, 3H), 2.37 0s, 3H), 2.94 0s, 2H),
5.03 0sbr, 2H); 13C NMR 0CDCl3, 125.8 MHz): dˆ8.3;
14.6; 28.4; 42.0; 64.9; 86.8; 101.0; 116.6; 117.0; 121.4;
;
Ä
3.1.7. 5-Acetyloxy-2,2,4,7-tetramethylcoumaran-6-yl ace-
tate +19). 0.10 g 00.48 mmol) 2,2,4,7-tetramethylcoumaran-
5,6-dione 02) were dissolved in 10 mL glacial acetic acid.
0.10 g zinc powder, 0.5 mL acetic anhydride and 0.02 g
pulverized, water free sodium acetate were added and the
mixture was warmed to 908C for 10 min. The reaction was
quenched with 10 mL water and extracted with 2£10 mL
diethyl ether. The combined organic layers were washed
0NaHCO3, H2O, NaCl) and dried 0Na2SO4). The product
was chromatographed on silica gel 0n-pentane/ethyl acetate
1
4:1); yield 0.12 g 084%); yellow oil; H NMR 0CDCl3,
300.13 MHz): dˆ1.39 0s, 6H), 1.89 0s, 3H),1.91 0s, 3H),
2.20 0s, 3H), 2.21 0s, 3H), 2.84 0s, 2H);); 13C NMR 0CDCl3,
75.5 MHz): dˆ9.4; 13.1; 20.2; 28.5; 42.2; 86.8; 110.9, 123.1;
124.5, 134.0; 140.6, 154.8, 168.4; 169.0; Anal. calcd for
C16H20O5: C, 65.73; H, 6.90. Found C, 65.58; H, 6.92.
122.4; 147.7; 153.7; 163.9; IR 0KBr) n 3340, 2980, 2310,
Ä
1650 cm21; GC-MS 070 eV): m/z, 0%) 257 017, 0M11)1),
256 0100), 241 09), 224 026), 214 015), 196 05), 128 07);
Anal. calcd for C15H16N2O2: C, 70.29; H, 6.29; N 10.93.
Found C, 69.92; H, 6.24; N 10.53.
3.1.8. 2,2,4,11-Tetramethyl-2,3-dihydrofuro[2,3-b]phen-
azine +20). 0.21 g 01.00 mmol) 2,2,4,7-tetramethyl-
coumaran-5,6-dione 02) and 0.22 g 02.00 mmol)
o-phenylendiamine were dissolved in 20 mL glacial acetic
acid and kept for 2 h at 908C. Then 20 mL water are added
and the mixture was extracted three times with 20 mL
diethyl ether. The etheric phases were washed 0NaHCO3,
H2O) and dried 0Na2SO4). The product was puri®ed on a
silica gel column 0n-pentane/ethyl acetate 2:1); bright
3.1.11.
2,2,4,9-Tetramethyl-2,3-dihydro-1,5,8-trioxa-
cyclopenta[b]naphthalene-6,7-dicarboxylic acid dimethyl-
ester +23). 0.30 g 01.50 mmol) 2,2,4,7-tetramethylcoumaran-
5,6-dione 02) were dissolved in 20 mL acetylendicarboxylic
acid dimethylester. The solution was stirred for three days at
room temperature. Excess ester was evaporated in vacuo and
the remaining yellowish oil was puri®ed on a silica gel
column 0n-pentane/ethyl acetate 4:1); yield 0.08 g 016%);
colourless crystals; mp 908C; 1H NMR 0CDCl3,
300.13 MHz): dˆ1.41 0s, 6H), 2.08 0s, 3H), 2.20 0s, 3H),
2.89 0s, 2H), 3.75 0s, 3H), 3.79 0s, 3H); 13C NMR 0CDCl3,
75.5 MHz): dˆ12.3; 17.1; 28.4; 42.5; 52.0; 52.2; 87.4; 115.8;
122.7; 128.0; 132.5; 134.4; 159.0; 168.4; 169.1; GC-MS
070 eV): m/z, 0%) 293 [9, 0M11)122 CvO%], 292 049),
261 0100), 245 092), 202 059), 174 022); Anal. calcd for
C18H20O7: C, 62.06; H, 5.79. Found C, 62.18; H, 5.82.
1
yellow crystals; yield 0.25 g 089%); mp 128±1308C; H
NMR 0CDCl3, 300.13 MHz): dˆ1.53 0s, 6H), 2.58 0s,
3H), 2.67 0s, 3H), 3.15 0s, 2H), 7.65 0m, 2H), 8.13 0dd,
2H, Jˆ7.6, 2.4 Hz); 13C NMR 0CDCl3, 75.5 MHz):
dˆ9.6; 14.0; 28.5; 42.5; 87.3; 127.9; 129.6; 129.0; 129.2;
130.2; 135.0; 140.0; Anal. calcd for C18H18N2O: C, 77.66;
H, 6.52; N 10.06. Found C, 77.42; H, 6.59; N 9.66.
3.1.9. 2,2,2-Triethoxy-4,6,6,8-tetramethyl-6,7-dihydro-
2l5-furo[2,3-f][1,3,2]benzodioxaphosphole +21). In an
argon atmosphere 0.17 g 01.00 mmol) freshlydistilled
triethylphosphite were added to a solution of 0.21 g
01 mmol) 2,2,4,7-tetramethylcoumaran-5,6-dione 02) in
20 mL dryTHF. The mixture was stirred for 4 h at room
temperature. During this time its original red colour changes
to light brown. The solvent was evaporated in vacuo and the
resulting brown oil was immediatelyexamined on a NMR
device. It contains 2,2,2-triethoxy-4,6,6,8-tetramethyl-6,7-
3.1.12. cis-N2,N2,N7,N7-Tetraethyl-4,6,6,8-tetramethyl-
6,7-dihydrofuro[2,3-f][1,3,2]-benzodioxaphosphol-2,7-
diamine +24). Synthesis from 0.21 g 01.00 mmol) 2,2,4,7-
tetramethylcoumaran-5,6-dione 02) and 0.25 g 01.00 mmol)
tris0diethylamino)phosphane as described above for 21.
After evaporation of the solvent the resulting oil was
immediatelyexamined on a NMR device. It contains cis-
N2,N2,N7,N7-tetraethyl-4,6,6,8-tetramethyl-6,7-dihydrofuro-
[2,3-f][1,3,2]benzodioxaphosphol-2,7-diamine 024, yield
35%), trans-N2,N2,N7,N7-tetraethyl-4,6,6,8-tetramethyl-6,7-
dihydrofuro[2,3-f][1,3,2]benzodioxaphosphol-2,7-diamine
025, yield 35%) and 5-hydroxy-2,2,4,7-tetramethyl-2H-
benzo-furan-6-on 08, yield 25%); 1H NMR 0CDCl3,
500.13 MHz): dˆ0.87 0m, 6H), 1.03 0t, 6H, Jˆ7.1 Hz),
1.30 0s, 3H), 1.32 0s, 3H), 1.96 0s, 3H), 2.09 0s, 3H), 2.71
0m, 4H), 2.82 0m, 4H), 3.73 0s, 1H); 13C NMR 0CDCl3,
125.8 MHz): dkˆ8.5; 12.4; 13.7; 15.0; 23.0; 28.1; 38.8;
47.6; 70.1k 0d) ; 88.9; 101.6; 115.5; 118.2; 138.1 0d)k;
144.5 0d) ; 151.4; 31P NMR 0CDCl3, 121.5 MHz):
dˆ149.3 0qui, JPHˆ7.9 Hz).
dihydro-2l5-furo[2,3-f][1,3,2]benzodioxaphosphole
021,
yield 82%) and 5-hydroxy-2,2,4,7-tetramethyl-2H-benzo-
furan-6-one 08, yield 8%); 1H NMR 0CDCl3,
4
500.13 MHz): dˆ1.21 0dt, 9H, Jˆ7.0 Hz, JPHˆ1.6 Hz),
1.40 0s, 6H), 2.06 0s, 3H), 2.08 0s, 3H), 2.82 0s, 2H), 3.98
3
0dq, 6H, Jˆ5.8 Hz, JPCˆ9.7 Hz); 13C NMR 0CDCl3,
3
125.8 MHz): dˆ8.6; 12.0; 15.9 0d, JPCˆ8.0 Hz); 28.2;
2
3
41.9; 63.5 0d, JP3Cˆ10.9 Hz); 85.3; 100.2 0d, JPCˆ
2
14.5 Hz); 113.2 0d, JPCˆ14.7 Hz); 114.5; 134.5 0d, JPCˆ
3.8 Hz); 141.9 0d, JPCˆ4.4 Hz); 150.8; 31P NMR 0CDCl3,
2
121.5 MHz): d 248.6.
3.1.10. 2-Amino-4,6,6,8-tetramethyl-5,6-dihydrobenzo-
[1,2-b;4,5-b0]difurano-3-nitrile +22). 0.25 g 01.21 mmol)
k
Overlapping signals, JPC not determined.

È
U. Schadel et al. / Tetrahedron 58 )2002) 5081±5086
5086
trans-N2,N2,N7,N7-Tetraethyl-4,6,6,8-tetra-
methyl-6,7-dihydrofuro[2,3-f][1,3,2]-benzodioxaphos-
3. Dean, F. M.; Orabi, M. O. A. J. Chem. Soc. Perkin Trans. 1
1982, 2617±2624.
3.1.13.
1
phol-2,7-diamine +25). H NMR 0CDCl3, 500.13 MHz):
Ê
4. Lars, J.; Nilsson, G.; Selander, H.; Sievertsson, H.; Skanberg,
I. Tetrahedron 1970, 26, 879±886.
dˆ0.87 0m, 6H), 1.03 0t, 6H, Jˆ7.1 Hz), 1.29 0s, 3H),
1.31 0s, 3H), 1.95 0s, 3H), 2.07 0s, 3H), 2.71 0m, 4H), 2.82
0m, 4H), 3.74 0s, 1H); 13C NMR 0CDCl3, 125.8 MHz):
dˆ8.5; 12.2; 13.7; 15.0; 22.9; 27.9; 38.3k; 47.6; 70.2; 89.0;
101.6; 115.3; 117.7; 138.0 0d)k; 144.5 0d) ; 151.4; 31P NMR
0CDCl3, 121.5 MHz): dˆ150.9 0qui, JPHˆ7.9 Hz).
5. Lars, J.; Nilsson, G.; Doyle Daves Jr, G.; Folkers, K. Acta
Chem. Scand. 1968, 22, 207±218.
6. Kohar, I.; Suarna, C.; Southwell-Keely, P. T. Lipids 1993, 28,
1015±1020.
7. Suarna, C.; Barca, M.; Craig, D. C.; Scudder, M.; Southwell-
Keely, P. T. Lipids 1991, 26, 847±852.
8. Rosenau, T.; Gruner, M.; Habicher, W. D. Tetrahedron 1997,
53, 3571±3576.
Acknowledgements
9. Smith et al. give the wrong formula for the oxidation of
2,4,6,7-tetramethylcoumaran-5-ol, that is 2,6,7-trimethyl-
coumaran-4,5-dione instead of 2,4,7-trimethylcoumaran-5,6-
dione; Smith, L. I.; Hoehn, H. H.; Whitney, A. G. J. Am.
Chem. Soc. 1940, 62, 1863.
The authors are indebted to Mrs Pinske for running the
elemental analyses and to Dr H. Kroschwitz for carrying
È
out the MS spectra. A grant of the Sachsisches Staats-
ministerium fuÈr Wissenschaft und Kunst to one of us
0U. S.) is greatfullyacknowledged.
10. Holmes, R. R.; Prakasha, T. K. Phosphorus Sulfur Silicon
Relat. Elem. 1993, 80, 1±22.
11. Holmes, R. R. Pentacoordinated PhosphorusÐStructure and
Spectroscopy; ACS Monograph 175, Vol. 1; American
Chemical Society: Washington, DC, 1980.
References
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1. Schadel, U.; Habicher, W. D. Synthesis 1998, 293±296.
2. Barclay, L. R. C.; Vinqvist, M. R.; Mukai, K.; Itoh, S.;
Morimoto, H. J. Org. Chem. 1993, 58, 7416±7420.