Isolation, reactivity and intramolecular trapping of phosphazide intermediates in the Staudinger reaction of tertiary phosphines with azides

Article abstract of DOI:10.1016/S0040-4020(00)00322-7

The Staudinger reaction of the N-substituted o-azidobenzamide 1 with triphenylphosphine or diphenylmethylphosphine allows the isolation of the intermediate phosphazides as crystalline solids, which have been characterized by spectroscopic methods. These compounds react in aza Wittig type fashion with isocyanates to give unexpectedly the corresponding 1,2,3- benzotriazinone derivative. Trapping of a Z-phosphazide by intramolecular aza Wittig reaction is reported for the first time. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4020(00)00322-7

TETRAHEDRON
Pergamon
Tetrahedron 56 (2000) 4079±4084
Isolation, Reactivity and Intramolecular Trapping of Phosphazide
Intermediates in the Staudinger Reaction of Tertiary Phosphines
with Azides
*
M. Desamparados Velasco, Pedro Molina, Pilar M. Fresneda and Miguel A. Sanz
  Â
Departamento de Quõmica Organica, Facultad de Quõmica, Universidad de Murcia, Campus de Espinardo, E-30071 Murcia, Spain
Received 3 February 2000; revised 28 March 2000; accepted 13 April 2000
AbstractÐThe Staudinger reaction of the N-substituted o-azidobenzamide 1 with triphenylphosphine or diphenylmethylphosphine allows
the isolation of the intermediate phosphazides as crystalline solids, which have been characterized by spectroscopic methods. These
compounds react in aza Wittig type fashion with isocyanates to give unexpectedly the corresponding 1,2,3-benzotriazinone derivative.
Trapping of a Z-phosphazide by intramolecular aza Wittig reaction is reported for the ®rst time. q 2000 Elsevier Science Ltd. All rights
reserved.
The reaction of a tertiary phosphine with an organic azide to
produce an iminophosphorane after nitrogen evolution is
known as the Staudinger reaction, which has proved to be
a very useful reaction in synthetic organic chemistry.1 The
primary imination products, phosphazides (triazeno-
phosphoranes or triazaphosphadienes), are sometimes
isolable and stable,2,3 but as a rule they lose nitrogen at
room temperature or even at lower temperature to give the
corresponding iminophosphorane compound in practically
quantitative yields. The only six isolated phosphazides have
been formed from sterically hindered components or the
electronic effects of substituents have been such as to
increase the electron density on the phosphorus atom or
decrease it on the N-a atom of the azide.4±7 The E-geometry
observed in the isolable phosphazides probably accounts for
their stability by making more dif®cult ring-closure to the
four-membered transition state necessary for nitrogen
elimination and iminophosphorane formation.
In spite of the important role of iminophosphoranes in
heterocyclic synthesis,8±10 the chemistry of their elusive
precursors phosphazides has been poorly studied, primarily
due to their rapid conversion to iminophosphoranes.
In this context, we have reported the ®rst trapping of phos-
phazides,11,12 from the reaction of o-azidobenzaldimines
with triphenylphosphine to give iminophosphoranes derived
from 2-aminoindazoles. This conversion involves formation
and further electrocyclization of the intermediate phos-
phazide across the central nitrogen atom. Similar behaviour
has also been observed with aryl azides bearing an unsatu-
rated functionality at the ortho-position: o-azidobenzalde-
hyde,13,14 diethyl(o-azidobenzyliden malonate and 2-(o-
azidophenyl) nitroethylene.15 Phosphazides derived from
aryl azides and triphenylphosphine have also been trapped
through formation of transition metal (Pd, V or W)
complexes16±18 (Scheme 1).
Scheme 1.
Keywords: Staudinger reaction; azides; phosphines; aza Wittig reaction.
* Corresponding author. Tel.: 134-968-30-71-00; fax: 134-968-36-41-49; e-mail: pmolina@fcu.um.es
0040±4020/00/$ - see front matter q 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(00)00322-7

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M. D. Velasco et al. / Tetrahedron 56 (2000) 4079±4084
We wish to report here the isolation of a new type of
phosphazide and its chemical behaviour in aza Wittig type
reactions.
which the phosphorus atom has partial phosphonium char-
acter and the negative charge is on the nitrogen atom linked
to the aromatic ring. Probably this fact allows a very strong
intramolecular hydrogen bonding between this nitrogen
atom and the amide proton (evidenced in the IR spectrum
by a strong absorption band in the region 3500±2900 cm21),
which prevents the E!Z isomerization necessary for the
nitrogen elimination. It has been reported21 that the stability
of a phosphazide molecule is determined by electronic (a
conjugative delocalization of the cationic charge on phos-
phorus) and steric factors (screening of the phosphorus atom
by bulky substituents). Stabilization of phosphazide 2 by
intramolecular hydrogen bonding is closely related to
those found in some N-aryl, heteroaryl iminophosphoranes
bearing an amide group at the ortho-position, which even
inhibits the aza Wittig reaction, due to conformational
restriction and lowered nucleophilicity of the imino nitrogen
atom.22,23 The unusual stability of 2 gave us the opportunity
to gain more of an insight into the reactivity of phos-
phazides, especially in aza Wittig-type reactions. Note
that so far the chemical reactivity of phosphazides remains
almost unexplored and only the regio- and stereo-speci®c
N-alkylation with retention of the nitrogen triad has been
reported.24
Results
Azide 1, readily available in 72% yield from the reaction of
4-methylbenzamide with o-azidobenzoyl chloride19 in the
presence of sodium hydride, reacted with triphenyl-
phosphine in dry dichloromethane at 08C to give the phos-
phazide 2 as a crystalline solid in 88% yield. Compound 2
can be stored for several weeks without any signs of decom-
position. The ®rst indication of the phosphazide nature was
provided by its 13C NMR spectrum in which coupling
between the phosphorus atom and the aromatic carbon
atoms of the o-azidobenzamide residue was not observed
as occurs in typical N-aryliminophosphoranes. In addition,
the 31P NMR spectrum displayed only one signal at
25.5 ppm which is in good agreement with previously
reported values for this type of compound,20 and in the
MS spectrum in FAB1 mode appeared a fragment at m/z
543 corresponding to the M111. Unfortunately, we were
not able to obtain suitable crystals for X-ray diffraction
studies.
When compound 2 was heated in toluene at re¯ux tempera-
ture the 4(3H)-quinazolinone 4 was isolated in 73% yield
along with triphenylphosphine oxide. This conversion takes
The stability showed by the phosphazide 2 could be due to
the essential zwitterionic character of phosphazides,1,2 in
Scheme 2.

M. D. Velasco et al. / Tetrahedron 56 (2000) 4079±4084
4081
Scheme 3.
place by nitrogen elimination of the phosphazide 2 to give
the iminophosphorane 3, which under the reaction condi-
tions undergoes an intramolecular aza Wittig reaction
involving the carbonyl group of the amide functionality to
give 4.
dichloromethane at room temperature, led to the formation
of 6 and 7 in almost the same yields.
Azide 1 also reacted with the more reactive diphenylmethyl-
phosphine under the same conditions to give a mixture of 4
in 33% yield and the new phosphazide 8 in 42% yield
(Scheme 3). We have also found that the ratio 4:8 strongly
depends on the reaction time. Short reaction times improve
the yield of 8 although starting material remains unchanged,
and longer period of times increase the yield of 4. These
results suggest that the formation of compound 4 arises from
8 by nitrogen elimination and subsequent intramolecular aza
Wittig reaction of the resulting very reactive diphenyl-
methyliminophosphorane. This assumption was con®rmed
by isolation of 4 in almost quantitative yield after stirring a
solution of 8 in dichloromethane at 08C for 24 h. As the
formation of 4 from 2 requires heating in toluene whereas
the conversion of 8 into 2 takes place under extremely mild
reaction conditions, we conclude that the factors which
determine the stability of this kind of phosphazides are
not only hydrogen-bonding interactions but also steric
factors which impose conformational restrictions to the
nitrogen evolution (E-con®guration). Spectroscopic data
of compound 8 are in good agreement with the proposed
structure and are quite similar to those observed for phos-
phazide 2. The 1H and 13C NMR were quite similar to those
observed for phosphazide 2. The 31P NMR spectrum
displayed a signal at d 29.13 ppm and the MS (FAB1)
showed a fragment at m/z 481 ppm. The chemical behaviour
of the phosphazide 8 in aza Wittig reactions towards aryl-
isocyanates is similar to that observed for compound 2 to
give the benzotriazinone 6 (42±49%), the corresponding
This conversion deserves some comments. First, the high
reactivity of the iminophosphorane 3 with respect to the
related iminophosphoranes A, which undergo intramolecu-
lar aza Wittig reaction across the more reactive carbonyl
group of the ester functionality under harsher reaction
conditions22 (6 h, 1108C versus 16±84 h, 1408C). Second,
and perhaps more importantly, these conversions support
the proposed structure of the phosphazide 2 and rule out
the cyclic structure B, originated from 2 by an intramolecu-
lar nucleophilic attack of the NH amide group on the central
nitrogen atom of the phosphazide moiety.
Reaction of phosphazide 2 with 1 equiv. of aryl isocyanate
(phenyl, p-methyl or p-metoxyphenyl) in dichloromethane
at room temperature for 7 h gave directly the 1,2,3-benzo-
triazine-4-one 6 in yields ranging from 51 to 75%, the corre-
sponding arylcyanoamide 7 and triphenylphosphine oxide.
However, when the less reactive aryl isothiocyanate were
used instead of arylisocyanate the starting phosphazide 2
together with a small amount of 4 (15%) were isolated.
The structure of these compounds have been con®rmed by
their spectroscopic data and mass spectrometry (Scheme 2).
cyanoamide
(Scheme 3).
7
and diphenylmethylphosphine oxide
Formation of the 1,2,3-benzotriazine-4-one 6 from the
reaction of phosphazides 2 or 8 with aryl isocyanates
could be understood by an initial aza Wittig reaction across
the nitrogen atom directly linked to the phosphorus atom to
give the aza Wittig adduct 5 and the corresponding
phosphine oxide. The very reactive intermediates 5 undergo
intramolecular nucleophilic attack of the amido group
on the central nitrogen atom of the remaining azide frame-
work followed by a retro-ene reaction with concomitant
Similar results, which also con®rm the open-chain structure
of 2, were obtained when the triazaphosphadiene adduct
pathway20 was used to study the behaviour of the N-(p-
methylbenzoyl)-o-azidobenzamide 1 in aza Wittig reactions
towards aryl isocyanates. In this way, the reaction is carried
out with the isocyanate present before addition of the tri-
phenylphosphine. Addition of a solution of triphenyl-
phosphine to a mixture of 2 and an arylisocyanate in

4082
M. D. Velasco et al. / Tetrahedron 56 (2000) 4079±4084
reactive intermediate takes place by a different way to
give products containing two nitrogen atoms which origi-
nate from the starting azide. Secondly, for the ®rst time a
phosphazide has been trapped with an unusual Z-con®gura-
tion by an intramolecular aza Wittig reaction giving rise to a
product which retains the three nitrogen atoms of the start-
ing azide.
Experimental
General methods
All melting points were determined on a Ko¯er hot-plate
melting point apparatus and are uncorrected. IR spectra
were obtained as Nujol emulsions or ®lms on a Nicolet
Impact 400 spectrophotometer. NMR spectra were recorded
on a Bruker AC200 (200 MHz) or a Varian Unity 300
(300 MHz). Mass spectra were recorded on a Hewlett±
Packard 5993C spectrometer or a Fisons AUTOSPEC 500
VG. Microanalyses were performed on a Perkin±Elmer
240C instrument.
Scheme 4.
elimination of the corresponding arylcyanoamide 7 to give 4
(Scheme 2).
It is worth noting that we have previously described25
similar type of carbodiimide fragmentation by a retro-ene
reaction to give arylcyanoamides, although under stronger
reaction conditions (toluene, 1408C, sealed tube, 36 h).
a
N-(4-Methylbenzoyl)-o-azidobenzamide 1. To a well-
stirred suspension of sodium hydride (2.87 g, 120 mmol)
in anhydrous dioxane (45 mL) was added under nitrogen
in portions 4-methylbenzamide (1.62 g, 12 mmol) at such
rate that the temperature remained below 108C. Then a solu-
tion of o-azidobenzoylchloride (2.17 g, 12 mmol) in the
same solvent (10 mL) was added dropwise. The resulting
reaction mixture was stirred at room temperature for 7 h.
After cooling, the solvent was removed under reduced pres-
sure and the residue was poured into a cooled 5% HCl
solution (150 mL) and then extracted with dichloromethane
(3£100 mL). The combined organic layers were washed
with brine (3£75 mL) and then dried over anhydrous
MgSO4. Filtration and elimination of the solvent gave a
crude product which was chromatographed on a silica gel
column with ethyl acetate/hexane (1:1) as eluent to give 1
(2.96 g, 88%); mp. 104±1068C (colourless prisms). 1H
NMR (200 MHz, CDCl3): dˆ2.43 (s, 3H, CH3±Ar),
7.23±7.33 (m, 4H), 7.59 (td, 1H, Jˆ7.8, 1.5 Hz), 7.84 (d,
2H, Jˆ8.2 Hz), 8.57(dd, 1H, Jˆ7.8, 1.5 Hz), 10.54 (bs, 1H,
NH). 13C NMR (50 MHz, CDCl3): dˆ21.6 (CH3), 118.4,
124.5 (q), 125.6, 129.4, 129.6, 130.6 (q), 132.9, 133.7,
137.1 (q), 143.9 (q), 163.1 (CvO), 165.1 (CvO). IR
(Nujol) nˆ3289 (m), 2142 (s), 1730 (vs), 1498 (s), 757
(m) cm21. MS: m/z (%) (EI positive): 280 (M1, 5), 252
(5), 119 (100), 91 (47). Anal. Calcd for C15H12N4O2: C,
64.28; H, 4.32; N, 19.99. Found: C, 63.98; H, 4.34; N, 20.11.
On the other hand, we have found that the reaction of
N-methoxymethyl-3-acetyl-2-azidoindole 9 with triphenyl-
phosphine in ether at 08C led to the expected imino-
phosphorane 10 in 90%. However, when tri-n-butyl-
phosphine was used instead of triphenylphosphine under
the same reaction conditions the triazino[4,5-b] indole deriva-
tive 12 was isolated in 78% yield as the sole reaction product
(Scheme 4).
The different behaviour of the azido compound 9 towards
triphenyl- and tri-n-butylphosphine could be due not only to
electronic effects but also to steric effects. In the proposed
intermediate Z-phosphazide 11 the adequate geometrical
disposition of the substituent on the phosphazide frame-
work, being the highly reactive tri-n-butylphosphinimino
group loosely connected to the carbonyl group, allows the
intramolecular aza Wittig reaction to give 12 to be faster
than the nitrogen elimination. For the case of the phos-
phazide derived from triphenylphosphine the more
sterically hindered triphenylphosphonium group prevents
such a geometrical disposition and nitrogen elimination
through the E-con®guration is the only reaction pathway.
General procedure for the preparation of phosphazides
2 and 8
Conclusion
These results clearly demonstrate that the chemistry of
phosphazides is not only restricted to nitrogen evolution,
giving the corresponding iminophosphoranes but also they
are able to undergo aza Wittig reaction. In this context, two
unprecedented aspects have surfaced from this work. First,
the aza Wittig adduct resulting from the reaction of tertiary
phosphines with azides and aza Wittig reagents do not
always lose nitrogen to give the expected aza Wittig
products, in some cases decomposition of this kind of
To a solution of N-(4-methylbenzoyl)-o-azidobenzamide 1
(0.62 g, 2.3 mmol) in dry dichloromethane (8 mL) was
added dropwise a solution of the appropriate phosphine
(2.3 mmol) in the same solvent (8 mL) at 08C under nitro-
gen. The solution was stirred at room temperature for 7 h.
For 2. The solvent was removed under reduced pressure
at room temperature and solid residue was slurried
with diethyl ether and ®ltered to give 2 (1.10 g, 88%) mp

M. D. Velasco et al. / Tetrahedron 56 (2000) 4079±4084
4083
1
156±1588C (evolution of N2) (yellow needles). H NMR
(200 MHz, CDCl3): dˆ2.33 (s, 3H, CH3), 7.13 (d, 2H,
Jˆ8.1 Hz), 7.23±7.37 (m, 4H), 7.53±7.81 (m, 15H), 8.42
(d, 2H, Jˆ8.1 Hz), 13.98 (bs, 1H, NH). 13C NMR (50 MHz,
CDCl3): dˆ21.5 (CH3), 116.5, 125.4 (q), 125.9, 126.1 (d,
1JP,Cˆ95.3 Hz, Ci), 128.9, 129.1, 129.2 (d, 3JP,Cˆ11.6, Cm),
131.4 (q), 132.0, 132.7, 133.2, (d, 4JP,Cˆ2.5 Hz, Cp), 133.5,
165.7 (CvO). 31P NMR (200 MHz, CDCl3): dˆ25.5. IR
(Nujol) n: 3500±2900 (m), 1724 (s), 1506 (s), 1468 (m),
1440 (m), 1262 (m), 1224 (m), 1160 (s), 1120 (m), 1104 (m)
cm21. MS: m/z (%) (FAB positive, NBA) 543 (M1H)1
(35), 278 (46), 236 (22), 119 (100), 90 (18). Anal. Calcd
for C33H27N4O2P: C, 73.05; H, 5.02; N, 10.33. Found: C,
72.74; H, 5.27: N, 10.19.
ture for 24 h. The precipitated solid formed was separated
by ®ltration, air-dried and identi®ed as 4 (0.11 g, 95%).
Reaction of phosphazides 2 and 8 with aryl isocyanates
To a solution of the phosphazide 2 or 8 (1 mmol) in dry
dichloromethane (10 mL) was added a solution of the corre-
sponding aryl isocyanate (1 mmol) in the same solvent
(5 mL). The mixture was stirred at room temperature
under nitrogen for 7 h. The solvent was removed under
reduced pressure at room temperature. The crude product
was chromatographed on a silica gel column with ethyl
acetate/hexane (2:1) as eluent to give 6 (0.13±0.20 g, 51±
75%) mp 157±1608C (colourless prisms). 1H NMR
(200 MHz, CDCl3) d: 2.45 (s, 3H, CH3), 7.31 (d, 2H,
Jˆ8.1 Hz), 7.79±7.91 (m, 3H), 8.04 (t, 1H, Jˆ8.0 Hz),
8.25 (d, 1H, Jˆ8.0 Hz), 8.40 (d, 1H, Jˆ8.0 Hz). 13C NMR
(50 MHz, CDCl3) d: 21.9 (CH3), 120.4 (C-4a), 125.6, 128.7
(C-10), 129.0, 129.7, 131.2, 133.3, 135.8, 143.4 (C-40),
146.4 (C-8a), 155.0 (C-4), 169.3 (CvO). MS: m/z (%)
(FAB positive, NBA) 266 (M1H)1 (65). IR (Nujol) n:
1730 (vs), 1703 (vs), 1607 (s) cm21. Anal. Calcd for
C15H11N3O2: C, 67.92; H, 4.18; N, 15.84. Found: C,
67.46; H, 4.29; N, 15.62. and 7 (Arˆ4-H3C±C6H4; IR
(:3304 (s), 2236 (s) cm21 MS: m/z (%) (EI positive) 132
(M1, 100), 106 (25), 105 (68), 91 (54).
2
(d, JP,Cˆ9.1 Hz, Co), 142.5 (q), 150.1 (q), 164.9 (CvO),
For 8. The precipitated solid formed was separated by ®ltra-
tion, washed with diethylether and identi®ed as 4 (33%).
The ®ltrate was concentrated to dryness under reduced pres-
sure at room temperature. The crude solid was slurried with
dry diethylether to give 8 (0.46 g, 42%) mp 162±1648C
1
(evolution of N2) (yellow needles) H NMR (200 MHz,
CDCl3) d: 2.33 (s, 3H, CH3), 2.45 (s, 3H, CH3±P), 7.13
(d, 2H, Jˆ8.1 Hz), 7.25±7.43 (m, 4H), 7.55±7.84 (m,
10H), 8.39 (d, 2H, Jˆ8.1 Hz), 13.48 (bs, 1H, NH). 13C
1
NMR (50 MHz, CDCl3) d: 12.1 (CH3±P, JP,Cˆ64.57),
21.5 (CH3), 116.5, 125.4 (q), 125.9, 127.1 (d,
3
1JP,Cˆ94.5 Hz, Ci), 128.9, 129.0, 129.3 (d, JP,Cˆ12.1,
N-Methoxymethyl-2-acetyl-3-(triphenylphosphoranyl-
idene)aminoindole 10. To a cooled 08C solution of tri-
phenylphosphine (0.53 g, 2.04 mmol) in dry diethyl ether
(10 mL), a solution of N-methoxymethyl-3-acetyl-2-azido
indole 926 (0.5 g, 2.04 mmol) in the same solvent (10 mL)
was added dropwise under nitrogen. The mixture was
allowed to warm to room temperature and stirred for 12 h.
After cooling, the precipitated solid was collected by ®ltra-
tion and recrystallized from benzene±n-hexane to give 10
(0.88 g, 90%) mp 152±1538C (colourless prisms). 1H NMR
(200 MHz, CDCl3) d: 2.15 (s, 3H, CH3CO), 3.24 (s, 3H,
CH3O), 5.62 (s, 2H, CH2O), 7.0±7.15 (m, 2H, H-51H-6),
7.20±7.33 (m, 1H, H-7), 7.34±7.48 (m, 9H, Hm1Hp),
7.49±7.57 (m, 1H, H-4), 7.58±7.72 (m, 6H, Ho). 13C
NMR (50 MHz, CDCl3) d:30.0 (CH3CO), 55.8 (CH3O),
71.7 (CH2O), 100.9 (C-3), 108.7 (C-7), 118.4 (C-4), 120.0
(C-6), 121.2 (C-5), 127.2 (C-3a), 128.1 (3JP,Cˆ12.8 Hz,
Cm), 131.0 (4JP,Cˆ2.9 Hz, Cp), 132 (2JP,Cˆ9.9 Hz, Co),
133.3 (1JP,Cˆ108.4 Hz, Ci), 133.9 (JP,Cˆ1.24 Hz, C-7a),
154.0 (JP,Cˆ10.9 Hz, C-2), 189.3 (CvO). 31P NMR
(CDCl3) d 11.74. IR (Nujol) n: 1619 (vs) cm21. MS: m/z
(%) (EI positive) 480 (M112, 6), 479 (M111, 32), 478
(M1, 100). Anal. Calcd for C30H27N2O2P: C, 75.30; H,
5.69; N, 5.85. Found: C, 75.18; H, 5.78; N, 5.69.
2
Cm), 131.4 (q), 131.9 (d, JP,Cˆ9.2 Hz, Co), 132.0, 132.6,
4
133.3 (d, JP,Cˆ2.3 Hz, Cp), 142.6 (q), 150.0 (q), 164.9
(CvO), 165.7 (CvO). 31P NMR (200 MHz, CDCl3):
dˆ29.13. IR (Nujol) n: 3500±2900 (m), 1724 (s), 1500
(s), 1467 (m), 1439 (m), 1265 (m), 1221 (m), 1162 (s),
1115 (m), 1098 (m) cm21. MS: m/z (%) (FAB positive,
NBA) 481 (M1H)1 (23), 303 (61), 275 (12), 237 (40),
200 (100), 119 (33), 90 (18). Anal. Calcd for
C28H25N4O2P: C, 69.99; H, 5.24; N, 11.66. Found:
C,69.71; H, 5.22 N, 11.50.
2-(4-Methylphenyl)-3H-quinazoline-4-one 4 from phos-
phazides 2 and 8
Procedure A. A solution of phosphazide 2 (0.3 g,
0.55 mmol) in dry toluene (10 mL) was treated at re¯ux
temperature for 6 h. After cooling the solvent was removed
under reduced pressure and the residue was chromato-
graphed on a silica gel column with ethyl acetate/hexane
(1:1) to give 4 (0.09 g, 73%) mp 240±2428C (colourless
prisms). 1H NMR (200 MHz, CDCl3) d: 2.46 (s, 3H,
CH3), 7.38 (d, 2H, Jˆ7.8 Hz), 7.94 (ddd, 1H, Jˆ8.1, 6.3,
2.1 Hz), 7.79±7.81 (m, 2H), 8.16 (d, 2H, Jˆ7.8 Hz), 8.33 (d,
1H, Jˆ7.5 Hz), 11.67 (bs, 1H, NH). 13C NMR (50 MHz,
CDCl3) d: 21.5 (CH3), 120.8 (q, C-4a), 126.4 (C-8), 126.5
(C-6), 127.3, 27.9 (C-5), 129.7, 130.0 (q), 134.7 (C-7),
142.1 (q), 149.7(q, C-8a), 151.7 (q, C-2), 163.8 (CvO).
MS: m/z (%) (EI positive) 236 (M1, 21), 119 (100). IR
(Nujol) n: 3178 (m), 1667 (vs), 1660 (s), 1599 (s), 1562
(m), 1343 (m), 771 (m) cm21. Anal. Calcd for C15H12N2O:
C, 76.25; H, 5.12; N, 11.86. Found: C, 75.97; H, 5.27: N,
12.07.
4-Methyl-9-methoxymethyl-triazino[4,5-b]indole 12. To
a cooled solution of compound 9 (0.3 g, 1.2 mmol) in dry
diethyl ether (10 mL) a solution of tri-n-butylphosphine
(0.33 mL, 0.27 g, 1.34 mmol) in the same solvent (5 mL)
was added dropwise under nitrogen. The mixture was
allowed to warm to room temperature and stirred for 5 h.
The solution was concentrated to dryness under reduced
pressure and the residue was chromatographed on a silica
gel column with diethyl ether/hexane as eluent to give 12
(0.20 g, 73%) mp 128±1308C (colourless prisms). 1H NMR
(200 MHz, CDCl3) d: 3.16 (s, 3H, CH3), 3.37 (s, 3H,
Procedure B. A solution of phosphazide 8 (0.24 g,
0.5 mmol) in dry diethyl ether was stirred at room tempera-

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M. D. Velasco et al. / Tetrahedron 56 (2000) 4079±4084
È
10. Wamhoff, H.; Richardt, G.; Stolben, S. Adv. Heterocycl.
CH3O), 6.05 (s, 2H, CH2O), 7.50±7.58 (ddd, 1H, Jˆ8.65,
1.5 Hz), 7.72±7.84 (m, 2H), 8.21 (d, 1H, Jˆ7.8 Hz). 13C
NMR (50 MHz, CDCl3)d: 20.5 (CH3), 56.9 (CH3O), 43.0
(CH2O), 109,3 (q), 111.7, 118.0,(q), 123.2, 124.5, 130.6,
139.4 (q), 150.7 (q), 152.7 (q). IR (Nujol) n: 1619 (s),
1587 (s), 1095 (vs), cm21. MS: m/z (%) (EI positive) 228
(M1, 22), 200 (M1-28, 5), 185 (15), 169 (56), 129 (100).
Anal. Calcd for C12H12N4O: C, 63.15; H, 5.30; N, 24.55.
Found: C, 62.91; H, 5.42; N, 24.36.
Chem. 1995, 64, 159±249.
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We gratefully acknowledge the ®nancial support of the
Â
Direccion General de Investigacion Cientõ®ca y Tecnica
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