Activation of carboxylic acids as their active esters by means of tert-butyl 3-(3,4-dihydrobenzotriazine-4-on)yl carbonate

Article abstract of DOI:10.1016/S0040-4039(02)00324-6

Carboxylic acids were activated in the presence of DMAP with tert-butyl carbonates (BOC-OX) 1, which were prepared in situ by reaction of X-OH and di-tert-butyl dicarbonate (BOC₂O). The most efficient active carbonate proved to be tert-butyl 3-(3,4-dihydrobenzotriazine-4-on)yl carbonate 1a, leading to efficient formation of benzotriazinonyl esters 3 and 6, which are intermediates in reactions with primary and secondary amines to afford amides or peptides in good yield. By-products in the formation of 3 or 6 are the environmentally safe tert-BuOH and CO₂. The hindered amino acid AIB also forms a dipeptide in good yield.

Full text of DOI:10.1016/S0040-4039(02)00324-6

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 2529–2533
Activation of carboxylic acids as their active esters by means of
tert-butyl 3-(3,4-dihydrobenzotriazine-4-on)yl carbonate†
Yochai Basel and Alfred Hassner*
Department of Chemistry, Bar-Ilan University, Ramat Gan 52900, Israel
Received 2 January 2002; revised 7 February 2002; accepted 15 February 2002
Abstract—Carboxylic acids were activated in the presence of DMAP with tert-butyl carbonates (BOC-OX) 1, which were
prepared in situ by reaction of X-OH and di-tert-butyl dicarbonate (BOC2O). The most efficient active carbonate proved to be
tert-butyl 3-(3,4-dihydrobenzotriazine-4-on)yl carbonate 1a, leading to efficient formation of benzotriazinonyl esters 3 and 6,
which are intermediates in reactions with primary and secondary amines to afford amides or peptides in good yield. By-products
in the formation of 3 or 6 are the environmentally safe tert-BuOH and CO2. The hindered amino acid AIB also forms a dipeptide
in good yield. © 2002 Elsevier Science Ltd. All rights reserved.
The formation of an amide bond is a fundamental
reaction in chemistry.2 Despite the efficiency of the use
of dicyclohexylcarbodiimide (DCC)3 as a dehydrating
reagent in amide bond formation, many other condens-
ing reagents were developed in order to minimize side
products and depress racemization. When DCC is used
in coupling reactions, an equimolar amount of urea
(DCU) is formed and can cause difficulties in purifica-
tion of the main product.
We describe herein the use of tert-butyl 3-(3,4-dihy-
drobenzotriazine-4-on)yl carbonate (BOC-ODhbt) 1a
as well as other active carbonates as condensing
reagents for activation of carboxylic acids as their
active esters 3 and subsequent synthesis of amides and
peptides. We found that reaction of carboxylic acids
with BOC-ODhbt 1a5 in the presence of a catalytic
amount of 4-dimethylaminopyridine (DMAP) afforded
the isolable 3-benzotriazinonyl esters 3a, which in turn
can react with primary and secondary amines to give
amides 4 (Scheme 2). The carbonate BOC-ODhbt 1a, a
relatively stable solid, can be prepared by reaction of
3-hydroxy-3,4-dihydrobenzotriazine-4-one (HODhbt)
and di-tert-butyl dicarbonate (BOC2O) in the presence
of triethylamine but the reaction requires several hours,
while with DMAP catalyst 1a is obtained quantitatively
within 15 min.6
In peptide synthesis, auxiliary nucleophiles (additives),
usually N-hydroxy amine reagents, are frequently used
together with the condensing reagents, such as carbodi-
imides or uronium salts,4 in order to prevent racemiza-
tion. Some of the condensing agents that were
developed, such as 2-(1H-benzotriazol-1-yl)-1,1,3,3-tet-
ramethyluronium
hexafluorophosphate
(HBTU),4
already carry a N-hydroxylamine component, which
is subsequently liberated during the reaction of
the carboxyl group with the coupling reagent and is
used in the next step leading to an active ester (Scheme
1).
HODhbt is used in peptide synthesis as an auxiliary
nucleophile (together with an in situ coupling reagent)
because of its ability to prevent racemization.7,8 How-
ever, when DCC is used as the coupling agent, a side
Scheme 1.
* Corresponding author.
† See Ref. 1.
0040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)00324-6

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Y. Basel, A. Hassner / Tetrahedron Letters 43 (2002) 2529–2533
were carried out in order to find the best conditions for
the formation of the active esters 3. Reaction of a-
methylcinnamic acid (CA) 2a with preformed and iso-
lated carbonate 1a in MeCN at room temperature for
1.5 h afforded active ester 3a in high yield (93–98%).
N-Hydroxy reagents other than HODhbt, such as N-
hydroxysuccinimde (HOSu), N-hydroxyphthalimide
(HOPh), and 1-hydroxybenzotriazole (HOBt), as well
as other acidic (aromatic) alcohols such as 2-hydroxy-
pyridine (HOPy), 3-hydroxypyridinium oxide (HOPO),
4-nitrophenol (HONPh) and 4-carbethoxyphenol
(HOCEPh), were also examined for the preparation of
their tert-butyl carbonates for coupling reactions lead-
ing to active esters 3b–h and the results are given in
Table 1.
Preparation of active esters 3 by reactions of carboxylic
acids with active carbonates 1 can be performed in one
step by mixing RCO2H, BOC2O, auxiliary nucleophile
(X-OH) and DMAP (Scheme 3). Since the auxiliary
nucleophile (e.g. HODhbt) is a better nucleophile than
RCO2H, it reacts first with BOC2O to produce an
active carbonate 1, which in the presence of DMAP,
reacts further with the carboxyl component to give the
desired active ester 3. This pathway was confirmed by
stopping the reaction after a short time (ca. 15 min),
which led to isolation of the carbonate 1 as the main
product together with a small amount (5–10%) of the
active ester 3.
Scheme 2.
reaction with HODhbt takes place leading to an azide
derivative,8 which decreases the popularity of HODhbt.
Recently, Goodman et al.9 reported the use of 3-
(diethoxyphosphoryloxy) - 3,4 - dihydrobenzotriazin - 4-
one (DEPBT) as a condensing reagent for amide bond
formation with a resistance to racemization.
In reactions with carboxylic acids leading to active
esters, the active carbonate BOC-ODhbt 1a combines
the functions of a dehydrating (condensing) agent as
well as of an auxiliary nucleophile carrier. Reaction of
a carboxyl group with BOC-ODhbt proceeds readily in
the presence of DMAP to liberate HODhbt and leads
to the formation of an active ester. That the DMAP
catalyst10 plays an essential role in the reaction of
BOC-ODhbt with carboxylic acids leading to the for-
mation of the active esters was shown by the fact that
in the absence of DMAP the reactions proceeded in
very poor yield (5%) and required a long time (24 h).
Reaction of HODhbt with CA (2a) and BOC2O in the
presence of DMAP catalyst at room temperature
afforded ester 3a11 in high yield (entries 1–3, Table 1).
The reaction can be carried out without TEA base in
Scheme 3.
First, reactions of 1a with simple carboxylic acids 2a–d
Table 1. Reaction of a-methylcinnamic acid 2a (1 equiv.) with BOC2O (1.2–1.4 equiv.)/DMAP (0.5 equiv.)/auxiliary nucleo-
phile (X-OH) at room temperature with formation of active esters 3a–h
Entry
X-OHa (equiv.)
Solventb/basec
Time
Active ester, yieldd (%)
1
2
3
4
5
6
7
8
9
HODhbt (1.1)
HODhbt (1)
HODhbt (1)
HOSu (1.1)
HOPh (1)
MeCN/–
MeCN/–
CH2Cl2/TEA
MeCN/–
MeCN/TEA
MeCN/TEA
Toluene/TEA
MeCN/TEA
MeCN/TEA
MeCN/TEA
1 h
3a, 99
3a, 96
3a, 94
3b, 99
3c, 94
3d, 82
3e, 92
3f, 92
3g, 90
3h, 88
50 min
1.5 h
45 min
35 min
15 min
2 h
2 h
5 h
4 days
HOBte (1)
HOPy (1)
HOPO (1)
HONPh (1)
HOCEPh (1)
10
a HODhbt: 3-hydroxy-3,4-dihydrobenzotriazine-4-one; HOSu: N-hydroxysuccinimde; HOPh: N-hydroxyphthalimide; HOBt: 1-hydroxybenzotria-
zole; HOPy: 2-hydroxypyridine; HOPO: 3-hydroxypyridinium oxide; HONPh: 4-nitrophenol; HOCEPh: 4-carbethoxyphenol.
b Solvents MeCN (HPLC grade), CH2Cl2 (AR) or toluene (AR) were used.
c 1 equiv. of triethylamine (TEA) was used.
d Yields were calculated on the basis of the 1H NMR spectra integration of the crude reaction mixture.
e Mixture of preformed O-BOC and N-BOC HOBt was used.

Y. Basel, A. Hassner / Tetrahedron Letters 43 (2002) 2529–2533
2531
which case DMAP catalyst also serves as a base. When
HOSu or HOPh was used as the auxiliary nucleophile
in the reaction of CA with BOC2O in the presence of
DMAP, active ester 3b or 3c was formed in high yield
(entries 4 and 5). HOBt, which is commonly used in
amide and peptide synthesis as an auxiliary nucleophile,
afforded the active ester 3d in a somewhat lower yield
(82%) after a short time (15 min) (entry 6), but isolation
of the ester was difficult.12 In contrast, isolation of
HODhbt ester as a solid was simple leading to a high
yield of the ester 3a. Hydroxy pyridines HOPy and
HOPO (entries 7 and 8) afforded active esters 3e and 3f
in high yield (92%) within 2 h, but HOPy gave less
clean results than HOPO.13 While 4-nitrophenol
HONPh gave active ester 3g in 90% yield in 5 h,
reaction of the less acidic phenol HOCEPh required
days (4 days) to give ester 3h in 88% yield (entries 9 and
10).
the more polar solvent (MeCN) in competition with the
slow reaction of the carbonate 1a with the hindered
carboxylic acid.
It was important to evaluate amide formation from
3-benzotriazinonyl ester 3a by examining the reaction
of the latter with primary as well as secondary amines
(see Scheme 2). The formation of 3a can be carried out
in situ. For example, reaction of CA with BOC2O/
DMAP/HODhbt in MeCN at room temperature for 1
h followed immediately by addition of glycine ethyl
ester afforded secondary amide 4a within 15 min in
93–96% yield with complete consumption of the inter-
mediate active ester (see Table 2). We found that even
reactions with secondary amines proceeded at a reason-
able rate, affording tertiary amides in over 93% yield.
For instance, addition of N-ethylbenzylamine (1.2
equiv.) to in situ formed active ester 3a afforded the
tertiary amide 4b after 3.5 h. Amide formation was
faster with diallylamine (2.5 h), with morpholine (1 h)
or with pyrrolidine (0.5 h) leading to amides 4c,15 4d
and 4e, respectively, while the use of the less basic
N-methoxymethylamine afforded the amide 4f after 4
h. In order to minimize formation of the N-BOC side
product resulting from the reaction of the amine with
remaining unreacted BOC-ODhbt, an excess of HOD-
hbt should not be used. Reactions of secondary amines
with active esters 3b–h derived from auxiliary nucleo-
philes X-OH other than of HODhbt were also exam-
ined and found to be less efficient.
Other carboxylic acids (2b–d) were also reacted with
BOC2O/DMAP/HODhbt to afford active esters 3i–k
(Table 2, Scheme 2)). Benzoic acid (BA, 2b) and even
the hindered pivalic acid (PA, 2c) gave active esters 3i
and 3j, respectively, in high yields. However, the
branched diphenylacetic acid (DPAA) was activated
only with difficulty; its reaction with BOC-ODhbt 1a in
MeCN for 1 h afforded the ester 3k in 62% yield with
complete consumption of 1a and isolation of 13% of
mixed anhydride D (see Scheme 5). Changing the sol-
vent to CH2Cl2 and allowing the reaction to proceed
for 3 h raised the yield of the DPAA ester 3k to 85%.
The effect of solvent can be explained by the faster
decomposition of the active carbonate by DMAP14 in
Activation of N-protected amino acids 5 as stable
active esters 6 by means of HODhbt/BOC2O/DMAP
(Scheme 4) was successful when the reaction was car-
Table 2. Reaction of RCO2H 2a–d with BOC2O (1.2–1.4 equiv.)/DMAP (0.5 equiv.)/HODhbt at room temperature with
formation of active esters 3a,i–k and amides 4a–f
RCO2Ha (1 equiv.)
HODhbt (equiv.)
Solventb/basec
Time
Active ester, yieldd (%)
Amide,e yieldd (%)
CA (2a)
BA (2b)
PA (2c)
DPAA (2d)
DPAA (2d)
1
MeCN/–
50 min
40 min
30 min
1 h
3a, 96
3i, 95
3j, 98
3k, 62
3k, 85
4a–f, 93–96
1.1
1.1
1.1)
1.1
MeCN/TEA
MeCN/TEA
MeCN/TEA
CH2Cl2/TEA
3 h
a CA: a-methylcinnamic acid; BA: benzoic acid; PA: pivalic acid; DPAA: diphenylacetic acid.
b Solvents MeCN (HPLC grade) or CH2Cl2 (AR) were used.
c 1 equiv. of triethylamine (TEA) was used.
d Yields were calculated on the basis of the 1H NMR spectra integration of the crude reaction mixture.
e 4a: Ethyl N-(a-methylcinnamyl)glycinate; 4b: N-benzyl-N-ethyl-a-methylcinnamamide; 4c: N,N-diallyl-a-methylcinnamamide; 4d: N-a-Methyl-
cinnamyl morpholine 4e: N-a-methylcinnamoyl pyrrolidine; 4f: N-methoxy-N-methyl-a-methylcinnamamide.
Scheme 4.

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Y. Basel, A. Hassner / Tetrahedron Letters 43 (2002) 2529–2533
Table 3. Reaction of amino acids 5a–d with BOC2O (1.4 equiv.)/DMAP (0.5 equiv.)/HODhbt at room temperature with
formation of active esters 6a–d and dipeptides 7a–d
Entry
RCO2H (1 equiv.)
HODhbt
(equiv.)
Solventa/baseb Time (h)
Active ester, yieldc (%)
Dipeptide,d yieldc (%)
1
2
3
4
5
Z-Ala-OH (5a)
Z-Ala-OH (5a)
BOC-AIB-OH (5b)
BOC-Asp(OBzl)-OH (5c)
Fmoc-AIB-OH (5d)
1.1
1.1
1
1
1
MeCN/TEA
CH2Cl2/TEA
CH2Cl2/TEA
CH2Cl2/TEA
CH2Cl2/TEA
2.5
2.5
3
3
3
6a
7a, 10
7a, 95
7b, 94
7c, 80
7d, 75
6a, 85
6b, 92
6c, 75
6d, 75
a Solvents MeCN (dry) or CH2Cl2 (dry) were used.
b 2 equiv. of triethylamine (TEA) were used.
c Calculated by NMR integration.
d 7a: Z-Ala-Phe-OMe; 7b: BOC-AIB-Gly-OEt; 7c: BOC-Asp(OBzl)-Phe-OMe; 7d: Fmoc-AIB-Phe-OMe.
ried out in the less polar dry solvent CH2Cl2 rather
than in polar MeCN (Table 3, entries 1 and 2 for
Ala-OH). Subsequent addition of O-protected amino
acid (free amine) afforded dipeptides 716 in 95% yield.
Activation of N-BOC protected a-aminoisobutyric acid
(BOC-AIB-OH), which is considered a very hindered
a-amino acid, was also successful. Using the conditions
described above afforded AIB-ODhbt ester 6b in 92%
yield after 3 h (entry 3). Other N-protected amino acids
were activated by reaction with BOC2O/DMAP/HOD-
hbt and were used further in the preparation of dipep-
tides in slightly lower yields (entries 4 and 5).
with anhydride D at the carboxylic carbonyl group
(path b), with or without the mediation of DMAP, to
afford the active ester 3 with release of tert-butyl
alcohol and carbon dioxide. Reaction of the alcohol
anion XO− with mixed anhydride D at the undesirable
carbonic carbonyl site (path a) will lead back to car-
bonate 1 which reenters the cycle. Similarly, reaction of
DMAP with D on the carbonic carbonyl (path a) gives
back BOC-pyridinium 8, while at site b it will ulti-
mately produce 3.
Normally, when mixed anhydrides (e.g. D) are used in
reaction with nucleophiles, for instance with amines or
even with RCO2H, attack at either carbonyl moiety (see
‘a’ and ‘b’ in D) can take place, and thus leads to side
products. The advantage of Scheme 5, using active
carbonates 1, is that side reactions are avoided by the
fact that intermediates such as 8, D, 1, and DMAP
reenter the cycle to ultimately produce active ester 3.
The only side products are the environmentally safe
tert-butyl alcohol and CO2.
We believe that the reaction of carboxylic acids with
BOC-ODhbt 1a and with other active carbonates in the
presence of DMAP leading to active esters of type 3
involves the formation of a tert-butyl mixed anhydride
(see D in Scheme 5). Based on previous studies,17 it
appears reasonable that first DMAP reacts with the
carbonate 1 to release auxiliary nucleophile X-OH (e.g.
HODhbt) as its anion XO− and to form intermediate 8.
The latter reacts further with the carboxylic acid to
form a mixed anhydride D. The released XO− can react
In summary, tert-butyl carbonate 1a, which can be
prepared in situ by reaction of HODhbt with BOC2O/
DMAP, is useful in activation of simple carboxylic
acids and amino acids as their active esters 3a and 6a
and in subsequent formation of amides and peptides
with easily separable tert-BuOH and CO2 as by-prod-
ucts. HODhbt ester 3a reacts readily with primary or
secondary amines. Activation of hindered N-BOC-AIB-
OH was also successful.
Acknowledgements
Support of this research by a grant from the Marcus
Center for Pharmaceutical and Medicinal Chemistry is
gratefully acknowledged.
References
1. Synthetic methods 55. For Part 54, see: Kumareswaran,
R.; Hassner, A. Tetrahedron: Asymmetry 2001, 12, 2269.
2. For instance: (a) Bodanszky, M. Principles of Peptide
Synthesis, 2nd ed.; Springer: Berlin, 1992 and references
Scheme 5. Pathway for reaction of carboxylic acids with
active carbonates 1 (derived from reaction of X-OH, BOC2O
and DMAP) leading to active esters (e.g. 3a).

Y. Basel, A. Hassner / Tetrahedron Letters 43 (2002) 2529–2533
2533
cited therein; (b) Klausner, Y. S.; Bodanszky, M. Synthe-
sis 1972, 453.
3. (a) Hamphery, J. M.; Chamberlin, A. R. Chem. Rev.
1997, 97, 2243; (b) Gilon, C.; Klausner, Y.; Hassner, A.
Tetrahedron Lett. 1979, 3811.
m/z (%)=325 (MNH4+, 2), 308 (MH+, 100), 182 (53), 165
(71), 137 (99), 120 (74); HRMS m/z calcd for
C17H14N3O3 308.1035, found 308.1035.
12. Reaction of HOBt with BOC2O gave mainly the N-BOC
in addition to the O-BOC derivative, which may interfere
with ester formation. See: Singh, J.; Fox, R.; Wong, M.;
Kissick, T. P.; Moniot, J. L.; Geugoutas, J. Z.; Malley,
M. F.; Kocy, O. J. Org. Chem. 1988, 53, 205.
4. Dourtoglou, V.; Lambropoulou, V.; Ziorrou, C. Synthe-
sis 1984, 572.
5. All new compounds were characterized by 1H and 13C
NMR and high resolution mass spectroscopy. Data for
3-(tert-butoxycarbonyloxy)-3,4-dihydrobenzotriazin-4-one
1a: White solid; mp 102–104°C; 1H NMR (300 MHz,
CDCl3) l 8.40 (dm, 1H), 8.24 (dm, 1H), 8.02 (tm, 1H),
7.85 (tm, 1H), 1.62 (s, 9H); 13C NMR l 150.20 (C),
149.84 (C), 144.16 (C), 135.37 (CH), 132.62 (CH), 128.90
(CH), 125.62 (CH), 122.17 (C), 88.07 (C), 27.41 (3CH3);
MS (CI/NH3) m/z (%)=281 (MNH4+, 8), 264 (MH+,
100), 164 (13); HRMS m/z calcd for C12H14N3O4
264.0984, found 264.0995.
13. Reaction of HOPy with BOC2O also gave an N-BOC
product (carbamate), which may lead to side reactions.
14. In the same manner that BOC2O is decomposed by
DMAP. See: Basel, Y.; Hassner, A. Synthesis 2001, 550.
15. Typical procedure for preparation of amides 4: To a
solution of BOC2O (1.2 equiv.) dissolved in 4 mL of
MeCN were added consecutively a-methylcinnamic acid
(0.5 mmol, 1 equiv.), HODhbt (1 equiv.), Et3N (1 equiv.)
and DMAP (0.5 equiv.). After 1 h diallylamine (1.2
equiv.) was added and the reaction was allowed to pro-
ceed for 2.5 h. Chloroform or dichloromethane (10 mL)
was then added and the solution was washed with 2%
HCl (20 mL), a saturated NaHCO3 solution and water,
dried with MgSO4 and evaporated to give amide 4c in
93–96% yield (see also Table 2). Data for N,N-diallyl-a-
methylcinnamamide 4c: Colorless oil; 1H NMR (300
MHz, CDCl3) l 7.41–7.23 (m, 5H), 6.58 (q, J=2 Hz,
1H), 5.80 (ddt, J=16, 8, 5.5 Hz, 2H), 5.25 (dd, J=8, 1.5
Hz, 2H), 5.19 (dd, J=16, 1.5 Hz, 2H), 4.04 (d, J=5.5 Hz,
4H), 2.11 (d, J=2 Hz, 3H); 13C NMR l 173.82 (C),
135.95 (C), 133.09 (C), 133.06 (CH), 129.03 (2CH),
128.97 (2CH), 128.27 (2CH), 127.54 (CH), 117.63 (2CH),
50.16 (br, CH2), 47.08 (br, CH2), 16.19 (CH3); MS (dci/
IBu) m/z (%)=242 (MH+, 33), 144 (100), 117 (64), 115
(35). HRMS m/z calcd for C16H20NO 242.1544, found
242.1530.
16. Typical procedure for preparation of dipeptides 7: To a
solution of BOC2O (1.4 equiv.) dissolved in 4 mL of dry
CH2Cl2 were added consecutively Z-Ala-OH (0.5 mmol, 1
equiv.), HODhbt (1 equiv.), triethylamine (2 equiv.) and
DMAP (0.5 equiv.). After 3.5 h, H-Gly-OEt or H-Phe-
OMe (1.2 equiv.) was added and the reaction was allowed
to proceed for 1 h in the case of H-Gly-OEt or 2 h in the
case of H-Phe-OMe. Chloroform or dichloromethane (10
mL) was then added and the solution was washed with
water, 2% HCl (20 mL), a saturated NaHCO3 solution
and water, dried with MgSO4 and evaporated to give the
dipeptide (see also Table 3).
6. No symmetrical carbonate was formed in contrast to the
reactions of other alcohols with BOC2O/DMAP.17
7. Atherton, E.; Holder, J. L.; Meldal, M.; Sheppard, R. C.;
Valerio, R. M. J. Chem. Soc., Perkin Trans. 1 1988, 2887.
8. Ko¨nig, W.; Gieger, R. Chem. Ber. 1970, 103, 2034.
9. Li, H.; Jiang, X.; Ye, Y.; Fan, C.; Romoff, T.; Goodman,
M. Org. Lett. 1999, 1, 91.
10. For DMAP catalyst in acylation, see: (a) Ho¨fle, G.;
Steglich, W.; Vorbru¨ggen, H. Angew. Chem., Int. Ed.
Engl. 1978, 17, 569; (b) Scriven, E. F. V. Chem. Soc. Rev.
1983, 12, 129; (c) Hassner, A.; Krepski, L. R.; Alexanian,
V. Tetrahedron 1978, 34, 2069.
11. Typical procedure for the preparation of active esters 3:
To a solution of BOC2O (1.2 equiv.) dissolved in 4 mL of
MeCN were added consecutively a-methylcinnamic acid
(0.5 mmol, 1 equiv.), HODhbt (1–1.1 equiv.), and DMAP
(0.5 equiv.). At the end of the reaction (50 min–1 h, see
Table 1), chloroform or dichloromethane (10 mL) was
added and the solution was washed with 2% HCl (20
mL), saturated NaHCO3 solution and water, dried with
MgSO4 and evaporated to give active esters 3a in over
96% yield (see also Table 1). Data for 3-hydroxy-3,4-dihy-
drobenzotriazin-4-onyl a-methylcinnamate 3a: White solid;
mp 96–98°C; 1H NMR (300 MHz, CDCl3) l 8.41 (dm,
1H), 8.25 (dm, 1H), 8.09 (q, J=2 Hz, 1H), 8.02 (tm, 1H),
7.85 (tm, 1H), 7.52–7.35 (m, 5H), 2.33 (d, J=2 Hz, 3H);
13C NMR l 164.57 (C), 150.50 (C), 144.40 (C), 143.63
(CH), 135.31 (CH), 134.81 (C), 132.63 (CH), 130.02
(2CH), 129.40 (CH), 128.97 (CH), 128.60 (2CH), 125.76
(CH), 123.94 (C), 122.34 (C), 14.24 (CH3); MS (CI/NH3)
17. Basel, Y.; Hassner, A. J. Org. Chem. 2000, 65, 6368.