Synthesis and Application of 3,5-Di-tert-butylbenzyl chloroformate for the Protection of Amino Functions and the Improvement of Solubility in Polyurethane Synthesis

Article abstract of DOI:10.1002/(sici)1521-3897(199901)341:1<29::aid-prac29>3.0.co;2-e

The benzyloxycarbonyl (BOC) group was used for the protection of amino functions in the stepwise synthesis of molecularly uniform oligourethanes based on 1,5-naphthalene diamine (NDA) as well as polyurethane (PUR) elastomers with molecularly uniform NDA-b

Full text of DOI:10.1002/(sici)1521-3897(199901)341:1<29::aid-prac29>3.0.co;2-e

_____________________________________________________________________________ FULL PAPER
Synthesis and Application of 3,5-Di-tert-butylbenzyl chloroformate for the
Protection of Amino Functions and the Improvement of Solubility in
Polyurethane Synthesis
1
Gunter Festel* )
Bayreuth, Lehrstuhl Makromolekulare Chemie II der Universität
Claus D. Eisenbach
Stuttgart, Institut für Technische Chemie II der Universität
Received August 18th, 1998, respectively November 5th, 1998
Keywords: Oligomers, Polymers, Protecting groups, Synthetic methods
Abstract. The benzyloxycarbonyl (BOC) group was used
for the protection of amino functions in the stepwise synthe-
sis of molecularly uniform oligourethanes based on 1,5-naph-
thalene diamine (NDA) as well as polyurethane (PUR) elas-
tomers with molecularly uniform NDA-based hard segments.
Whereas the poor solubility of the BOC terminated key in-
termediates 5 in solvents suitable for condensation reactions
of oligourethane building blocks in the planned synthesis
route prevented the employing of this convenient protective
group, the modified 3,5-di-tert-butyl substituted BOC (3,5-
di-tBBOC) group was found to significantly improve of the
solubility of the compounds 16. This allowed the stepwise
building-up of oligourethane model compounds and of tele-
chelic hard segments precursors 18. Furthermore, due to the
better solubility, the 3,5-di-tBBOC protective group also led
to considerable improvement of the purification of interme-
diate products 13b by liquid chromatography as compared
to the purification of corresponding BOC terminated com-
pounds 13a.
Segmented polyurethane (PUR) elastomers based on
1,5-naphthalene diisocyanate (NDI) are of considera-
ble technological relevancy [1–4]. Molecularly uniform
oligourethanes with methyl urethane and 4-methoxy-
butyl urethane end groups (1b,c, Scheme 1) as well as
PUR elastomers with molecularly uniform hard seg-
ments served as model compounds for the detailed anal-
ysis of the structure-property relationships of these
materials [5–7].
Starting with 1,5-naphthalene diamine (NDA) and
1,4-butanediol (BDO), oligourethanes 1 with one to five
NDA/BDO repeating units were built-up in a stepwise
procedure. The urethane linkage was formed by con-
densation of amines with chloroformates, which were
obtained by the reaction of an alcohol with phosgene.
The chloroformateamine condensation reaction had con-
siderable advantages over the addition of an alco-
hol to an isocyanate, as chloroformates are less sensiti-
ve to moisture than isocyanates; furthermore, one can
take advantage of the higher activity of the amino group
as compared to the hydroxyl function [8], and there-
fore, the chloroformate route is preferred to the reac-
tion of carbamic acid chlorides with alcohols [9].
A basic requirement for obtaining molecular uniform-
ity in the condensation reaction of basically bifunction-
1
a
R
n=1 n=2 n=3
20 22 18
b
c
d
e
19
21
17
Scheme 1 Molecularly uniform oligourethanes 1 with various
end groups; n = number of NDA/BDO repeating units
1) Present Address: Bayer AG, D-51368 Leverkusen, Germany
J. Prakt. Chem. 1999, 341, No. 1
© WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999 1436-9966/99/34101-29 $ 17.50 + .50/0
29

G. Festel, C. D. Eisenbach
FULL PAPER___________________________________________________________________________
al compounds is that one functional group of the bi-
functional educts NDA and BDO is protected before
each condensation reaction, as it is extremely difficult
to remove the oligomeric by-products. Therefore, the
tert-butyl (tB) group was used for protecting the hy-
droxyl functions and the benzyloxycarbonyl (BOC)
group for amino functions. The BOC group was intro-
duced by Bergmann in the 1930’s for the protection of
amino functions in the peptide synthesis [10]. Today,
the BOC group is widely used as amino protective group
in various types of syntheses [11]. The BOC protective
group for the amino function has also been successfully
employed in the controlled syntheses of oligourethanes,
including NDA/BDO model compounds. This protec-
tive group is well suited for the protection of amino
groups in the stepwise building-up of molecularly uni-
form oligourethanes by the chloroformateamine con-
densation reaction, because it can be removed selec-
tively and quantitatively by hydrogenolysis, and with-
out any decomposition of the urethane group [12].
The characteristic features of the stepwise and se-
quential building-up of the oligourethanes by using se-
lectively removable protective groups are illustrated in
the reaction Scheme 2 (cf. ref. [12]). A key building
block is the molecule 2 on top of Scheme 2, which ac-
tually represents one repeat unit of an oligourethane with
a BOC protected amino function and a tert-butyl pro-
tected hydroxyl function. The reaction sequence shows
the extension of the starting diprotected compound 2
by one repeat unit to give 6 with n=1; the higher oli-
gomers are synthesized accordingly either by stepwise
chain extension of N- or O-terminal activated oligom-
ers 6 by one repeating unit (employing 5 or 4, respecti-
vely), or by the condensation of oligomers 6 with one
activated (deblocked) end group.
A problem in the realization of the planned synthesis
route as shown in Scheme 2 was that the NDA-based
Scheme 2 General reaction scheme for the sequential syn-
oligourethanes – due to the rigid structure of the naph-
thesis of molecularly uniform oligourethanes by using pro-
thalene core – had a very low solubility in the organic
tective groups for the amino and hydroxyl function; the
solvents suitable for the different synthetic steps. As a
consequence, the stepwise building-up of model com-
pounds involving the cleavage of the BOC group, and
the subsequent reactions could only be carried out for
oligomers with a maximum of 2 NDA/BDO repeating
units, and only in very small quantities. In order to over-
come this problem, the solubility of the BOC terminat-
ed building blocks had to be improved. Thus the 3,5-di-
tert-butyl substituted BOC (3,5-di-tBBOC) group,
which had already been employed in the peptide syn-
thesis for the protection of amino functions, was select-
ed; this group can be easily cleaved by moderately acidic
hydrolysis [16–18], and the tert-butyl substitution is
known to have a solubility increasing effect. This modi-
fied protective group could be employed in the oli-
gourethane synthesis analogously to the conventional
BOC group, and the solubility of the (oligomeric) build-
bracket in 6 indicates the repeating unit, and n=1 in this
example. The detailed synthesis of corresponding oligo-
urethanes based on methylene biphenyl [13], methylene bis
(4,4'cyclohexyl) [14] and N(H)RN(H) piperazinyl [15] is des-
cribed elsewhere
ing blocks was substantially improved due to the tert-
butyl group effect.
In this paper we describe the preparation of the 3,5-
di-tert-butylbenzyl chloroformate reagent, its employ-
ing to protect the amino group of building blocks and
oligourethanes, and the removal of 3,5-di-tBBOC. The
detailed synthesis and characterization of the molecu-
larly uniform oligourethanes and the different PUR elas-
tomers with molecularly uniform hard segments con-
taining the naphthalene diurethane constitutional unit
is given elsewhere [6, 7].
30
J. Prakt. Chem. 1999, 341, No. 1

Synthesis and Application of 3,5-Di-tert-butylbenzyl chloroformate for Protecting
_____________________________________________________________________________FULL PAPER
nol, toluene/THF and cyclohexane/THF solvent mix-
tures were tested as eluent, whereby the best results were
obtained with toluene/THF 10:1 v/v.
Results and Discussion
3,5-Di-tert-butylbenzyl chloroformate was synthesized
in a 4-step reaction (Scheme 3). Starting with toluene
(7), the tert-butyl groups were introduced by Friedel-
Crafts-alkylation with tert-butyl chloride and AlCl3. As
both the 4-mono- and the 3,5-disubstituted products
were obtained in this reaction, 3,5-di-tert-butyltoluene
(8) was removed from 4-tert-butyltoluene by distilla-
tion [19]. The oxidation of the methyl group to the car-
boxyl function was carried out with potassium perman-
ganate under basic conditions in pyridine [20, 21]. 3,5-
Di-tert-butylbenzoic acid (9) was reduced to 3,5-di-tert-
butylbenzyl alcohol (10) by the reaction with lithium
aluminum hydride in tetrahydrofuran (THF). In the last
step, 3,5-di-tert-butylbenzyl chloroformate (11b) was
formed by reaction of 10 with phosgene. 11b was used
without further purification by distillation, because ben-
zyl chloroformates could explosively decompose dur-
ing heating.
-C(CH )
3 3
R
-H
11a
13a
14a
11b
13b
14b
Scheme 4 Synthesis of the single protected 13a and double
reacted 14a BOC NDA derivative as well as the correspon-
ding single protected 13b and double reacted 14b 3,5-di-
tBBOC compounds
One advantage of using the 3,5-di-tBBOC instead of
the conventional BOC group is the more efficient chro-
matographical isolation of the single protected product
13b, which is partially due to the solubility enhancing
effect of the tert-butyl substituents. Whereas in the case
of the BOC group 13a only 2 g of the crude reaction
product could be given on the column due to its rela-
tively low solubility, the purification of 13b with the
3,5-di-tBBOC protective group could be carried out in
10 g quantities (the crude reaction product was solved
in 100 ml of toluene/THF 10:1, given on the column
and flashed with toluene/THF 10:1; diameter of the col-
umn 7 cm, height of silica gel 25 cm).
The differences of the Rf -values between NDA 12,
single protected 13 and double reacted 14 product as
determined by thin-layer chromatography was signifi-
cantly larger for the tert-butyl substituted system as
compared to the corresponding BOC terminated com-
pounds. The Rf -values of the starting material NDA
and the reaction products, according to Scheme 4 and
determined by thin-layer chromatography (toluene/THF
10:1 v/v as solvent), are as follows: NDA 12 0.26, sin-
gle BOC protected NDA 13a 0.31, double BOC substi-
tuted NDA 14a 0.55, single 3,5-di-tBBOC protected
NDA 13b 0.40 and double 3,5-di-tBBOC substituted
NDA 14b 0.79. As a result of both the increased solu-
bility in the eluent and the higher resolution in the chro-
matographical purification, the overall yield of 13b
was distinctly higher (42%) than the yield of 13a (33%).
A comparison of the solubility of oligourethanes 1 with
Scheme 3 Synthesis of 3,5-di-tert-butylbenzyl chloroformate
11b in a 4-step reaction
The synthesis of the single protected NDA with ei-
ther the conventional BOC or the 3,5-di-tBBOC is
shown in the Scheme 4. The course of the reaction was
similar for benzyl chloroformate 11a and the di-tert-
butyl substituted reagent 11b. The condensation reac-
tion of NDA 12 with an equimolar amount of 11a or
11b at 0 °C in CH2Cl2 and using Na2CO3 to neutralize
the HCl gave the single protected benzyl-N-1,5-naph-
thalene diamine carboxylate 13a or the 3,5-di-tert-butyl-
benzyl-N-1,5-naphthalene diamine carboxylate 13b as
the main reaction product. Besides, unreacted NDA as
well as the bisurethanes 14a,b (benzyl- or 3,5-di-tert-
butylbenzyl-N,N'-1,5-naphthalene diamine dicarboxy-
late) were also present in the reaction mixture. The pure
monoprotected 13a or 13b were obtained by purifica-
tion of the crude reaction product by flash chromato-
graphy over a silica gel column.Different toluene/metha-
J. Prakt. Chem. 1999, 341, No. 1
31

G. Festel, C. D. Eisenbach
FULL PAPER___________________________________________________________________________
the same number of repeating units but different end
groups (amino, methyl urethane, 4-methoxybutyl ure-
thane, BOC and 3,5-di-tBBOC) showed that the BOC
terminated oligourethanes 1d had the lowest solubility.
Even in the case of oligourethanes with only two NDA
units (1 with n=1) the solubility of the compounds with
the conventional BOC protective group 1d was so poor
that it could be dissolved only under heating in very
polar solvents such as N,N-dimethylformamide, N,N-
dimethylacetamide, and dimethyl sulfoxide. Therefore,
the reactions for the synthesis of oligomers with n>1
following Scheme 2 were not possible using the BOC
protective group because of the insolubility of the oli-
gourethanes in appropriate solvents. However, these
reactions could be carried out when introducing the 3,5-
di-tBBOC group. This is illustrated in the following in
detail for three examples.
First, the phosgenation, which was necessary to ob-
tain chloroformates by the reaction of an alcohol with
phosgene, could be carried out more easily using the
3,5-di-tBBOC group, as the solubility was higher in
suitable solvents. Due to the sufficient difference in re-
activity of the two carbonyl chloride functions of phos-
gene, the forming of carbonate by-products was avoid-
ed. As an example, Scheme 5 shows the reaction of (3,5-
di-tert-butyl) benzyl (4-hydroxy) butyl-N,N'-1,5-naph-
thalene diamine dicarboxylate 15 with phosgene to form
the 3,5-di-tert-butylbenzyl 4-chloroformyloxybutyl-
N,N'-1,5-naphthalene diamine dicarboxylate 16 which
was an important building block for the synthesis of the
higher oligomeric model compounds as already ex-
plained in Scheme 2; the conversion of 15 to 16 in
Scheme 5 corresponds to the conversion of 3 to 5 in
Scheme 2.
was not possible, because they react with phosgene and
with chloroformates [22]. Dimethyl sulfoxide is non-
phosgene reactive [23], but this solvent could introduce
traces of sulphur, so that the hydrogenation with the Pd
catalyst (removal of amine protective group, e.g., con-
version of 2 into 4, Scheme 2) would fail. Therefore,
the phosgenation could only be carried out in non-phos-
gene reactive solvents like chloroform, THF or 1,4-di-
oxane, and the latter turned out to be the best solvent.
The alcohol 15 was treated with the fivefold excess of
phosgene at 0 °C. Because of the melting point of 1,4-
dioxane of 12 °C, it is advantageous to use a 9:1 v/v
1,4-dioxane/THF-mixture for this reaction. While only
0,3 g of the alcohol 3 (Scheme 2), dissolved in 1 l of
1,4-dioxane, could be treated using the conventional
BOC group, the 3,5-tert-butyl substituted BOC in 15
allowed to run the phosgenation of the tenfold higher
concentration.
Another example is the conversion of the end group
protected oligourethane 1d or 1e (Scheme 1) into the
α,ω-diamino oligourethane building block (1a, Scheme
1) which can be employed for the synthesis of segmented
polyurethanes with molecularly uniform hard segments
(cf. Ref. [12]). The oligourethane with 3 NDA/BDO
repeating units and BOC end groups (1d with n=3,
Scheme 1) was insoluble in solvents suitable for the
catalytical hydrogenation; therefore the removal of the
BOC protecting group (see conversion of 2 into 4,
Scheme 2) could not be carried out accordingly. The
analogous tetramethylene bis {5-{4-[5-(3,5-di-tert-butyl
benzyloxy carbonyl)-1,5-naphthalene diamine-1-yl car-
bonyloxy]butoxy carbonyl}-1,5-naphthalene diamine-
1-carboxylate} (17) (1e with n=3, Scheme 1) was suf-
ficiently soluble in DMA so that a cleavage of the pro-
tective groups at 10 bar H2-pressure and a temperature
of 80 °C was possible (Scheme 6). The solubility of the
resulting amino terminated tetramethylene bis{5-[4-
(1,5-naphthalene diamine-1-yl carbonyloxy) butoxycar-
bonyl]-1,5-naphthalene diamine-1-carboxylate} (18) (1a
with n=3, Scheme 1) was even better than that of 17.
In the context of the removal of the BOC or 3,5-di-
tBBOC protective group by catalytical hydrogenation
it has to be mentioned that in NDA based compounds,
for a successful cleavage, it was necessary to purify the
starting NDA material (12) from sulphur by twice re-
crystallizing the derivative N,N'-bis(benzylidene)-1,5-
naphthalene diamine (which was obtained by on react-
ing of 12 with benzaldehyde) from 1,4-dioxane [7]. Even
small amounts of sulphur, which originated from the
technical synthesis of 12, contaminated the catalyst re-
quired for the hydrogenolytical cleavage of the BOC or
3,5-di-tBBOC group to such an extend that almost no
conversion occurred.
The phosgenation in good solvents for urethanes such
as N,N-dimethylformamide and N,N-dimethylacetamide
The complete and selective cleavage of the BOC as
well as of the 3,5-di-tBBOC protective group could be
verified by 1H NMR spectroscopic analysis, as it is ex-
Scheme 5 Formation of the NDA building unit 16 with a
3,5-di-tBBOC protected amino and a reactive chloroformate
end group by phosgenation of the corresponding alcohol 15
32
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Synthesis and Application of 3,5-Di-tert-butylbenzyl chloroformate for Protecting
_____________________________________________________________________________FULL PAPER
a)
b)
Scheme 6 Cleavage of the 3,5-di-tBBOC protective group
of the oligourethane 17 (1d with 3 NDA/BDO) repeating units
by hydrogenolysis to give the oligourethane diamine 18 (1a
with n=3)
b
emplarily shown for the 3,5-di-tBBOC terminated te-
a
c
d
tramethylene bis [5-(3,5-di-tert-butyl benzyloxy carb-
onyl)-1,5-naphthalene diamine-1-carboxylate] 19 with
one NDA/BDO repeating unit (1e with n=1, Scheme
1). The signals of the tert-butyl protons at δ = 1.29 (h),
the methylene protons of the benzyl group at δ = 5.17
(e) and the urethane NH group of the 3,5-di-tBBOC
group at δ = 9.66 (d), which are characteristic for the
3,5-di-tBBOC group (Figure 1a), disappeared after the
hydrogenolytical removal, and the amino end groups
were detected by the signal at δ = 5.66 (d) (Figure 1b).
The 13C NMR spectrum of the corresponding tetrame-
thylene bis (1,5-naphthalene diamine-1-carboxylate) 20
(1a with n=1, Scheme 1) no longer showed the peaks
of the tert-butyl carbon atoms at δ = 31.6 and 34.8 and
the methyl carbon atom of the benzyl group at δ = 66.7.
IR spectroscopical analysis also showed the success-
ful cleavage of the 3,5-di-tBBOC group. While the ab-
sorption of the NH vibration at the 3,5-di-tBBOC ter-
minated 4-[5-(3,5-di-tert-butyl benzyloxy carbonyl)-
1,5-naphthalene diamine-1-yl carbonyloxy]butyl-N,N'-
1,5-naphthalene diamine dicarboxylate 21 with
2 NDA/BDO repeating units (1e with n=2, Scheme 1)
was seen at 3290 cm–1 (Figure 2a), the 4-(1,5-naphtha-
lene diamine-1-yl carbonyloxy) butyl-N,N'-1,5-naphtha-
lene diamine dicarboxylate 22 with amino end groups
(1a with n=2, Scheme 1) showed the peak at 3370 cm–1
(Figure 2b). The peak of the CO group was shifted from
1700 to 1740 cm–1.
d6-DMSO
10
9
8
7
6
5
4
3
2
1
0
δ (ppm)
1
Fig. 1 H NMR spectra (d6-DMSO as solvent) of a) the 3,5-
di-tBBOC terminated compound 19 (oligourethane 1e with
n=1) and b) the corresponding amino terminated compound
20 (oligourethane 1a with n=1) after cleavage of the protective
group
lecularly uniform hard segments was also more efficient
when using the 3,5-di-tBBOC group instead of the BOC
group. The usual method to synthesize model elasto-
mers with monodisperse hard segments by condensa-
tion of polyol bischloroformates with amino terminat-
ed, molecularly uniform hard segment precursors 1a
(Scheme 1) was severely restricted by the limited solu-
bility of the amino terminated oligourethanes with more
than 2 NDA/BDO repeating units. However, the syn-
thesis could be realized by employing an α,ω-amino
naphthalene urethane telechelic prepared from polyether,
polyester or polysiloxane polyols by reaction of the
polyol bischloroformates with single BOC protected
NDA 13a and the subsequent hydrogenolytical remov-
Finally, the synthesis of the PUR elastomers with mo-
J. Prakt. Chem. 1999, 341, No. 1
33

G. Festel, C. D. Eisenbach
FULL PAPER___________________________________________________________________________
Experimental
a)
Silica gel layers Polygram Sil G/UV254 from Macherey-Nagel
(size 4×8 cm) were used for thin-layer chromatography
(toluene/THF 10:1 as eluent). – Flash chromatography was
carried out with a column filled with silica gel 60 from Fluka
(diameter 7 cm, height of silica gel 25 cm) and 0.4 bar N2-
pressure (toluene/ THF 10:1 as solvent). – H NMR and
13C NMR spectra were recorded at 25 °C on a Bruker AC 250
spectrometer at 250 MHz and 62.9 MHz, respectively, using
tetramethylsilane as internal standard. – IR measurements
were made with a FTIR spectrometer Bio-Rad Digilab
NH
1
CO
Division 3240-SPC FTS-40. – NDA was provided by Bayer,
all other chemicals were from Fluka.
4000
2000
1000
500
Wave number (cm -1)
Benzyl (4-tert-butoxy)butyl-N,N'-1,5-naphthalene diamine
dicarboxylate (2)
b)
3 g (10.2 mmol) of 13a were dissolved in 100 ml of THF and
1.5 ml (18,8 mmol) of pyridine. After adding a solution of
2.5 g (12 mmol) of 4-tert-butoxybutyl chloroformate in
50 ml of THF dropwise at –78 °C and warming up to room
temperature, the solution was stirred for 8 h. After evaporating
the solvent, washing with methanol and drying, the product
was recrystallized from 20 ml of THF. Yield 4.2 g (88%) with
m.p. 148 °C. – IR (KBr): ν/cm–1 = 3299 (m), 1694 (s). –
1H NMR (250 MHz, d6-DMSO): δ/ppm = 1.12 (s, 9H, -O–
C(CH3)3), 1.61 (m, 4H, -O–CH2–CH2–CH2-), 3.32 (t, 2H,
-CH2–O–C(CH3)3), 4.12 (t, 2H, -CO–O–CH2–CH2-), 5.18 (s,
2H, -O–CH2–C=), 7.34–7.52 (m, 7H), 7.61 (t, 2H), 7.90 (d,
2H), 9.50 (s, 1H, -NH–CO–O–CH2–CH2-), 9.68 (s, 1H, -NH–
CO–O–CH2–C=). – 13C NMR (62.9 MHz, d6-DMSO): δ/ppm
=25,8 (-CO–O–CH2–CH2–CH2-), 26.7 (-CO–O–CH2–CH2-),
27.4 (-O–C(CH3)3), 60.5 (-CH2–O–C(CH3)3), 64.4 (-CO–O–
CH2–CH2-), 65,9 (-O–CH2–C=), 71,9 (-CH2–O–C(CH3)3),
119.8, 120.0, 121.5, 125.2, 125.3, 127.8, 127.9, 128.4, 128.9,
134.0, 134.1, 136.9, 154.8 (-CO–O–CH2–C=), 155,0 (-CO–
O–CH2–CH2-).
NH
CO
2000
4000
1000
500
Wave number (cm -1)
Fig. 2 IR spectra (KBr) of a) the 3,5-di-tBBOC terminated
compound 21 (oligourethane 1e with n=2) and b) the cor-
responding amino terminated compound 22 (oligourethane
1a with n=2) after cleavage of the protective group
Benzyl (4-hydroxy)butyl-N,N'-1,5-naphthalene diamine di-
carboxylate (3)
A mixture of 4 g (8,6 mmol) of 2, 100 ml of dioxane and
20 ml of 4N HCl were refluxed for 8 h under an argon
atmosphere. After cooling, 4N NaOH was added, until the
solution was alkaline. The dioxane was evaporated, and the
product was filtered off, washed with a lot of water, dried and
recrystallized from 50 ml of THF. Yield: 2.9 g (84%) with
m.p. 178 °C. – IR (KBr): ν/cm–1 = 3294 (m), 1695 (s). –
1H NMR (250 MHz, d6-DMSO): δ/ppm = 1.61 (m, 4H, -O–
CH2–CH2–CH2-), 3.45 (t, 2H, -CH2–OH), 4.13 (t, 2H, -CO–
O–CH2–CH2-), 5.19 (s, 2H, -O–CH2–C=), 7.36–7.53 (m, 7H),
7.61 (t, 2H), 7.90 (d, 2H), 9.50 (s, 1H, -NH–CO–O–CH2–
CH2-), 9.68 (s, 1H, -NH–CO–O–CH2–C=). – 13C NMR (62.9
MHz, d6-DMSO): δ/ppm = 25.7 (-CO–O–CH2–CH2-), 29.1
(-CO–O–CH2–CH2-), 60.7 (-CH2–OH), 64.7 (-CO–O–CH2–
CH2-), 66.2 (-CH2–C=), 120.1, 120.3, 121.9, 125.7, 128.2,
128.7, 129.2, 134.1, 134.3, 137.1, 155.1 (-CO–O–CH2–C=),
155,4 (-CO–O–CH2–CH2-).
al of the BOC groups; further reacting of this NDA ure-
thane terminated polyol with 16, whereby the solubility
was improved by employing the 3,5-di-tBBOC protec-
tive group and subsequent deblocking, amino terminat-
ed prepolymers with 2 naphthalene units at each end of
the polyols were accessible. The polycondensation re-
action of such diamino telechelics representing polyols
carrying a full hard segment repeating unit at both ends
with suitable bischloroformates (e.g. of BDO or hy-
droxybutylurethane terminated hard segment building
blocks), PUR elastomers with up to 4 NDA/BDO re-
peating units in the molecularly uniform hard segment
were obtained [5].
Financial support of this study by the German Ministry of
Research and Technology (Grant no. 03M40436) is gratefully
acknowledged. The authors are also indebted to the Bayer
AG in Leverkusen for the support of this work, which was
carried out at the Universität Bayreuth, Makromolekulare
Chemie II.
4-tert-Butoxybutyl-N-1,5-naphthalene diamine carboxylate
(4)
200 mg of Pd on charcoal (5%) were added to a solution of
34
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Synthesis and Application of 3,5-Di-tert-butylbenzyl chloroformate for Protecting
_____________________________________________________________________________FULL PAPER
128.1, 128.6, 129.2 (-NH–C= -CH=CH–CH=C–), 134,1
(-NH–C= -), 137.0, 155.1 (-NH–CO–O-).
5 g (10,8 mmol) of 2 in 200 ml of THF. The reaction mixture
was treated under stirring with H2 at 50 °C for 2 h at an initial
pressure of 5 bar. The catalyst was removed by filtration, the
solvent evaporated and the product recrystallized from 100
ml of THF. Yield 3.2 g (91%) with m.p. 69 °C. – IR (KBr):
3,5-Di-tert-butylbenzyl-N,N'-1,5-naphthalene diamine dicar-
boxylate (14b)
1
ν/cm–1 = 3370 (m), 1736 (s). – H NMR (250 MHz, d6-
3 g (19 mmol) of 12, dissolved in 300 ml of CH2Cl2, 13.6 g
(48 mmol) of 11b and 90 ml of a 1M Na2CO3 solution were
reacted as described for compound 14a. Yield 10.3 g (84%)
with m.p. 203 °C. – IR (KBr): ν/cm–1 = 3282 (m), 1697 (s). –
1H NMR (250 MHz, d6-DMSO): δ/ppm = 1.26 (s, 36H,
(CH3)3C-), 5.15 (s, 4 H, -O–CH2-), 7.24 (d, 4H, (CH3)3C–C=
-CH=C– -CH2-), 7.34 (s, 2H, (CH3)3C– C= –CH=C–
-C(CH3)3), 7.45 (t, 2H, -NH– C= –CH=CH-), 7.56 (d, 2H),
7.88 (d, 2H), 9.64 (s, 2H, -NH–CO-). – 13C NMR (62.9 MHz,
d6-DMSO): δ/ppm = 31.4 ((CH3)3C-), 34.6 ((CH3)3C-), 66.7
(-CH2-), 120.3, 121.5, 121.9, 122.0, 125.4, 134.2, 136.2 (-O–
CH2– C= -), 150.7 (-C= -C(CH3)3), 155,1 (-NH–CO–O-).
DMSO): δ/ppm = 1.13 (s, 9H, -C(CH3)3), 1.60 (m, 4H, -O–
CH2–CH2-), 3.32 (t, 2H, -CH2–O–C(CH3)3), 4.10 (t, 2H, -
NH–CO–O–CH2-), 5.61 (s, 2H, -NH2), 6.70 (d, 1H), 7.16–
7.28 (m, 2H), 7.33 (d, 1H), 7.49 (d, 1H), 7.88 (d, 1H), 9.12 (s,
1H, -NH–CO–O–CH2-). – 13C NMR (62,9 MHz, d6-DMSO):
δ/ppm = 25.9 (-O–CH2–CH2–CH2-), 26.7 (-O–CH2–CH2-),
27.5 (-C(CH3)3), 60.5 (-CH2–O–C(CH3)3), 64.3 (-O–CH2–
CH2-), 72.0 (-C(CH3)3), 107.9, 110.4, 119.5, 121.3, 123.1,
123.5, 126.6, 129.5, 133.7, 144.9 (C= -NH2), 155.1 (-NH–
CO–O–CH2-).
Benzyl 4-chloroformyloxybutyl-N,N'-1,5-naphthalene di-
amine dicarboxylate (5)
The synthesis and experimental data of the other presented
compounds 8–11b, 13a,b and 15–22 have been described
elsewhere [6, 7].
0,2 g (0,5 mmol) of 3, dissolved in 700 ml of dioxane was
slowly added dropwise into 0,5 ml (6,8 mmol) of phosgene
under ice cooling and stirred for 2 h at room temperature.
The excess phosgene was removed by heating up to 50 °C in
a water bath, and the remaining product was dried. Cleaning
of the chloroformate by distillation was not possible, as benzyl
chloroformates could explosively decompose during heating.
References
[1] E. C. Prolingheuer, J. J. Lindsey, H. Kleimann, J. Elasto-
mers Plast. 1989, 21, 100
[2] H.-J. Kogelnik, H. H. Huang, M. Barnes, R. Meichsner, J.
Elastomers Plast. 1991, 23, 314
[3] E. C. Prolingheuer, J. M. Barnes, R. Kopp, E. Seggern, Rub-
ber Plast. News 1992, 21, 15
[4] E. C. Prolingheuer, J. M. Barnes, R. Kopp, E. Seggern, J.
Elastomers Plast. 1992, 24, 221
[5] G. Festel, C. D. Eisenbach, Polym. Prepr. (Am. Chem. Soc.,
Div. Polym. Chem.) 1996, 37/1, 535
[6] G. Festel, K. Fischer, C. D. Eisenbach, Macromol. Chem.
Phys. 1997, 198, 3105
[7] G. Festel, C. D. Eisenbach, Macromol. Chem. Phys. 1998,
199, 1365
[8] S. L. Kwolek, P. W. Morgan, J. Polym. Sci. A 1964, 2, 2693
[9] L. L. Harrell, Macromolecules 1969, 2, 607
[10] M. Bergmann, L. Zervas, Ber. Dtsch. Chem. Ges. 1932, 65,
1192
[11] T. W. Greene, P. G. M. Wuts, Protective Groups in Organic
Synthesis, John Wiley, New York 1991, p. 335
[12] C. D. Eisenbach, H. Nefzger, in: Handbook of Polymer Syn-
thesis, Part A, ed. by H. R. Kricheldorf, Marcel Dekker, New
York 1991, p. 685
[13] C. D. Eisenbach, M. Baumgartner, C. Günter, in: Advances
in Elastomers and Rubber Elasticity, ed. by J. Lal and J. E.
Mark, Plenum, New York 1986, p. 51
Yield 0.2 g (84%) with m.p. 156 °C. – IR (KBr): ν/cm–1
=
3296 (m), 1780 (s), 1699 (s). – 1H NMR (250 MHz, CDCl3):
δ/ppm = 1.80 (m, 4H, -O–CH2–CH2-), 4.23 (t, 2H, -O–CH2–
CH2-), 4.31 (t, 2H, -CH2–O–C(CH3)3), 5.24 (s, 2H, -O–CH2–
C=), 7.36–7.53 (m, 7H), 7.61 (t, 2H), 7.90 (d, 2H), 9.48 (s,
1H, -NH–CO–O–CH2–CH2-), 9.65 (s, 1H, -NH–CO–O–CH2–
C=). – 13C NMR (62,9 MHz, CDCl3): δ/ppm = 25.1 (-CH2–
CH2–O–CO–Cl), 30.3 (-NH–CO–O–CH2–CH2-), 64.6 (-NH–
CO–O–CH2-), 68.1 (-O–CH2–C=), 71,5 (-CH2–O–CO–Cl),
120.1, 120.3, 121.9, 125.7, 128.2, 128.7, 129.2, 134.1, 134.3,
137.1, 155.1 (-NH–CO–O–CH2-C=), 155,4 (-NH–CO–O–
CH2–CH2-).
Benzyl-N,N'-1,5-naphthalene diamine dicarboxylate (14a)
After dissolving 3 g (19 mmol) of 12 in 300 ml of CH2Cl2, a
solution of 8,2 g (48 mmol) of 11a in CH2Cl2 and 50 ml of
1M Na2CO3 solution were added dropwise at 0 °C. After
warming up to room temperature, the mixture was stirred for
8 h. The CH2Cl2 phase was separated from the water phase
and dried with Na2SO4. The CH2Cl2 was evaporated, and the
crude product dried. For the purification by flash chroma-
tography 2 g were solved in 100 ml of toluene/THF 10:1,
given on the column and flashed with toluene/THF 10:1. After
500 ml, 100 ml fractions were taken. The composition of the
fractions was controlled by thin-layer chromatography. After
evaporating the solvent, the product was recrystallized from
150 ml of THF. Yield: 7 g (86%) with m.p. 250 °C. – IR
[14] C. Steinlein, L. Hernandez, C. D. Eisenbach, Macromol.
Chem. Phys., 1996, 197, 3365
[15] C. D. Eisenbach, H. Nefzger, in: Contemporary Topics in
Polymer Science, ed. by W. M. Culbertson, Plenum, New
York 1990, 6, Multiphase Macromolecular Systems, p. 339
[16] W. Voelter, J. Müller, W. Heinzel, C. T. Beni, in: Peptides:
Structure and Function, Proceedings of the 8th American
Peptide Symposium, ed. by V. J. Hruby and D. H. Rich, Pier-
ce, Rockford 1983, p. 131
[17] W. Voelter, J. Müller, C. T. Beni, W. Heinzel, H. Kalbacher,
A. Morel, H. Wollmann, in: Peptides: Proceedings of the 17th
European Peptide Symposium, ed. by K. Blaha and P. Ma-
lon, de Gruyter, Berlin 1983, p. 125
1
(KBr): ν/cm–1 = 3268 (m), 1690 (s). – H NMR (250 MHz,
d6-DMSO): δ/ppm = 5.18 (s, 4H, -O–CH2-), 7.29–7.52 (m,
10H), 7.50 (d, 2H), 7.60 (d, 2H), 7.88 (s, 2H, -NH–CO-),
9.66 (s, 2H, -NH–CO-). – 13C NMR (62,9 MHz, d6-DMSO):
δ/ppm = 66.2 (-CH2-), 120.2 (-NH–C= -CH=CH-), 121.8
(-NH–C= -CH=), 125,6 (-NH–C=-CH= -CH–CH=), 128.0,
[18] J. Müller, W. Voelter, in: Biologically Active Principles of
J. Prakt. Chem. 1999, 341, No. 1
35

G. Festel, C. D. Eisenbach
FULL PAPER___________________________________________________________________________
[23] Z. Y. Quin, C. W. Macosko, S. T. Wellinghoff, Macromole-
Natural Products, ed. by W. Voelter and D. G. Daves, Thie-
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Address for correspondence:
Dr. Gunter Festel
c/o Bayer AG
Bayerwerk, K 10
D-51368 Leverkusen
E-mail: Gunter.Festel@web.de
[22] R. Richter, B. Tucker, J. Org. Chem. 1983, 48, 2625
36
J. Prakt. Chem. 1999, 341, No. 1