Synthesis of allylic and propargylic primary amines by reaction of organometallic reagents with α-amidoalkyl sulfones

Full text of DOI:10.1021/jo9911544

8970
J . Org. Chem. 1999, 64, 8970-8972
Sch em e 1
Syn th esis of Allylic a n d P r op a r gylic
P r im a r y Am in es by Rea ction of
Or ga n om eta llic Rea gen ts w ith
r-Am id oa lk yl Su lfon es
Tiziana Mecozzi and Marino Petrini*
Dipartimento di Scienze Chimiche, Universita` di Camerino,
via S. Agostino, 1, I-62032 Camerino, Italy
difficult.11 Furthermore, the cleavage of the acyl moiety
to give the free amino group frequently requires harsh
conditions.12 In this context, nitrones present an en-
hanced reactivity as electrophiles and can be treated with
vinyl and ethynyl organometallic reagents to give the
relative hydroxylamines, which can be further reduced
to the parent amino compounds.13 Finally, the use of
metalloalkyne complexes with N-metallo imines repre-
sents a valid option to the above cited methods for the
synthesis of primary unsaturated amines.8c,14
The troubles associated with the preparation of N-acyl
imines have spurred the search for some synthetic
analogues of these substrates that would behave as
reactive imines but are endowed by easy access and
stability. 1-(R-Amidoalkyl)benzotriazoles partially exist
as benzotriazolide-iminium ion pair in solution and,
therefore, may react with organometallic reagents to give
the corresponding amino derivatives.15 This method
permits the synthesis of tertiary propargylamines through
the use of alkynyllithium reagents generated from
1-alkynes.
Received J uly 20, 1999
In tr od u ction
Allylic and propargylic amines play a prominent role
in organic synthesis, and their importance continues to
grow with time.1 A plethora of synthetic methods have
been devised for the preparation of allylic amines, includ-
ing substitution reactions with nucleophilic nitrogen,2 use
of azallylic anions,3 coupling reactions,4 and palladium-
catalyzed reactions.5 Similar approaches can also be used
for the synthesis of propargylamines,6 but the most
reliable and efficient method for the preparation of allylic
and propargylic amines still remains the addition of an
appropriate organometallic reagent to imino derivatives.7
The reaction of strongly basic organometallic reagents
to N-alkyl imines rarely produces synthetically useful
results because R deprotonation of the imine often
competes with the addition reaction.8 This unwanted side
reaction can be partially suppressed by using organome-
tallic reagents with low basicity, whose preparation is
not always straightforward.9 These reagents sometimes
give unexpected results, as in the case of vinylcerium
dichloride, which reacts with imines to give a regio- and
stereoisomeric mixture of homoallylic amines.10
Resu lts a n d Discu ssion
We have found that a similar behavior is displayed by
R-amidoalkyl sulfones 3, which can be easily prepared
by reaction of a carbamate 1 with a suitable aldehyde 2
and sodium benzenesulfinate, in the presence of formic
acid16 (Scheme 1, Table 1). The utilization of sulfones 3
as N-acyl imine equivalents is particularly advantageous
because these derivatives are mostly stable solids and
can be recovered from the reaction mixture by simple
filtration and purified by crystallization. R-Amidoalkyl
sulfones 3 are known to react with stabilized carbanions,
giving a product that arises from a formal substitution
of the phenylsulfonyl anion with the nucleophile.17 Vi-
nylmagnesium bromide 4 is able to react with sulfones
3 at -20 °C in THF affording in good yields the corre-
The utilization of more electrophilic N-acyl or N-tosyl
imines considerably improves the efficiency of the process
even though the preparation of these derivatives is rather
* Phone: +39 0737 402253. Fax: +39 0737 637345. E-mail:
Petrini@camserv.unicam.it..
(1) Reviews: (a) J ohannsen, M.; J orgensen, K. A. Chem. Rev. 1998,
98, 1689. (b) Cheik, R. B.; Chaabouni, R.; Laurent, A.; Mison, P.; Nafti,
A. Synthesis 1983, 685.
(2) (a) Sen, S. E.; Roach, S. L. Synthesis 1995, 756. (b) Tomassy, B.;
Zwierzak, A. Synth. Commun. 1998, 28, 1201. (c) Srivastava, R. S.;
Nicholas, K. M. J . Am. Chem. Soc. 1997, 119, 3302.
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Z.; Shiro, M. J . Chem. Soc., Chem. Commun. 1992, 1498.
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F.; Schneider, M. P.; Fazio, F. J . Org. Chem. 1999, 64, 3767. (b)
Marshall, J . A.; Wolf, M. A. J . Org. Chem. 1996, 61, 3238. (c) Hauske,
J . R.; Dorrf, P.; J ulin, S.; Martinelli, G.; Bussolari, J . Tetrahedron Lett.
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J .; Weinreb, S. M. J . Org. Chem. 1990, 55, 393. (b) Franc, C.; Denonne,
F.; Cuisinier, C.; Ghosez, L. Tetrahedron Lett. 1999, 40, 4555.
(12) Greene, T. W.; Wuts, P. G. M. Protective Groups in Organic
Synthesis, 2nd ed.; Wiley: New York, 1991.
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1069. (b) Bloch, R. Chem. Rev. 1998, 98, 1407. (c) Enders, D.;
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59, 5865. (c) Matsubara, S.; Ukita, H.; Kodama, T.; Utimoto, K. Chem.
Lett. 1994, 931.
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(b) Enders, D.; Schankat, J . Helv. Chim. Acta 1995, 78, 970. (c) Reetz,
M. T.; J aeger, R.; Drewlies, R.; Hu¨bel, M. Angew. Chem., Int. Ed. Engl.
1991, 30, 103. (d) Matsumoto, T.; Kobayashi, Y.; Takemoto, Y.; Ito,
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10.1021/jo9911544 CCC: $18.00 © 1999 American Chemical Society
Published on Web 10/30/1999

Notes
entry
J . Org. Chem., Vol. 64, No. 24, 1999 8971
Ta ble 1. Syn th esis of r-Am id oa lk yl Su lfon es 3
Sch em e 4
carbamate
aldehyde
sulfone yielda
1
2
3
%
1
2
3
4
5
6
7
8
9
1a
1a
1a
1b
1b
1b
1b
1b
1a
n-C7H15CHO
C5H11CHdCHCH2CH2CHO
PhCH2CH2CHO
BnOCH2CH2CH2CH2CHO
PhCHO
(CH3)2CHCH2CHO
c-C6H11CHO
3a
3b
3c
3d
3e
3f
3g
3h
3i
90
84
82
75
70
89
83
77
88
efficiently removed when the free primary amine is
required. 1-Alkynyllithium 6 can be opportunely gener-
ated from the corresponding alkynes using n-butyllithium
as a base and presents a better synthetic flexibility than
vinyl organomagnesium reagents. Indeed, the inclusion
of several extra functions into the lithium derivatives 6
as alkoxy, ester, and trimethylsilyl groups allows a
supplementary synthetic manipulation of the propargyl-
amines 7 obtained.19
PhCH2CH2CHO
(CH3)2CHCH2CHO
a
Yields of pure, isolated products.
Sch em e 2
R-Amidoaryl sulfone 3e, prepared from benzaldehyde,
is known to undergo a base-assisted elimination of
phenylsulfinate anion, giving the corresponding N-acyl
imine.16a This eliminative process is, however, less ef-
ficient when attempted on sulfones 3 coming from
aliphatic aldehydes. Indeed, when sulfone 3f is treated
with 1 equiv of DBU in THF at room temperature, a
diastereomeric mixture of enamines 9f is recovered in
Ta ble 2. Syn th esis of Allyla m in es 5 by Rea ction of
Vin ylm a gn esiu m Br om id e 4 w ith Su lfon es 3
sulfone
allylamine
yielda
%
entry
3
5
1
2
3
4
5
3a
3b
3c
3d
3e
5a
5b
5c
5d
5e
80
92
90
85
93
a
Yields of pure, isolated products.
Sch em e 3
55% yield. In light of these facts, the proposed mechanism
for the synthesis of N-protected allylic and propargylic
amines is portrayed in Scheme 4. The organometallic
reagent initially acts as a base, converting the sulfone 3
into the imine 8, which immediately reacts with another
molecule of the reagent to give the addition product 5 or
7. As a matter of fact, 2 equiv of the organometallic
reagent are needed to obtain the primary amine in
satisfactory yields. When 1 equiv of the reagent is used
all of the sulfone 3 is consumed; however, the yield of
the N-protected amine is low, and it is possible to observe
the presence of a certain amount of the corresponding
enamine coming from a tautomerization of the unreacted
imine 8.
In conclusion we have demonstrated that R-amidoalkyl
sulfones 3 can be used as synthetic equivalents of N-acyl
imines, a class of reactive substrates hardly achievable
through a direct reaction from aldehydes.11a Addition of
a suitable organometallic reagent to sulfones 3 allows in
a straighforward fashion the synthesis of allylic and
propargylic N-protected primary amines that are ame-
nable for useful synthetic transformations.
Ta ble 3. Syn th esis of P r op a r gyla m in es 7 by Rea ction of
1-Alk yn yllith iu m s 6 w ith Su lfon es 3
sulfone
alkynyllithium
propargylamine
yielda
%
entry
3
6 R2
7
1
2
3
4
5
6
7
8
9
3a
3a
3c
3d
3e
3f
3g
3h
3h
3h
Ph
7a
7b
7c
7d
7e
7f
7g
7h
7i
78
75
70
68
78
81
88
89
77
88
CO2Me
MOMOCH2
Ph
Ph
Ph
Ph
n-Bu
Me3Si
Ph
10
7j
a
Yields of pure, isolated products.
sponding N-protected allylamines 5 (Scheme 2, Table 2).
It is worth noting that this reaction also shows an
interesting chemoselectivity as the carbamoyl group is
not affected by the organomagnesium reagent used.
Analogously, simple or functionalized 1-alkynyllithium
reagents 6 react at -78 °C in THF with sulfones 3 to
give N-protected propargylamines 7 in satisfactory yields18
(Scheme 3, Table 3). The use of carbamates 1 as nitro-
geneous derivatives for the synthesis of sulfones 3 is
particularly beneficial because, unlike other N-substit-
uents such as alkyl, acyl, and tosyl groups, they are
Exp er im en ta l Section
1H NMR were performed at 300 MHz in CDCl3 as solvent.
THF was dried by refluxing it over sodium wire. All chemicals
used are commercial. Vinylmagnesium bromide 4 was prepared
from vinyl bromide and magnesium turnings using standard
conditions. 4-(Benzyloxy)pentanal,20 3-(methoxymethoxy)prop-
1-yne,21 and tert-butyl phenylsulfonylphenylmethylcarbamate
3e16a were prepared following literature methods.
(18) For similar reactions on 4-phenylsulfonylazetidin-2-one see: (a)
Maruyama, H.; Hiraoka, T. J . Org. Chem. 1986, 51, 399. (b) Shibasaki,
M.; Nishida, A.; Ikegami, S. J . Chem. Soc., Chem. Commun. 1982,
1324.
(19) Review: The Chemistry of Triple-bonded Functional Groups;
Patai, S., Ed.; Wiley: Chichester, 1994.
(20) Ohtsuka, Y.; Oishi, T. Chem. Pharm. Bull. 1991, 39, 1359.
(21) Piers, E.; Tillyer, R. D. J . Org. Chem. 1988, 53, 5366.

8972 J . Org. Chem., Vol. 64, No. 24, 1999
Notes
Gen er a l P r oced u r e for th e P r ep a r a tion of r-Am id oa lk yl
Su lfon es 3. Carbamate 1 (5 mmol) was dissolved in THF (2 mL),
and then water (5 mL), sodium phenylsulfinate (5 mmol), and
the appropriate aldehyde (5.4 mmol) were sequentially added
at room temperature. Formic acid (1.2 mL) was added, and the
mixture was strirred for 12 h. The resulting white precipitate
was filtered and purified by crystallization (hexanes-ethyl
acetate (4:1)).
Ben zyl 1-p h en ysu lfon yloctylca r ba m a te (3a ): yield 90%;
mp 90 °C; IR (cm-1, KBr) 3340, 1698, 1310, 1140; 1H NMR δ
ppm 0.87 (t, 3H, J ) 6.3 Hz), 1.19-1.53 (m, 9H), 1.60-1.81 (m,
1H), 2.18-2.32 (m, 1H), 2.40-2.65 (m, 1H), 4.78-4.95 (m, 3H),
5.25 (d, 1H, J ) 10.4 Hz), 7.15-7.53 (m, 7H), 7.55-7.70 (m, 1H),
7.83-7.94 (m, 2H). Anal. Calcd for C22H29NO4S (403.53): C,
65.48; H, 7.24; N, 3.47. Found: C, 65.57; H, 7.17; N, 3.52.
ter t-Bu tyl 5-(ben zyloxy)-1-p h en ylsu lfon ylp en tylca r ba m -
a te (3d ): yield 75%; waxy solid; IR (cm-1, neat) 3337, 1719, 1308,
1143; 1H NMR δ ppm 1.20 (s, 9H), 1.41-1.90 (m, 5H), 2.21-
2.38 (m, 1H), 3.48 (t, 2H, J ) 5.6 Hz), 4.48 (s, 2H), 4.81-4.98
(m, 1H), 5.18 (d, 1H, J ) 11.5 Hz), 7.29-7.38 (m, 4H), 7.45-
7.68 (m, 4H), 7.90-7.99 (m, 2H). Anal. Calcd for C23H31NO5S
(433.56): C, 63.72; H, 7.21; N, 3.23. Found: C, 63.81; H, 7.26;
N, 3.29.
mixture was allowed to reach room temperature. The mixture
was extracted with CH2Cl2, and the organic phase was dried
over MgSO4. After removal of the solvent the N-protected
propargylamine 7 obtained was purified by column chromatog-
raphy (hexanes-ethyl acetate (8:2)).
Ben zyl 1-h eptyl-3-ph en ylpr op-2-yn ylcar bam ate (7a): yield
78%; mp 57 °C; IR (cm-1, KBr) 3340, 2230, 1700; 1H NMR δ
ppm 0.89 (t, 3H, J ) 6.8 Hz), 1.16-1.62 (m, 10H), 1.68-1.80
(m, 2H), 4.55-4.79 (m, 1H), 4.93-5.05 (m, 1H), 5.14 (s, 2H),
7.29-7.45 (m, 10H). Anal. Calcd for C24H29NO2 (363.49): C,
79.39; H, 8.04; N, 3.85. Found: C, 79.31; H, 7.99; N, 3.91.
Met h yl 4-[(b en zyloxyca r b on yl)a m in o]u n d ec-2-yn oa t e
(7b): yield 75%; mp 79 °C; IR (cm-1, KBr) 3330, 1690; 1H NMR
δ ppm 0.86 (t, 3H, J ) 6.5 Hz), 1.12-1.40 (m, 10H), 1.50-1.78
(m, 2H), 3.36 (s, 3H), 4.78-4.93 (m, 1H), 4.95-5.10 (m, 1H), 5.13
(s, 2H), 7.29-7.42 (m, 5H). Anal. Calcd for C20H27NO4 (345.43):
C, 69.54; H, 7.88; N, 4.05. Found: C, 69.48; H, 7.97; N, 4.00.
Ben zyl 4-(m eth oxym eth oxy)-1-p h en eth ylbu t-2yn ylca r -
ba m a te (7c): yield 70%; oil; IR (cm-1, neat) 3350, 2180, 1705;
1H NMR δ ppm 1.95-2.10 (m, 2H), 2.76 (t, 2H, J ) 8.1 Hz),
3.38 (s, 3H), 4.24 (s, 2H), 4.50-4.67 (m, 1H), 4.71 (s, 2H), 4.93-
5.05 (m, 1H), 5.11 (s, 2H), 7.12-7.41 (m, 10H). Anal. Calcd for
C22H25NO4 (367.44): C, 71.91; H, 6.86; N, 3.81. Found: C, 71.83;
H, 6.95; N, 3.76.
ter t-Bu t yl cycloh exylp h en ylsu lfon ylm et h ylca r b a m a t e
(3g): yield 83%; mp 134 °C; IR (cm-1, KBr) 3345, 1710, 1325,
ter t-Bu tyl 1-p h en eth yl -3-tr im eth ylsilylp r op -2-yn ylca r -
ba m a te (7i): yield 77%; oil; IR (cm-1, neat) 3322, 2200, 1715;
1H NMR δ ppm 0.18 (s, 9H), 1.45 (s, 9H), 1.85-2.05 (m, 2H),
2.76 (t, 2H, J ) 7.3 Hz), 4.32-4.51 (m, 1H), 4.63-4.70 (m, 1H),
7.15-7.40 (m, 5H). Anal. Calcd for C19H29NO2Si (331.53): C,
68.84; H, 8.82; N, 4.22. Found: C, 68.93; H, 8.77; N, 4.30.
ter t-Bu tyl 1-p h en eth yl-3-p h en ylp r op -2-yn ylca r ba m a te
1
1150; H NMR δ ppm 1.05-1.48 (m, 12H), 1.61-1.82 (m, 6H),
2.05-2.18 (m, 1H), 2.40-2.53 (m 1H), 4.69 (dd, 1H, J ) 11.3,
3.3 Hz), 5.14 (d, 1H, J ) 11.3 Hz), 7.45-7.70 (m, 3H), 7.85-
7.93 (m, 2H). Anal. Calcd for C18H27NO4S (353.47): C, 61.16;
H, 7.70; N, 3.96. Found: C, 61.09; H, 7.75; N, 4.03.
Gen er a l P r oced u r e for th e P r ep a r a tion of Allyla m in es
5. Sulfone 3 was dissolved in dry THF (15 mL), and the solution
was cooled at -20 °C. Vinylmagnesium bromide 4 (4.1 mmol,
0.8 M in THF) was then added dropwise over 15 min, and after
30 min at -20 °C the temperature was slowly raised to 0 °C.
The reaction mixture was then quenched with saturated aqueous
NH4Cl (3 mL), and after exctraction with CH2Cl2 the organic
phase was dried over MgSO4. Removal of the solvent afforded
the crude N-protected allylamine 5, which was purified by
column chromatography (hexanes-ethyl acetate (7:3)).
Ben zyl 1-h ep tyla llylca r ba m a te (5a ): yield 80%; mp 44 °C;
IR (cm-1, KBr) 3330, 1700, 1650; 1H NMR δ ppm 0.88 (t, 3H,
J ) 6.8 Hz), 1.15-1.42 (m, 10H), 1.45-1.62 (m, 2H), 4.05-4.25
(m, 1H), 4.62-4.80 (m, 1H), 5.07 (d, 1H, J ) 1.3 Hz), 5.11 (s,
2H), 5.21 (d, 1H, J ) 1.3 Hz), 5.67-5.81 (m, 1H), 7.29-7.40 (m,
5H). Anal. Calcd for C18H27NO2 (289.41): C, 74.70; H, 9.40; N,
4.84. Found: C, 74.61; H, 9.46; N, 4.78.
ter t-Bu t yl 1-[4-(b en zyloxy)b u t yl]a llylca r b a m a t e (5d ):
yield 85%; oil; IR (cm-1, neat) 3320, 1710, 1650; 1H NMR δ ppm
1.40-1.55 (m, 13H), 1.60-1.77 (m, 2H), 3.47 (t, 2H, J ) 6.4 Hz),
4.05-4.15 (m, 1H), 4.35-4.45 (m, 1H), 4.50 (s, 2H), 5.05-5.20
(m, 2H), 5.65-5.85 (m, 1H), 7.30-7.42 (m, 5H). Anal. Calcd for
C19H29NO3 (319.44): C, 71.44; H, 9.15; N, 4.38. Found: C, 71.56;
H, 9.09; N, 4.41.
1
(7j): yield 88%; mp 96 °C; IR (cm-1, KBr) 3330, 2205, 1720; H
NMR δ ppm 1.45 (s, 9H), 2.00-2.15 (m, 2H), 2.81 (t, 2H, J )
8.1 Hz), 4.60-4.75 (m, 1H), 4.80-4.95 (m, 1H), 7.15-7.50 (m,
10H). Anal. Calcd for C22H25NO2 (335.44): C, 72.77; H, 7.51; N,
4.18. Found: C, 72.88; H, 7.52, N, 4.25.
Ben zyl 3-m eth ylbu t-3-en ylca r ba m a te (9f). Sulfone 3f (0.33
g, 1 mmol) was dissolved in dry THF (8 mL), and DBU (0.18 g,
1.2 mmol) was added at room temperature. After the mixture
strirred for 1 h at room temperature, the solvent was evaporated,
and the crude product was purified by column chromatography
(hexanes-ethyl acetate (95:5)), giving 0.12 g (55% yield) of a
colorless oil: IR (cm-1, neat) 3325, 1708. 1H NMR δ ppm (E)-
isomer: 0.99 (d, 6H, J ) 6.8 Hz), 2.29 (sextet, 1H, J ) 6.5 Hz),
4.98 (dd, 1H, J ) 14.2, 7.0 Hz), 5.14 (s, 2H), 6.20-6.35 (m, 1H),
6.44 (dd, 1H J ) 14.2, 10.8 Hz), 7.30-7.48 (m, 5H); (Z) -isomer:
0.98 (d, 6H, J ) 6.6 Hz), 2.25-2.45 (m, 1H), 4.45-4.60 (m, 1H),
5.15 (s, 1H), 6.25-6.45 (m, 2H), 7.30-7.45 (m, 5H). Anal. Calcd
for C13H17NO2 (219.28): C, 71.21; H, 7.81; N, 6.34. Found: C,
71.33; H, 7.89; N, 6.30.
Ack n ow led gm en t. Financial support from Univer-
sity of Camerino (National Project “Stereoselezione in
Sintesi Organica. Metodologie e Applicazioni”) is grate-
fully acknowledged.
Gen er a l P r oced u r e for th e P r ep a r a tion of P r op a r gyl-
a m in es 7. 1-Alkyne (4 mmol) was dissolved in dry THF (15 mL),
and the solution was cooled to -20 °C. BuLi (4.1 mmol, 2.7 mL,
1.5 M in hexane) was added dropwise, and after 30 min at -20
°C the temperature was lowered to -78 °C. Sulfone 3 (2 mmol)
dissolved in dry THF (5 mL) was added, and the temperature
was kept at -78 °C for 1 h. Quenching was made at -78 °C by
rapid addition of saturated aqueous NH4Cl (4 mL), and the
Su p p or tin g In for m a tion Ava ila ble: Spectral and physi-
cal data for compounds not included in the Experimental
Section. This material is available free of charge via the
Internet at http://pubs.acs.org.
J O9911544