Co(III)DMG-Catalyzed Synthesis of Allylamides from Allyl Alcohols and Acetonitrile

Full text of DOI:10.1021/jo960557q

J . Org. Chem. 1997, 62, 1843-1845
1843
Ch a r t 1
Co(III)DMG-Ca ta lyzed Syn th esis of
Allyla m id es fr om Allyl Alcoh ols a n d
Aceton itr ile
Manoj Mukhopadhyay and J aved Iqbal*
Department of Chemistry, Indian Institute of Technology,
Kanpur 208 016, India
Received March 26, 1996
A recent study from our group has demonstrated1 that
cobalt(II) chloride catalyzes the conversion of allylic
alcohols to the corresponding allylic amides in acetonitrile
medium. This conversion requires the presence of acetic
anhydride or acetic acid (Scheme 1, eq 1, path a), as no
amide formation is observed in their absence and the
allylic alcohols are recovered as a mixture of regioisomers
(Scheme 1, eq 1, path b). A careful study of this reaction
revealed that allylamide formation is occurring via allyl
acetates that are formed by cobalt-catalyzed acylation2
with acetic acid or acetic anhydride. These results clearly
establish that acetic anhydride or acetic acid plays an
important role during the cobalt(II)-catalyzed formation
of allylic amides from the corresponding alcohols or
acetates. In contrast to these observations, we now
demonstrate that Co(III)DMG complex3 (Chart 1) ef-
ficiently catalyzes the conversion of allyl alcohol to the
corresponding allylamide4 in the absence of acetic acid
or acetic anhydride (Scheme 1, eq 1, path c). A brief
account of these findings is described below.
Ta ble 1. Co(III)DMG-Ca ta lyzed Am id a tion of Allylic
Alcoh ols in th e P r esen ce of Nitr ile
Typically, heating the allyl alcohols in acetonitrile in
the presence of Co(III)DMG complex (5 mol %) at 80 °C
for 12-14 h afforded the corresponding allylamides in
good yields. According to this protocol, the allyl alcohol
1 underwent transformation to give a 1:3 mixture of
regioisomers of the corresponding allylamide (Table 1,
entry 1). Similarly, the cyclohexyl allylic alcohol 3
afforded a 1:1 mixture of the corresponding allylic amides
in moderate yields (Table 1, entry 2), whereas the
aromatic allylic alcohols 4 and 5 (Table 1, entries 3 and
4) could be transformed to the corresponding amides in
good yields. The diene alcohol 7 underwent conversion
to the corresponding amide as the only regioisomer (Table
1, entry 5). The cyclic allylic alcohol 8 anti-carviol, from
carvone was transformed to the corresponding amides as
1:1.7 mixture of diastereomers; however, no attempt was
made to separate them (Table 1, entry 6). Similarly, the
tertiary alcohol 9 derived from carvone underwent smooth
transformations to a 1:1.25 mixture of regioisomers, and
each regioisomer was found to be a mixture of diastere-
omers. Interestingly, the ene-yne secondary and ter-
tiary 10 and 11 alcohols underwent complete rearrange-
ment to give the corresponding amide in good yields
(Table 1, entries 8 and 9). It is noteworthy that these
reactions could also be performed in acetic acid medium
a
b
Isolated yield. The ratio for the regioisomers was determined
by the chemical shift of methyl signals in 1H NMR. c A mixture of
diastereomers was obtained. The ratio of E:Z was found to be
d
nearly 1 in these cases. The chemical shift of the olefinic proton
in the E alkene was upfield compared to the corresponding Z
alkene. e Carveol (8) was obtained after purification as a single
anti diastereomer from sodium borohydride reduction of optically
pure (-)-carvone. f The isomer ratio of this alcohol (obtained from
carvone) could not be determined as the crude alcohol was used.
g
h
The E:Z ratio was determined by NMR. Obtained mainly as
the E isomer.
using a stoichiometric amount of acetonitrile in compa-
rable yields. The regiochemistry of amidation here does
not change to any significant extent compared to the
transformation conducted in acetonitrile medium. We
were unable to form the amide from allyl alcohol 12.
However, the corresponding acetate 13 underwent ami-
dation to afford a 1:1.7 mixture of the regioisomers in
good yields (eq 2). It is also interesting to note that CoCl2
did not catalyze amide formation from the allyl acetate
13. In view of these observations, it is evident that CoCl2-
and Co(III)DMG-catalyzed amidation reactions are oc-
(1) Mukhopadhyay, M.; Reddy, M. M.; Maikap, G. C.; Iqbal, J . J .
Org. Chem. 1995, 60, 2670.
(2) Iqbal, J .; Srivastava, R. R. J . Org. Chem. 1992, 57, 2001.
(3) Co(III)DMG complex was prepared according to the known
procedure: Costa, G.; Tauzher, G.; Puxeddu, A. Inorg. Chim. Acta 1969,
3, 45. There is no detailed structural information available on this
complex. The proposed structure incorporates an undefined stereo-
chemistry of oxime anion.
(4) For some recent syntheses of allylamide and amines see: (a)
Singer, S. P.; Sharpless, K. B. J . Org. Chem. 1978, 43, 1448. (b)
Helquist, P.; Connell, R. D.; Akermark, B. J . Org. Chem. 1989, 54,
3359. (c) Buchwald, S. L.; Watson, B. T.; Wannamakar, M. W.; Dewan,
J . C. J . Am. Chem. Soc. 1989, 111, 4486.
S0022-3263(96)00557-9 CCC: $14.00 © 1997 American Chemical Society

1844 J . Org. Chem., Vol. 62, No. 6, 1997
Notes
Sch em e 1
(1)
(2)
Sch em e 2
Sch em e 3
an intermediate 14c. An intramolecular attack on 14c
by acetate will afford the imidate ester 14d , which on
base hydrolysis during the workup will afford the allyl
amide 15. On the other hand, Co(III)DMG-catalyzed
amidation may be proceeding via a well-known outer-
sphere electron-transfer process from allylic alcohol to
cobalt(III) to afford a radical cation 16a , which may exist
in equilibrium with 16b (Scheme 3). An attack by
acetonitrile on 16b or the corresponding π-allyl complex
16c will afford 16d , which on an intramolecular attack
of hydroxide will yield the allylamide 15. This mecha-
nistic proposal seems reasonable as reduction of allyl
acetate by cobalt(II) is shown to proceed easily by cyclic
voltammetric studies. Similarly, reduction of cobalt(III)
by allylic alcohol via an electron-transfer process is very
well precedented in literature.8
curring via different pathways. It is also noteworthy that
Co(III)DMG-catalyzed reactions are not occurring via a
[3,3] sigmatropic rearrangement of acetamidate5 obtained
in a Pinner reaction6 as such a process would lead to a
completely rearranged allylic amide that is contrary to
our observations.
The preliminary mechanistic exploration based on
cyclic voltammetric studies7 indicates that allyl acetates
can easily be reduced in the presence of cobalt(II). This
indicates that coordination of cobalt(II) to acetate results
in lowering of reduction potential of acetate and the
cobalt complexed acetate is easily reduced by an electron
transfer from another cobalt(II) species to give a radical
anion 14a (Scheme 2). The latter may form an π-allyl
complex, 14b, which on attack by acetonitrile may give
(5) For rearrangements of allylic imidates see: Overman, L. E. Acc.
Chem. Res. 1980, 13, 218.
(6) For the Pinner reaction see: Compagnon, P. L.; Miocque, M. Ann.
Chim. (Paris) 1970, 5, 23.
(7) Cyclic voltammetry on acetate 14 (R ) Ph, R′ ) Et) in the
presence of CoCl2 in acetonitrile showed an oxidative response at +0.04
V (vs saturated calomel electrode in 15 mL of dry acetonitrile) in the
form of a catalytic current presumably arising due to the oxidation of
this acetate. This oxidative response was not observed in the absence
of CoCl2. This observation supports the assumption that addition of
CoCl2 lowers the reduction potential of acetate 14 through coordination.
The coordination of acetate 14 to cobalt(II) will result in charge transfer
to the metal, and this process may facilitate an electron transfer to
acetate from another cobalt(II) species.
In conclusion, Co(III)DMG-catalyzed amidation offers
a viable alternative to the corresponding Co(II)-catalyzed
transformation. This methodology has the advantage
that it does not require the mandatory formation of allyl
acetate prior to the reaction. We are currently persuing
studies to delineate the mechanism of Co(II)- and
Co(III)-catalyzed amidation reactions.
(8) Sheldon, R. A.; Kochi, J . K. Metal Catalyzed Oxidation of Organic
Compounds; Academic: New York, 1981.

Notes
J . Org. Chem., Vol. 62, No. 6, 1997 1845
and brine (2 × 20 mL). Drying (Na2SO4) and removal of the
solvent yielded a residue that on column chromatography (SiO2)
afforded the amides. The ratio of regioisomers was determined
by 1H NMR of the crude reaction mixture.
Exp er im en ta l Section
Ma ter ia ls a n d Meth od s. Acetonitrile, acetic acid, and all
other solvents and reagents were purified by the standard
procedure before use.9 CoCl2 was purchased from LOBA India
Ltd., Bombay, and dried at 110 °C for 2-3 h before the reaction.
The Co(III)DMG complex was prepared according to the litera-
ture procedure.3 Column chromatography was performed using
60-120 mesh (ACME) TLC silica gel or neutral alumina. 1H
NMR spectra were recorded at 60 and 80 MHz in CDCl3 or CCl4.
Chemical shifts are referenced relative to TMS and reported in
δ units. All of the starting allylic alcohols were prepared
according to literature procedures and compared with their 1H
NMR spectra.1 All of the known amides were characterized by
comparison with the literature data.1
The reaction of allyl acetate (13)1,10 (10 mmol) was carried
out as described in the general procedure by heating in MeCN
and Co(III)DMG (5 mol %) at 80 °C for 11 h to afford 13a and
13b as a 1:1.7 regioisomeric mixture.
Meth yl 3-a ceta m id o-2-m eth ylen eh exa n oa te (13a ): 1H-
NMR (CDCl3) 7.2 (bd, 1H), 6.2 (d, J ) 2.5 Hz, 1H), 5.6 (d, J )
2.5 Hz, 1H), 5.6 (m, 1H), 3.65 (s, 3H), 2.10 (s, 3H), 1.25-1.60
(m, 4H), 0.85 (t, J ) 5.0 Hz, 3H); IR (thin film) 3280, 2972, 1710,
1640 cm-1; FABMS m/ z (rel intensity) 199 (28) [M+], 200 (100)
[M+ + 1].
Meth yl 2-(m eth yla ceta m id o)h ex-2-en oa te (13b): 1H-NMR
(CDCl3) 7.2 (bd, 1H), 6.9 (t, J ) 7.0 Hz, 1H), 4.2 (s, 2H), 3.65 (s,
3H), 1.95 (s, 3H), 1.25-1.60 (m, 4H), 0.85 (t, J ) 5.0 Hz, 3H);
Gen er a l P r oced u r e for th e Co(III)DMG-Ca ta lyzed Am i-
d a tion of Allylic Alcoh ol/Aceta te. Allylic alcohol/acetate (10
mmol) was added to a solution of Co(III)DMG (5 mol %) in dry
acetonitrile (30 mL). The reaction mixture was heated at 80 °C
for 12-14 h while the progress of the reaction was monitored
by TLC. The solvent was removed in vacuo, and the residue
was dissolved in EtOAc (50 mL). The organic layer was washed
successively with aqueous NaHCO3 solution (3 × 15 mL), water,
IR (thin film) 3280, 2972, 1710, 1640 cm-1
.
Ack n ow led gm en t. MM wishes to thanks the CSIR,
New Delhi for senior research fellowship.
J O960557Q
(10) Allyl acetate 13 was prepared from the corresponding alcohol
12 obtained according to the following procedure: Basavaiah, D.
Tetrahedron Lett. 1986, 27, 2031.
(9) Vogel’s Textbook of Practical Organic Chemistry, 4th ed.; Vogel,
A. I., Ed.; ELBS: England, 1984.