Mendeleev
Communications
Mendeleev Commun., 2008, 18, 16–17
Unusual reactions of 1-(alk-1-ynyl)-1-chlorocyclopropanes
with lithium monoalkylamides
Konstantin N. Shavrin,a Valentin D. Gvozdev,*a Serafim V. Yurovb and Oleg M. Nefedova
a N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 119991 Moscow, Russian
Federation. Fax: +7 499 135 5328; e-mail: vgvozdev2006@yandex.ru
b D. I. Mendeleev University of Chemical Technology of Russia, 125047 Moscow, Russian Federation
DOI: 10.1016/j.mencom.2008.01.007
Depending on the substituent at the triple bond, the reaction of 1-(alk-1-ynyl)-1-chlorocyclopropanes 1 with lithium mono-
alkylamides in THF gives hitherto unknown conjugated iminocyclopropenes 2 or 4-substituted 1,1-dimethylbuta-1,2-dienes 3 in
up to 60% yields.
Recently,1 we found that the reaction of 1-(alk-1-ynyl)-1-chloro-
cyclopropanes 1 with lithium dialkylamides in THF results in
hitherto unknown 1-dialkylamino-2-alkynylcyclopropanes, which
are formed by the addition of dialkylamide anions to inter-
mediate conjugated alkynylcyclopropenes. In continuation, we
studied the reactions of 1-(alk-1-ynyl)-1-chlorocyclopropanes 1
with various lithium monoalkylamides.
Cl
RNHLi/THF
20 °C
Ph
Ph
NR
1a
2a R = Me
2b R = Pr
2c R = Bu
Unexpectedly, the addition of 1-chloro-2,2-dimethyl-1-phenyl-
ethynylcyclopropane 1a to a fivefold excess of lithium mono-
alkylamides in THF at 20 °C gave conjugated iminocyclo-
propenes 2a–c† in 50–60% yields rather than expected alkynyl-
(monoalkylamino)cyclopropanes (Scheme 1).
Scheme 1
However, under the same conditions, the reaction of lithium
monoalkylamides with alkynylchlorocyclopropanes 1b,c carrying
bulky substituents such as tert-butyl and adamantyl at the triple
bond gave 4-(tert-butyl)- and 4-(adamant-1-yl)-1,1-dimethyl-
buta-1,2-dienes 3a,b,† respectively, in 40–50% yields; the latter
compounds had one carbon atom less than the original ones
(Scheme 2).
†
The structures of the new compounds obtained were proved by 1H and
13C NMR and mass spectra. NMR spectra were measured on a Bruker
AC200p spectrometer (200 and 50 MHz for 1H and 13C, respectively) in
CDCl3 solutions. Mass spectra were determined on a Finnigan MAT
INCOS-50 mass spectrometer.
R1
1
Cl
For 2a: H NMR, d: 1.27 (s, 6H, 2Me), 2.50 (q, 2H, CH2, J 1.3 Hz),
RNHLi/THF
R1
C
3.29 (t, 3H, NMe, J 1.3 Hz), 6.78 (s, 1H, =CH, cyclo-C3H), 7.24–7.43
(m, 3H, m-H, p-H in Ph), 7.68–7.73 (m, 2H, o-H in Ph). 13C NMR, d:
28.7 (2Me), 40.3 (CMe2), 40.8 (NMe), 43.3 (CH2), 127.4, 127.8, 128.0
(Ph), 133.7 (C-1 in Ph), 141.2 (C=CH), 155.5 (C=CH), 176.5 (C=NMe).
MS, m/z: 199 [M+].
20 °C
1b R1 = But
1c R1 = Ad
3a R1 = But
3b R1 = Ad
R = Me, Pr, Bu
For 2b: 1H NMR, d: 1.06 (t, 3H, Me in Pr, J 6.9 Hz), 1.29 (s, 6H,
2Me), 1.69–1.85 (m, 2H, CH2), 2.52 (t, 2H, CH2, J 1.2 Hz), 3.37 (tt, 2H,
NCH2, J 7.1 Hz, J 1.2 Hz), 6.80 (s, 1H, =CH, cyclo-C3H), 7.25–7.45 (m,
3H, m-H, p-H in Ph), 7.75–7.82 (m, 2H, o-H in Ph). 13C NMR, d: 12.3
(Me in Pr), 23.0 (CH2 in Pr), 29.0 (2Me), 40.5 (CMe2), 43.7 (CH2), 55.8
(NCH2), 127.5, 128.0, 128.6 (Ph), 134.0 (C-1 in Ph), 141.1 (C=CH),
155.3 (C=CH), 174.3 (C=NPr). MS, m/z: 227 [M+].
For 2c: 1H NMR, d: 1.05 (t, 3H, Me in Bu, J 6.9 Hz), 1.29 (s, 6H,
2Me), 1.42–1.63 (m, 2H, CH2), 1.70–1.85 (m, 2H, CH2), 2.51 (t, 2H,
CH2, J 1.2 Hz), 3.42 (tt, 2H, NCH2, J 7.1 Hz, J 1.2 Hz), 6.71 (s, 1H,
=CH, cyclo-C3H), 7.25–7.44 (m, 3H, m-H, p-H in Ph), 7.68–7.73 (m,
2H, o-H in Ph). 13C NMR, d: 14.0 (Me in Bu), 20.8 (CH2 in Bu), 28.9
(2Me), 33.0 (CH2 in Bu), 40.3 (CMe2), 43.5 (CH2), 53.6 (NCH2), 127.5,
127.9, 128.4 (Ph), 133.9 (C-1 in Ph), 141.0 (C=CH), 155.1 (C=CH),
174.1 (C=NBu). MS, m/z: 241 [M+].
Scheme 2
By analogy with the reactions of lithium dialkylamides with
chlorides 1, it can be assumed that the reactions of the latter
with lithium monoalkylamides most likely proceed via inter-
mediate alkynylcyclopropenes 4. This assumption is supported,
for example, by the fact that the reaction of 1-(tert-butylethynyl)-
3,3-dimethylcyclopropene1 4b with an excess of lithium propyl-
amide results in corresponding allene 3a. Resulting alkynyl-
cyclopropenes 4 add monoalkylamide ions to the double bond
of the cyclopropene ring to give 1-(alk-1-ynyl)-2-(alkylamino)-
cyclopropanes 5; subsequent transformations of the latter under
the conditions used are governed by the nature of the substi-
tuent at the triple bond. In the case of the electronegative phenyl
group, the main reaction pathway involves the intramolecular
addition of the amino group to the triple bond followed by its
abstraction from the cyclopropane ring to give eventually cor-
responding iminocyclopropenes 2a–c. In the case of electron-
donating tert-butyl or adamantyl groups, a rearrangement into
corresponding intermediate iminocyclopropanes 6 is most likely
to occur. The latter decompose with elimination of an isonitrile
to give allenes 3a,b, similarly to the known precedents2,3
(Scheme 3).
For 3a: 1H NMR, d: 0.89 (s, 9H, 3Me), 1.56 (d, 6H, CMe2, J 3.0 Hz), 1.83
(d, 2H, CH2CMe3, J 7.8 Hz), 4.89 (t sept., 1H, CH2CH=, J 7.8 Hz, J 3.0 Hz).
13C NMR, d: 20.7 (2Me), 29.0 (CMe3), 31.1 (CMe3), 44.2 (CH2CMe3),
85.6 (CH2CH=), 93.2 (=CMe2), 203.2 (=C=). MS, m/z: 138 [M+].
1
For 3b: H NMR, d: 1.51 (d, 6H, 2Me, J 2.8 Hz), 1.63–1.71 (m, 6H,
3CH2 in Ad), 1.70 (d, 6H, 3CH2 in Ad, J 2.7 Hz), 1.72 (d, 2H, CH2Ad,
J 7.9 Hz), 1.92–2.02 (m, 3H, 3CH in Ad), 4.89 (t sept., 1H, CH2CH=,
J 7.9 Hz, J 2.8 Hz). 13C NMR, d: 20.8 (2Me), 28.9 (2CH in Ad), 33.1
(C-1 in Ad), 37.3 (3CH2 in Ad), 42.3 (3CH2 in Ad), 44.8 (CH2Ad), 84.2
(CH2CH=), 93.1 (=CMe2), 203.3 (=C=). MS, m/z: 216 [M+].
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