674
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 3, March, 2004
Tomilov et al.
Scheme 7
5ꢀ(Cyclopropylazo)ꢀ8ꢀhydroxyquinoline (9).5 A solution of
isoamyl nitrite (0.58 g, 5 mmol) in 5 mL of CHCl3 was added at
5 °C for 20 min to a stirred mixture of 8ꢀhydroxyquinoline
(0.37 g, 2.5 mmol), TFA (6 mg, 0.5 mmol), and cyclopropylꢀ
amine (0.29 g, 5 mmol) in 10 mL of CHCl3. The reaction mixꢀ
ture was kept at 5 °C for 13 to 16 h. The solvent and the isoamyl
alcohol that formed were removed in vacuo and the target prodꢀ
uct was isolated by preparative TLC with MeOH—benzene (1 : 2)
as an eluent to give compound 9 (0.11 g, 21%), Rf 0.73.
2ꢀ(Cyclopropylhydrazono)malononitrile (10).6 A solution of
cyclopropylamine (0.32 g, 5.6 mmol) in 1 mL of CHCl3 was
added at 5 °C to a magnetically stirred solution of malononitrile
(0.23 g, 3.5 mmol) in 20 mL of CHCl3. The reaction mixture
was kept at 5 °C for 13 to 16 h. Then a solution of isoamyl nitrite
(0.66 g, 5.6 mmol) in 2 mL of CHCl3 was added with stirring at
the same temperature for 20 min. The mixture was stirred for
2 h and kept at 5 °C for an additional 16 h. The solvent and
isoamyl alcohol were removed in vacuo. Preparative TLC
(Et2O—benzene, 1 : 3) of the residue gave hydrazone 10 (0.24 g,
52%), Rf 0.80.
diazonium 1 reacts with 2ꢀnaphthol itself, while in the
second case, more reactive naphtholate anions are inꢀ
volved.
Thus, we showed for the first time that cyclopropylꢀ
diazonium ions can be generated by the reactions of
cyclopropylamine with alkyl nitrites in the presence of
some weak protonating reagents and trapped in azo couꢀ
pling. Malononitrile and 1ꢀ and 2ꢀnaphthols are reactive
substrates in this reaction; in the case of 8ꢀhydroxyquinoꢀ
line, an acid (e.g., 10 mol. % TFA) is required. The presꢀ
ence of reactive unsaturated compounds (e.g., acryloniꢀ
trile or methyl methacrylate) in a reaction mixture allows
diazocyclopropane to be trapped under the same condiꢀ
tions in 1,3ꢀdipolar cycloaddition, which, along with deuꢀ
terium exchange data,12 suggests rapid interconversions
of cyclopropyldiazonium ions and diazocyclopropane. In
the absence of appropriate scavengers, cyclopropylꢀ
diazonium intermediates easily undergo deazotization to
give cyclopropyl and allyl esters of the acids employed for
activation of alkyl nitrites.
Nitrosation of cyclopropylamine in the presence of an equimoꢀ
lar amount of benzoic acid. Benzoic acid (30 mg, 0.25 mmol) was
added at 5 °C to a solution of cyclopropylamine (14 mg,
0.25 mmol) and BunONO (25 mg, 0.25 mmol) in 0.4 mL of
CHCl3. The reaction mixture was kept for 16 h, whereupon
volatile components were removed. Microdistillation of the resiꢀ
due in vacuo (10 Torr, bath temperature 80—90 °C) gave a
fraction (24 mg, 60%) containing allyl and cyclopropyl benꢀ
zoates 11a and 12a in the molar ratio ∼4 : 1, respectively
1
(1H NMR data). H chemical shifts for ester 11a agree with the
literature data13 for PhCOOCDHCH=CH2.
1
Cyclopropyl benzoate (12a). H NMR (CDCl3), δ: 0.85 (m,
4 H, CH2CH2); 4.35 (m, 1 H, CH); 7.31—7.50 and 8.05—8.20
(m, 5 H, Ph). Earlier,14 ester 12a was synthesized by cycloꢀ
propanation of vinyl benzoate with CH2I2 in the presence of
EtZnOCOCF3.
6ꢀMethoxycarbonylꢀ6ꢀmethylꢀ4,5ꢀdiazaspiro[2.4]heptꢀ4ꢀene
(13).8 A solution of BunONO (0.36 g, 3.5 mmol) in 5 mL of
CHCl3 and then cyclopropylamine (0.2 g, 3.5 mmol) in 5 mL of
CHCl3 were added at 5 °C for 10 min to a stirred mixture of
methyl methacrylate (0.35 g, 3.5 mmol) and PhCOOH (4 mg,
0.35 mmol) in 10 mL of CHCl3. The reaction mixture was kept
at 5 °C for 11 days. The solvent and the nꢀbutanol that formed
were removed in vacuo. Distillation of the residue in vacuo gave
compound 13 (0.36 g, 61%).
Nitrosation of cyclopropylamine in the presence of methyl
acrylate. The reaction between methyl acrylate (0.33 g,
3.8 mmol), cyclopropylamine (0.2 g, 3.5 mmol), and isoamyl
nitrite (0.41 g, 3.5 mmol) in 25 mL of CHCl3 in the presence of
PhCOOH (4 mg, 0.35 mmol) (reaction time 40 h) was carried
out according to the above procedure. After the solvent and
volatile compounds were removed from the reaction mixture,
the residue (0.25 g) contained 6ꢀmethoxycarbonylꢀ4,5ꢀdiazaꢀ
spiro[2.4]heptꢀ5ꢀene (14)9 and methyl 3ꢀ(cyclopropylamiꢀ
no)propionate (15)10 in the molar ratio ∼1 : 1.4 (1H NMR data).
Nitrosation of cyclopropylamine in the presence of methyl
methacrylate and an equimolar amount of Me3CCOOH. A mixꢀ
ture of methyl methacrylate (0.175 g, 1.75 mmol), cyclopropylꢀ
amine (0.10 g, 1.75 mmol), Me3CCOOH (0.18 g, 1.75 mmol),
and nꢀbutyl nitrite (0.18 g, 1.75 mmol) in 4 mL of CHCl3 was
kept at 5 °C for 16 h. The solvent and the nꢀbutanol that formed
Experimental
1
H NMR spectra were recorded on Bruker ACꢀ200 and
Bruker AMꢀ300 spectrometers (200 and 300 MHz, respectively)
in CDCl3 with 0.05% Me4Si as the internal standard. Reaction
products were isolated by preparative TLC on Merck silica gel 60
(0.040—0.063 mm). Commercial Merck naphthols, malonoꢀ
nitrile, acrylates, and cyclopropylamine were used without adꢀ
ditional purification. 1ꢀNitrosoꢀ2ꢀnaphthol was prepared acꢀ
cording to a standard procedure.7 The physical and spectroꢀ
scopic characteristics of the compounds obtained correlate with
the literature data.5,6
Azo coupling of cyclopropyldiazonium with naphthols. A soluꢀ
tion of alkyl nitrite (5 mmol) in 5 mL of CHCl3 was added at
5 °C to a stirred solution of 1ꢀ or 2ꢀnaphthol (3.5 mmol) and
cyclopropylamine (5 mmol) in 10 mL of CHCl3. The reaction
mixture was kept for 13 to 16 h. Then the solvent and the
isoamyl alcohol or nꢀbutanol that formed were removed in vacuo
and the reaction products were isolated by preparative TLC with
benzene—Et2O (5 : 1) as an eluent. 1ꢀ(Cyclopropylazo)ꢀ2ꢀnaphꢀ
thol (3) was obtained from 2ꢀnaphthol in ∼60% yield, Rf 0.75. In
the reactions with 1ꢀnaphthol, a mixture of 2ꢀcyclopropylazoꢀ
(4) and 2,4ꢀdi(cyclopropylazo)ꢀ1ꢀnaphthols (6) (molar ratio
1 : 1, Rf 0.85) and 4ꢀcyclopropylazoꢀ1ꢀnaphthol (5) (Rf 0.75)
was isolated (see Ref. 1).