Synthesis of α-arylalkylamines by addition of Grignard reagents to N- (diethoxyphosphoryl)aldimines

Article abstract of DOI:10.1055/s-1999-3496

Addition of organomagnesium bromides to N-(diethoxyphosphoryl) aldimines 1 carded out in tetrahydrofuran at 20-25°C affords diethyl N-alkyl- phosphoramidates 2a-w in high yields and spectroscopic purity. Deprotection of the latent amino groups in 2 results in the formation of α-arylalkylamine hydrochlorides 3a-w.

Full text of DOI:10.1055/s-1999-3496

930
PAPER
Synthesis of a-Arylalkylamines by Addition of Grignard Reagents to
N-(Diethoxyphosphoryl)aldimines
Andrzej Zwierzak,* Anna Napieraj
Institute of Organic Chemistry, Technical University (Politechnika), Øeromskiego 116, PL-90924 £ódü, Poland
Fax +48(42)6365530
Received 14 September 1998
yl N-alkylphosphoramidates 2a–r in high yields (85–
95%) (Scheme). Crude adducts 2 were spectroscopically
pure (31P NMR, see Table 1) and could be used for subse-
quent dephosphorylation without additional purification.
It turned out to be essential to use 1 mole excess of Grig-
nard reagent in order to secure high yields of addition and
to avoid the formation of undesirable impurities. A variant
of the Barbier procedure11 was used to effect the addition
of an alkyl group to N-(diethoxyphosphoryl)aldimines 1.
In our hands the addition of allyl bromide to the solution
of imine 1 in tetrahydrofuran containing magnesium at
ambient temperature afforded diethyl N-aryl-N-homoal-
lylphosphoramidates 2s–w in high yields (83–92%) and
excellent purity (31P NMR). The formation of side prod-
ucts was entirely suppressed under such conditions.
Abstract: Addition of organomagnesium bromides to N-(diethoxy-
phosphoryl) aldimines 1 carried out in tetrahydrofuran at 20–25°C
affords diethyl N-alkyl-phosphoramidates 2a–w in high yields and
spectroscopic purity. Deprotection of the latent amino groups in 2
results in the formation of a-arylalkylamine hydrochlorides 3a–w.
Key words: N-Phosphorylated imines, nucleophilic addition, de-
phosphorylation of phosphoramidates, Barbier reaction
The development of methods for the synthesis of primary
amines is still an active area of research in organic chem-
istry.2,3 Among the various procedures leading to this
class of compounds two general approaches have been
most widely recommended recently. Nucleophilic ring-
opening of N-activated aziridines with various copper-
modified Grignard reagents usually proceeds regiospecif-
ically at the less hindered carbon atom affording, after
deprotection, the respective primary amine with
a-branched carbon skeleton.4 Alternative construction of
a primary amine molecule from two different building
blocks may also involve nucleophilic addition of organo-
metallic compound to the C=N bond of suitably ”masked”
imine derivatives,5 such as sulfenimines,6 sulfonimines,7
N-(trimethylsilyl)imines,8 N-diphenylphosphinylimines,9
and recently also resin-immobilized aldimines on Rink
resin.2 Addition followed by the removal of the protecting
group leads to a primary amine with a suitably elaborated
carbon skeleton. The wide implementation of N-activated
aziridines into synthetic practice is evidently still ham-
pered by their limited preparative accessibility. The rela-
tively poor electrophilicity of the imine carbon atom and
often difficult deprotection of the adducts leading to un-
satisfactory yields and/or low purity of the target amines
is the notorious drawback of all methods utilizing
”masked” imines.
In a search for a simple, effective and economic procedure
which could be applicable especially for multigram scale
preparation of primary a-arylalkylamines we have fo-
cused our attention on N-(diethoxyphosphoryl)aldimines
1 recently prepared in our laboratory.10 These easily avail-
able N-protected imines can be considered as natural pre-
cursors of primary amines because the diethoxy-
phosphoryl group can function both as C=N bond activa-
tor and be easily detached once nucleophilic addition has
been attained. N-(Diethoxyphosphoryl)aldimines 1 react-
ed easily and smoothly with organomagnesium bromides
in tetrahydrofuran at 20–25°C to give the respective dieth-
Scheme
The standard removal4 of the diethoxyphophoryl group
from diethyl N-substituted phosphoramidates 2 by reflux-
Synthesis 1999, No. 6, 930–934 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Synthesis of a-Arylalkylamines
931
ing them with 20% hydrochloric acid (Method A) was in chloride. Crude a-arylalkylamine hydrochlorides 3 deliv-
some cases totally ineffective leading to very poor yields ered analytically pure samples after recrystallization from
of impure amine hydrochlorides. The use of (1:1, v/v) ethanol/diethyl ether. Yields, melting points, and the rele-
mixture of 20% hydrochloric acid and tetrahydrofuran at vant spectral assignments of compounds 2 and 3 are com-
room temperature (Method B) was then found to be the piled in Tables 1 and 2.
method of choice for deprotection (Scheme) although the
reaction times were long (Table 1). The resultant solutions
The outlined method for the synthesis of a-arylalkyl-
amines represents a versatile and relatively inexpensive
of a-arylalkylamine hydrochlorides 3 were transformed
approach to these compounds from easily available start-
into free amines, isolated by extraction with diethyl ether,
ing materials.
and characterized as amine hydrochlorides 3a–w obtained
by saturation of ethereal solutions with dry hydrogen
Table 1 a-Arylalkylamine Hydrochlorides 3 Prepared
Product
31P NMR of 2
δ
Deprotection Meth-
oda
Yield (%)b
mp (oC)
found
reported
3a
3b
3c
8.04
8.27
8.60
A (1 h)
A (1 h)
A (1 h)
47
66
49
156–158
192–193
265–267 dec
(157–158,12 160–16213)
(192–193,14 189.515)
(275–277 dec,16
195-19617)
3d
3e
3f
8.55
7.75
7.88
8.03
8.35
8.37
7.59
7.73
8.28
8.67
8.20
8.39
7.97
7.73
8.50
8.06
8.12
7.96
8.34
7.57
A (1 h)
B (9 d)
B (6 d)
A (1 h)
A (1 h)
A (1 h)
B (10 d)
B (7 d)
B (1 d)
B (8 h)c
B (2 d)
B (8 d)
B (2 d)
B (3 d)
B (2 d)
B (3 d)
B (4 d)
_f
76
56
59
63
82
56
54
61
58
55
63
42
34d
59
54e
65
63
59
47
57
310 dec
(310 de,18 33014)
255–257 dec)
163–165
(256–260,19 27320
–
3g
3h
3i
262–263
(272–27317)
273–290 dec
290 dec
–
–
3j
269–270 dec
230–232 dec
221–223
–
3k
3l
–
(217–21821)
3m
3n
3o
3p
3q
3r
217–219 dec
205–207
–
–
200–202 dec
142–144 dec
173–175
(203 dec,19 181–18222)
–
–
212–214 dec
223–225 dec
212–214 dec
204–205
–
3s
3t
(224–22614)
–
–
–
–
3u
3v
3w
B (30 h)
B (3 d)
163–165
194–196 dec
a Reaction time is given in parentheses.
b Overall yields of analytically pure compounds. Satisfactory microanalyses obtained:C ± 0.21, H ± 0.35, N ± 0.25.
c Deprotection was carried out at 35–40oC.
d Isolated as amine tosylate.
e The compound was identified as pure a-allylcinnamylamine hydrochloride.
f Deprotection was carried out by refluxing with ethanolic hydrogen chloride for 2 h.
Synthesis 1999, No. 6, 930–934 ISSN 0039-7881 © Thieme Stuttgart · New York

932
A. Zwierzak, A. Napieraj
PAPER
Table 2 Spectroscopic Data for α-Arylalkylamine Hydrochlorides 3
Product
3a
IR (nujol)a
(cm-1)
1H NMR (CD3OD/TMS)
d, J (Hz)
MS–FAB
m/z, MH+ –HCI (%)
2990, 2570, 1610, 15121458,
1370, 1072
1.64 (d, 3 H, J = 7.0, CH3), 4.44 (q, 1 H, J = 7.0, CH), 4,87
(s, 3 H, NH3), 7.40–7.45 (m, 5 H, ArH)
122 (51)
3b
2995, 2660, 2000, 1605, 1516,
1480, 1370, 1120, 1079
0.89 (t, 3 H, J = 7.5, CH3, 1.92–2.14 (m, 2 H, CH2), 4.16
(dd, 1 H, J = 9.3, 6.0, CH), 4.87 (s, 3 H, NH3), 7.41–7,49 (dd, 1
H, J = 9.3, 6.0, CH), 4.87 (s, 3 H, NH3), 7.41–7,49
136 (52)
150 (42)
3c
2968, 2672, 2568, 1968, 1604,
1512, 1484, 1460, 1376, 1160,
1096, 1072
0.80, 1.15 (2 d, 6 H, J = 6.6, CH3), 2.10–2.30 (m, 1 H, CH), 3.92
(d, 1 H, J = 9.3, CH-Ph), 4,87 (s, 3 H, NH3), 7.38–7.46 (m, 5 H,
ArH)
3d
3e
2912, 2696, 2672, 1608, 1568,
1512, 1448
0.83–2.09 (m, 1 H, CH), 3,94 (d, 1 H, J = 9.3 CH-Ar), 4.87
(s, 3 H, NH3), 7.36–7.46 (m, 5 H, ArH)
190 (59)
198 (20)
2968, 2656, 2616, 2224, 2040,
1604, 1560, 1516, 1504, 1496,
1448, 1408, 1384, 1192, 1032
2.35 (s,3 H,CH3), 4.87 (s,3 H,NH3), 5.59 (s,1 H, CH),
7.24–7.31 (m,4 H,ArH), 7.39–7.49 (m,5 H,ArH)
3f
2864, 2056, 1600, 1512, 1448,
1360
4.55 (s,3 H,NH3),5.04 (d,1H, J = 6.5,CH), 5.44 (dd,1 H, J =
17.3, 1.3, =CH), 5.51(dd,1 H, J = 10.6, 1.0, =CH), 6.19 (ddd, 1
H, J = 17.3, 10.6, 6.5, =CH), 7.43–7.57 (m,5 H,ArH)b
134 (32)
3g
3960, 3248, 2872, 2656, 2616,
2288, 2024, 2000, 1592, 1512,
1496, 1484, 1416, 1364, 1304,
1120, 1072, 1008
0.89 (t,3 H, J = 7.4,CH3), 1.88–2.10 (m,2 H,CH2), 4.18 (dd,1 H,
J = 9.1, 6.0, CH), 4.89 (s,3 H, NH3), 7.36–7.65 (m,4 H,ArH)
214 (59), 216 (56)
3h
3i
2896, 2032, 2000, 1596, 1500,
1488, 1424, 1392, 1384, 1376,
1312, 1216, 1072, 1008
0.80, 1.14 (2 d,6 H, J = 6.8,CH3), 2.09–2.83 (m,1 H CH), 3.95
(d,1 H, J = 9.3,CH-Ar). 4.87 (s,3 H ,NH3,), 7.27–7.66
(m,4 H,ArH)
228 (62), 230 (61)
268 (64), 270 (60)
274 (8), 276 (8)
212 (32), 214 (31)
166 (5)
2928, 2000, 1596, 1520, 1504,
1496, 1448, 1424, 1384, 1072,
1008
0.84–2.00 (m,11 H,6 x CH2,CH), 3.95 (d,1 H, J = 9.3, CH-Ar),
4.89 (s,3 H,NH3), 7.30–7.65 (m,4 H,ArH)
3j
2944, 2632, 2600, 2024, 2000,
1604, 1564, 1524, 1500, 1488,
1416, 1380, 1192, 1072
2.26 (s,3 H,CH3), 4.87 (s,3 H,NH3), 5.60 (s,1 H,CH), 7.28
(brs,4 H,ArH), 7.29–7.64 (m,4 H,ArH)
3k
3l
2888, 040, 1596, 1512, 1416,
1072
4.84 (s,3 H,NH3), 4.96 (d,1 H, J = 6.5,CH), 5.43 (dd, 1 H,
J = 17.3, 1.5,=CH), 5.51(dd,1 H, J = 10.5, 1.0, =CH), 6.13 (ddd,
1 H, J = 17.3, 10.5, 6.5,=CH), 7.36–7.66 (m,4 H,ArH)
2936, 2576, 2544, 2000, 1616,
1592, 1560, 1516, 1464, 1388,
1312, 1248, 1184, 1032
0.88 (t,3 H, J = 7.5,CH3), 1.90–2.07 (m,2 H, CH2), 3.82
(s,3 H,CH3O), 4.09 (dd,1 H, J = 9.5, 6.0, CH-Ar), 4.87
(s,3 H,NH3), 6.97–7.39 (m,4 H,ArH)
3m
3296, 2968, 2224, 2000, 1592,
1580, 1544, 1500, 1380, 1308,
1296, 1260, 1188, 1080, 1064,
1028
0.79, 1.13 (2 d,6 H, J = 6.8,CH3), 2.09–2.32 (m,1 H, CH), 3.81
(s,3 H,CH3O) 3.85 (d,1 H, J = 9.3,CH-Ar), 4.86 (s,3 H, NH3),
6.96–7.40 (m,4 H,ArH)
180 (4)
3n
3o
3p
2936, 1608, 1512, 1460, 1388,
1252, 1184, 1032
0.91 (t,3 H, J = 7.0,CH3), 1.07–1.46 (m, 4 H, 2 x CH2), 1.94–
2.03 (m, 2 H,CH2), 3.84 (s,3 H,CH3O), 4.19 (dd,1 H,J=9.3,
J = 6.3,CH-Ar), 4.88 (s,3 H,NH3), 6.99–7.41 (m,4 H,ArH)
194 (5)
2968, 2604, 2224, 2000, 1604,
1560, 1505, 1460, 1380, 1184,
1030
3.79 (s,3 H,CH3O), 4.87 (s,3 H,NH3) 5.59 (s,1 H, CH),
6.96–7.37 ( m,4 H, ArH), 7.39–7.50 (m,5 H,ArH)
214 (15)
–
0.95 (t,3 H, J = 7.5,CH3), 1.96–2.10 (m,2 H, CH2), 2.39
(s,3 H,CH3), 4.34(dd,1 H, J = 9.0, 6.0,CH-Ar), 6.49(dd,1 H,
J = 3.3, 1.8,=CH), 6.55 (brd, 1 H, J = 3.3,=CH), 7.25
(m,2 H,ArH), 7.62 (brd,1 H, J = 3.3,=CH), 7.73 (m,2 H,ArH)
126 (78) (MH+ –
TsOH)
Synthesis 1999, No. 6, 930–934 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Synthesis of a-Arylalkylamines
933
Table 2 (continued)
Product
IR (nujol)a
1H NMR (CD3OD/TMS)
δ, J (Hz)
MS–FAB
(cm-1)
m/z, MH+ –HCI (%)
3q
2880, 2648, 2624, 2048, 1609,
1512, 1384, 704
0.80 (t,3 H, J = 7.4,CH3), 1.75–2.13 (m,2 H, CH2), 4.38–4.50
(m,1 H,CH-Ar), 7.06(dd,1 H, J = 3.6, 5.1,=CH), 7.28 (dd, 1 H,
J = 3.6, 1.0,=CH). 7.56 (dd,1 H, J = 5.1, 1.0,=CH), 8.71
(brs,3 H,NH3)c
142 (55)
3r
3s
3t
2920, 2632, 2576, 2536, 2056,
1600, 1520, 1448, 1384, 968,
696
1.02(t,3 H, J = 7.5,CH3), 1.74–1.92 (m,2 H, CH2), 3.80 (dt,1 H,
J = 8.5,5.5,CH), 4.86(s,3 H,NH3), 6.16 (dd,1 H, J = 15.9, 8.5,
=CH), 6.80 (d,1 H, J = 15.9,=CH), 7.26–7.49 (m,5 H,ArH)
162 (35)
148 (85)
162 (37)
198 (22)
174 (17)
2888, 1600, 1512, 1440
2.71–2.75 (m,2 H,CH2), 4.35 (t,1 H, J = 7.5, CH), 7.26–7.49
(m,5 H,ArH) 4.87 (s,3 H,NH3), 5.13–5.24 (m,2 H,=CH2), 5.61–
5.79 (m,1 H, =CH), 7.41-7.47 (m,5 H,ArH)
2872, 1596, 1512, 1440
2.36 (s,3 H,CH3), 2.69–2.76 (m,2 H,CH2), 4.30 (t,1 H,
J = 7.6,CH), 4.85 (s,3 H,NH3), 5.12–5.23 (m, 2 H,=CH2), 5.61–
5.77 (m, 1 H,=CH), 7.25–7.39 (m,4 H,ArH)
3u
3v
2920, 1640, 1592, 1512, 1440
2880, 1596, 1512, 1448, 1384
2.72–2.94 (m,2 H,CH2), 4.95–5.10 (m, 2 H,=CH2), 5.20–5.28
(m,1 H,CH), 5.60–5.76 (m,1 H,=CH), 7.55–8.22 (m,7 H,ArH),
8.82 (br s. 3 H, NH3)c
2.59 (t,2 H, J = 7.3,CH2), 3.99 (q,1 H, J = 7.3, CH), 4.86
(s,3 H,NH3), 5.22–5.32 (m,2 H, =CH2) 5.76–5.92 (m, 1 H,=CH),
6.21 (dd, 1 H, J = 8.3,16.0,=CH), 6.78 (d,1 H, J = 16.0, =CH),
7.16–7.49 (m,5 H,ArH)
3w
2912, 2640, 2592, 2040, 1604,
1512, 1436, 1384, 1248
2.58–2.87 (m,2 H,CH2), 4.58–4.64 (m,1 H,CH) 5.01–5.13
(m,2 H,=CH2), 5.56–5.72 (m,1 H, =CH), 7.04 (dd,1 H,
J = 3.5,5.0,ArH),7.28 (dd,1 H,J = 5.0, 1.0,ArH), 7.55 (dd,1 H,
J = 5.0, 1.0,ArH), 8.74 (bs,3 H,NH3)c
154 (36)
a The strongest absorptions are only given
b Measured in D2O
c Measured in DMSO-d6
All solvents and reagents were of reagent grade and were purchased
from Fluka. The solution of vinylmagnesium bromide in THF was
purchased from Aldrich. All mps (determined in open capillary
tubes) are uncorrected. IR spectra (nujol mulls) were measured us-
ing a Specord M80 (C.Zeiss). instrument. 1H NMR spectra were re-
corded on a Bruker AVANCE DPX-250 spectrometer oparating at
250 MHz, using CD3OD solutions unless otherwise stated. 31P
NMR spectra were recorded at 101.255 MHz with the same spec-
trometer. Positive chemical shifts are downfield from 85% H3PO4.
FAB/MS were measured on an APO Electron (Ukraine) Model MI
12001 E mass spectrometer equipped with a FAB ion source
(thioglycerol matrix).
Anal. calcd for C9H14O3NPS (248.1): C, 43.72; H, 5.71; N, 5.67; P,
12.53. Found C, 43.42; H, 5.58; N, 5.92; P, 12.39.
Grignard Addition of Organomagnesium Bromides to N-(Di-
ethoxyphosphoryl)aldimines 1; General Procedure
A solution of imine 1 (0.01 mol) in THF (15 mL) was added with
stirring at 20–25°C to a solution of organomagnesium bromide pre-
pared from Mg grit (0.49g, 0.02 mol), alkyl or aryl bromide (0.02
mol), and THF (20 mL) at 40–45°C. Stirring was then continued for
2 h at r.t. The resultant mixture was quenched with satd aq NH4Cl
solution (ca 30 mL) below 10°C. The aqueous phase was extracted
with CH2Cl2 (3 î 15 mL) and the combined organic solutions were
washed with H2O (2 î 15 mL), dried (MgSO4), and evaporated un-
der reduced pressure. Crude diethyl N-alkylphosphoramidates 2a–r
thus obtained were spectroscopically pure after heating for ca 1 h at
40–50°C/1 Torr. Compound 2a was obtained by addition of MeMgI
to N-(diethoxyphosphoryl)benzylideneimine (1, Ar = Ph) in Et2O.
All N-(diethoxyphosphoryl)aldimines 1 were obtained as described
previously.10
N-(Diethoxyphosphoryl)-2-thienylideneimine (1, Ar = 2-thienyl)
The synthesis was performed according to the previously described
procedure10 starting from 2-thiophene carboxaldehyde diethyl ace-
tal and diethyl phosphoramidate. Yellow oil; yield: 74%; bp 154°C/
0.7 Torr.
Barbier Addition of Allylmagnesium Bromide to N-(Diethoxy-
phosphoryl)aldimines 1; General Procedure
A solution of allyl bromide (1.33g, 11 mmol) in THF (10 mL) was
added with stirring at 0°C to a mixture of imine 1 (10 mmol), Mg
grit (0.29 g, 12 mmol), and THF (10 mL). The temperature was then
raised to 10°C and stirring was continued at this temperatue for ca
15 min and then at 20–25°C for 1.5 h. The resultant mixture was
quenched with satd aq NH4Cl solution (ca 25 mL). The aqueous
phase was extracted with CH2Cl2 (3 î 15 mL) The combined organ-
ic solutions were washed with H2O (2 î 15 mL), dried (MgSO4),
1H NMR (CDCl3): d = 1.36, 1.37 (2 t, 6 H, J = 7.0 Hz, CH3), 4.13–
4.26 (m, 4 H, CH2), 7.18–7.22 (m, 1 H, ArH), 7.69–7.72 (m, 2 H,
ArH), 9.14 (d, 1 H, J = 31.3 Hz, =CH).
31P NMR (CDCl3): d = 8.20.
MS: m/z (%) = 248 (M+ +1, 100).
Synthesis 1999, No. 6, 930–934 ISSN 0039-7881 © Thieme Stuttgart · New York

934
A. Zwierzak, A. Napieraj
PAPER
and heated at 40–50°C/1 Torr for ca 1h to give crude 2s–w in spec-
troscopically pure state.
(4) Gajda, T.; Napieraj, A.; Osowska-Pacewicka, K.; Zawadzki,
S.; Zwierzak, A. Tetrahedron 1997, 53, 4935, and references
cited therein.
Cantrill, A.A.; Osborn, H.M.I.; Sweeney, J. Tetrahedron
1998, 54, 2181.
Deprotection of Diethyl N-Alkylphosphoramidates 2a–w to a-
Arylalkylamines 3a–w; General Procedure
(5) Review: Bloch, R. Chem. Rev. 1998, 98, 1407.
(6) Davis, F.A., Mancinelli, P.A.; J. Org. Chem. 1977, 42, 398.
(7) Sisko, J.; Weinreb, S.M. J. Org. Chem. 1990, 55, 393, and re-
ferences cited therein.
(8) (a) Hirao, A.; Hattori, I.; Yamaguchi, K.; Nakahama, S. Syn-
thesis 1982, 461
(b) Hart, D.J.; Kanai, K.-i.; Thomas, D.G.; Yang, T.-K. J. Org.
Chem. 1983, 48, 289.
(9) (a) Guijarro, D.; Pinho, P.; Andersson, P.G. J. Org. Chem.
1998, 63, 2530.
Method A: Crude phosphoramidate 2 (5 mmol) was refluxed with
20% HCl (15 mL) for 1 h. The resultant solution was cooled to r.t.
and extracted with Et2O (15 mL). The extract was discarded and the
solution was made strongly alkaline with solid NaOH. The amine
was extracted with Et2O (4 î 15 mL), the extract was dried (KOH)
and saturated with dry, gaseous HCl at r.t. for ca 15 min. Crystalline
a-arylalkylamine hydrochloride 3 was filtered, washed with Et2O,
and dried in vacuo over solid KOH. Recrystallization from EtOH/
Et2O afforded analytically pure samples of 3.
Method B: To a solution of the crude phosphoramidate 2 (5 mmol)
in THF (5 mL) was added 20% HCl (5 mL) and the mixture was left
at r.t. (1–10 d, see Table 1). Progress of deprotection was monitored
by 31P NMR (disappearance of the signal at d = 7.5 – 8.7). The re-
sultant mixture was made strongly alkaline with solid NaOH and
worked up as in the Method A. Yields, melting points, and spectro-
scopic data of a-arylalkylamine hydrochlorides 3a–w obtained by
methods A and B are compiled in Tables 1 and 2.
(b) Andersson, P.G.; Guijarro, D.; Tanner, D. J. Org. Chem.
1997, 62, 7364, and references cited therein.
(10) Zwierzak, A.; Napieraj, A. Tetrahedron 1996, 52, 8789.
(11) Blomberg, C. The Barbier Reaction and Related One-Step
Processes; Springer-Verlag: Berlin, Heidelberg, 1993.
(12) Sugimori, S. Nippon Kagaku Zasshi 1971, 92, 528; Chem. Ab-
str. 1972, 76, 58609.
(13) Traynellis, V.J. J. Org. Chem. 1970, 35, 2207.
(14) Asai, T.; Aoyama, T.; Shioiri, T. Synthesis 1980, 811.
(15) Hartung, W.H.; Much, J.C. J. Am. Chem. Soc. 1931, 53, 1875.
(16) Konowalow, M. Ber. Dtsch. Chem. Ges.1895, 28, 1852.
(17) de Roocker, A.; de Radzitzky, P. Bull. Soc. Chim. Belg. 1963,
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Acknowledgement
Financial support by a grant 3 T09A/095/08 from the Polish Com-
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Synthesis 1999, No. 6, 930–934 ISSN 0039-7881 © Thieme Stuttgart · New York