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Competing [3+4]- and [2+4]-Cycloadditions of Allenyl Cations.

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small amounts of dimers formed from methoxycarbonylcarbene-dimethyl fumarate and maleate-could easily be removed by filtration through aluminum oxide.
i 3)
(4)
Y-Y
n-
THF
Table 1 Synthesized methyl siloxycyclopropanecarboxylates(5) and methyl 4oxoalkanoates (66).
[ I ] Review R. V Stevens, Acc. Chem. Res. 10, 193 (1977); S. Danishefsky. rbid.
12, 66 (1979); D Seebach, Angew. Chem. 91, 259 (1979); Angew. Chem. Int
Ed. Engl. /8, 239 (1979) and references cited therein
(21 E. Wenkerr, Acc. Chem. Res. 13, 27 (1980).
131 G. Stork. P. F. Hudrlrk. I. Am. Chem Soc. YO, 4462, 4464 (1967): H. 0.
House, L. J. Czuba, M Gall. H. D. Olmsfed, J. Org. Chem. 34. 2324 (1969);
for new methods see R. D. Miller, D. R. McKean. Synthesis 1079, 730; G. A .
Olah, B. G. B. Gupra. S. C. Narang, R. Malhorra. J. Org. Chem. 44, 4272
(1979) and references cited therein.
[4] The reactions of (30) and (3B with ethyl diazoacetate did not afford the cyclopropanes. but directly the corresponding yketo esters: R LeCoaller, J:L.
Pierre. C. R Acad. Sci. C 276, 193 (1973); the publication does not contain
any experimental details.
[5] First synthetic utilization of the high affinity of the fluoride ion towards silicon: E. I. Corey, A . Venkafeswarlu.J . Am. Chem. Soc. 94, 6190 (1972).
161 S Hunig, G. Wehner, Synthesis 1975, 180.
Competing [3+ 41- and [2 + 41-Cycloadditions of
Allenyl Cations'*'I
By Herbert Mayr and Inge K . Halberstadt"]
Dedicated to Professor Rolf Huisgen on the occasion of
his 60th birthday
a
b
c
d
e
f
g
h
t-C4Hr
H
H
CH,
CH,
H
-(CHdH
-(CHd-(CH2)3H
-(CHZ)~H
-(CHdH
-(CH&OSi(CH2)3
H
87
66
58
75
71
75
76
55
65/0.1
80/20
80/0.05
100/0.05
70/0.01
90/0.01
100/0.01
100/0.01
83
89
80
93
80
83
78
67 [dj
Rs=OH
[a] cis/rrans Mixture. [b] Yields isolated after bulb-to-bulb distillation; all the
new compounds gave satisfactory elemental analyses and characteristic spectra.
[c] Bath temperature. [dl Yields of crude product (NMR spectroscopically
pure).
The removal of the trimethylsilyl group with ring opening
of the cyclopropane to give the 1,4-dicarbonyl compounds
(6) could be achieved smoothly with fluoride ions[5]under essentially neutral conditions. (6) is most conveniently liberated by the readily accessible triethylammonium fluoride''].
This gentle method (1 h, 25 "C, tetrahydrofuran) also enables
straightforward synthesis of the aldehyde esters (6b-d) and
of the alcohol (6h).
Procedure
(5): A solution of methyl diazoacetate (4) (1.28 g, 12.8 mmol)
in anhydrous benzene (50 ml) is added dropwise in 3 h to a
suspension of copper(r1) pentanedionate in (3a) (2.00 g, 11.6
mmol) kept at 90°C. After cooling and removal of solvent
the residue is dissolved in pentane and filtered through 35 g
aluminum oxide (neutral, activity grade 111). On evaporation
of the eluate there remains 2.58 g (91%) (5a) as a colorless,
NMR spectroscopically pure oil. Bulb-to-bulb distillation at
65 "C/O.I torr furnishes 2.47 g (87%) of analytically pure
(54.
Received: March 24. 1980 12 573 IE]
German version: Angew. Chem. 92. 839 (1980)
CAS Registry numbers:
(3a]. 17510-46-2; (3b), 6651-34-9 ( 3 ~ 160484-91-5;
,
(3d). 53282-55-6; (3e). 1998043-9; (3n,6651-36-1; (3g)~22081-48-7, (3hj. 6838-67-1; (4). 6832-16-2: ~;.9~(5aj.
75032-05-2; rrans-(5a), 75032-06-3; cis-(5b), 75032-07-4; rrans-fjb).75032-08-5;
cis-(5c), 75032-09-6; lrans-(5c), 75032-10-9; cis-(5d), 75045-86-2; rrans~(Sd),
75032-1 1 - 0 cis-(5e), 75032-12.1; rruns-(5e], 75081-68-4; cis-(5fl, 75032-13-2;
rrans-(Sfi. 75081-69-5; cis-(Sg), 75032-14-3: frans-(Sg). 75081-70-R; crs-{Sh),
75032-15-4; frans-(5h). 75081-71-9 (6a). 34553-32-7: (66). 52398-45-5; (6~1,
75032-16-5; (64,75032- 17-6; (6ej, 4934-95-6: (6fl. 13672-645; (6g). 75032-18-7;
(6h). 75032-19-8; (6h). (R'=OH). 75032-20-1
814
0 Verlag Chemie, GmbH, 6940 Wernherm, 1980
The number of synthetic applications of cationic cycloadditions is steadily increasing. Whereas [3 + 41-cycloadditions"' of ally1 cations are already one of the most widely
used synthetic approaches to seven-membered carbocyclesi21,
the first [2+ 21-cycloaddition of a solvolytically generated vinyl cation to cyclohexene has only just been acc~mplished[~].
The acid catalyzed cyclodimenzation of acetylenes and allenes to give cyclobutanes also proceeds via vinyl cations[41.
We recently demonstrated the formation of [3.2.l]bicyclic
compounds by treatment of propargyl halides (1) and cyclopentadiene with equimolar amounts of silver trifluoroacetate; this reaction was rationalized in terms of [3 +4]-cycloadditions of intermediate allenyl cations[51.
R = H,CH,
We now report that trisubstituted allenyl cations can be
generated more easily from propargyl halides (3) and catalytic amounts of zinc chloride; the type of cycloaddition depends upon the nature of the substituents.
Vinyl halides (2a, b) and (4c-h) were obtained in 2065% yield from propargyl halides (3a-h) and cyclopentadiene (molar ratio 1 : 1-2) at - 30 to - 50 "C in the presence
of zinc chloride-ether, a complex soluble in dichloromethane
(Table 1). Apart from higher-molecular-weight compounds,
the only side products observed were enynes (9) and (10) arising from hydrogen chloride elimination from (3e) and (3h).
Spontaneous increase of temperature could not be avoided
when the reactions were carried out under heterogeneous
conditions (suspension of zinc chloride in dichloromethane)
and only traces of the addition products could be isolated.
The bicyclooctadienes (2) have 'H- and I3C-NMR spectra
similar
to
3-chloro-4,4-dimethyl-bicyclo[3.2.l]octa-2,6['I Dr. H Mayr. 1. K. Halberstadt
Institut fur Organische Chemie der Universitat Erlangen-Nurnberg
Henkestrasse 42. D-8520 Erlangen (Germany)
[**I
Presented at the 1st European Symposium on Organic Chemistry. Cologne.
August 1979. This work was supported by the Deutsche Forschungsgemeinschaft.
0570-0833/80//0/0-08/4
$02.50/0
Angew Chem In1 Ed Engl 19 (/980] No. 10
R2
R'
- CZ C-
I
C - ~ 2
I
(3)
A
&(
\\
/ 3 4
CH3
R2
c -R1
/
(4) x
i
ZnCl,
Table 2. 'H-NMR chemical shifts (6 values) of the benzylidenenorbornenes (4)
in CCL.
bR2
hi2
(4c) [a]
(44
/o
\\
14ej
14n
(4g) [a]
R'
(4h)
H-t
H-2, H-3
H-4
H-7a
2.41
2.41
2.85
2.41
2.41
2.53
6.27
6.25
6.24
6.23
6.20
6.23
3.89
3.83
3.87
-3.80
3.81
3.87
1.55
153
H-7b
I 85
1.90
masked
1 54
1 86
1.53
1 82
masked
6-CH3
0.68. 1.09
0.66. 1.09
-
0.69, 1.1 1
0.67, 1.08
-_
[a] In CDCI,
Table 1 . Addition products (2j and (4) of propargyl halides (3) lo cyclopentadiene [a].
Yield w ]
R'
R'
CH,
CH,
CH,
CH,
C'HI
CH,
CHI
[el
CI
Cl
C1
Br
CI
CI
CI
CI
(2)
(41
36
28
-
-
65
24
35
38
40
20
-
B.p. ["C/rorr] [b]
M.P. ["Cl
37/0.05
90-95/15
79-80
81.5-82.5
110-l15/0.02
74-75.5
101-I02
77-78.5
[a) Reaction products confirmed by IR, NMR. MS. and CH analyses. [b] Bath
temperature. [c] Side product: 4% (9). [d] Side product: 7% ( I O j . [el
-R'-R'= --(CHz)4--.
dieneI5]. Whereas the two bridgehead protons of both (2a)
and (26) show similar chemical shifts (6=2.48-2.63), H-4 is
considerably more deshielded than H-I in the norbornenes
(4) (Table 2). The significant upfield shift of one methyl
rides (2) and (4); (8) is selectively attacked from the sterically
less hindered side, resulting in the exclusive formation of
(044).
According to force-field calculations, bicyclo[3.2.l]octa2,6-diene [type (2)]is 9 kcal/mol more stable than the isorneric 5-methylene-2-norbornene [type (4)]['l. This energy difference is responsible for the formation of the cyclic vinyl cation (6) when R ' = alkyl even though the ideal geometry of
the vinyl cation fragment cannot be achievedlxI. In contrast,
an aryl group R ' directly attached to the cationic center stabilizes (8) to such a n extent that the higher strain energy of
the norbornene is overcompensated.-The formation of (4)
cannot be due to isomerization of (3) to haloallenes which
then might undergo Diels-Alder reaction with cyclopentadiene: non-activated allenes d o not react with 1,3-dienes at
low temperatures[']. Furthermore, 3-chloro-3-methyl-l-b~tyne does not undergo zinc chloride-catalyzed reaction with
cyclopentadiene but yields l-chloro-3-methyl-l,2-butadiene,
which is stable under these conditions.
Procedure
ZnC12 (1.2 g) was dissolved in ether (1.5 ml), diluted with
CH2C12(30 ml), and cooled to - 40 "C. A solution of (3fl (5.2
g , 25.0 mmol) and cyclopentadiene (1.65 g, 25.0 mmol) in
CH2C12(20 ml) was added dropwise with stirring. After 1 h
( - 40°C) the catalyst was washed out with conc. aqueous
ammonia and the organic phase was dried over CaCI2. Filtration over silica gel (10 g) afforded (4fl (2.62 g, 38%) as
NMR-pure oil which crystallized from a solution in light petroleum on scratching (colorless prisms).
Received: February 29, 1980 [Z 575 IE]
German version: Angew. Chem. 92. R40 (1980)
group in the 5-(a-halobenzylidene)-6,6-dimethylnorbornenes (4) indicates the presence of the (@-isomers; steric interactions prevent a coplanar arrangement of the phenyl
group with the exocyclic double bond so that one methyl
group moves into the positive shielding zone of the benzene
ring161.Reaction of (4c) with silver trifluoroacetate in boiling
ether and alkaline work-up affords exo- and endo-(ll) with a
carbonyl band at 1670 cm-'.
We propose that the propargyl halides (3) initially dissociate under the influence of zinc chloride to give the allenyl
cations (5). Cyclopentadiene then attacks the sp2 carbon of
(51, forming the cyclopentenyl cation (7) which cyclizes to
the vinyl cations (6) or (8).A concerted mechanism with unequal extent of bond formation in the transition state is also
conceivable. Addition of a halide ion gives the vinyl chloAngew. Chem. Int. Ed. Engl. I 4 (1980) No. 10
0 Verlag Chemie, GmbH, 6940
CAS Registry numbers:
(2uj, 751 t 1-02-3; (261, 751 11-03-4; ( h j , 999-79-1; (3bj, 17553-39-8; (3cj. 335529.1; (3dj. 75111-04-5; (3e), 75111-05-6; (38.75111-06-7: (3gj. 75111-07-X. (3h).
75111-08-9 (E)-(4c),75111-09-0;(E)-(4dj. 75111-10-3;(E)-(4e~.75111-11-4.(€)~
(48. 75111-12-5, (E)-f4gj. 75111-13-6; (E)-(4hj. 75111-14-7: /9). 75111-15-8; / l O j .
551 10-61-7: endo-(11). 751 11-16-9, exo-(11). 751 11-17-0; cyclopentadiene. 54292-7
[I] Ring size classification according to Hursgen: R. Huisgen. Angew. Chem. 80.
329 (1968); Angew. Chem. Int. Ed. Engl 7, 321 (1968).
[2) H M R. Hofffmunn, Angew. Chem. 85. 877 (1973): Angew. Chem. Int. Ed.
Engl. 12, 819 (1973); D. I . Ruwson. B K Curpenter, H. M. R. Hoffmunn. J .
Am. Chem. SOC.101, 1786 (1979). and references cited therein.
131 G.Hummen, M . Hunuck, Angew. Chem. 91, 649 (1979); Angew. Chem Int.
Ed. Engl. 18, 614 (1979).
[4] K. Criesboum, Angew. Chem. X I , 966 (1969); Angew. Chem. Int. Ed. Engl. X,
933 (1969) and later publications.
Weinheim, I980
0570-0833/80/1010-0815
$ 02.50/0
815
they are suitable in a general way for the introduction of the
oxopropenyl moiety. For this purpose they are allowed to
react with a n alkyl, aryl, or heteroarylmagnesium bromide
(1); after work-up in acid solution one obtains the corresponding a,P-unsaturated aldehydes (6) in yields between
ca. 30 and 60% (Table 1). Comparable reactions with
enols['"I, with enol ethers[*'', and with open-chain enamino
have already been described.
That the oxopropenylation proceeds via the alcohol (4) is
supported by the isolation of the intermediates ( 4 4 and (4y)
(R' = 2-pyridyl, R 2=methyl or ethyl), which are stabilized
by a n intramolecular hydrogen bond. The hydrolysis of the
alcohol (4) to the aldehyde (6) on heating in 2 N sulfuric acid
is almost quantitative. The alcohol (4) can also be detected
NMR spectroscopically in the product mixture obtained on
gentle hydrolysis of other Grignard reagents (3) (e.g. in icecold ammonium chloride solution).
151 H. Muyr, B. Grubmuller, Angew. Chem. 90. 129 (1978): Angew. Chem. Int.
Ed. Engl. 17. 130 (1978).
161 The (€)-configuration also follows from the chemical shift of H-4, as demonstrated by comparison of similar (€)- and (27-isomers: H. M a y . unpublished.
(71 Calculated according to N L. Allinger. MMI Molecular Mechanics. QCPE
Program No. 318. Indiana University, Bloomington. Indiana 1975. We thank
D. Wilhelm performing the calculations.
[S] W D. Pfeger, C. A . Bahn. P. 1'. R. Schleyer. S. Borher, C. €. Hardrng. K.
Hummel, M Hanack, P. J. Slang, J Am. Chem. SOC. 93, 1513 (1971); E.
Lumpurter, M. Hanack. Chem. Ber. 105. 3789 (1972).
191 H. Pledger. Jr.. J Org. Chem. 25. 278 (1960).
Oxopropenylation of Grignard Compounds with
3-Etho~yacroleins'"~
By Klaus Rustemeier and Eberhard Breitmaierl'l
Dedicated to Professor Rudolf Tschesche on the occasion
of his 75th birthday
3-Ethoxyacroleins (2) are versatile C, building blocks, especially in heterocyclizations"'. We have now found that
R'-MgBr
+ O=&H<=dH-OCzH5
A2
i1)
(3)
8'
+ Ha
- Mg",
R2
- Br'
H
CHO
'HR2
R'
R2
R'
)=(
(Z)-(6)
CHO
The compounds (6) synthesized were identified by elemental analysis, 'H- and 13C-NMR spectroscopy, and by
mass spectrometry. Compounds (6) are found to exist in the
E-form, though the isopropyl-substituted compounds, in particular, contain small amounts of the Z-form (NMR data).
--+
(2)
R'
I
B r M g 0 - C H-C =CH-OC 2H5
I
(E)-/6/
HO-C H - C = C H - O C zH5
Procedure
I
R2 ( 4 )
(1): 2 g of magnesium turnings are covered with 20 ml of
the solvent quoted in Table 1. 0.055 mol of the bromide is
then added dropwise, such that the solution constantly boils.
After addition of the total amount of bromide the solution i s
boiled under reflux for a further 30 min and then allowed to
cool.
Table 1. 3-Alkyl-, 3-aryl-, and 3-heteroarylacroleins (6); physical data and yields. ( I ) is generated wlth stoichiometric amounts of R'Br.
(6)
Solvent [a]
R'
R'
a
Et20
Phenyl
Me
B.p. ["Citorr]
~~~
b
El
C
iPr
nPr
Me
El
rPr
nPr
Me
El
iPr
nPr
Me
El
rPr
nPr
Me
El
Me
Me
Me
Me
Me
Me
Et
d
e
THFiEt20
p-Methoxyphenyl
THFiEt20
p-Biphenylyl
THF/Et20
2-Thienyl
THF/Et,O
a-Naphthyl [c]
1'
g
h
1
i
k
I
m
n
0
P
4
r
S
THF
r
Et,O
U
U
W
THF
X
Styryl
n-Butyl
n-Pentyl
n-Hexyl
n-Octyl
2-Pyridyl
Y
M.p. ["C] (solvent)
Yield
PI [bl
Ref
52
45
49
49
42
40
42
39
56
53
55
45
40
49
39
48
52
42
28
56
39
41
50
50
131
141
151
141
161
161
~
64-65/0.5
62-64iO.l
77-7810.2
79/0.5
101-102/0. I
I02- I04/0.1
1 14- 1 15/0.2
110-l15/0.05
140- 145/0.05
145--150/0.05
150- I60/0.05
160--170/0.1
92-93/0 2
84--85/0.1
92--94/0.2
85/0 05
120--121/0.07
124-- I28/0.05
108--1 IO/O.OS
64-65/15
84-85/15
98-100/15
124115
70-72/0.2
7 I -73/0.2
79 (n-hexane)
78 (ligroin)
75-78 (ligroin)
52-58
(ligroin)
(ligroin)
58 (MeOH/H20)
4-51
39
Oil
5:
[a] Solvent in the Grignard reaction. THF/Et,O: tetrahydrofuran: diethyl ether 3:2. [b] Referred to Initial amount of (2). Yields referred to (2) consumed are on average
20% higher. [c] The commercial a-naphthyl bromide used in the reactlon contained about 20% of the p-isomer.
['I Prof. Dr. E. Breitmaier. Dip1.-Chem. K. Rustemeier
Institut fur Organische Chemie und Biochemie der Universitat
Gerhard-Domagk-Strasse I . D-5300 Bonn 1 (Germany)
["I
This work was supported by the Deutsche Forschungsgemeinschaft
816
0 Verlag Chemie. GmbH, 6940 Weinherm, 1980
(6): The solution of (1) is added dropwise with stirring to
an ice-cooled solution of (2) (0.05 mol) in diethyl ether (100
ml). The mixture is stirred for 2 h at room temperature,
cooled with ice and then treated dropwise in the cold with
0570-0833/80/1010-0816
$ 02 50/0
Angew. Chem. Inr. Ed. Engl 19 (1980) No. I0
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