close

Вход

Забыли?

вход по аккаунту

?

Thermal [2 + 2]-Cycloadditions of Tetracyanoethylene to Cyclic Thioenol Ethers.

код для вставкиСкачать
141 a) G. Kinasr, L.-F Tiefre, Chem. Ber. 109, 3626 (1976); b) L.-F. Tierze, G.
Kinasr. H C. Uzar, Angew. Chem. 91, 576 (1979); Angew. Chem. Int. Ed.
Engl. 18. 541 (1979).
[SJ B. D. Challand. H. Hikino. G. Kornis, G. Lange, P. de Mayo, J. Org. Chem.
34, 794 (1969).
[6] The fluoride-induced fragmentation of a trimethylsilylcarbon compound
has already been described: H. Gerlach, Helv. Chim. Acta 60, 3039 (1977).
[7] W. Vichnewski. 1. Org. Chem. 42, 3910 (1977). and references cited therein.
[8] a) The relative configuration at C-3 in (9) and (11) was determined 'HNMR spectroscopically using the shift reagent Yb(fod),; b) the isomeric methanesulfonates (2) and (12) decompose in the pure form at room temperature. After 48 h a mixture of (3) and (4) could be isolated from the black oil
in 16%yield.
191 G Hufle. W. Sfeglich, H. Vorbrirggen, Angew. Chem. 90, 602 (1978); Angew. Chem. Int. Ed. Engl. 17, 569 (1978).
[lo] 'H-NMR (100 MHz. CDCI,): (3): S=5.56 (m. 7-H). 3.55 [m, Jz..~.=9.5 Hz
(determined by decoupling experiments, irradiation at 6 = 1.63). 3a-H], 2.77
(m. 8a-H), 2 55 (br. s. 5-H2). 1.70 (s, CHI), 2.40-1.30 (m. 8 aliphatic H).
(4): F = 5.56 (m, 7-H), 3.04 (m, 3a-H), 2.95-2.65 (m, 8a-H), 2.39 (br. s. 5H2), 1.78 ( s , CHI), 2.40-1.30 (m. 8 aliphatic H).
[ 11J Synthesis by reaction of rrans-(2-hydroxycyclopentylmethyI)-p-toluenesulfonate [4a] with trimethylsilyl chloride in pyridrne/ether; yield 82%.
Thermal [2 + 21-Cycloadditions of
Tetracyanoethylene to Cyclic Thioenol
By Siegfried Fries and Klaus Gollnick['l
Dedicated to Professor Rolf Huisgen on the occasion of
his 60th birthday
Thermal [2 + 2]-cycloadditions of tetracyanoethylene (1)
to acyclic thioenol ethers have recently been the subject of
numerous reports[2'.
We have now found that thermal [2 + 21-cycloadditions of
(1) to the cyclic thioenol ethers (2a, b) (3,4-dihydro-2H-thiopyrans) and (2d-f) (2,3-dihydrothiophenes) occur--via spontaneously formed, deep-blue C T complexes which disappear
(31
.1.CN
within minutes at room temperature and at about - 2 0 ° C
respectively-to give the corresponding tetracyanocyclobutane derivatives (4), which generally crystallize analytically
pure in 85-95% yieldf3'.
The oxygen analogues (2c) and (2g) react with (1) to give
red C T complexes which are stable at - 20 "C, but cyclize at
+ 20 " C within 4 h and = 1 min, respectively, to the corresponding tetracyanocyclobutanes (4c) and (4g). Obviously,
3,4-dihydro-2H-thiopyrans
such as (2a) and 2,3-dihydrothiophenes such as (2e) react with (1) much more rapidly than
their oxygen analogues. Under otherwise equal conditions
the rates of cycloaddition (determined as the time elapsed up
to disappearance of the CT complexes) of (1) to the cyclic
thioenol ethers increase along the series (2a) < (2b) < (2d)
< (28 s (2e). Thus, 2,3-dihydrothiophenes react faster than
3,4-dihydro-2H-thiopyrans, and the methyl-substituted derivatives such as (2b) and (2e) react better than their unsubstituted parent compounds (2a) and (Zd), respectively. The relatively bulky isopropyl group in (2f) only moderately retards the rate of cycloaddition. Increasing solvent polarity
promotes the cycloaddition; thus, the reaction rates of
(1)+ (2a) in tetrahydrofuran (&I4' = 37.4), dichloromethane
(ET=41.1), and acetonitrile (ET=46.0) are in the ratio of
about 1:2:10.
Increasing solvent polarity promotes not only the cycloaddition, but also the dissociation of the cyclobutane derivatives (4d,f, g) to their educts. The cycloreversion is easily recognized by the characteristic color of the C T complexes
which appear o n dissolution of the cyclobutanes in dimethyl
sulfoxide or acetonitrile. Furthermore, elimination of hydrogen cyanide occurs; compounds (51, however, were not
intercepted. Formation of HCN is also observed in the reaction of (1) with the 2,3-dihydrothiophenes in acetonitrile at
room temperature, whereas with 3,4-dihydro-2H-thiopyrans
onIy cycloaddition reactions occur.
Our results can only be explained by assuming that in the
rate-determining step zwitterionic intermediates of type (3)
are formed, as is the case in the reaction of (1) with enol ethers Is'. Depending upon the solvent polarity, the zwitterions
(3) then undergo competition reactions to give the cycloadducts (4) or eliminate HCN with formation of (5). Alkyl substituents R ' (such as CH3) stabilize a n intermediate carbenium ion and thus lower the energy of the transition state
which leads to the zwitterion. The reaction of (1) with cyclic
thioenol ethers is therefore accelerated by a n a-methyl group
as is the dissociation of the cycloadducts. The increased rate
of cyclization of thioenol ethers with (1) and the enhanced
cycloreversion of their cycloadducts as compared to the reactions of the corresponding oxygen derivatives are then due to
the fact that sulfonium ions (3), X = S , are more resonancestabilized than the corresponding oxonium ions (3), X = 0.
Since all steps of the cycloaddition reactions are reversible,
we assume that the cycloadducts (4) exhibit the thermodynamically more stable cis-fusion of the rings.
R2
Received: March 12, 1980 [Z 574a IE]
German version: Angew. Chem. 92. 848 (1980)
CAS Registry numbers:
(1). 670-54-2, (Za), 13042-80-3; (2b). 13042-79-0 ( 2 ~ ) 110-87-2,
.
(2d). 1120-59-8;
(2e). 4610-02-0 (2J). 75066-71-6; (Zg), 1487-15-6; (4a). 75066-72-7; (4b). 75066.
(4dJ.75066-74-9; (4e), 75066-75-0 (4J). 75066-76-1. (50).
73-8; ( 4 ~ )69798-90-9;
75066-77-2; (56). 75066-78-3; (Sc), 75066-79-4; (5d). 75066-80-7; (Se). 75066-818 (5B.75066-82-9; (Sg). 75066-83-0 (4g). 75066-84-1
H
[ I ] From the Dissertation S. Fries, Universitat Miinchen 1977.
['I
Prof. Dr. K Gollnick, Dr. S. Fries
Institut fur Organische Chemie der Universitat
Karlstrasse 23. D-8000 Munchen 2 (Germany)
["I
This work was supported by the Deutsche Forschungsgemeinschaft and the
Fonds der Chemischen Industrie.
Angew. Chem Inr Ed. Engl. 19 (1980) No. 10
[2] a) J. K. Williams. D. W. Wiley, B. C. McKusick, J. Am. Chem. SOC.X4, 2210
(1962); b) T. Okuyama, M. Nakada. K . Tuyoshima, T. Fueno, J Org. Chem.
43, 4546 (1978); c) H. Graf; R. Huisgen, ibid 44, 2594 (1979).
[3] 'H-NMR [(CD1)2CO]:(4aJ: 6=3.75 (m. H J 4.90 (d. J a h = 9 Hz. R'=H,).
3.0 (m, 2H,. R2=H,); (46). 6=3.72 (m, Ha).3.0 (m. 2H,, R'=H,), 2.00 ( 5 .
3 H . R'=CH,); (4d): 6=4.50 (m. Ha), 5.05 (d, J a h = 9 Hz. R'=H,), 3.25 (m,
0 Verlag Chemie. GmbH, 6940 Weinherm, 1980
0570-0833/80/1010-0x31
S 02.50/0
83 1
2H,. R'=H,); (4f):6=3.80 (m. H4), 4.05 (m, Hc), 2.00 ( s . 3H. R'=CH,).
1.05 (d, J = 6 H z , 6 H , RZ=CH(CH3),).
141 C. Reichardr: Solvent Effects in Organic Chemistry Verlag Chemie, Wein
heim 1979, p. 242ff.
[ 5 ] Review: R Huisgen, Acc. Chem. Res. 10, 117 (1977).
R'
k.9
Thermal Cycloadditions of
Dimethyl Acetylenedicarboxylate to
Cyclic Enol Ethers and Thioenol Ethers[**]
(8)
(9)
By Klaus Gollnick and Siegfried Fried']
Dedicated to Professor Rolf Huisgen on the occasion of
his 60th birthday
(6a). R ' = R2= H
(6b). R ' = C H 3 , R 2 = H
( 6 0 , R ' = CH,, R2= i-C,H,
Cyclic enol ethers and thioenol ethers cycloadd to tetracyanoethylene (TCNE) in high yields under mild conditions[']. On attempting to react dimethyl acetylenedicarboxylate (f), E = C02CH3, with 3,4-dihydro-2H-pyran, 2,3-dihydrofuran, or 5-methyl-2,3-dihydrofuran (2), only the a-methylated enol ether (2) proved to be reactive enough to give
via a pale yellow C T complex the [2 + 21-cycloproduct (4)121
as well as dimethyl 2-(2-methyl-4,5-dihydro-3-furyl)fumarate (5)['1.
(140 "C), in which only (6c) underwent olefin elimination to
give (86).
The results may be easily explained in terms of a (2 + 3Jcycloaddition of (1) to the thioenol ethers (6) to afford the
bicyclic sulfonium ylides (7), which subsequently react according to a retro-[2 + 31-cycloaddition by elimination of an
alkene (8) to give a 2,3-thiophenedicarboxylicacid ester (9).
The sulfonium ylide (7) may be stabilized by an overlap of
the sp' anion orbital with a sulfur d-orbital19];in the oxygen
analogue of (7), however, the formation of a (p-d)T bond is
impossible. The reaction of (1) with (2) therefore appears to
prefer the energetically favored route via the 1,4-dipole (3).
(1) should also react with the 3,4-dihydro-2H-thiopyrans
(lOa, b) via C T complexes to give sulfonium ylides ( l l ) ,but
this route proves to be a dead end, since the stabilization by a
retro-[2 + 3]-cycloaddition to give (1) + (10) is apparently far
more effective than by a fragmentation to 2,3-thiophenedicarboxylic ester + cyclopropane.
E
CI
OcH,+
Benzene
50°C
F CT-Complex p
&:
H3
c
Formation of (5) from the cycloadduct (4) is ruled out,
since (4) is stable evenin boiling toluene (llO°C). We assume that a zwitterionic intermediate (3) is formed from the
C T complex, as was similarly discussed for [2 + 21-cycloadditions with TCNE. Only then is the formation of (5) easily explained by prototropy in the dipole. The remarkable reaction-promoting influence of a methyl group, which has also
been observed in the 12 + 21-cycloaddition of (I) to 2-alkoxy3,4-dihydr0-2H-pyrans[~I and of T C N E to enol ethers and
thioenol ethers"], is then due to a stabilization of the oxonium ions of type (3); alkyl groups thus lower the transition
states which have to be passed in the rate-determining step
that leads to the zwitterion.
The thioenol ethers (6a-c) and (IOa, b) form yellow C T
complexes on reaction with (f) in benzene. However, whereas the 3,4-dihydro-2H-thiopyrans (ZOa, b) are recovered unchanged from boiling benzene, the 2,3-dihydrothiophenes
react with (1) in boiling benzene within several hours to give
the alkenes (8) and dimethyl 2,3-thiophenedicarboxylates
(9)ISl.
Of the three 2,3-dihydrothiophenes, (6c) reacts most rapidly. 3-Methyl-1-butene (Sb) is apparently a better leaving
group than ethylene. This was shown also in an attempt to
react (6a-c)
with methyl propiolate in boiling xylene
['I
Prof. Dr. K. Gollnick. Dr. S. Fries
Institut fur Organische Chemie der Universitat
Karlstrasse 23. D-8000 Munchen 2 (Germany)
[**I
This work was supporled by the Deutsche Forschungsgemeinschaft and the
Fonds der Chemischen lndustrie
832
0 Verlag Chemre, GmbH, 6940 Weinheim, 1980
(70)
(a). R
(b), R
+
+
+
R2=H
i (9a). R ' = H
(Ha), R 2 = H
i(9b), R i = C H ,
(Sb), R 2= i-C,H, i (9b), R ' = CH,
@a),
(77)
E
H
CH3
Received: March 12, 1980 [Z 574b I€]
German version: Angew. Chem. Y2. 848 (1980)
CAS Registry numbers:
( I ) , 762-42-5. (2). 1487-15.6. (4). 75067-10-6; (S), 75067-1 1-7: (60). 1120-59-8:
(6b).4610-02-0 (6c). 75066-71-6: (80). 74-85-1; (Xb). 563-45-1: (90). 14300-68-6.
(96).75067-12-8: (IOU). 13042-80-3. (lob). 13042-79-0
[ I ] S. Fries. K. Gollnrck. Angew. Chem 92. 848 (1980). Angew. Chem Int. Ed.
Engl IY. 831 (1980).
[2] After chromatography on silica gel (CH2CIZ). 15% yield, crystalline, analytically pure 'H-NMR (CDCI?):6=3.15 (m.H.J 4.10 (m, 2H,). I 9 0 ( m . 2Hd).
1.60 ( s . 3H. CH,), 3.79 and 3.81 (each s. 3H. OCH,).
131 After Chromatography on silica gel (CH2CIZ). 20% yield. oily substance, analytically pure. 'H-NMR (CDCI,): 8 = 6 6 5 (5. Hh). 4 4 0 (t, J,,=9 Hz, 2H,).
2.90 (I. J L d = 9 Hz, 2H,). 1.67 (s, 3H. CH,); 3.74 and 3.80 (each s, 3H,
OCH,). (In diethyl fumarate the oletinic protons appear at 6 = 6.83, in diethyl
maleate al 6=6.28.)
141 S S. Hull. A. J. Duggan, J . Org. Chem. 39, 3432 (1974).
[ 5 ] ( Y u i 16% yield. analytically pure, m.p. 35°C [6]: 'H-NMR (CDC13): 6=7.27
(d. J.,h=45 Hz. Hd), 7.46 (d. J,,=4.5 Hz, R'=Ht,). 3.89 ( s , 6H. 20CH3):
(Yb): 16% yield [from (6611 or 37% yield [from (6r)], analytically pure. after
distillation at 170"C/15 torr [7]. 'H-NMR (CDCI,): 6=6.93 (q, J = 1 Hz,
H,,), 2.50 (q. J=1 Hz. 3H. R'=CH.,), 3.86 and 3.84 (each s. 3H. OCH,):
structure determination see [8]
161 J. S K ~J ,. Org. Chem 19. 70(1954).
171 R. G. Junes, J . Am. Chem. SOC 77, 4069 (1955).
[S] K. Gollnick. S. Fries. to be published.
191 a ) D. Seebach. Angew. Chem 81.690(1969); Angew Chem. Int. Ed. Engl 8,
639 (1969): b) B. M. Trosr. L. S. Melvin. Jr.: Sulfur Ylides. Academic Press,
New York 1975. p. 23.
O S 7 0 - 0 X 3 3 / ~ 0 / I 0 t 0 - 0 ~ ~ 2$ 02 SO/0
Angen. Chem. In!. Ed. Engl. I Y (19X0) No. 1 0
Документ
Категория
Без категории
Просмотров
2
Размер файла
241 Кб
Теги
thermal, cyclic, ethers, cycloadditions, thioenol, tetracyanoethylene
1/--страниц
Пожаловаться на содержимое документа