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Fluoride-Induced Fragmentation of Trimethylsilyloxysulfonates to Form cis-Coupled Hexahydrozulenones.

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CAS Registry numbers:
( I ) , 71-30-7; (2), 66-22-8, (3), 65-71-4 (4). 10010-80-7;(5). 1194-23-6; (6). 1351492-6; (7). 108-134; (81, 67-52-7; (Y), 2417-22-3: (10). 50-71-5; 1/11, 1113-63-9;
112). 120-89-8: 113). 591-07-1: (14). 616-03-5: (Is),471-46-5; (16). 471-47-6; (17).
57-13-6
[I] a ) E. Fahr, Angew. Chem. 81.581 (1969): Angew Chem. Int. Ed Engl. 8,578
(1969); b) S. Y. Wang, Photochemistry and Photobiology of Nucleic Acids.
Academic Press, New York 1976.
I21 R. Beukers, J filsrra, W Berends, Rec Trav. Chim. Pays-Bas 78, 879 (1959);
I . H.Brown, H. E. Johns, Photochem. Photobiol. 8, 273 (1968). J. H.Fendler,
G Bogan. ibid. 20. 323 (1974): C. L. Greenstock. I . H . Brown, J. W Hunt. H.
E. Johns, Biochem. Biophys. Res. Commun. 27, 431 (1976).
131 a) R. Alcanrara, S. Y. Wang, Photochem. Photobiol. 4, 473 (1965); b) ibid. 4,
465 (1965); c) S Y. Wang, R. Alcuntura. ibid. 4. 477 (1965).
141 S. Y. Wang, J. Am. Chem. SOC. 80, 6199 (1958): Nature 184, B. A. 59
(1959).
I S ] K H. Liebl. W. Seiler in H. G. Schlegel. J. Corrschalk. N . Pfennig: Proc.
Symp Microbial Production and Utilization of Gases. Verlag E. Goetze,
Gottingen 1976. p. 2l5ff.
[61 K . Bauer. R. Conrad, W. Seiler, Biochim. Biophys. Acta 589, 46 (1980). and
references cited therein; K. Bauer, W. Seiier. H . Ciehl. Z . Pflanzenphyaol. 94,
219 (1979). and references cited therein.
Fluoride-Induced Fragmentation of
Trimethylsilyloxysulfonates to Form cis-Coupled
Hexahydroazulenones"*'
slowly owing to strong steric shielding, and was still not complete after 100 h.
Reaction of (2) and of (12) with potassium fluoride in the
presence of [ 18lcrown-6 in dichloromethane gave the czscoupled bicycle (3) as sole product in 78% and 76% yield, respectively. Thus, for the synthesis of (3) it is not necessary to
separate (7) and (8). The formation of the (2)-C---C double
bond in (3) is consistent with the trans arrangement of the
substituents on C-2 and C-3 in (2) and (12).
(9)R=H
d
G ( 2 ) R = SO2MQ
(10) R= SiMe3
By Lutz-E Tietze and Ulrich Reichertl']
Cleavage reactions of the heterolytic fragmentation typel'l
have great importance in the stereoselective synthesis of olefinsr2],in the preparation of cyclic compounds of medium
ring
and in the formation of substituted ring systems
of definite c o n f i g ~ r a t i o n A
~ ~general
~.
and simple method is
the base-induced fragmentation of the monosulfonates of
1,3-diols. However, this method has the great disadvantage
that condensations[41and isomerizations at the a-position to
the newly formed carbonyl group can occur in a strongly basic reaction
Thus, in the fragmentation of compounds of the structural type (1) with potassium tert-butoxide or potassium hydroxide mainly the thermodynamically
stable trans-coupled bicyclic system of type (4) is formed.
The fluoride-induced fragmentationf6]of the silyl ether (2),
on the other hand, leads exclusively to the cis-coupled hexahydroazulenone (3). (3) corresponds to the substructure of
the sesquiterpene of the eregoyazine type171.
For the synthesis of (2) a 35:l mixture of cyclopentene
and the trimethylsilyl ether (6), which can be prepared in
9 1% yield by reaction of 2-methylcyclopentane-l,3-dione
with hexamethyldisilazane/imidazole,was photolyzed at
- 60 "C (Scheme 1). After chromatography the cyclobutane
derivatives (7) and (8) are obtained in a ratio of ca. 3 :2 (total
yield 51%). (7) and (8) were reduced to the crystalline alcohols (9) (m.p. 74 "C) and (11) (m.p. 71 oC)IRaJ,
which on reaction with methanesulfonyl chloride gave the sulfonates (2)
and (12)[8b).
In the case of (11) the reaction proceeded very
['I
["I
Prof. Dr. L.-F. Tietze, DiplLChem. U. Reichert
Organisch-chemisches Institut der Universitat
Tammannstrasse 2, D-3400 Gottingen (Germany)
This work was supported by the Fonds der Chemischen Industrie.
830
0 Verlag Chemre, CmbH. 6940 Weinheim, 1980
(11) R:H
(12) R = 50ZMo
(13) R = SiMe3
Scheme 1 . a: high-pressure mercury lamp, quartz apparatus, 4 h, - 60 "C, chromatography on silica gel with ether/pentane ( I :3); 31% (7). RF=0.56: 21% (8).
Rr-=0.58.-b: LiAIHI. ether, 3 h, 42°C (83X).-c: LiAIH4, ether, 3 h. 42°C
(90%)-d: MeS02CI. pyridine, dimethylaminopyridine (DMAP) 191. 8 h, 20 "C
(86%).-e: KF, [18]crown-6. CH2C12,4 h. 20°C (78/76%).--f. MeS02CI. pyridine. DMAP 191. I 0 0 h, 20°C (68%).The yields refer to isolated and analytically
pure products.
(3) did not isomerize under the given reaction conditions,
even after 48 h. Treatment of (3) with potassium tert-butoxide, on the other hand, led to a 1 :4-mixture of (3) and (4).
The structures of (3) and (4) are in agreement with the analytical data (cf. [''I).
Experiments with other nucleofugal groups were less
clear-cut. Thus, reaction of (9) with trifluoromethanesulfonic
anhydride/pyridine gave the fragmentation product (3) directly in 50% yield together with 35% (10);(li)afforded 46%
(3) and 35% (13). Presumably the trifluoromethanesulfonates
are initially formed, at least partially, and then these fragment to (3) by nucleophilic attack of the trifluoromethanesulfonate ion at the silyl group. The trimethylsilyl trifluoromethanesulfonate formed in this reaction could then silylate
unreacted (9) and ( i l )to (10)and (13), respectively.
The scope of the above fragmentation reaction appears to
be limited to strained cyclic systems. Thus the silyl ether
(.5)011'1does not react with potassium fluoride/[l8]crown-6
within 24 h at 20 " C .
Received: May 13, 1980 [Z 568 I€]
German version: Angew. Chem 92.832 (1980)
CAS Registry numbers:
(1). 74965-23-4; (2). 74965-24-5; (3). 74965-25-6; (4), 74965-26-7; (6). 1121-05-7:
(7). 14965-27-8; (S), 74985-50-5; (9). 74965-28-9; ( l o ) , 74965-29-0; ( l l ) , 7498551-6; (12). 74985-52-7: (13). 74985-53-8: cyclopenlene, 142-29-0
[I] C A. G o b , P. W Schiess, Angew. Chem. 79, 1 (1967); Angew. Chem. In!.
Ed. Engl. 6, I (1967); C. A. G o b , ibid. 81, 543 (1969) and 8. 535 (1969). and
references cited therein.
[2] Examples from the field of natural products include, inter alia: E J. Core)..
R. B. Milm, H Uda, J. Am. Chem. SOC.86, 485 (1964): R. Zurflch. E. N .
Wall, J. B. Sidall. J. A. Edwards. rbid. 90. 6224 (1968)
131 Entry to macrolides is also possible by double fragmentation: a) D. Srernbach, M. Shibuya, F. Jaisli, M . Bonetri, A . Eschenmoser, Angew. Chem. 91,
670 (1979); Angew Chem. In! Ed. Engl. 18, 634 (1979); b) M Shibuya, E
Jaisli. A. Esrhenmoser. ibid. 91. 672 (1979) and 18.636 (1979); c) see ref. [3]
in [3al.
0570-0833/80/1010-0830
$ 02.50/0
Angew. Chem. In1 Ed. Engl. 19 (1980) No. 10
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
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forma, hexahydrozulenones, induced, fluoride, trimethylsilyloxysulfonates, fragmentation, coupled, cis
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