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New Spironorcaradienes. Ч Demonstration of a Reversible Norcaradiene-Cycloheptatriene Valence-Isomerization

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[8] Further, no fluorescence is at first observed on 253.7-nm irradiation
of ( l a ) and ( I b ) or ( 3 a ) and ( 3 b ) although indistinctly fluorescing
by-products are formed on prolonged irradiation.
[9] All the new compounds were characterized by elemental analysis
and spectroscopic techniques.
[lo] H! Tochtermann, K . Oppi,nliinder, and M . Nguyen-Duong Hoang,
Liebigs Ann. Chem. 701, 117 (1967);H . Prinzbach, P . Wiirsch, P . Vogel,
W Tochtermann, and C . Franke, Helv. Chim. Acta 51, 911 (1968); cf.
footnote 10 in [Zb]. We thank Dr. W Tochtermann for a gift of (1 b ) and
(lei[ I l l H . Prinzbach and D. Hunkler, unpublished.
[12] G. N . Schrauzer and P . Glockner, Chem. Ber. 97,2451 (1964).
[13] E. Lippert, W Niigele, I . Seibold-Blankenstein, U.Staiger, and W
Voss, 2. Analyt. Chem. 170, I (1959).
[I41 J . B. Birks: Photophysics of Aromatic Molecules. Interscience,
New York 1970, p. 122.
[IS] I . B. Berlman: Handbook of Fluorescence Spectra of Aromatic
Molecules. Academic Press, New York 1965.
[16] A . A . Lainah, G. S . Hammond, and F . B. Mallory, Photochem.
Photobiol. 4, 259 (1965); E . H . White and J . P . Anhalt, Tetrahedron
Lett. 1965, 3937; K . A . Muszkat and E . Fischer, J. Chem. SOC.B 1967,
662; C . D. DeBoer and R . H . Schlessinger, J. Amer. Chem. SOC.90,803
(1968); E. !I Blackburn and C . J . Timmons, Quart. Rev. Chem. SOC.
23,482 (1969).
[17] K. Alder and 1. Haydn, Liebigs Ann. Chem. 570, 201 (1950).
[IS] H . Prinzbach and P . Wiirsch, unpublished.
[19] E. Druckrey, M . Arguelles, and H . Prinzbach, Chimia 1966,432;
H . Prinzbach, E. Druckrey, G. Philippossian, and G. Kaupp to be published ;C. Ahlgren, Stockholm, personal communication (Sept. 8,1970).
New Spironorcaradienes.-Demonstration of a
Reversible Norcaradiene-Cycloheptatrienene
Valence-Isomerization[**l
By Heinz Diirr and Helge Kober'']
Some time ago[', 21 we postulated that spiro-norcaradienes
or -cycloheptatrienes occur as intermediates in the photolysis of unsubstituted or substituted diazo-cyclopentadienes
in benzene. In the meantime two relatively unstable spironorcaradienes [( 3 a ) and ( S ) ] have been ~ynthesized'~.~].
(3)+(4)
Yield(%)
(a), R = H
30-40[4]
30
8-10
(b), R=C1
(c/
(kcal./mole)
"(cal.
6) deg-!$,mole- ')
-
-
+0.994
+ 0.45
+4
+2
This paper describes the synthesis of a stable spiro-norcaradiene ( 3 c ) which is in equilibrium with its valence isomer
thespiro-cycloheptatriene( 4 c ) . Theless stable (3b)*(4b)
has also been prepared.
The valence tautomers (3)+(4) can be synthesized very
easily by photolysis of diazo-cyclopentadienes ( 1 ) in benzene (2) at 17-20°C using a Hg high pressure lamp.
(3c)+(4c) is so stable that it can be purified by chromatography on basic aluminum oxide at ordinary temperatures (see '"''). Pure ( 3 c ) e ( 4 c ) in C,D, can be kept at
100°C for 10 hours without decomposition. ( 3 a ) S ( 4 a )
isomerizes at room temperature within 24 hours". 'I. The
complete isomerization of ( 3 b ) 2 ( 4 b ) takes about 15
hours at 37°C.
Proof of structure is based on elementary analysis and,
mainly, on spectroscopic data". 21. The equilibrium between the valence isomers ( 3 ) and ( 4 ) is established unequivocally by temperature dependent NMR spectra. The
spectrum of ( 3 c ) S ( 4 c ) in CS, at 40°C shows the following signals : z= 5.26 (2 H/d), J =9.2 Hz; 3.84 (4 H/m); 2.86
ppm (8 H/m). The doublet begins to broaden at -60°C
and gives a very broad signal at -80°C. At -90°C new
signals appear at .r=4.8 and 3.0ppm, which at -100°C
give rise to a broad singlet at 6.98 and a doublet at 4.77 ppm
(J=9.5 Hz). These signals can be assigned to the Ha-protonsr5]of ( 3 c ) and ( 4 c ) , respectively. On rewarming to
room temperature the original spectrum appears again.
The same holds for ( 3 b ) e ( 4 b ) . It can be concluded from
the chemical shift of the H,-protons of the known compounds ( 3 a ) and ( 5 ) that here, too, a fast equilibrium (on
the NMR time scale) exists13- 'I. Thus it is provedc5' that
the spiro-compounds ( 3 )e ( 4 ) undergo a fast reversible
valence isomerization. Evaluation of the temperature dependent NMR-~pectra[~l
allows calculation of the enthalpy
and entropy differences of the valence tautomers (3)+(4)
(see Table).
Spiro[fluorene-9,7'-norcaradiene]2 S p i r o [2,4,6-cycloheptatriene-l,9'-fluoreneJ (3c)*(4c)
A solution of diazofluorene ( 1 c ) (10.0g) in distilled benzene (350 ml) was photolyzed at room temperature
(17-20°C) with a Philips HPK 125 W lamp (Pyrex filter).
After 4 hours 80% conversion was achieved (N, evolution).
Benzene was evaporated in vacuo and the residue extracted
3 times with petroleum ether (b. p. 40-80°C). After evaporation of the petroleum ether the residue was subjected
to chromatography on 250g of basic aluminum oxide.
Petroleum ether eluted 800mg (8%) [based on reacted
( l c ) ] ( 3 c ) = ( 4 c ) as colorless crystals; m.p : 98-99°C
(from ether/pet. ether); thin-layer chromatography showed
only one spot; IR (KBr): 1476(w),1454(s),1092(m),1042(w),
1038(w),804(s), 791(s), 743(s), 728(s) cm-'; UV(CHC1,):
h,&)=302(4230), 287(6870), 262(11990); Raman spectrum (solid): 1554 cm- ' (norcaradiene band).
Received: March 10, 1971 [Z 380 IE]
German version: Angew. Chem. 83,362 (1971)
[l] H . Diirr and G. Scheppers, Angew. Chem. 80, 359 (1968); Angew.
Chem. internat. Edit. 7, 371 (1968).
[2] H . Diirr and G. Scheppers, Tetrahedron Lett. 1968, 6059.
[*] Doz. Dr. H. Diirr and DipLChem. H. Kober
Institut fur organische Chemie der Universitat
66 Saafbriicken 11 (Germany)
[**I Photochemistry of small ring compounds, Part 24.-Part
H . Diirr,L. Schrader, and H . Seidl, Chem. Ber. 104,391 (1971).
342
23:
[3] M . Jones jr., A . M . Harrison, and K . R. Rettig, J. Amer. Chem. SOC.
91, 7462 (1969).
[4] D. Schonleber, Chem. Ber. 102, 1789 (1969).
[ S ] H . Giinther and H. Gdrlitz, Tetrahedron 25, 4467 (1969); further
literature cited therein.
Angew. Chem. internat. Edit. / Vol. 10 (1971) / No. 5
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valence, reversible, spironorcaradiene, demonstration, norcaradiene, isomerization, cycloheptatriene, new
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