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Synthesis and Intramolecular Charge-Transfer Interaction in 1 4-Dihydro-1 4-ethanobenzotropylium Tetrafluoroborate.

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18) R. C. Whelund, E. L. Martin. J Org. Chem. 40. 3101 (1975).
[Y] The electronic spectrum of the cyclophane (3) showed no solvent dependence, S. Mnumi, personal communication.
[lo] The anomalous high-energy shifts on increasing the solvent polarity for (7a)
and 176) have not been completely elucidated.
Synthesis and Intramolecular Charge-Transfer
Interaction in 1,4-Dihydro-1,4-ethanobenzotropylium
Tetrafluoroborate'**I
By Tomoo Nakazawa, Yoshihide Niimoto, Keiji Kubo, and
Zchzro Murata['I
Reduction of the bridged tropone (3~)"'[NaBH, in aq.
CH30H,at room temp.] gave the dienol (4a)['],colorless needles, m.p. 90.5-91.5 "C, in 65% yield. Compound (4a) was
converted into its mesylate [CH3S02Cland Et3N in CH2Cl2]
which (without isolation) was subjected to elimination with
1,5-diazabicyclo[5.4.0]undec-5-enein CHzC12to give the tropylidene (5a)I3]in 77% yield. Subsequent hydride abstraction
with trityl tetrafluoroborate afforded, in 57% yield, the salt
( 2 ~ ) as
' ~colorless
~
needles, m.p. 116-117 "C (dec.). The dihydro derivative (2b)I3l, colorless leaflets, m. p. 130.5 "C
(dec.), was prepared in the same manner starting from
(3b)I'l.
We have previously reported strong intramolecular
charge-transfer (CT) interactions between the tropylium unit
and remote benzene rings in (1) despite the minimized overlap of the orbital systems of both donor and acceptor''! In
principle, olefins should conceivably be able to replace the
12al
111
12b1
aromatic hydrocarbon moiety as donor. Thus, the title compound (2a) seems to be a reasonable candidate for examination of intramolecular remote T-T interaction. This communication describes the synthesis and properties of (2a) together with those of the dihydro analog (2b) as a reference compound.
The structural assignment of (2a) and (26) was based on
spectral data (Table 1). As a consequence of the strong interaction in an excited state, (2a) exhibits characteristic absorptions, absent from the saturated reference compound (2b)f4]
(Fig. 1). The spectrum of (2a) in acetonitrile exhibits inter
alia a new absorption maximum at 325 nm which is shifted
Table 1. Comparison of physical properties of (2aJ and (2b) with those of tropylium tetrafluoroborate
uv
Cpd.
A,,
I201
Tropylium
BFi'
[nml (log&)
in CHzC12
in CH,CN
236 (4.58)
279.4 (3.78)
334 (3.14)
230.7 (4.65)
276 (3.77)
325 (3.15)
230.3 (4.57)
285 (3.70)
225 (4.64)
284 (3.68)
300 (3.66)
296.5 (3.64) sh
217
280 [a]
'H-NMR
in CDIC12
6 values
"c-NMR
in C D K N
S values
24.0 (C-10, 1 I )
48.4 (C-I, 4)
134.9 (C-2. 3)
174.8 (C-4a. 9a)
149.5 (C-5, 9)
152.5 (C-6, 8)
150.8 (C-7)
1.41-1.66 (m. H-2, 3, 10, 11 syn) 24.5 (C-2, 3, 10. 11)
2.06-2.30
(m, H-2. 3. 10, I I 4 2 5 (C-I. 4)
anti)
176.6 (C-4a. 9a)
3.82 (m, H-I, 4)
151.5 (C-5, 9)
9.04 (m. C,H$
152.2 (C-6. 8)
151.2 (C-7) [c]
9.30 in C H K N [b]
155.4 [d]
1.55-2.05 (m. H-10. 11)
4.80 (m, H-I. 4)
6.76 (m,H-2. 3)
9.06 (m. C,H%
PKK [el
+
€,,I
[V 1:s SCEl [Q
8.4,
-0.44
8 S2
-0.45,
4.70
- 0.24,
[a] J. Feitlson, J . Chem. Phys. 43, 251 1 (1965); A. Julg, J. Chim. Phys. 62. 1372 (1965). [b] G. Fraenkel, R. E. Carter. A. McLachlan, J. J. Richards, J. Am. Chem. SOC.82.
5846 (1960). K. M. Harmon, A. B. Harmon, B. C. Thompson, rbid. 89, 5309 (1967); R. W. Hurray. M. L. Kuplan, Tetrahedron Lett. 1967, 1307. [c] K. Okamoto, unpublished
data. We thank Prof. K Okamoto for informing us of his data. [d] H. Spiesecke. W. C Schneider, Tetrahedron Lett. 1961.468. [el Measured spectrophotometrically in 20%
aq. C H K N . [fJ Measured in CH3CN by polarography using tetraethylammonium perchlorate as supporting electrolyte at 25 "C.
r]Prol. Dr. T. Nakazawa. Y . Niimoto, K. Kubo, Prof. Dr. I. Murata [ * I
Department of Chemistry, Faculty of Science, Osaka University
Toyonaka, Osaka 560 (Japan)
[ ' 1 Author to whom correspondence should be addressed.
[**I This work was supported in part by a Grant-in-Aid for Scientific Research
(No. 343007) from the Ministry of Education. Japan. We thank Prof. S. Ikeda,
T. Ozekr and K. Yokoz of this department for measurement of the reduction
potentials
Angew Chem In!. Ed Engl. 19 (1980) No. 7
to 334 nm upon changing the solvent to less polar dichloromethaners1,suggesting a CT interaction between the tropylium ring
- and the remote ethvlene 7r-system[61.
In order to examine the effect of the electronic interaction
on the ground state stability of the tropylium unit we have
determined PKR and the reduction potentials Of 124 and
(2b) which are also shown in Table 1. The tropylium is con-
0 Verlag Chemie, GmbH, 6940 Weinheim, I980
+
0570-0833/8~/0707-054S
$ 02.S0/0
545
siderably more stable in ( 2 4 and (Zb), corresponding to the
increase in reduction potentials (decrease in electron affinity)
when compared with the parent tropylium ion. The remarkably high pKR+ values and reduction potentials of (2a) and
(26) appear to be due to a n electron donating inductive effect
of the bridging alkyl group[']. At first glance, the apparent
C T interaction observed in the UV spectrum of (2a) would
seem to stabilize the tropylium unit. Interestingly, however,
LO
'
30
'y,
20
1
200
I
300
h Inml
Fig. I UV spectra of (Za) (....) and (26) (-)
-
1
LOO
in C H K N
the pKR x value of (2a) is found to be less than that of (Zb),
albeit by only 0.35 pK units. This trend is also reflected in
the slight decrease in the reduction potential of (2a) as compared with that of (2b)"l. This indicates that the C T interaction between the tropylium ring and the remote ethylene T system is more favorable in the excited state than in the
ground state of (2a).
Received: April 15, 1980 [Z 495b IE]
German version. Angew. Chem. 92, 566 (1980)
CAS Registry numbers:
(20). 73701-19-6; (2bj. 73701-21-0 (3a). 67074-21-9; (36). 67074-23.1: (40).
74128-85.1; (4%) -mesylate, 74128-86-2; (5a). 74128-87-3, tropylium tetrafluoroborate. 27081-10-3
L-Gulose or D-glum-Hexodialdose from
~-Glucurono-6,3-lactoneby Controlled Reductions'"'
By WiIhelm V. Dahlhoff, Peter Idelmann, and Roland
Koster"]
The reduction of 0-ethylboron-protected -onic and uronic
acid lactones with ethyldiboranes(6)[***l
is well suited for the
preparation of aldoses and dialdoses. In some cases, by incorporating monofunctional 0-(diethylboryl)-L1".21or difunctional O-(ethylboranediyl)-"dl protecting groups, the reactions can also be directed, so that various pure end products
become accessible in high yield from the same starting material.
We obtained highly pure L-gulose (3) by reduction of the
free ~-~-glucurono-6,3-lactone
(1) with ethyl-hydro-borane~(3)'"'~.The lactone (1) is converted in a single step at
N 50 " C with diethyl-hydro-borane(3) (molar ration s 1 : 5)
into a n 0-ethylboron-protected cu/P-gulofuranose (2), from
which the anhydrous solid L-gulose (3) can be liberated without loss by treatment with methanol/ethylene glycol
(Scheme 1).
However, if the non-reduced compound (4) is initially prepared from (1) with the aid of various 0-(ethylboranediyl)
reagents e. g. triethy1boroxin[ld1or triethylborane/ethyldiborane~(6)"'~
the treatment of the product with ethyldiboranes(6)
gives an essentially quantitative yield of an equimolar mixture of ethylboron-protected D-gluco-hexodialdose (5) and
D-glucose (6). Compound (S) can easily be separated completely from (6) and transformed quantitatively by methanol
into pure anhydrous D-gluco-hexodialdose (7) (Scheme 1).
The chemical analyses [C, H, B values, ethane number""],
hydride numberlidl] and spectroscopic data [IR, MS, 'H-,
I3C-NMR] of (2) to (7) confirm their composition, structure,
and purity.
Hitherto, L-gulose (3) was known only as a hydrate syrup;
the older method of preparation from (1) led to impure (3) in
ca. 10% yield. Likewise, (7) was accessible from (1) in only
moderate yields ( 5 22%)['1.-With the new 0-ethylborane
method, (3)13 61 and (7)f3.41
can be prepared in pure form considerably more simply and in better yields than previously.
Procedure
(2): To a solution of ethyldiboranes(6) (23.4 g, 335 mmol
in tetrahydrofuran heated to 45 "C is added
11.3 g (64.2 mmol) of (1) within 3.5 h from a swivel-mounted
side arm. An increase in temperature (to 50-60 "C; exothermic reaction!) is accompanied by evolution of HZ (= 4.2 Nl).
Ethene is passed ( N30 min) into the colorless, clear solution
(trapping by excess BH) at = 50 "C. On evaporating the
(bath)/lO-l torr, 20.4 g (98%) of
solution down at ~ 8 0 ° C
(2) is obtained as a colorless syrup; [a]?= +24.7 (c=7.4,
CHCI,); 'H-NMR (CDCl3): 6=5.65 (J,,,<l Hz; H ' , p-(2)),
5.74 ( J , , 2 = 5 Hz (HI, ~ ( 2 ) )a :;p = 3 8 : 6 2 (after 1 h).
(3): Methanol ( = 100 ml) is added dropwise to 12.9 g (39.8
mmol) of (2) with continuous removal of MeOBEt2/MeOH
from the mixture by distillation. After subsequent further
evaporation at l o - ' torr the residue is treated with 15 ml of
1,2-ethanediol and once again evaporated down ( s80 "C
(bath)/lO- torr). The boron-free residue is treated with
> BH, 14% H')
T.Nakazawa. I . Murara, J. Am. Chem. SOC.9Y, 1996 (1977); see also D. N .
Burler, I. Gupfa.Can. J. Chem. 56. 80(1978); f Nakazawa. N. Abe. K. Kubo,
I. Murara, Tetrahedron Lett. 1979, 4995.
[ 2 ] T Nakamwa, Y. Niimoto. I Murara. Tetrahedron Lett. 197X. 569.
[3] Elemental analyses and 'H-NMR spectra are in agreement with the structures given.
[4] C. Hohlneicher, R. Kiessling, H. C. Jutz, P. A . Srraub, Ber. Bunsenges. Phys.
Chem. 70, 60 (1966): P. Schusler. D. Vedrilla. 0.E. Po1ansk.v. Monatsh.
Chem. 100. l(1969).
[S] E. Kosower, J. Am. Chem. Soc. XO. 3253 (1958); K. Dimrorh, C. Reichardr, T
Siepmann, F. Bohlmunn, Justus Liebigs Ann. Chem. 661. I (1963); C. Rerchardr. K. Dimrorh, Fortschr. Chem. Forsch. 11. 1 (1968); M. Feldmann. 8. G.
Graces, J. Phys. Chem. 70, 955 (1966).
[6] The CT-band of (Za) is also observed in its MCD spectrum and is confirmed
by modified CNDO/2 calculations. M. Harano and A . Tajri, to be published.
[7] It has been observed that the reduction potential of the tropylium ion increases with increasing methyl substitution; see K. Takeuchi, Y. Yokomrchi.
T.Kurosaki. Y. Kimura, K. Komarsu. K. Okamoro, Abstracts M33, The 29th
Symposium on Organic Reaction Mechanisms, Osaka. Japan, October C -7.
1978.
181 This fact could be interpreted by considering the difference in inductive effect between the ethano- and the etheno-bridges of (2b) and (Za), respectively. The stabilization of the tropylium unit /2a) by electron supply from the remote ethylene .ir-orbital would not be significant in the ground state of this
molecule. Cf. H. Iwamura. K. Makino. J. Chem. Soc. Chem. Commun. lY7X.
720 K. Yamamura. f Nakarawa, I. Murara. Angew. Chem. 92, 565 (1980);
Angew. Chem. Int. Ed. Engl. 19, 543 (1980).
[I]
546
0 Yerlag Chemie. GmbH. 6940 Wernherm. 1980
>
[*] Prof. Dr R. Koster. Dr. W. V. Dahlhoff, DipLChem. P. Idelmann
Max-Planck-Institut fur Kohlenforschung
Kaiser-Wilhelm-Platz 1, D-4330 Miilheim an der Ruhr (Germany)
["I Organoboron Monosaccharides. Part 6 (Part of a planned dissertation by P.
Idelmann. Universitat Bochum, 1980).-Parts 1-5: [la-el.
['"'I
Ethyldiboranes(6) or ethyl-hydro-boranes(3) mentioned in the text and the
EtlBH denoted in Scheme 1 are actually equilibrium mixtures with the overall
cornposition of "tetraethyldiborane(6)"; cf. R. Kosrer and P. Binger. Inorg.
Synth. XV. 141 (1974).
1)570-0X3.Z/X0/07o7-0~46 $ 02 50/0
Angew. Chem. Inr. Ed. Engl. 19 (1980) No. 7
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dihydro, synthesis, intramolecular, tetrafluoroborat, interactiv, transfer, ethanobenzotropylium, charge
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