Synthesis of dipolar nitronyl nitroxides

Article abstract of DOI:10.1021/ol0060329

(equation presented) The synthesis of a nitronyl nitroxide radical with a dipolar (mesomeric betaine) unit is reported.

Full text of DOI:10.1021/ol0060329

ORGANIC
LETTERS
2000
Vol. 2, No. 15
2269-2270
Synthesis of Dipolar Nitronyl Nitroxides
Stefan Greve,† Christian Na1ther,‡ and Willy Friedrichsen*
,†
Institutes of Organic Chemistry and Inorganic Chemistry, UniVersity of Kiel,
D-24118 Kiel, Germany
friedrichsen@oc.uni-kiel.de
Received May 9, 2000
ABSTRACT
The synthesis of a nitronyl nitroxide radical with a dipolar (mesomeric betaine) unit is reported.
Since the discovery of nitronyl nitroxides (NIT) by Ullman
et al.,1 this class of radicals has attracted considerable interest
as units for the preparation of molecular based magnets.2 In
1991 ferromagnetic ordering in a NIT radical was observed.3
Since then numerous publications have appeared that il-
lustrate the use of NIT as building block(s) for magnetic
materials.4 One of the challenges in this field is the design
of crystals with ferromagnetic ordering of the radical units.5
As a rational design of crystals with these properties is
still lacking, it is interesting to study the effects of highly
dipolar moieties upon the structure-property relationship of
the compounds. In this paper we report the synthesis of a
NIT radical with a pyrimidiniumolate unit6 starting with
terephthalaldehyde 1. Acetalization with triethylortho-
formiate10 to the corresponding monoacetal (67%) with
subsequent Willgerodt-Kindler reaction (MeNH2, S) yields
thioamide 2 (69%). Treatment of 2 with methyliodide and
then with methylamine gives amidine 3 (83%, two steps).12
Heating 3 with phenyl-bis(2,4,6-trichlorophenyl)-malonate13
in anisole (reflux, 3 min) yields pyrimidiniumolate 4 (69%).
Removal of the protecting group (Lewatit S 100 furnishes
the corresponding aldehyde (88%), which in treatment with
2,3-bis(hydroxylamino)-2,3-dimethylbutane yields 5 as nearly
colorless crystals (52%). Dehydrogenation could be ac-
† Institute of Organic Chemistry.
‡ Institute of Inorganic Chemistry.
(1) Osiecki, J. H.; Ullman, E. F. J. Am. Chem. Soc. 1968, 90, 1078-
1079.
(2) (a) Miller, J. S. AdV. Mater. 1994, 6, 322-324. (b) Gatteschi, D.
AdV. Mater. 1994, 6, 635-645. (c) Nakatsuji, S.; Anzai, H. J. Mater. Chem.
1997, 7, 2161-2174. (d) Plass, W. Chem. Unserer Zeit 1998, 32, 323-
333.
(6) Mesomeric betaines7 of this type have been reported repeatedly.
(7) For a definition see: (a) Newton, C. G.; Ramsden, C. A. Tetrahedron
1982, 38, 2965-3011. (b) Ollis, W. D., Stanforth, S. P., Ramsden, C. A.
Tetrahedron 1985, 41, 2239-2329.
(3) Turek, P.; Nozawa, K.; Shiomi, D.; Awaga, K.; Inabe, T.; Maruyama,
Y.; Kinoshita, M. Chem. Phys. Lett. 1991, 180, 327-331.
(4) Recent work: (a) Catala, L.; Turek, P.; Le Moigne, J.; De Cian, A.;
Kyritsakas, N. Tetrahedron Lett. 2000, 41, 1015-1018. (b) Fe´lix, O.;
Hosseini, M. W.; De Cian, A.; Fischer, J.; Catala, L.; Turek, P. Tetrahedron
Lett. 1999, 40, 2943-2946. (c) Alcaˆntara, A. F. C.; Dos Santos, H. F.; De
Almeida, W. B.; Vaz, M. G. F.; Pinheiro, L. H. M.; Stumpf, H. O. Struct.
Chem. 1999, 10, 637-674. (d) Heise, H.; Ko¨hler, F. H.; Mota, F.; Novoa,
J. J.; Veciana, J. J. Am. Chem. Soc. 1999, 121, 9659-9667. (e) Romero, F.
M.; Ziessel, R. Tetrahedron Lett. 1999, 40, 1895-1898. (f) Stroh, C.; Turek,
P.; Ziessel, R. J. Chem. Soc., Chem. Commun. 1998, 2337-2338. (g) Garc´ıa-
Mun˜oz, J. L.; Cirujeda, J.; Veciana, J.; Cox, S. F. J. Chem. Phys. Lett.
1998, 293, 160-166. (h) Hamachi, K.; Matsuda, K.; Iwamura, H. Bull.
Chem. Soc. Jpn. 1998, 71, 2937-2944. (i) Matsushita, M. M.; Izuoka, A.;
Sugawara, T.; Kobayashi, T.; Wada, N.; Takeda, N.; Ishikawa, M. J. Am.
Chem. Soc. 1997, 119, 4369-4379. (j) Frank, N. L.; Cle´rac, R.; Sutter,
J.-P.; Daro, N.; Kahn, O.; Coulon, C.; Green, M. T.; Golhen, S.; Ouahab,
L. J. Am. Chem. Soc. 2000, 122, 2053-2061 and references cited therein.
(5) (a) Kinoshita, M. Jpn. J. Appl. Phys. 1994, 33, 5718-5733. (b)
Deumal, M.; Cirujeda, J.; Veciana, J.; Novoa, J. J. AdV. Mater. 1998, 10,
1461-1465.
(8) Review: Friedrichsen, W.; Bo¨ttcher, A.; Kappe, T. Heterocycles 1982,
19, 1083-1148.
(9) Recent work: (a), Kappe, T.; Lube, W.; Thonhofer, K.; Kratky, C.;
Wagner, U. G. Heterocycles 1995, 40, 681-690. (b) Abd El-Sayed Issac,
Y. Bull. Chem. Soc. Jpn. 1999, 72, 503-509. (c) Potts, K. T.; Rochanapruk,
T.; Coates, S. J.; Hadjiarapoglu, L.; Padwa, A. J. Org. Chem. 1993, 58,
5040-5042.
(10) As reported for o-phthaldialdehyde: Powell, M. R.; Rexford, D. R.
J. Org. Chem. 1953, 18, 810-814. This method is superior to the procedure
described in the patent literature,11 as the amount of the corresponding
bisacetal was only small.
(11) Jpn. Kokai Tokkyo Koho JP 81.156.229 (Dec. 2, 1981); Chem.
Abstr. 1982, 96, 142458m.
(12) This methodology has been worked out by A.-C. Koch: Ph.D.
Dissertation, University of Kiel, 1991.
(13) (a) Kappe, T. Encyclopedia of Reagents in Organic Synthesis;
Paquette, L. A., Ed.; John Wiley & Sons: New York, 1995; Vol. 1, 557-
579. (b) Kappe, T.; Lube, W. Monatsh. Chem. 1971, 102, 781-787. (c)
Friedrichsen, W.; Schmidt, R.; van Hummel, G. J.; van den Ham, D. M.
W. Liebigs Ann. Chem. 1981, 521-531.
10.1021/ol0060329 CCC: $19.00 © 2000 American Chemical Society
Published on Web 06/21/2000

complished with lead dioxide (DMF, rt) to give 6 as dark
bluegreen crystals with mp 238 °C (54%)14 (Scheme 1).
Scheme 1
Figure 1. ∆Hf as a function of ϑ (a-b-c-d) for 7 (PM3 values).
7 is only small (see Figure 1). The same holds for ∆Hf° )
∆Hf°(ϑ3) for compound 9 (rotational barrier, 2.9 kcal/mol
(PM3)), whereas the rotational barrier (∆Hf° ) ∆Hf°(ϑ2))
in 8 is high.18
An X-ray crystal structure determination15 revealed that
in line with expectation the molecule is not planar. Torsion
angles between the rings are determined as ϑ(a-b-c-d) )
ϑ1 ) 38.51° (39.93°), ϑ(a′-b′-c′-d′) ) ϑ2 ) 68.71°
(69.98°), ϑ(a′′-b′′-c′′-d′′) ) ϑ3 ) 52.04° (51.80°).16 Values
calculated by semiempirical methods (AM1, PM3)17 differ
considerably (AM1, ϑ1 ) 29.6°, ϑ2 ) 87.4°, ϑ3 ) 35.0°;
PM3, ϑ1 ) 70.5°, ϑ2 ) 90.3°, ϑ3 ) 67.3°) although one
should keep in mind a variation of ∆Hf° with δ1 in compound
The synthetic methodology described in this paper has also
been extended to the preparation of other NIT radicals with
a pyrimidiniumolate group.19 Magnetic measurements of 6
and related compounds20 will be reported in due course.
(14) On the basis of spectroscopic evidence, including EI-MS. The
structures of all new compounds were unequivocally authenticated (see
Supporting Information).
(15) X-ray data for 6: C25H27N4O4, Mr ) 447.51, orthorhombic, a )
9.919(3), b ) 10.921(1), c ) 20.876(6), V ) 2261.2 Å3, space group
P212121, Z ) 4, dcalc ) 1.315 gcm-3, µ(Μï ΚR) ) 70.073 pm, crystal
dimensions 0.6 × 0.5 × 0.1 mm3 (slow evaporation of ethyl acetate). Data
were measured at room temperature on a PW-1100 4-circle diffractometer.
R1 for 1906 Fo > 4σ(Fo) ) 0.0483 wR2 for all 2445 independent reflections
) 0.1474 (Fo). Crystallographic data (excluding structure factors) for the
structure reported in this paper have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication CCDC 145335.
Copies of the data can be obtained, free of charge, on application to CCDC,
12 Union Road, Cambridge CB2, 1EZ, U.K. Fax: +44-(0)1223-336033.
Email: deposit@ccdc.cam.ac.uk.
Acknowledgment. The continuous support of our work
by The Fonds der Chemischen Industrie is gratefully
acknowledged.
Supporting Information Available: Experimental pro-
1
cedures and IR, UV, H NMR, 13C NMR, and MS for
compounds 2-5. This material is available free of charge
via the Internet at http://pubs.acs.org.
(16) For crystal structures of 3-aryl(heteroaryl)-substituted nitronyl
nitroxides, see, e.g.: (a) Caneschi, A.; Ferraro, F.; Gatteschi, D.; le Lirzin,
A.; Novak, M. A.; Rentschler, E.; Sessoli, R. AdV. Mater. 1995, 7, 476-
478. (b) Akita, T.; Kobayashi, K. AdV. Mater. 1997, 9, 346-349. (c) Zhang,
D.; Zhou, W.; Zhu, D. J. Mater. Chem. 1999, 9, 1409-1413. (d) Zheludev,
A.; Barone, V.; Bonnet, M.; Delley, B.; Grand, A.; Ressouche, E.; Rey, P.;
Subra, R.; Schweizer, J. J. Am. Chem. Soc. 1994, 116, 2019-2027 and ref
4b and 4i.
OL0060329
(18) Laackmann, P.; Friedrichsen, W. Tetrahedron 1996, 52, 5475-5475.
(19) Greve, S.; Friedrichsen, W.; unpublished material. Part of the Ph.D.
Dissertation of Greve, S., University of Kiel, 2000.
(20) Presented in part at the XIth Winter School on Coordination
Chemistry, Karpacz, Poland, 7-11 December 1998: Friedrichsen, W.,
Greve, S.; Mrozinsky, J.; Skrupa, A.; Pochaba, A.; Naether, C.; Friedrichsen,
W., manuscript in preparation.
(17) These calculations were performed with the program system
MOPAC, version 7.00.
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Org. Lett., Vol. 2, No. 15, 2000