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Cycloadditions with Mesomeric Pyrimidine Betaines.

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Recrystallization of the cis-trans mixture from diethyl
ether/pentane after chromatography on SiO, affords a
pure sample of the more sparingly soluble cis compound
( I ) ; in contrast, the more readily soluble trans isomer ( 2 )
has not yet been separated completely from the cis isomer.
We therefore limited our attempts to resolve the atropisoTable. T values from the 'H-NMR spectrum of the isomeric mixtures
in various solvents (15% solutions).
to give five-membered ring systems, the mesomeric sixmembered ring betaines ( I ) ought to be suitable for 1,4dipolar cycloadditions leading to six-membered heterocycles.
This is in fact shown to be the case in the reaction of ( I )
with dimethyl acetylenedicarboxylate ( 2 ) and maleic anhydride (3)IS1.Thus, ( l a ) and ( I b ) react with ( 2 ) with
loss of phenyl isocyanate to give, respectively, the 2pyridones ( 5 a ) and ( 5 b ) in good yields. As in the case of
the analogous reactions with acetylene derivativesF4, the
tendency to rearomatization leads to elimination of a
neutral molecule (in this case C,H,N=C=O)
from the
primary addition product (4).
mers to the cis compounds ( I ) . After repeated fractional
crystallization (18 x ) from diethyl ether/pentane the more
sparingly soluble fraction containing the levorotatory diastereoisomer exhibited a specificrotation of [a]& = - 168".
The highest rotations recorded so far for the fractions of
the mother liquor enriched in the more readily soluble
dextrorotatory diastereoisomers are [a]&= +46". The
rotations were measured with approximately
solutions in benzene. The four doublets of the methyl
groups of ( l a ) , ( I b ) , ( 2 a ) , and ( 2 b ) are retained in the
'H-NMR spectrum at 70°C in CD30D solution. Like the
thermal interconversion of cis and trans isomeric amino
carbene complexes[51,the transition between the atropisomers ( l a ) - ( l b ) and ( 2 a ) - ( 2 b ) is so slow that it
cannot be determined from the temperature dependence
of the 'H-NMR spectrum.
Received: August 2,1971 [Z 508 IE]
German version: Angew. Chem. 83, 1022 (1971)
[l] Optically active transition metal complexes, Part 7. This work was
supported by the Deutsche Forschungsgemeinschaft and the Fonds
der Chemischen Industtie.- Part 6: H. Brunner and H.-D. Schindler,
J. Organometal. Chem. 24, C 7 (1970). Also Part 37 of the series: Transition metal carbene comp1escs.- Part 36: E . 0. Fischer, M . Leupold, C .
G. Kreiter, and J . Miiller, Chem. Ber., in press.
[2] G . Krow, Top. Stereochem. 5 , 31 (1970).
[3] E. 0. Fischer, C . G. Kreiter, H. J . Kollmeier, J . Miilfer, and R. D.
Fischer, J. Organometal. Chem. 28, 237 (1971).
[4] P . Lazlo: Progress in Nuclear Magnetic Resonance Spectroscopy.
Pergamon Press, Oxford 1967,Vol. 3, p. 231 ;E. Moser and E. 0.Fischer,
J. Organometal. Chem. 13, 387 (1968); J . A. Connor and E . 0. Fischer,
J. Chem. SOC.A 1969, 578.
[ 5 ] E. Moser and E. 0. Fischer, J. Organometal. Chem. IS, 147 (1968).
Cycloadditions with Mesomeric Pyrimidine
By Thomas Kappe and Wolfgang Lube"]
Recently, we reported on the synthesis of mesomeric
pyrimidine betaines ( A ) , whose structure can only be
described by a series of zwitterionic canonical
The distribution of charge in these compounds is best expressed in terms of formulation (B). Huisgen's "sextet
limiting formula" (C) I3]suggests that such compounds
are potential starting materials for 1,4-dipolar cycloadditions[3? Since five-membered mesoionic heterocycles
can, in many cases, be used for 1,3-dipolar cycloadditionsr4]
[*] Doz. Dr. Th. Kappe and W. Lube
Institut fur Organische Chemie der Universitat
A-8010 Graz, Heinrichstrasse 28 (Austria)
Angew. Chem. internat. Edit. 1 Vol. I0 (1971) No. I 2
In the reaction of ( I b ) with maleic anhydride, however,
we have been able to isolate the 1 : I adduct ( ~ 5 ) ~The
structure of (6) has been confirmed by mass spectrometry,
molecular weight determination (528), and NMR spectroscopy (in DMSO). The NMR spectrum contains one singlet
at 6 = 3.70 due to the methylene protons of the benzyl group,
two doublets .of the cis-protons in positions 7 and 8 at
6=4.32 and 5.53, 3=9.5 Hz, as well as signals for 20
aromatic protons at 6 = 6.8-8.8. The IR spectrum (in KBr)
with anhydride bands at 1860 and 1790 cm-' and C=O
bands at 1710 and 1670 cm-', is also in agreement with
this structure.
2-Pyridones ( 5 a ) and ( 5 b )
The solutions of ( I a ) and ( I b ) (5 mmol) in chlorobenzene
(25 ml) are heated under reflux with (2) (1.4 ml. 10 mmol)
for 16 h. The residue recovered after evaporation under
vacuum is digested with petroleum ether. ( 5 a ) : yield
83%, colorless needles recrystallized from methanol, m. p.
168-170°Cr71 ; free dicarboxylic acid (by hydrolysis with
1 N NaOH): m. p. 253-256°C[71. (5 b) : yield 67%, colorless needles recrystallizedfrom ethanol, m. p. 235-237 OC['].
Joctane-7,8-dicarboxylic anhydride ( 6 )
( l b ) (1.07 g, 2.5 mmol) and (3) (0.25 g, 2.5 mmol) are
vigorously ground together and then heated at 170°C for
15 min. After digestion of the melt with cyclohexane and
recrystallization from chlorobenzene, compound ( 6 ) ,
m. p. 231-233 "C, was obtained in 61 % yield"].
Received: August 16, 1971 [Z 492 IE]
German version: Angew. Chem. 83, 967 (1971)
[I] Mesionic Malonyl Heterocycles, Part 2.-Part 1: [2].
[2] Th. Kappe and W Lobe, Monatsh. Chem. 102,781 (1971).
[ 3 ] R . Huisgen, Z. Chem. 8, 290 (1968).
[4] For summaries see: M . Ohta and H . Kato in J . P. Snyder: Nonbenzoid Aromatics. Academic Press, New York 1969, p. 117ff.; R. Huisgen in "Aromaticity", Chem. SOC.Spec. Publ. No. 21, London 1967,
p. 51.
[ S ] Analogous reactions of the bicyclic "anhydro-2-hydroxyl-1-methyl4-oxopyrido[ 1,2-a]pyrimidinium hydroxide" with acetylenedicarboxylate derivatives have been described recently by K . 7: Potts and M .
Storm, J. Org. Chem. 36, 8 (1971).
[6] The reason for adducts such as ( 6 ) being difficult to isolate is that
if R = H in compound (1) only "ene-addition" occurs, as observed by
Potts [ 5 ] in the reaction of zwitterions with tetracyanoethylene or
azodicarboxylate. We have found that the addition is also hindered(1) contains a
for electronic, and particularly steric reasons-if
substituent such as C,H,.
171 The structures of the products were confirmed by elemental analysis (C, H, N) and IR and NMR spectroscopy.
Preferred syn-Elimination from
By Jifi Sicher, Girald Jan, and Manfred Schlosser"'
The mechanisms of elimination of hydrogen bromide from
secondary alkyl bromides and from cycloalkyl bromides
of medium ring size differ significantly"!
A detailed discussion of these divergencies is only possible
if one can differentiate between the four elementary elimination processes syn +cis, syn + trans, anti --t cis, and anti -+
trans[21.Keeping this in mind we have extended our investigations to ~ic-dihaloalkanes[~~
and 1,2-dihalocyclodecanes. Such substrates exist in two diastereoisomeric
forms, for each of which two of the stereochemical pathways are blocked : I-halo-trans-cyclodecene
( Z isomer) can
arise from cis-1,2-dihalocyclodecaneonly by syn elimination, and from the trans isomer by anti elimination. Conversely, the I-halo-cis-cyclodecene ( E isomer) must be
formed from the cis-dihalide by anti-coplanar elimination
and from the trans-dihalide by syn-coplanar elimination
(Scheme 1).
Cyclodecane derivatives have been chosen as cyclic model
compounds since their elimination behavior differs most
typically from that of acyclic substrates. Furthermore, the
heats of formation of the configurational isomers of 1,2dihalocyclodecanes and especially those of the configurational isomers of I-halocyclodecenes should be very
similar, so that differences in reactivity due to differences
in thermodynamic stability (Polanyi-Hammond principle !)
should be negligible.
was readily prepared from
cis-cyclodecene and trichlor~arnine[~~,
and trans-12-di[*] Prof. Dr. J. Sicher (deceased) and Dipl.-Chem. G. Jan
Institut de Chimie Organique de I'Universitt
Rue de la Barre 2, CH-1005 Lausanne (Switzerland)
Doz. Dr. M. Schlosser
Organisch-Chemisches Institut der Universitat and
Institut fur experimentelle Krebsforschung am
Deutschen Krebsforschungs-Zentrum
69 Heidelberg, Im Neuenheimer Feld (Germany)
This work was supported by the Schweizerischer Nationalfonds.
= trans
t runs-dihalocyclodecane
Scheme 1. Elimination pathways open to cis- and trans-1,2-dihalocyclodecanes. R,R'= -(CH2)*-.
bromocyclodecane by addition of bromine to cis-cyclodecene in ethanol-free carbon tetrachloride at - 10°Cr5361.
Unfortunately, we have not yet been able to prepare the
~ i s - d i h a l i d e showever,
the results obtained on treating
the trans isomers with bases and observations from earlier
workrEJalready permit a first comparison of the dehydrohalogenation mechanisms of ten-membered cyclic dihalides
with those of the corresponding acyclic substrates.
anfr -cis
syn -CIS
ant, + trans
Figure. Relative rates kre, of the four individual stereochemical elimination processes which can take part in the base-induced dehydrohalogenation of acyclic substrates (haloalkane-rcis- and trans-alkene; uicdihaloalkane+Z- and E-I-haloalkene; see left-hand side of figure) and
cyclic substrates (halocyclodecane-cis- and trans-cyclodecene; uicdihalocyclodecane+Z- and E-I-halocyclodecene; see right-hand side
of figure). Base/solvent system : potassium butoxide in terr-butyl alcohol.
As can be seen from the above figure, going from the acyclic
series to the cyclodecane derivative-at least in tert-butyl
alcohol-always favors syn-coplanar cleavage, and particularly the syn + trans process. Evidently, the transition
states profit from the reduction in transannular repulsive
forces. On the other hand anti elimination is considerably
retarded in the ten-membered ring system. In addition to
steric hindrance of attack by bases['', steric hindrance of
halogen solvation may play an important role here too.
The most striking consequence of this situation is the
cross-over of syn + cis and anti -+ trans reactivities. In the
case of the ten-membered ring system, the anti + trans
route, most favored with acyclic substrates, falls back to
Angew. Chem. internat. Edit. 1 Vol. 10 (1971) No. 12
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cycloadditions, mesomeric, pyrimidine, betaine
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