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Formation of 1 2-Dimethylcyclobutadiene on Photolysis of Dimethylcyclobutenedicarboxylic Anhydride.

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The Hydrolysis of 6-Methylthio-8-azapurines to
Thiol Esters of 1,2,3-Triazolecarboxylic Acids
By A . Albert [*I
When boiled for 15 minutes with 1 M hydrochloric acid, 6methylthio-8-azapurine ( I ) gives a n almost quantitative
yield of 4-amino-5-(methylthio)carbonyl-l,2,3-triazole(Za),
m.p. 201 ' C , which could be isolated by filtration.
The 7-, 8-, and 9-methyl derivatives of ( I ) "1 gave ( 2 d ) . (Zc),
and (2b). melting at 132, 108, and 215 OC, respectively. They
are:all sparingly soluble in boiling water, but recrystallize well
from a little methanol. They are stable to acid.
[*I Prof. A. Albert
Department of Medical Chemistry
John Curtin School of Medical Research
Australian National University
Canberra (Australia)
[l] For preparation of the four starting materials, see a) R .
Weiss, R . K. Robins, and C . W. Noel[, J. org. Chemistry 25,765
(1960); b) A . Albert and K. Tratt, J. chem. SOC.(London) C
1968, 344; c) A . Albert, ibid. 2076; d) A. Albert, ibid. 1969, 152.
121 R. A . Nyquist and W . J. Ports, Spectrochim. Acta 15, 514
(1959).
[3] L. J . Bellamy in N. Kharasch: Organic Sulphur Compounds.
Pergamon Press, Oxford 1961, Vol. 1, p. 55.
141 Cf. [lc]: 254nm (log E = 3.98) for 6-hydroxy-9-methyl-8azapurine.
[51 E. Musetfig, Org. Reactions 8, 229 (1954).
SCH3
SCH,
(Za), R = H
(Zb), R = CH3
Formation of 1,2-Dimethylcyclobutadieneon
Photolysis of Dimethylcyclobutenedicarboxylic
Anhydride111 [**I
By G . Maier and U.Mende [ *I
Irradiation of tetramethylcyclobutenedicarboxylic anhydride
leads to products lpermethylated derivatives of (6), (7),(1.51,
and (16)l whose formation can be readily interpreted o n the
assumption of tetramethylcyclobutadiene as an intermediate
stage. The products found, however, d o not suffice to prove
this hypothesis [I].
On irradiation of the anhydride ( I ) (Hanovia 450-W H g
high-pressure lamp; Vycor filter; ether; 18 OC; 2 h) and subsequent chromatography o n silica gel we obtained a mixture
of the three isomeric tetramethylcyclooctatetraenes (7), (IOj,
n
A prominent peak occurs, in the ultraviolet spectrum of each
compound, between 287 and 312nm (log E about 4.0, in
methanol). The infrared spectrum (solid state) shows two
very strong peaks at about 1640 (C=O stretching) and
900 cm-1 (=C-S stretching). The IH-NMR spectrum (in
[Da]-DMSO/D20) shows two peaks at T = 6.2 (N-CH3) and
7.7 (S-CH3) (TMS internal standard).
(31
Until now, thiol esters have been almost unknown in heterocyclic chemistry, but many examples are known in the
benzene series with very strong infrared absorption in these
two regionsI21. That the new triazoles are not the isomeric
thione esters is shown by the stability of (2a)-(2d), and by
the absence of infrared absorption between 1000 and 1200
cm-1 131.
With aqueous ammonia (stirred at 20 "C and then refluxed),
(2a)-(2dj give almost quantitative yields of the carboxamides, identical with authentic specimens [Ib-ldl (much
methanethiol is liberated). Aqueous methylamine similarly
gives N-methylamides, e.g. those compounds derived from
(2b) and (2d) (m.p. 105 and 235OC. respectively). Such N methylamides have not previously been made. 4-Amino-3methyl-1.2,3 - triazole - 5 - carboxymethylamide [from ( 2 b ) ] ,
when heated with formamide at 225 "C, gives 19-dimethyl6-oxodihydro-8-azapurine( 3 ) , m.p. 207 "C, h,,
= 257 nm
(log E = 3.92 in H 2 0 [41), quite free from 9-methyl-6-0x0-dihydro-8-azapurine, and which was isolated by filtration.
(9)
Reductive desulfurization of the thiol esters affords 4-amino1,2,3-triazole-5-carbaldehyde and 4-amino-5-aminomethyl1,2,3-triazole (and nuclear methylated derivatives of these) 151.
Received: November 5, 1968
[ Z 900 IE]
German version: Angew. Chem. 81, 115 (1969)
132
(14)
(15)
6
Angew. Chem. internat. Edit.
1 Vol.8 (1969) No.2
and ( 1 3 ) 121 (total yield 8.873, o-xylene (0.6OA, durene
(1.OX),pseudocumene (3.0%). an inseparable mixture of
ketones (11.5%). the dimer (15) of dimethylcyclopentadienone ( 3 ) (8.1 %). and the cage diketone (16)(6.0%). The decisive intermediates seem to be the ketones, for the isolated
mixed ketones gave the same hydrocarbons on renewed
irradiation [though less (10)was formed] as did ( I ) .
The aromatic compounds were identified by gas chromatography and NMR spectroscopy. From the mixture of cyclooctatetraenes, only (I3)could be separated cleanly; according
to analysis of the NMR spectrum, the mixture contained the
proportions (7):(10):(13) = about 5:2:10. In order to
analyze the mixed ketones better, they were reduced by
LiAlH4; the alcohols formed could be separated by column
chromatography; each ketone gave only one alcohol,
stereospecifically. The alcohols (5) and (If), and thus the
ketones ( 6 ) and (121, occurred in the ratio 1:2.
(31 M. 1. S. Dewar and G. J . Gleicher, J. Amer. chem. SOC.87,
3255 (1965).
[***I Note added m proof (January 8 , 1969): On irradiation of
tetramethylcyclobutenedicarboxylic anhydride [l] in an organic
glass (ethanol, isopentane, ether) at -196 "C, aldeep yellow color
appears which disappears immediately when the matrix melts.
The adduct of tetramethylcyclobutadiene to tetramethylcyclopentadienone and the dimer of tetramethylcyclopentadienone
[permethylatedanalogs of (6) and (Is)]were isolated as the sole
products. These compounds could not have been present during
photolysis, since otherwise - as shown by control experiments their photoproducts 1e.g. octamethylcyclooctatetraene or the
permethylated cage diketone (Id)] would also have been detectable.
These results show that tetramethylcyclobutadiene and tetramethylcyclopentadienone can exist as monomers when frozen
into a glass at the temperature of liquid nitrogen.
Mesoionic 3-Methylene-lY2,4-triazoles
I * *1
88-89
4.55 (I) Q, 5.92 (1) T , 7.25 (1) M,
7.75 (1) M, 8.10 (2) M, 8.40 (3) br. S,
8.46 (3) S, 8.49 (3) D , 8.57 (3) S
40-41.5
[bl 4.55 (2) M, 6.40 (1) M, 7.66 (1) M,
8.08 (1) M, 8.43 (3) D, 8.52 (1) S,
8.56 (3) D, 8.63 (3) S, 8.94 (3) S
142-144
By R. Grashey and Margit Baumann [*I
6.04 (1) T, 7.12 (2) M, 7.75 (2) M,
8.18 (1) br. S, 8.42 (6) S, 8.53 (6) S
137-139
[Cl
148-150 [dl
3.99 (1) Q, 6.94 (l),double D,
7.36 (1) D, 7.58 (1) D, 7.95 (3) D,
8.32 (6) S, 8.65 (3) S
7.69 (2) S, 7.86 (2) S, 8.79 (6) S,
8.89 (6) S
[a1 T values, no. of protons, type of splitting; solvent CDCln; TMS as
internal standard.
[b] In CCI4. Icl IR fCC14): C=O bands at 1705
and 1785 cm-1.
[d] IR (CCI.,): band at 1755 cm-1.
The alcohol ( 8 ) was not found, but instead a small amount
of the isomeric (14). [The structure was derived from the
NMR spectrum.]
For the following reason, the products isolated prove that
cyclobutadiene is actually formed on photolysis of anhydrides
of type ( I ) : photolytic removal of C02 to yield (2). ring
opening of the latter to yield (31, and addition to (3) of the
dimethylcyclobutadiene arising from (2) on elimination of
CO should give the ketones (6). (9).and (12). Insofar as
cyclobutadiene is a rectangular singlet molecule with localized
double bonds 131 and undergoes rapid valence isomerization,
the three ketones must arise in the proportion 1:1:2 provided that steric factors do not lead to selectivity. In all
the other plausible ways [dimerization of (2) or ( 3 ) . or reaction of (2) with (3) and subsequent removal of C O ] ,only
the ketones (6) and (9) or compounds of totally different
structure would be formed. The relative amounts of the
tetramethylcyclooctatetraenes isolated, and of the aromatic
compounds and alcohols, indicate that dimethylcyclobutadiene reacts in the two forms (4a) and (4b), the doubly
methylated double bond in (4a) being, however, Iess amenable to addition than the unsubstituted double bond [***].
Numerous mesoionic systems
contain heteroelements
bound exocyclically. We now report mesoionic 1,2,4-triazole
derivatives (7) with carbon as the exocyclic atom; we obtained these from Nz,N3-disubstituted amidrazones and 3.3bis(methy1thio)acrylonitrile derivatives (5) [2,31.
The classical synthesis of amidrazones of type (3)
(method B) [4,51 from imidoyl chlorides and monosubstituted
hydrazines gives mainly N1,N3-disubstituted amidrazones ( 4 )
when arylhydrazines are used, and the products (3) and ( 4 )
must be separated before the treatment with (5). However, if
methylhydrazine in acetonitrile solution is used, then formation of (3) (R2 = CH3) is dominant, so that isolation of the
amidrazones can be omitted and the mixture of (7) with a
little ( 8 ) arising in the subsequent reaction with ( 5 ) can be
readily separated by crystallization.
H'-C-N-NH,
II
I
K'-C=N-R3 i H2-NH-NH2
I
S RZ
method A k H , i
Received: November 18, 1968
[ Z 907 IE]
German version: Angew. Chem. 81, 114 (1969)
[*I Doz. Dr. G. Maier and Dip1.-Chem. U. Mende
Institut fur Organische Chemie der Universitat
75 Karlsruhe, Richard-Willstatter-Allee (Germany)
[**I This work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie.
R2
111 Part 6 of Small Rings. - Part 5: G. Muier and U. Mende.
Angew. Chem. 80, 532 (1968); Angew. Chem. internat. Edit. 7
537 (1968).
[21 R. Criegee, W. Eberius, and H.-A. Brune, Chem. Ber. 101,
94 (1968).
Angew. Chem. internat. Edit. 1 Vol. 8 (2949) f NO.2
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133
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anhydride, photolysis, dimethylcyclobutadiene, dimethylcyclobutenedicarboxylic, formation
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