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How УAromaticФ are 5-Phosphorins Electrophilic Substitution Reactions.

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5’-0-Nitrouridine ( 1 )
Uridine (1.2g, 4.9mmol) is added with vigorous stirring
to 90% nitric acid (p = 1.48; 7.5 ml) precooled to - 70°C.
The solution, which soon becomes clear, is stirred for
1 h at -70°C and after addition of further 90% HNO,
(7.5ml) for a further 30min at -70°C[71. The mixture
is then stirred into ice-water (80ml), covered with a layer
of ethyl acetate (50ml), and neutralized by portionwise
addition of solid NaHCO,. The aqueous phase[81 is
extracted with ethyl acetate (6 x SOml), and the combined
extracts are dried (MgSO,) and evaporated. When the
residual foam is taken up in hot ethanol, treated with
charcoal, and slowly cooled, the ester ( I ) crystallizes as
colorless needles of m. p. 139”C, [a];’=
16” ( c = 1,
DMF).
+
Received: January 24, 1973 [Z 788 IE]
German version: Angew. Chem. 85, 765 (1973)
[I]Nucleosides, Part 15.-Part 14 is considered to be J. dernd, I . Rychlik,
and F. W Lichtenthaler, FEBS Lett. 30, 147 (1973).
[2] P . A . Leuene and F . B. La Forge, Ber. Dtsch. Chem. Ges. 45, 608
(1912); J . Wempen, J . L. Doerr, L. Kap/an, and J . J . Fox, J. Amer.
Chem. SOC.82, 1624 (1960).
R. Duschinsky and U . Eppenberger, Tetrahedron Lett. 1967, 5103;
R. Duschinsky, Swiss Pat. 492721 (1967); Chem. Abstr. 73, 131272 (1970).
[4] 7: Kanai, C. Yamashila, and M . lchino, Jap. Pat. 7127463 (1968);
Chem. Abstr. 75, 130077 (1971).
[3]
[ S ] The only nucleoside 5’-nitrate known, also directly accessible from
the unprotected nucleoside by reaction with in situ generated 0,Odiethyl 0-nitrophosphorothioate (yield 30%). appears to be 5’-O-nitro-
thymidine: I . Schwandt, H. Teichmann, G . Hilgetag, G Kowollik, and
P. Lngen, 2. Chem. 8, 176 (1968).
[6] All the new compounds described gave satisfactory analytical data
on combustion. Rotations were all determined for N,N-dimethylformamide solutions at c = 1.
[7] Vigorous stirring is essential to prevent the mixture from solidifying.
[8] The organic phase contains the mononitrate ( 1 ) and dinitrate in
the approximate proportion 1: 1 (TLC in CHCI,/CH,OH 9: 1); separation
by preparative layer chromatography (20 x40cm plates with 1.75mm
of Merck silica gel PF35r+ and 9: I CHClJmethanol as eluant) atrords
a further IWmg (7%) of ( I ) .
converted into 4- or 2-substituted 1,1 -diphenyl-h5-phosphanaphthalenes by bases; on reaction with acid chlorides
these products were formed directly by transylidation.
Since other concepts of aromaticity suggest that 1,l-dialk~xy-h~-phosphorins[~~
are considerably more “aromatic”
than 1,l-dialkyl or l,l-diaryl-h5-phosphorinsf’2~,
these very
weakly basic compounds ought to be suitable for electrophilic aromatic substitutions at C-2 or C-4. Experimental
tests of this deduction have, however, been impossible
since 1,l-dialkoxy-h5-phosphorins
with a replaceable H
atom on C-2 or C-4 have hitherto been inaccessible.
In an earlier communication we reported the synthesis
of h5-phosphorins containing electrofugal groups other
than a proton on C-4rs1. We are now able to show that
these derivatives can be electrophilically substituted,
smoothly and in high yield, even in acidic media, without
any evidence of a phosphonium salt as intermediate.
One of these h5-p~osphorins is (l,l-dimethoxy-2,6diphenyl-h5-phosphorin-4-y1)carbeniumtetrafluoroborate
In acetonitrile containing a little water it first produces the alcohol (2), which immediately undergoes electrophilic substitution, losing formaldehyde cation, by ( I )
still present in the solution to give (3)I61 or by aryldiazonium tetrafluoroborates to give ( 4 ) .
(3) also contains a good electrofugal group. It reacts
with diazonium salts, giving ( 4 ) , and the yields of ( 4 )
in the presence of water are almost quantitative by the
route ( I ) -+ (2) shown. In another electrophilic substitution (3) can be alkylated by triethyloxonium salts to give
4-ethyl-l,l-dirnethoxy-2,6-diphenyl-h5-phosphorin ( 5 ) ,
which is also accessible by another
Treatment
of (3) with triphenylcarbenium tetrafluoroborate (6)
L
How “Aromatic” are A5-Phosphorins?
Electrophilic Substitution Reactions
J
By Werner Schafer and Karl Dimroth“’
Dedicated to Professor Karl Winnacker on the occasion of
this 70th birthday
“Aromaticity”f‘1 from the standpoint of preparative
organic chemistry characterizes the chemical behavior of
compounds like benzene where substitution of an H atom
by another group with retention of the unsaturated system
is preferred over addition leading to a more saturated
system. On treatment of phosphonium ylides with electrophiles a two-step reaction is always observed: addition
to the phosphonium salt and, if a sufficiently strong base
is present, loss of a proton. If the new, substituted ylide
is sufficiently stabilized by mesomerism, the proton can
also be transferred to the less stabilized initial ylide, a
mechanistic sequence which is called “transylidation”[21.
Reactions of this kind were also observed by Mark1 et
al. on treatment of cyclic 6z-delocalized phosphonium
ylides such as 1,l-diphenyl- and 1,1,2-triphenyl-phos~hanaphthalenef~’.
With methyl iodide or diazonium salts
the first products are phosphonium salts which can be
(5)
Anion: BF4@
~~~~
[*] Dr. W. Schafer and Prof. Dr. K . Dimroth
Organische Chemie im Fachbereich Chemie der Universitat
355 Marburg, Lahnberge (Germany)
Angew. Chem. internat. Edit. 1 Yo/. I 2 (1973) 1 No. 9
p-CH,CeH,
p-CH3OfoH,
2-CH,-4-N0,C,H3
186-188
153-156
181-183
210-211
194
247-250
753
forms only' bis( 1,I-dimethoxy-2,6-diphenyl-h5-phosphorin4-ylkarbenium tetrafluoroborate (7) by hydride transfer.
However, the nitrile ( 8 ) , readily obtained by addition
ofcyanide to ( 7 ) , reacts smoothly with (6) in an electrophilic substitution yielding 1,1-dimethoxy-2,6-diphenyl-4-trityl-h5-phosphorin ( 9 ) , m. p. 144-145 "C.
- +(C,Ii,),C@
R
(6)
+ H ~
+CNO
+H@
&H-CN
e
CsH5
Anion: BF,O
(9)
Electrophilic substitution with removal of the cation of
formaldehyde or benzaldehyde instead of a proton has
long been known in the benzene seriesl8I. This reaction
has been used to synthesize aldehydes starting from suitably
The
C-substituted derivatives of N~V-dirnethylaniline[~].
high x-electron density at position 4 of the above h5-phosphorin derivatives is in full accord with theoretical calculations[l0I and photoelectron spectroscopy1' '1. The complete
analogy of the reactions described with those of corresponding derivatives of N,N-dimethylaniline thus underlines the typical "aromatic" electron-rich character of 1,l-
dialk~xy-h~-phosphorins[~
zl.
The azo compounds ( 4 ) are protonated by acid, not on
the nucleus (C-4) to give phosphonium salts, but on the
P-N atom to give (10). Deprotonation by ethyldiisopropylamine regenerates ( 4 ) .
I:
~gAr
HzCO'
CGH5
"OCH,
Elemental analyses, mass spectra and NMR, IR, and UV
spectra of all the new compounds accord with the formulas
assigned.
Received: May 28, 1973 [Z 860 IE]
German version: Angew. Chem. 85. 815 (1973)
Publication delayed at authors' request
[I] D. Lloyd and D. R . Marshall, Angew. Chem. 84,447 (1972); Angew.
Chem. internat. Edit. 1 1 , 404 (1972).
121 H . Bestmann and R. Ztmmermann, Fortschr. Chem. Forsch. 20, 1
(1971).
[3] G. Miirkl and K . H . Heier, Angew. Chem. 84, 1066 (1972); Angew.
Chem. internat. Edit. 1 1 , 1016 (1972).
[4] K . Dimroth and W Stade, Angew. Chem. 80, 966 (1968); Angew.
Chem. internat. Edit. 7 , 881 (1968).
[ 5 ] K . Dimroth, ti! Schafer, and H. H . Pohl, Tetrahedron Lett. 1972,
839.
[6] W Schafer and K . Dimrorh, Tetrahedron Lett. 1972, 843.
[7] H . H . Pohl, Diplomarbeit, Universitat Marburg 1972.
[8] E. Ziegler, &err. Chem.-Ztg.53,31 (1952); E. Ziegler and G . Snatzke,
Monatsh. Chem. 84, 610 (1953).
[9] M . Stiles and A. J . Sisli, J. Org. Chem. 25, 1691 (1960); 27, 279
(1962); Org. Synth. 44, 4 (1964).
[lo] H. Oehiing, W Sckifer, and A. Sckweig, Angew. Chem. 83, 723
(1971); Angew. Chem. internat. Edit. 10, 656 (1971).
[ll] A. Schweig, W Schafer, and K . Dimroth, Angew. Chem. 84, 636
(1972); Angew. Chem. internat. Edit. 11, 631 (1972).
[ I 2 3 For a summary see: K . Dimrork, Fortschr. Chem. Forsch. 38, 1
(1973).
[I31 A. Hettcke and K . Dimroth, Chem. Ber. 106, 1001 (1973).
Ligand Influences in Heterogeneous
Catalysis: Modification of the
Phillips Catalystp*l
By G. Henrici-Olive' and S. Olivev]
Catalyst tailoring by a systematic variation of the ligands
seems to be on its way to becoming a powerful tool in
homogeneous catalysis on transition metal centers[']. It
appears opportune to apply the same principles to heterogeneous catalysts. We reported recently on the influence
of titanium containing ligands on molybdenum oxide catalysts for the metathesis of olefinsf''. The present communication deals with the modification of the heterogeneous
catalyst for the polymerization of ethylene, based on S O z supported chromium oxide (Phillips catalyst), and its interpretation in terms of ligand influences.
The molecular weight of polymer in this type of catalysis
depends on the relative rates of chain propagation (rate
constant kJ and chain transfer (P-hydrogen transfer ; rate
constant k t J :
v4N-Ar
Y
N,N-Ar
Cr-CH,-CH,-(P)
( 4 'I
111)
Anion: BF,@
Reaction with acids containing easily polarizable anions,
e. g. HCl, yields, irreversibly, with loss of methyl chloride,
the phosphinic acid derivatives (11). These can be transformed back into azo compounds ( 4 ' ) by alkylation with
triethyloxonium tetrafluoroborate in the presence of ethyldiisopropylamine' 31.
754
C r H + CH,=CH-(P)
(P), stands for a polyethylene chain of n monomer units.
The latter reaction is enhanced by increasing the electron
affinity of the metal centerr31, and can in principle be
controlled by choosing the proper ligands.
[*] Dr. G. Henrici-Olivt and Dr. S. Olivt
Monsanto Research S. A.
CH-8050 Zurich, Eggbuhlstrasse 36 (Switzerland)
We recognize valuable experimental help from Miss E. Arnold
and Mr. H. Kull.
[**I
Angew. Chem. internat. Edit. 1 Vol. 12 (1973) 1 No. 9
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