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Novel Metastable Germanium Modifications allo-Ge and 4H-Ge from Li7Ge12.

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A Novel Synthesis of
Nucleoside Methylphosphonates
By Joachim Engels* and Alfred Jager
Dedicated to Professor Klaus Weissermel on the occasion
of his 60th birthday
Nonionic analogues of DNA are of interest in the study
of DNA-DNA and DNA-protein interactions. In this connection, phosphonic acid esters of deoxyribonucleosides
should be particularly suitable because of their chemical
stability.
We report here a novel two-step route to nucleoside methylphosphonic acid esters, involving the direct synthesis
of phosphonous acid esters and their subsequent oxidation[’]. Dichloro(methy1)phosphane is treated successively
with two protected nucleosides in a one-pot reaction at
- 78 “C in tetrahydrofuran (THF). The resulting dinucleoside methylphosphonic acid diester is not isolated but oxidized to the corresponding methylphosphonate by addition of tert-butyl hydroperoxide (Scheme 1).
with BF3.0Et2. The NMR spectrum of the major deblocked product is identical with that of (TPT)~,
described
by Ts‘o ef al., and that of the other isomer with (TPT)~~“].
The phosphonic acid ester intermediate also reacts
smoothly with sulfur and selenium and, hence, opens up a
route to the previously unknown thio- and selenophosphonate analogues. Because of the similarity with the
phosphite method of Letsinger et al.[’I, this synthetic route
can also be combined with the Letsinger-DNA synthesis.
Received: June 18, 1982:
revised: October 14, 1982 [Z 69 IE]
German version: Angew. Chem. 94 (1982) 931
The complete manuscript of this communication appears in:
Angew. Chem. Suppl. 1982. 2010-2015
[I1 See also A. W. Frank in G. M. Kosolapoff, L. Maier:
Organic Phosphor-
ous Compounds. Vol. 4, p. 268 and 288, Wiley, New York 1972: K. Weis-
sermel, H.-J. Kleiner, M. Finke, U:H. Felcht, Angew. Chem. 93 (1981)
256: Angew. Chem. Iur. Ed. Engl. 20 (1981) 223.
[2] P. S. Miller, J. Yano, E. Yano, C. Carroll, K. Jayaraman, P. 0. P. Ts’o,
Eiorhemrsrry 18 (1979) 5 134.
131 TpT signifies the compound analogous to TpT but with 3’,S’-methylphosphonate-internucleotide bonding.
[4] L. S. Kan, D. M. Cheng, P. S. Miller, J. Yano, P. 0. P. Ts’o, Eiochemisrry
19 (1980) 2122.
[S] R. L. Letsinger, J. L. Finnan, G . A. Heavner, W. €3. Lunsford, J . Am.
Chem. Sor. 97 (1975) 3278.
Q
H~C-P-OR’
I
OK2
1-3
Novel Metastable Germanium Modifications
d o - G e and 4H-Ge from Li7GeI2
When CH,PCI, is treated with two equivalents of 5‘-0tritylthymidine or 3’-O-benzoylthymidine, the symmetric
3’,3‘- or 5’,S’-linked phosphonates 2 or 3 are accessible.
Reaction of 5’-O-tritylthymidine (RI-OH)
and 3‘-0benzoylthymidine (R‘-OH)
with CH,PCI, affords 1
(81%) with 3’,5’-methylphosphonate-internucleotide
bonding. The 3’,3’-phosphonate 2 always occurs as a side product @%), whereas formation of 3 (by reaction of 3‘-O-benzoylthymidine with unconsumed CH,PCI,) can be avoided
by using a slight excess (0.06 equiv.) of 5’-0-tritylthymidine.
1 consists of two diastereomers, which can be separated
by thin layer chromatography: the P-CH3 group exhibits
two doublets in the ‘H-NMR spectrum. Although
CH3PCI2 is not a sterically demanding reagent, the reaction nevertheless proceeds more stereoselectively than the
synthesis of dinucleoside methylphosphonate derivatives
by Ts’o et al., which results in a 1 : 1.5 isomer ratio‘*]; using
the method described here we obtained the diastereomers
of 1 in the ratio 4:1, whereby the major product is the
isomer with the larger R r value. Selectivity only occurs,
however, when 5’-O-tritylthymidine is the first alcohol
component. Each of the two isomers was converted into
the corresponding dinucleoside methylphosphonate TpTl3l
by debenzoylation with fert-butylamine and detritylation
By Andreas Gruttner, Reinhard Nesper. and
Hans Georg uon Schnering*
Dedicated to Professor Albrecht Rabenau on the occasion
of his 60th birthday
A renewed investigation of the binary systems Li-Sil’I
and Li-Ge[2,71led to discovery of the phase Li7GeI2;it is
formed as leaf-shaped metallic gray crystals on cooling a
stoichiometric melt of the elements (Ta-crucible; 0 up to 3
cm; T,,, = 1025 K). The compound crystallizes orthorhombically with a structure (Fig. 1) containing a characteristic
complex two-dimensional infinite polyanion 2[Ge:;][s1.
One of the Li atoms is situated in a Ge cage, the other six
are intercalated between the G e l a y e r ~ J P m n 2(No.
~
31);
a = 11.541(3), b=8.073(2), c = 15.359(4) A; Z = 4 ; 1788 hkl,
R = 0.071. The outstanding chemical property of Li7GeI2is
the spontaneous evolution of H2 on reaction with protic
solvents, leading to topotactic formation of allo-germanium[’], a novel metastable Ge-modifi~ation[~l.
The Hz is extruded strictly parallel to the layers of the two-dimensional
anion; at the same time, a linking of adjacent layers takes
place with formation of a three-dimensional structure (Fig.
I).
aNo-Ge is formed in these reactions as gray shiny metallic frits or leaflets which can be ground like graphite. Single crystals of allo-Ge are formed on reaction of Li7Gel,
single crystals with benzophenone in tetrahydrofuran,
whereby strong topotactic demetalation of Li7GeI2leads to
Li and the radical anion of Ph2C0. Mechanical strains in
allo-Ge crystals are largely avoided under these mild conditions.
allo-Germanium is a diamagnetic semiconductor. It
crystallizes orthorhombically with considerable stacking
disorder [Pmc2, (No. 26): a = n *23.887(9), b =7.787(3).
[ * ] Priv.-Doz. Dr. J. Engels, A. J2ger
I*]
I
OBal
Scheme I . Trt=trityl: Thy=thymine residue.
Fakultat fur Chemie der Universitat
Postfach 5560, D-7750 Konstanz (Germany)
912
0 Verlag Chemie GmbH. 6940 Wemheim. 1982
+
Prof. Dr. H. G. von Schnering, Dr. A. Griittner, Dr. R. Nesper
Max-Planck-lnstitut fur Festkorperforschung
Heisenbergstrasse I . D-7000 Stuttgart 80 (Germany)
0570-0833/82/12/2-0912
S 02.50/0
Angew. Chem. Inr. Ed. Engl. 21 (1982) No. I 2
c = 16.304(5) A; Z = 1281. The essential structural unit is
the original two-dimensional polyanion of Li,Gel,, resulting from homonuclearly coupled four-, three- and twobonded atoms of the type (4b)Geo, (3b)Ge'- and
(2b)Ge'-. The valences that become free on demetalation
are saturated by new Ge-Ge bonds within the layers and
between adjacent layers, so that only atoms of type
(4b)Ge" are still present (Fig. 1).
Li,Ge12
8/10
- Ge
-
Cyclobutadienes or Acetylenes from
(2-Cyclopropen-I-y1)carbenesA Question of Spin Multiplicity?**
By Pllilipp Eisenbarth and Manfred Re@*
Diazomethylcyclopropenes such as la1'] o r lb'*] are
promising precursors for the synthesis of cyclobutadienes.
Thus, on irradiation in pentane, they afford the tri-tert-butylcyclobutadienecarboxylates5a[I1(Table I ) and 5b"', respectively, together with the 3-hexyne 3 and the pentynoates 4a and 4b. The formation of alkynes in the photolysis of lbi2' was overlooked. In both cases, the ratio of cyclobutadiene formation to acetylene fragmentation is ca.
70 :30 and is markedly dependent upon temperature and
solvent.
Ph2C0
x
420K
1
I
N,
1
t
Ill
3
.
i
+
Ill
4
5
a , R = IBu; b , R = M e
a-Ge
Table I.(Selected data). Yields and physical and spectroscopic properties of
5a and 6.
4H-Ge
Fig. I. Formation of the novel Ge modifications a h - G e and 4H-Ge. allo-Ge
(schematic) is formed in a strongly topotactic reaction from Li7Gell: it is not
converted directly into a-Ge, but firstly into 4H-Ge, which, so far, has only
been obtained in this way. The slow transformation from the 4H-Ce into the
u-Ge phase commences at 770 K.
On heating under inert conditions, do-Cie is exothermally and irreversibly converted at 420 K into a further
metastable Ge-modification. In this form, germanium crystallizes hexagonally with the known structure of the polymorphic compound 4H-Sic. The novel modification 4HGe[" could previously be obtainedaonly in the powdered
form [P6,mc (No. 186); a=3.989 A, c=13.107 A; Z = 8 ;
c / a = 3.2861. On further prolonged heating, the similarly
exothermic conversion of 4H-Ge into the stable a - G e commences at 770 K.
On rapid heating 4H-Ge melts at 1198 K. i.e. 10 K below rsGe. The formation of d o - G e from Li7GeI2encourages increased activity in the search for metastable forms
of the elements.
5a:67%:orangecrystals; m.p.=56--57"C: b.p.= 155--156"C/O.I torr: ' H NMR(CDCI,):6=1.14(s, IXH), 1 , 1 6 ( ~ , 9 H )1.46(s,9H)
,
6: 20%; colorless crystals; m . p . = 175-17'7 " C ; 'H-NMR (CDCI,): fi=O.X7,
1.15, 1.31, 1.44 (in each case s, in each case 9H), 7.10-8.20 (m, I O H )
What is the reason for this diversion in reaction behavior? By analogy to the Wolff rearrangementr3], singlet-2
should rearrange ( 2 + 5 ) and triplet-2 ought to fragment
(2- 3 4)14]. Sensitization of the reaction with benzophenone should decisively influence the product ratio. The experiment with l a confirms this supposition (5a : 3
4a = 20 :70, 10% unidentified products). In any case, the
excess of sensitizer reacts with 5a in a [2+2]-cycloaddition
to give the 2-oxabicyclo[2.2.0]hex-5-enederivative 6 (7%)"'
(Table I). To our knowledge photochemical cycloadditions
of cyclobutadienes have so far never been reported in the
literature.
+
+
Received: July 5, 1982 [Z 82 I€]
German version: Angew. Chem. 94 (1982) 933
6
CAS Registry number:
Li ,,Ge ,?. 80188-08-5
- L .
7
The question as to whether 3 and 4a could also be
formed from 5a by benzophenone-sensitized photolysis
[ I ] H. G. von Schnering, R. Nesper, K. F. Tebbe, J. Curda, Z. Merallkd. 71
(1980) 357.
121 A. Gruttner, R. Nesper, H. G. von Schnering, Int. Union Crysrallogr.. 12.
Int. Congr., Ottawa, Canada; Acta Craysfallogr. A 3 7 (1981) C 161.
[31 A. Gruttner, Disserfafion.Universitat Stuttgart 1982.
141 A. Gruttner, R. Nesper, H. G . von Schnering, DPA 3 109229.2.
[51 A. Gruttner, R. Nesper, H. G. von Schnering, Z. Anorg. Allg. Chem., in
press.
Angew. Chem. I n f . Ed. Engl. 21 (1982) No. I2
[*] Prof. Dr. M. Regitz, P. Eisenbarth
I**]
Fachbereich Chemie der Universitat
Paul-Ehrlich-Strasse, D-6750 Kaiserslautern (Germany)
Carbenes, Part 29. This work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen 1ndustrie.- Part
28: [I].
0 Verlag Chemie GmbH, 6940 Weinheim, 1982
0570-0833/82/12l2-U913 S 02.50/0
913
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