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Anodic Oxidation of Trihexylmethoxyborate in Presence of Butadiene.

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2-Phenyl-3-cyclohexylimino-4,4-bis(trifluoromethyl) -I-azetine ( 2 c ) :
2-Phenyl-4,4- bis(trifluoromethyl)-5,5,5-trimethoxy-4,5-dihydro-1,3,5-oxazaphosph(v)ole( I c ) (4.32 g, 11 mmol) and
cyclohexyl isocyanide (1.09 g, 10 mmol) are refluxed for
12-24 h in anhydrous benzene. Removal of solvent and
phosphoric acid ester by vacuum distillation gives a crystalline residue; yield after recrystallization from methanol/
water: 2.95 g (82%) of ( 2 c ) .
Received: September 3,1971 [ Z 523 IE]
German version: Angew. Chem. 84,35 (1972)
the second equivalent of thallium(I1r) nitrate to give the
oxopyrazole (4).Solvolysis by methanol, with concomitant
elimination of nitrogen and thallium(r), yields the 2-alkynoic ester ( 5 ) directly. Previous observations that S-pyrazolones mercurate at position 416]and undergo oxidation to
o x o p y r a z o l e ~support
this interpretation.
Table. Synthesis of 2-alkynoic esters (S) from 5-pyrazolones (1) with
thallium(lr1) nitrate in methanol. Products were identified by comparison with authentic material and/or spectral data and yields determined
by GLPC.
[I] Reactions of 4,5-dihydro-1,3,5-0xazaphosph(v)oles,
Part 3.-Part
2: [3 b].
[2] K . Burger, J . Fehn, and E. Moll, Chem. Ber. 104. 1826 (1971).
[3] a) K . Burger and J . Fehn, Angew. Chem. 83, 761 (1971); Angew.
Chem. internat. Edit. 10, 728 (1971); b) Angew. Chem. 83, 762 (1971);
Angew. Chem. internat. Edit 10, 729 (1971).
[4] R . Huisgen, Angew. Chem. 80, 329 (1968); Angew. Chem. internat.
Edit. 7, 321 (1968); J . A . Deyrup, Tetrahedron Lett. 1971, 2191.
[5] A . B . Lecy and A . Hassner, J. Amer. Chem. SOC.93,2051 (1971).
[6] G. Ptffeeri, P . Consonni, G. Pefiraa, and E. Testa, J. Heterocycl.
Chem. 4, 619 (1967); D. Bormann, Liebigs Ann. Chem. 725, 124 (1969);
A . Hassner, J.O. Currie, A . S . Steinfeld, and R . F . Atkinson, Angew. Chem.
82. 772 (1970); Angew. Chem. internat. Edit. 9,731 (1970).
A Facile Synthesis of 2-Alkynoic Esters'']
By Edward C. Taylor, Roger L. Robey, and
Alexander McKillop[*]
We report a facile one-step synthesis of 2-alkynoic esters
( 5 ) from the readily available 5-pyrazolones ( I ) by treatment with two equivalents of tha1lium(111)nitrate"] in methanol. Yields are high and reaction conditions are extremely
mild. Since 5-pyrazolones may be prepared in quantitative
yield by the reaction of hydrazine with P-keto estersr3],this
conversion represents in a formal sense the dehydration of
P-keto esters to 2-alkynoic
In fact, the direct conversion of P-keto esters into 2-alkynoic esters ( 5 ) without
isolation of the intermediate 5-pyrazolones ( I ) can be
achieved by treatment in methanol solution first with
hydrazine and then with thalliurn(I1r) nitrate ; comparable
overall yields are obtained. Representative conversions
are summarized in the Table.
(4) CH~'OH
Yield (%)
A solution of thallium(1rr) nitrate (0.021 mol) in methanol
(25 ml) is added to a suspension or solution of the 5-pyrazolone (0.010 mol) in methanol (25 ml), and the reaction
mixture is stirred for 15 min at room temperature and then
for an additional 15 min at reflux (water bath). The cooled
reaction mixture is filtered to remove precipitated thallium(1) nitrate and the filtrate diluted with water and
extracted with chloroform. The extracts are washed with
water, dried over anhydrous Na,S04, filtered through a
short column of Florisil and evaporated to give the pure
(GLPC) 2-alkynoic esters.
Received: August 30,1971 [Z 524 IE]
German version: Angew. Chem. 84,60 (1971)
113 Thallium in
Organic Synthesis, Part 30.-Part 29: E. C. Taylor,
F . Kienzle, and A. McKiflop, Synthesis, in press.
[2] A. McKillop, J . D. Hunt, E . C . Taylor, and F. Kienzle, Tetrahedron
Lett. 1970, 5275.
[3] R. H . Wiley and P. Wiley in A . Weissberger: The Chemistry of
Heterocyclic Compounds. Interscience, New York 1964, Vol. 20.
[4] Oxidation of 5-pyrazolones to 2-alkynoic esters with thallium(rrr)
nitrate in methanol, as herein described, represents a considerable
simplification over the only previously available procedure for effecting this type of overall conversion, which involves chlorination of the
5-pyrazolone to give a 4,4-dichloro-2-pyrazolin-5-one,
which is subsequently treated with strong alkali to give a 2-alkynoic acid (L.A . Carpino, P . H . Terry, and s. D. Thatte, J. Org. Chem. 31, 2867 (1966)).
[5] A . R . Katritzky and J . M . Lagowski, Advan. in Heterocycl. Chem.
2, 28 (1963).
[6] See ref. [3], pp. 104-105.
[7] 8. T Gillis and R . Weinkam, J. Org. Chem. 32, 3321 (1967).
Anodic Oxidation of Trihexylmethoxyborate
in Presence of Butadiene['ll**l
By Hans Schafer and Dietrich Koch"]
We suggest that this transformation involves initial electrophilic thallation of the 3-pyrazolin-5-one tautomer ( 2 )
to give (3), which undergoes a subsequent oxidation by
Prof. Dr. E. C. Taylor and R. L. Robey
Department of Chemistry
Princeton University
Princeton, N. J. 08540 (USA)
Dr. A. McKillop
School of Chemical Sciences
University of East Anglia
Norwich NOR 88C (England)
Alkyl groups in borates can be dimerized with Ag(I)['' or
made to give alkyl-metal compounds by reaction with
active anodesf4];aryl groups in borates can be dimerized
electrochemically~31.In the course of our work on the
anodic bifunctionalization of olefinsr5' we have now been
p] Doz. Dr. H. Schafer and DipLChem. D. Koch
Organisch-Chemisches Institut der Universitat
34 Gottingen, Windausweg 2 (Germany)
[**I This work was supported by the Deutsche Forschungsgemeinschaft.
Angew. Chem. internat. Edit. I Yol. I 1 (1972) 1 No. I
able to transfer anodically the hexyl group from trihexylborane to butadiene.
(8)-(1l) by electrophilic attack of ( 4 ) on ( I ) is also
M solution of
Voltammetric measurements on a
trihexylborane prepared in situ in the electrolyte 0.3 mol/l
NaClO,/O.S mol/l NaOCH,/methanol at a graphite disk
anodef6]revealed the peak potentials: E,(I)= -0.04 V and
E,(2)= +0.3 V (us. Ag/AgCl). Comparison of the corresponding peak currents i,(l) and i,(2) with that of an
aqueous solution of K,Fe(CN), shows that both oxidation
steps involve transfer of a single electron.
The electrolysis of alkyl borates in the presence of olefins
is of interest as a method for the alkylation of olefins. It
complements the anodic addition of Grignard compounds['] since it starts from alternative precursors and
can be carried out in protic solvents. Owing to the lower
anionic reactivity of the borates it should be possible to
use boranes or olefins carrying substituents such as halogen,
NO2, COOR, or S 0 2 R .
The preparative electrolysis of hydroborated I-hexene
(50 mmol) and NaOCH, (80 mmol) in methanol employing
a diaphragmless electrolysis cell with a graphite anode at
an anode potential of I
t 0 . 5 V (us. Ag/AgCl), a current
density of 25 mA/cm2, and a temperature of - 5 "C affords
dodecane ( 3 ) (25% current yield; 48% based on reacted
borane). Under otherwise identical reaction conditions
but at -20°C and in the presence of 0.63 mol/l of butadiene a 41 % yield (based on reacted borane) of the following products is obtained: 9%17] of dodecane ( 3 ) ; I S % of
8-hexadecene (6) ; 23% of I-methoxy-2-decene ( 8 ) ; 20%
of 3-methoxy-I-decene ( 9 ) ; 16% of 8,12-eicosadiene (10);
and 13% of 8-vinyl-10-octadecene ( 1 1 ) . Three isomeric dimethoxyoctadienes (7), methoxy-substituted dimers of
butadiene['], are formed simultaneously in a current yield
of 17%.
Received: August, 27. 1971 [Z 519 IE]
German version: Angew. Chem. 84,32 (1972)
As a working hypothesis we assume that trihexylmethoxyborate ( I ) -and
presumably also dihexylborate-and
butadiene are oxidized simultaneously to the hexyl radical
(2) and the butadiene radical cation ( 4 ) , respectively,
which give ( 3 ) and (7) on dimerization and (8) and ( 9 )
on mixed coupling. The products ( 6 ) , ( l o ) , and (11)
could be formed by addition of (2) to butadiene and
subsequent coupling of the primary adduct (5) ; oxidation
of (5) would give (8) and ( 9 ) . Formation of (6) and
[1] Anodic oxidation of organic compounds, Part 8.-Part 7. H .
Schafer and E . Steckhan, Tetrahedron Lett. 1970, 3835.
[2] H . C . Brown and C . H . Snyder, J. Amer. Chem. SOC.83,1002 (1961).
[3] D. H . Geske, J. Phys. Chem. 66, 1743 (1962); W R . Turner and
P. J . Eluing, Anal. Chem. 37, 207 (1965).
[4] K . Ziegler and 0. Sreudel, Liehigs Ann. Chem. 652, 1 (1962).
[5] H . Schafer, Chemie-Ing.-Techn. 42, 164 (1970).
[6] Platinum is unsuitable as anode material because of pronounced
[7] Relative yields; all products were identified by IR, NMR, MS, and
C,H analysis or by gas-chromatographic comparison with authentic
[8] H . Scha/er and E. Steckhun, Angew. Chem. 81, 532 (1969); Angew.
Chem. internat. Edit. 8, 518 (1969).
[9] H . Schhfer and H . Kiintrel, Tetrahedron Lett. 1970, 3333.
Angew. Chem. internal. Edit.
Vol. 11 (1972) / No. I
Solvolysis of 7,7-Bis(alkylthio)norcaranes.
A New Method of Homologation
By Dieter Seebach and Manfred Braun"]
Bis(alky1thio)cyclopropanes (cyclopropanone dithioacetals) (Z) are readily available either from epoxides'"
(with extension by one carbon atom) or from a$-unsaturated aldehydes". (with conservation of the carbon skeleton). Their solvolysis should produce derivatives (2) of
Effectively, this would provide a means of
"intermolecular"- route A -or "intramolecular"- route
B-insertion of a carbonyl group between the carbons of
a double bond.
Because of the potential synthetic value of such transformations we investigated the solvolytic behavior of the norcaranes ( 3 a ) and ( 3 b ) obtained from cyclohexene oxide
Prof. Dr. D. Seebach and DipLChem. M. Braun
Institut fur Organische Chemie der Universitat Karlsruhe
Present address:
Institut fur Organische Chemie der Universitat
63 Giessen, Ludwigstrasse 21 (Germany)
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presence, oxidation, anodic, trihexylmethoxyborate, butadiene
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