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Diethylborylation and Determination of Water with Activated Triethylborane.

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ed on GC-MS of the original acid fluoroheptyl ester mixture['] at the retention time of ester (1f).
In addition, two stereoisomeric C,,-steroid carboxylic
acids were identified. Although structural proof is not
complete, present results suggest that they are 5a- (Ig)
and 5 B-cholanic acids.
The significance of this work is that these are the first polycyclic naphthenic carboxylic acids ever reported in petroleum as individual compounds; and on top of this they
possess biological precursor hydrocarbon skeletons and,
therefore, are geochemically significant. Animal bile acids
are considered to be the most likely precursors.
We consider it remarkable that an anion should be formed
B to the COOLi group, which leads to destabilization of
the ether linkage and thereby to a reversal of the Perkin
coumarin-benzofuran ring contraction. The reaction probably represents a route to hitherto inaccessible coumarins
and o-coumaric acid derivatives.
Elemental analyses, IR and NMR spectra were all compatible with the above formulations.
Received: May 13, 1971;
revised: July 16, 1971 [ Z 477 IE]
German version: Angew. Chem. 83, 755 (1971)
[I] B. Libis and E. Habicht, Belg. Pat. 733768 (1969), Geigy SA.
Received: July 26,1971 [ Z 475 IE]
German version: Angew. Chem 83, 805 (1971)
[l]Part ofthis work was presented at the Gordon Research Conference
of Organic Geochemistry, Holderness, New Hampshire, September
1970, and at the Pacific Conference of Chemistry and Spectroscopy,
San Francisco, California, October 1970.
[2] W K . Seijerr and R. M . Teeter, Anal. Chem. 42,180, 750 (1970).
[3] W. K . Sefert and W G. Howeffs,Anal. Chem. 41, 560 (1969).
[4] W K . Seferf, R . M . Teeter, W G . Howells, and M . J . R. Cantow,
Anal. Chem. 41, 1638 (1969).
[5] W K . Seifert and R . M . Teeter, Anal. Chem. 41,786 (1969).
Ring Expansion in the Benzofuran Series
[2] P. E. Pfeff.. and L. S. Silbert, J. Org. Chem. 35, 262 (1970); P. L.
Creger, J. Amer. Chem. SOC.89,2500 (1967).
[3] ?: Nakabayashi and K . Yamasaki, J. Pharm. SOC.Japan 74, 590
(1954).
[4] P. Chuit and F. Bolsing, Bull. SOC.Chim. France 35, 82.
Diethylborylation and Determination of Water
with Activated Triethylborane
By Rokand Koster, Klaus-Ludger Amen, Hans BeIEut, and
Wolfgang Fenzl"
Protolyses of trialkylboranes to yield alkane and 0- or N alkylboryl derivatives according to
+ H-X
By Bernard Libis and Ernst Habicht"
R,B
2,3-Dihydro-6-methylbenzofuran-2-carboxylicacid"] is
converted into 2,3-dihydro-2,6-dimethylbenzofuran-2-car-
R=C,H,, C3H,, CH(CH3)2,CH,CH(CH,),
X = 0-alkyl, 0-aryl, 0-acyl, 0-SO,-alkyl, -0-SO,-aryl,
alkyl,, 0-N=C-aryl,,
N-alkyl,, N-allyl,, NH-aryl
boxylic acid ( 1 ) (for procedure see Ref. [2]).
If compound ( I ) is treated with 2.2 mol. equiv. of lithium
diisopropylamide at 0°C under N,, the reaction mixture
turns orange and a benzyl anion is formed. The dihydrofuran ring is cleaved between atoms 1 and 2, and acidification gives the known13]coumarin (2) as the major product.
The acid (3),m. p. 200"C, whose stereochemistry precludes
ring closure, appears as a minor product.
-t
R,B-X
+ RH
0-N=C-
proceed at differing rates, depending upon R and X. In
general, trialkylboranes react with carboxylic acids['' at
about room temperature. In contrast, temperatures of
160-170°C are necessary for reaction of alcohols[21or
phenols['], 170-200°C for dialkylamines'21, and about
100"C for alkane- and benzenesulfonic acids[3J.At these
temperatures certain functional groups can be reduced by
transiently formed B-H
bonds (dehydroboronation)
during the reaction.
We have found that protolyses of triorganoboranes can be
considerably accelerated by catalytic amounts of pivalic
acid or various pivalic acid derivatives :
(CH,),C-COX,
X=e.g. (C,H,),B-0
>
(CH3),C-CO-O-CH,-CH20
P(CH3)3C-CH,O>
H3 c
2,3-Dihydro-6-methylbenzofuran-2-carboxylicacid gives
the dicarboxylic acid ( 4 ) when treated according to Ref.
[2] and on adding CO,. Reaction of ( 4 ) with 3.3mol.
equiv. of lithium diisopropylamide furnishes the known'41
coumarincarboxylic acid ( 5 ) .
COOH
+
H3C
[*] Dr. B Libis and Dr. E. Habicht
Departement Forschung der Division Pharma
Ciba-Geigy AG
CH-4002 Base1 (Switzerland)
74%
C,H,O
Triethylborane to which 0.1 to 1mol-% of pivalic acid has
been added reacts rapidly and quantitatively with water
or alcohols at room temperature, one of its ethyl groups
being eliminated as ethane.
+
Z(C,H,),B
H,O '2 (C2H5),BOB(C,H,)z
Cat. =(C,H,),B-O-CO-C(CH3)3
+ 2C2H.5
This reaction can be utilized for a very simple determination
of the water content of numerous hydrates of metal salts
(see Table) with the aid of triethylborane/diethylboryl
pivalate (b. p. 54"C/8 torr). The salts nearly always remain
[*I
Doz. Dr. R. Koster, Dr. K.-L. Amen, Dr. H. Bellut, and
Dr. W. Fenzl
Max-Planck-Institut fur Kohlenforschung
433 Miilheim/Ruhr, Kaiser-Wilhelm-Platz 1
Angew. Chem. internat. Edit. J Vol. I0 (1971) J No. 10
undissolved and can readily be isolated in the anhydrous
state.
Like triethylborane, trimethyl-, tripropyl-, triisopropyl-,
and triisobutylborane also react considerably faster with
water, alcohols, or phenols on addition of pivalic acid.
bory1)-L-(+)-ascorbic acid, which are readily soluble in
hydrocarbons, can be vacuum distilled without decomposition. The diethylboryl groups can be removed quantitatively and under extremely mild conditions by treatment with methanol. The boron-free sugar is obtained
after the azeotropic mixture of methoxydiethylborane
Table. Determination [a] of water content of hydrates with triethylborane in the presence of diethylboryl pivalate.
H2O (%) [.I
Hydrate [b]
calc. [b]
Li,SO,.H,O
Na,S.9 H,O
Na,S,0,,3 H,O
Na,PO,.I2 H,O
Na,Cr,07.2 H,O
NaVO,.4 H,O
MgSiF,.6 H,O
CaCI,.4 H,O
Ca(N03),.4 H,O
Ca(SCN),.4 H,O
MnC1,.4 H,O
FeCI,.4 H,O
14.08
67.51
36.29
56.87
12.09
37.15
39.38
39.37
30.51
31.56
36.41
36.25
foundx 102
found [d]
(with
catalyst)
found [el
(without
catalyst)
calc.
with
catalyst [d]
13.66
64.94
36.70
57.64
12.18
38.98
39.51
39.70
31.43
31.79
37.40
36.17
11.85
11.60
33.58
7.54
12.29
24.34
16.48
28.91
27.61
29.96
32.46
34.10
97.2
96.4
101.1
101.1
100.8
104.8
100.1
100.9
102.9
100.5
102.4
I00
without
catalyst [el
84.2
17.2
92.6
13.2
101.7
65.6
41.8
73.5
90.4
95.5
90
94.6
[a] Volumetric determination of the ethane liberated.
[b] Commercial samples, water contents according to manufacturers' specifications.
[c] The determinations can be carried out much more rapidly and at lower temperatures (20-50°C) in the
presence of catalyst, cf. [d] and [el.
[d] Evolution of ethane is exothermic and is generally complete after 5 min. The reaction mixture is then heated
to boiling. The values obtained are reproducible. The considerable deviations from the calculated H,O contents
are due to the impurity of the commercial hydrates.
[el Values obtained after 1 to 2 hours' heating in boiling triethylborane.
However, the catalyzed protolyses of the trialkylboranes
BR, proceed at varying rates, in the order :
(b. p. 88.8 "C/770 torr; ngo= 1.3869) and methanol
[CH,OB(C,H,),: CH,OH=ca. 1:2.8; b.p. 59.7"C/770
torr; nko = 1.3620; dio=0.7675] has been distilled off.
R=C,H, > C3H7 > CH(CH,), P CH,CH(CH,),
Introduction of the diethylboryl group into numerous NH
compounds is also facilitated by the presence of pivalic
acid derivatives. In addition to pyrrole and its derivat i v e ~ ' ~ammonia,
],
amines, hydrazines, and carboxamides
and carbohydrazides all react under milder conditions than
in the absence of catalyst. Aldo and keto phenylhydrazones
as well as phenylosazones also react under relatively mild
conditions with "activated" triethylborane. In general,
NH compounds react at 50-80°C in the presence of diethylboryl pivalate. Temperatures of about 140°C are
required for ammonia and some mono- and dialkylamines.
Whereas even at temperatures above 100°C only one alkyl
group of the trialkylboranes reacts with alcohols, triphenylborane in the presence of diethylboryl pivalate is already
degraded to boric acid at about 100°C.
We have used catalyzed protolysis to prepare a large
number of alkoxy- and aryloxydialkylboranes, some of
which have functional groups such as C=C or C G C bonds
or NO, groups in the organic residue RO. The dialkylboryl derivatives of alkane- and benzenesulfonic acids
were also obtained in high yields.
Sulfuric acid, phosphoric acid, boric acid, and iodic acid
are also esterified with the diethylboryl group in the presence of diethylboryl pivalate at room temperature. In the
absence of catalyst the higher temperatures required for
the reaction usually result in mixtures of boron-containing
and the boron-free acid anhydrides being formed.
Diethylborylation of polyhydroxy compounds also proceeds particularly smoothly on addition of pivalic acid.
The hydroxyl group content of soluble, and also of insoluble, compounds, e. g. starch and cellulose, can therefore be accurately determined. Introduction of O-diethylboryl protective groups into sugars and sugar derivatives
is also of preparative interest. The per-diethylborylated
monosaccharides and their .derivatives, e. g. 1,2,3,4,5pentakis(diethylbory1)-D-(+)-glucose
(b. p.
136"C/
+ )0.001 torr), 2,3,4,6-tetrakis(diethylboryl)-cc-methyl-~-(
glucoside (b. p. 13OoC/0.001torr), 2,3,5,6-tetrakis(diethylAngew. Chem. internat. Edir.
Vol. 10 (1971) / N o . 10
Bis(diethylbory1) sulfate :
Sulfuric acid (98% ; 15.6 g, i. e. 345 mg-atom of Ho) is added
dropwise over about 2 h to triethylborane (79 g, 806 mmol)
containing diethylboryl pivalate (ca. 0.5 ml). The temperature rises to about 50°C. Ethane (7.321, 327mmol) is
evolved. A clear pink liquid results from which a small
amount of dark solid precipitates. Vacuum distillation
yields firstly 51 g of a mixture (triethylborane and tetraethyl diboroxide), b.p. up to 25"C/15torr, and then 30g
(81%)['I of bis(diethylbory1) sulfate, b. p. 66-67 oC/O.OOl
torr; 1.9g of residue was left in the distillation flask.
Borylation of Cellulose:
Triethylborane (6.3 g, 64.3 mmol) containing 0.1 ml diethylboryl pivalate is added dropwise to a stirred suspension of cellulose (2.7 g, 16.65 m equiv) in 40 ml heptane at
60-70°C (bath) over a period of 70min. 700Nml of
ethane are evolved during the addition. Following a further
749
1.5 hours at 70-80°C a total of 1135 Nml(lOI%) ethane
is evolved. The voluminous white solid is filtered off and
washed three times with pentane before being vacuum dried
(yield 5.85 g, 96%). Found 5.84% B (on C)'61,calc. 5.90% B
(on C). The per-0-diethylborylated cellulose is insoluble
in both aliphatic and aromatic hydrocarbons as well as in
carbon tetrachloride.
Received: July 22, 1971 [Z 479a IE]
German version: Angew. Chem. 83,805 (1971)
[I] Cf. D. B. Bigley and D. W Payling, J. Inorg. Nucl. Chem. 33, 1157
(1971), and further literature cited therein.
[2] B. M. Michailow, W A . Wnwjer, and Ju. N. Bubnow, Doklady
Akad. Nauk SSSR 126, 575 (1960); Chem. Ahstr. 54,261 (1960).
[3] S. Trofimenko, J. Amer. Chem. SOC.91, 2139 (1969).
[4] H. BelIut and R. KBsrer, Liebigs Ann. Chem. 738, 86 (1970).
[5] Based on reacted amount of sulfuric acid (165 mmol).
[6] Determined using trimethylamine N-oxide, see R. Kdsrer and Y
Morita, Liehigs Ann. Chem. 704, 70 (1967).
Reactions of Dialkyl Ketones with Triethylborane
By Wolfgang Fenzl and Roland Koster"]
When heated to 50-70°C in the presence of diethylboryl
pivalate, triethylborane and diethyl ketone form trans-3diethylboryloxy-2-pentene ( 2 a ) ; 98% of ethane and only
2% of ethylene are evolved during the reaction (see Table).
Cycloketones having seven or more ring members also
react with triethylborane under catalytic conditions to
give diethylboryl cycloenolates and hardly any reduction
products. Cyclododecanone affords exclusively a mixture
of the two cisltrans isomers of diethylboryloxycyclododecene. Cycloheptanone, however, gives only 70% of diethylboryloxy-cis-cycloheptenealongside 30% of a C,,H,,O
ketone, a condensation product of two ketone molecules.
Methyl ketones and particularly acetone, as well as cyclic
ketones having five- and six-membered rings (cyclopentanone, cyclohexanone, 2-cyclohexenone), react with triethylborane in the presence of diethylboryl pivalate to give
only aldol condensation products. In contrast to the basecatalyzed aldol condensation[31the yields can be as high
as 95%. Compounds that are sensitive to air or to alkalis,
e. g. the 6-(2-cyclohexenylidene)-2-cyclohexenones (3a)
and (3b), are also readily obtained. The condensations of
cyclopentanone and cyclohexanone proceed particularly
rapidly. The dimeric or trimeric condensation products,
Enolizable aldehydes and ketones do not generally react
with trialkylboranes below 100°C. Above this temperature
reduction (Red.) and enolysis (En.) compete with each
other, depending upon the carbonyl compound and trialkylborane used. For example, diethyl ketone and triethylborane react at 150°C to give an almost equimolar
mixture of ethylene and ethane. The boron-containing
products are 3-diethylboryloxypentane (1 a ) and 3-diethylboryloxy-2-pentene (2 a ) (see Table).
We have found that, like the protolysis of trialkylboranes
with hydroxy compounds['], the enolysis of trialkylboranes
with certain carbonyl compounds can be greatly accelerated
by pivalic acid derivatives (CH,),CCOOR, e. g. with
R = BR; or CH,CH,-0-CO-C(CH,),.
Depending
formed according to the molar ratio ketone/triethylborane,
are obtained free from boron [e.g. ( 4 ) ] or as diethylboryl
enolates [e. g. (S)].
(3a) and (3 b ) , as well as, e.g., (41, can also be diethylborylated at 80°C. Methanolysis quantitatively regenerates
the intact boron-free starting materials.
3-Diethylboryloxy-2-pentene( 2 a) :
upon the alkyl groups of the dialkyl ketones, the reaction
furnishes substituted vinyloxydiethylboranes (2) (yield
60-98%), which are important for additions to nitrilesc2].
Table. Yields of diethylboryl enolates (2) and ethane in the reaction
of ketones with triethylborane in the presence of diethylboryl pivalate.
3-Pentanone (43 g, 0.5 mol) is added dropwise over 80 min
40-60°C
to boiling triethylborane (49 g, 0.5 mol) to
which diethylboryl pivalate (2 ml) has been added. Evolution of gas occurs. The reaction mixture is then heatedJo
about 100°C for about 15 h and 12 1 of gas contaiding
(GC) 98% of C,H6 and 2% of C,H, is collected. Vacuum
distillation gives, after 9 g of fore-run up to 44"C/15 torr,
compound ( 2 a ) (61 g, 82%), b.p. 57-59"C/15 torr, containing no other isomer; hardly any residue is left in the
distillation flask. I
R spectrum (neat liquid): 1680 cm(v,,~); 'H-NMR spectrum (neat liquid): T = 5.41 (vinylic
Hl.
6-(2-Cyclohexylidene)-2-cyclohexenone (3a) and (3 b) :
[a] Isolated.
[*I
750
Dr. W. Fenzl and Doz. Dr. R. Koster
Max- Planck-Institut fur Kohlenforschung
433 Mulheim/Ruhr, Kaiser-Wilhelm-Platz 1 (Germany)
2-Cyclohexenone (96 g, 1 mol) is added dropwise at 75 "C
over about 6 h to triethylborane (123 g, 1.25mol) to which
diethylboryl pivalate has been added. 281 of gas comprised of 98% C,H, and 2% of C,H, is liberated. After
initial distillation of about 100g of a mixture (triethylAngew. Chem. internat. Edit. Vol. I0 (1971) No. 10
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