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Nucleophilic Substitution of Vinylic Hydrogen Atoms by Carbanions.

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Stereoselective Hydride Elimination from OrganoLithium and -Magnesium Compounds[**][ l ]
By Manfred 7: Reetz and Wilfried Stephanp]
In contrast to olefin formation by base-induced hydrogen
halide elimination, little is known concerning hydride abstraction from carbanions. We report here on hydride acceptors
which effect elimination of 0-hydrogen atoms from organolithium and -magnesium compounds under mild conditions. Using
triphenylmethyltetrafluoroboraterzl,
tricyclohexylborane, and
tri(sec-butyl)boraner3] as hydride acceptors we were able to
convert structurally different lithium and magnesium compounds ( I ) into olefins (2) with simultaneous formation of
triphenylmethane and trialkylborohydrides, respectively (see
Table 1).
M = L i , Mg
Table 1. Olefins from organo-lithium and -magnesium compounds
Metal compound
Hydride acceptor
Olefin [a]
Yield
[“/.I
2-Hexylmagnesium chloride
Triphenylmethyltetrafluoroborate
Cyclohexylmagnesium
chloride
1-Decylmagnesium chloride
1.1-Diphenyl1 -hexyllithium
rerr-Butyllithium
1.1 -Diphenyl1 -hexyllithium
9.1 O-Dihydro-9anthracenyllithium
2-Hexyllithium
Tri(secbuty1)borane
75
1 -Decene
28
1,I -Diphenyl-1hexene
65
Isobutene
l,l-Diphenyl1 -hexene
Anthracene
1 -Hexene (68)
trans-2-Hexene (23)
cis-2-Hexene (9)
I-Decene
1-Decyllithium
2-Hexyllithinm
I-Hexene (79)
rrans-2-Hexene ( 1 0)
cis-2-Hexene (1 1 j
Cyclohexene
Tricyclohexylborane
1-Decyllithium
I-Hexene (68)
trar13-2-Hexene (22)
ci-2-Hexene (10)
I-Decene
74
> 95
80
86
60
Experimental
To a solution of triphenylmethyltetrafluoroborate (3.3 g,
0.01 mol) in dry methylene chloride (40ml) at - 78 “C is added
0.01 mol of 2-hexylmagnesium chloride. The mixture is stirred
at -78°C for 1 h, allowed to warm to room temperature
and hydrolyzed. The ethereal phase is analyzed gas-chromatographically (squalane, 90m capillary column, 6 0 T , 40ml
He/min): 74 ”/, yield of hexene; isomer ratio see Table 1.
Received: October 19, 1976 [Z 584a1
German version: Angew. Chem. 89,46 (1977)
CAS Registry numbers:
2-hexylmagnesium chloride, 13406-08-1 ;cyclohexylmagnesium chloride, 93151-1 ; I-decylmagnesium chloride, 201 57-33-9; I,l-diphenyl-I-hexyllithium,
3462-81-5: rerr-butyllithiurn, 594-19-4; 9,lO-dihydroanthracenyllithium,
17228-13-6; 2-hexyllithium, 13406-09-2: I -decyllithium, 4416-59-5; triphenylmethyl tetrafluoroborate, 341 -02-6; tri-(sec-butylborane), 1 1 13-78-6: tricyclohexylborane, 1088-01-3; I -hexene, 592-41-6: rruns-2-hexene, 4050-45-7; cis-2hexene, 7688-21-3; cyclohexene, 110-83-8; I-decene, 872-05-9; 1,l-diphenyl-lhexene, 1530-19-4: isobutene, 115-1 1-7; anthracene, 120-12-7
Part 2 of Hydride Eliminations.-Part
1 : M . 7: Rrerz and C. Wis,
Synthesis, in press.
[2] Triphenylmethyltetrafluoroborate is frequently employed as a hydride
acceptor in carbenium ion chemistry: L. F. Fieser and M . Fieser: Reagents for Organic Synthesis, Wiley, New York 1967, Vol. l. p. 1256:
Reactions with alkylmercury compounds: J . M. Jerkunicu and 7: G.
Traylor, J. Am. Chem. SOC.93,6274 (1971).
131 Triphenylborane was first employed by Wirrig t o effect hydride transfer
in tertiary phenyl-substituted alkyllithium compounds: G. Witfig and
19: Stilz, Justus Liebigs Ann. Chem. 598, 85 (1956); cf. E . I . Neyishi,
J . Organomet. Chem. 108, 281 (1976).
[4] In some cases addition products are detected as well as olefins.
[ 5 ] H. C . Brow1 and I . Mofitani, J. Am. Chem. Soc. 75, 4112 (1953); D.
C . Griffith, D. L . Meyes, and H . C. Brown, Chem. Commun. 1968, 90.
[I]
Nucleophilic Substitution of Vinylic Hydrogen Atoms
by Carbanions[**]
< 4
62
< 4
[a] Isomeric ratio given in brackets.
The good yields of olefin obtained with triphenylmethyltetrafluoroborate are surprising, since reaction of carbanions
with carbenium ions should lead to C-C bond formation[41.
While this hydride acceptor promotes smooth eliminations
within an hour already at - 20 to - 78 “C, the isoelectronic,
but neutral trialkylboranes require longer reaction times (> 16
hours) at 30 to 55°C. It can been seen from Table 1 that
the yields of olefin depend on the structure of the organometallic compound and increase clearly within the series primary
< secondary < tertiary. This is due to the influence of steric
factors on the competition between hydride elimination and
carbanion additionr4]. Formation of the thermodynamically
less stable Hofmann product is consistently favored. This
selectivity may arise, not so very much from a possibly
[*] Doz. Dr. M. T. Reetz and W. Stephan
Fachbereich Chemie der Universitat
Lahnberge, D-3550 Marburg (Germany)
[**I This work was supported by the Fonds der Chemischen Industrie.
44
increased “hydride character” of the 0-hydrogen atom on
the alkyl residue, but rather from steric influences: the attack
of the hydride acceptor on the lesser substituted alkyl residue
is easier due to steric reasonsrS1.The cisltrans ratios are more
difficult to explain.
By Manfred T Reetz and Dieter Schinzer[*]
Hydride abstractions from carbanions are of preparative
utility, since organometalliccompounds are not only accessible
via halogen-metal exchange or ether cleavage, but also by
addition to activated olefins, by deprotonation, and by rearrangement. We report here on addition-elimination reactions
which effect the substitution of vinylic hydrogen atoms by
a variety of carbon residues in a one-pot reaction.
When activated olefins of type (1) were allowed to react
with organolithium compounds, the lithium derivatives (2)[’]
were obtained from which a hydrogen atom 0 to lithium
could be eliminated as hydride ion by reaction with triphenylboraner3I. The end products were the olefins (3).
Table 1 shows that theseC-C bond formations with conservation of the olefin function proceeds smoothly even when
[“I
Dor. Dr. M. T. Reetz and DiplLIng. D. Schinzer
Fachbereich Chemie der Universitat
Lahnberge, D-3550 Marburg (Germany)
p*]This work was supported by the Fonds der Chemischen Industrie.
A n y e w . Chem. Int. Ed. Engl. 16 ( 1 9 7 7 ) N o . 1
Table I . Trisubstituted olefins by addition-elimination reactions [a].
Starting olefin
Alkyllithium
Product
Yield
ethylene, 60896-06-2: E-l-cyclopropyl-2-phenyI-2-(trimethylsilyl)ethylene,
60896-07-3; Z-l-phenyl-l-(diphenylphosphino)-1-hexene,
60896-08-4; E-Iphenyl-l -(diphenylphosphino)-1-hexme, 60896-09-5
[ 041
1,l-Diphenylethylene
1 -Phenyl-1 -(ti+met hylsily1)ethylene
n-Butyllithium
rrrr-Butyllithium
Phenyllithium
Cyclopropyllithium
1 , I -Diphenyl-Ihexene
1,l -Diphenyl-3,3dimethyl-1-butene
Triphenylethylene
I-Cyclopropyl-2.2diphenylethylene
n-Butyllithium
1 -Phenyl-l -(trimethylsily1)-1hexene [b]
1 -Pheuyl-I-(trimethylsilyl)-3,3dimethyl-1-butene [b]
I-Cyclopropyl-2phenyL2-(trime>hylsilyl)ethylene [b]
tert-Butyllithium
Cyclopropyllithium
I -Phenyl-I-(diphenylphosphin0)ethylene
n-Butyllithium
I -Phenyl-l -(diphenylphosphino)-l -hexene [b]
89
65
84
70
75
Part 3 of Hydride Eliminations.---Part 2: M . 7: Reerz and W S t e p h i ,
Angew. Chem. XY, 46 (1977): Angew. Chem. Int. Ed. Engl. 16. 44
( 1977).
[2] The addition of alkyllithium compounds t o conjugated olefins was first
described by K . Zirglrr, F. Crussrnunn, H . Kleinrr, and 0.Schafer,
Justus Liebigs Ann. Chem. 473, I (1929); for a review of addition reactions
of lithium compounds see U . S c h u k ~ p fin Houben-Weyl-Miiller: Methoden der Organischen Chemie. Thieme, Stuttgart 1970, Vol. 1311, p. I .
[3J Tri-(src-buty1)boranescan also be employed [I].
141 Review: R . F. Cunicu, J. Organomet. Chem. 109, 1 (1976).
[ S ] G. Kijhrrcli and J . Stiiher, Chem. Ber. 103, 2744 (1970).
[l]
80
85
90
Simple Synthesis of (Arylethyny1)triphenylphosphonium
Salts
By Hans Jiirgen Bestmann and WoIfgang Kloeters"]
Ethynylphosphonium salts are interesting synthetic building
blocks[']. We have now found a simple entry to the (arylethyny1)triphenylphosphonium salts ( 4 ) .
[a] Addition in tetrahydrofuran at 0°C; hydride abstraction with tripheuylboraue 131 at room temperature.
[b] Stereochemistry and composition of the Z / E mixture at present uncertain.
such sterically demanding groups as tert-butyl residues are
incorporated. The applicability of the reaction to vinylsilanes
is noteworthy, since these are readily modifiable and synthetically interesting[41.Finally, it should be mentioned that double
substitutions in one-pot reactions are also possible, as demonstrated by the preparation of ( 5 ) from ( 4 ) (61 % yield).
Preparation of 1 ,I -diphenyl-1 -hexene
13ml of a 1.65 M solution of n-butyllithium in n-hexane
is added dropwise at 0°C to a solution of 1,l-diphenylethylene
(3.65 g, 0.02 mol) in anhydrous tetrahydrofuran (50ml). The
mixture is stirred for 85min at room temperature and the
resulting deep-red solution treated with 5 g (0.021 mol) tripher~ylborane~~l
in 30ml tetrahydrofuran; a gradual decolorization takes place. After 15h the mixture is diluted with
50ml petroleum ether (b.p. 40 to 60"C), the two phases that
are formed are separated, and the lower phase is extracted
twice with petroleum ether. The combined petroleum ether
phases are washed with a 1 0 % sodium hydroxide solution
and water and dried over sodium sulfate. Removal of solvent
from the dried solution yields 4.2 g (89 %) of pure 1,l -diphenyl1 -hexene; 'H-NMR spectrum identical with that of an authentic sample['].
Received: October 19, 1976 [Z 584b IE]
German version: Angew. Chem. 89,46 (1977)
CAS Registry numbers:
I , I -diphenylethylene, 530-48-3; 1 -phenyl-I -(trimethylsilyl)ethylene,1923-01-9;
1 -pheuyl- I -(diphenylphosphino)ethylene.1 7620-97-2: n-butyllithium, 109-728; tert-butyllithium, 549-19-4; phenyllithium, 591 -51 - 5 : cyclopropyllithium,
3002-94-6: 1.1 -diphenyl-I-hexene, 1530-19-4; I,l-diphenyl-3,3-dimethyl-lbutene, 23586-64-3; triphenylethylene, 58-72-0; 1 -cyclopropyl-2,2-diphenylethylene, 14799-59-8: Z - I -phenyl-1.-trimethylsilyl-1 -hexene, 60896-02-8; E-lphenyl-l -t rimethylsilyl-l -hexme, 60896-03-9; Z-1 -phenyl-l -(trimethylsilyl)3,3-dimethyl-l-butene,
60896-04-0;
E-l-phenyI-l-(trimethylsilyl)-3.3dimethyl-1 -butene, 60896-05-1 ; 2-1
-cyclopropyl-2-phenyI-2-(trimethylsilylAngrw. Chern. l ! i t . Ed. Engl. 16 (1977) N u . 1
Reaction of aromatic acid chlorides ( 1 ,) with hexaphenylcarbodiphosphorane (2)['] leads initially to the compounds ( 3 ) ,
which on heating lose triphenylphosphane oxide and are converted into the phosphonium salts ( 4 ) . ( 4 a ) : m.p. t8O0C,
IR: 2175cm-' ( e C ) , 31P-NMR: 6 = -6.52pprnc3], yield
65 %.-(4b):
m.p. 183"C, IR: 2165cm-' (C-C), 31P-NMR:
6 = - 5.86 ppmr31, yield 68 %.-(4 c): m.p. 161 "C, IR:
2170cm-' ( e C ) , 31P-NMR: 6= -6.45ppml3I, yield 56%.
When phthaloyl dichloride is used as starting compound
the reaction furnishes the bisphosphonium salt ( 5 ) , m.p.
138°C; IR: 2175cm-' ( e C ) , 3LP-NMR:6 = -6.52ppmL3I,
yield 71 %[41.
In the 31P-NMR spectra of the phosphonium salts ( 3 ) ,
both phosphorus atoms give a signal between 6 = - 18.5 and
- 20.0ppm[31.In the case of the ethynylphosphonium salts
( 4 ), on the other hand, only one signal is observed at 6 = - 5.5
to - 6.8 ppm, which can be ascribed to a strong interaction
between the n-electron system of the triple bond and the
phosphorus atomc5].
General procedure:
A solution of the freshly distilled acid chloride ( I ) (20mmol)
in anhydrous benzene (20ml) is added dropwise under nitrogen
to a solution of hexaphenylcarbodiphosphorane (2) (20 mmol)
[*J Prof. Dr. H. J. Bestmann and Dipl.-Chem. W. Kloeters
lnstitut fur Organische Chemie der Universitat Erlangen-Niirnberg
Henkestrasse 42, D-8520 Erlangen (Germany)
45
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