Chiral boronates-versatile reagents in asymmetric synthesis

Article abstract of DOI:10.1016/S0022-328X(02)01323-2

The new, axially chiral borates 2, 9, and 11 and boronates 3-6 and 12 are synthesized in good yields. They are representatives of three different structural types. The bicyclic borates 2 and 9 are homochiral propeller compounds; their exclusive formation is used to increase the enantiomerical purity of 1. Especially the borates are efficient Lewis acidic catalysts for stereoselective Diels-Alder reactions. The new seven-membered boron compounds 4, 5, 6, and 12 are interesting reagents for different asymmetric synthetic steps. Activated vinylboronates 31 can serve as efficient cyclophiles in [3+2] cycloaddition reactions with methylenecyclopropane 27 giving borylated methylenecyclopentanes 32.

Full text of DOI:10.1016/S0022-328X(02)01323-2

Journal of Organometallic Chemistry 657 (2002) 136Á145
/
www.elsevier.com/locate/jorganchem
Chiral boronates*
/
versatile reagents in asymmetric synthesis
Sabine Thormeier a, Bertrand Carboni b, Dieter E. Kaufmann a,*
a Institut fur Organische Chemie der Technischen Universitat Clausthal, Leibnizstr. 6, 38678 Clausthal-Zellerfeld, Germany
¨
¨
b Synthe`se et e´lectrosynthe`se Organique UMR 6510, Institut de Chimie, Universite´ de Rennes 1, Campus Beaulieu, 35042 Rennes, Cedex, France
Received 3 September 2001; accepted 30 January 2002
Dedicated to Professor Dr. Dr.h.c. L.F. Tietze, Gottingen, on the occasion of his 60th birthday
¨
Abstract
The new, axially chiral borates 2, 9, and 11 and boronates 3Á
three different structural types. The bicyclic borates 2 and 9 are homochiral propeller compounds; their exclusive formation is used
to increase the enantiomerical purity of 1. Especially the borates are efficient Lewis acidic catalysts for stereoselective DielsÁAlder
reactions. The new seven-membered boron compounds 4, 5, 6, and 12 are interesting reagents for different asymmetric synthetic
steps. Activated vinylboronates 31 can serve as efficient cyclophiles in [3ꢀ2] cycloaddition reactions with methylenecyclopropane 27
giving borylated methylenecyclopentanes 32. # 2002 Elsevier Science B.V. All rights reserved.
/
6 and 12 are synthesized in good yields. They are representatives of
/
/
Keywords: Boronates; Biaryls; Asymmetric synthesis; [3ꢀ2] Cycloadditions; Cyclopentanes
/
1. Introduction
2. Results and discussion
The synthesis and application of axially chiral biaryls
has been the subject of many research reports over
the last years [1]. The biaryl unit is both, an important
structural feature of many natural products and
the conformationally stable backbone of powerful
chiral catalysts and reagents in asymmetric synthesis.
Chiral boronates have proved their great importance
in stereoselective synthesis during the last decades, [2].
Therefore, we have synthesized new borates and bor-
onates with a chiral biaryl backbone for stoichiometric
and catalytic asymmetric syntheses, [3] (Schemes 1 and
2).
2.1. Synthesis and catalysis
The reaction of biarylols with boron compounds is
complex and dependent on both, the boron substituents
and the substitution pattern of the biarylol. When 2,2?-
dihydroxy-1,1?-binaphthyl (b-binaphthol, 1) is reacted
with borane complexes, hydrohaloboranes or boric acid,
the bicyclic homochiral bisborate propeller compounds
2 with axially chiral 1,1-binaphthyl groups as ‘blades’ is
formed exclusively in very good yields [4]. Introduction
of either a bromo or trimethylsilyl substituent in 3,3?-
position of the b-binaphthol exclusively leads to the
formation of the seven-membered dioxadihydrobore-
pine system 3 to avoid additional steric strain.
Seven-membered ring systems are also formed exclu-
sively when allyl, phenyl (additional structure proof by
X-ray) or vinyl boranes are reacted with 1. The product
structures strongly depend on the substitution pattern of
the biarylol. In case of the 2,2?-dihydroxy-1,1?-dibenzo-
furanyl (8) [5] another propeller type compound 9 is
formed. Two biphenylols 10a/b with both, H or methyl
[6] in 6-position, were also reacted. Possibly due to the
* Corresponding author. Tel.: ꢀ
722834.
E-mail
Kaufmann).
/
49-5323-722027; fax: ꢀ
/
49-5323-
address:
dieter.kaufmann@tu-clausthal.de (D.E.
0022-328X/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 2 - 3 2 8 X ( 0 2 ) 0 1 3 2 3 - 2

S. Thormeier et al. / Journal of Organometallic Chemistry 657 (2002) 136Á
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137
Scheme 1. Reaction of b-binaphthols 1 with boranes.
Scheme 3. Boron Lewis acid catalyzed DielsÁAlder reactions.
/
different dihedral angles the first examples 11a,b of a
twofold formation of a seven-membered ring system 11
were observed. The attempted borylation reaction of the
isomers 3,3?-dihydroxy-4,4?-biphenanthryl and 10,10?-
dihydroxy-9,9?-biphenanthryl led to the formation of
polymeric material, only.
Scheme 2. Reaction of biarylols 8 and 10 with boraneÁ
sulfide.
/dimethyl

138
S. Thormeier et al. / Journal of Organometallic Chemistry 657 (2002) 136Á145
/
Since a number of boranes with a chiral biaryl
backbone has already been successfully employed as
effective Lewis acidic catalysts in stereoselectively in-
to obtain the optically enriched b-binaphthol 1. In
conclusion, a simple and efficient procedure to increase
the enantiomeric excess of partially resolved 1 was
developed.
duced DielsÁAlder reactions [7], we have examined the
/
applicability of the chiral borates 2, 5, 7, and 11a to the
reaction of cyclopentadiene with either methacrolein or
bromoacrolein. Whereas the uncatalyzed cycloadditions
provided only a poor yield even at 20 8C and a modest
exo-selectivity, conducting the reaction in dichloro-
2.3. Asymmetric hydroborane reduction
The asymmetric reduction of prochiral ketones is a
useful method for the preparation of chiral alcohols. A
number of enantioselective reduction methods with
chiral hydride reagents have been published [11].
We describe the asymmetric reduction of a prochiral
ketone with a hydroborane reagent bearing optically
pure 1 as a chiral ligand. The chiral reagent was
methane at ꢁ
borates led to the isolation of the cycloadducts in 48Á
97%. In general, the observed exo-selectivity is very high
(A: 96%); it is dropping distinctly (90Á93%) though,
/
78 8C in the presence of 3 mol% of the
/
/
when the phenyl boronate 5 is used (Scheme 3).
generated in situ from 1, BH3×
/
SMe2, and a primary
2.2. Increase of the enantiomerical purity of 1
aromatic amine. Treatment of acetophenone 13 with 12
in THF gave 1-phenylethanol in good to excellent yield
in each case. The effect of added amine on the
enantioselection was examined by using various aro-
matic amines and DBU. Results are summarized in
Scheme 5. The presence of all amines enhanced the
optical yield to some extent. The highest degree of
enantioselectivity was achieved by the use of m-nitroani-
line. DBU being more basic was less effective than the
N-arylamines in the extent of selection. These facts
suggest that both the amino group and the aromatic ring
influence the enantioselective reduction.
Optically active b-binaphthols are extremely useful
C2-symmetric compounds employed as chiral auxiliaries
or chiral catalysts in asymmetric synthesis.
Several methods such as optical resolution by separa-
tion of diastereomers [8], asymmetric synthesis from 2-
naphthol [9], and by separation of inclusion complexes
[10] are available to obtain 1 in enantiopure form.
However, the procedures often give only partially
resolved 1 and a further purification step is required.
It has been mentioned in the beginning, that the
reaction of racemic 1 with borane complexes results in
the formation of enantiomers of the C3-symmetric
propeller compound 2. It appears that the b-binaphthol
tends to form the homochiral (SSS) and (RRR)
enantiomers rather than the unsymmetrical (SRR) and
(RSS) isomers. This fact can be applied to increase the
optical purity of partially resolved 1 without using
another chiral source simply by formation of the
propeller compound 2 and separating it from the rest
of 1.
It is likely that a six-membered transition state is
formed during the reaction of acetophenone and 12
containing an N-arylamine as illustrated in Scheme 5.
The structure suggests a pÁp-interaction between the
/
naphthyl p-system and the p-system of the N-arylamine.
For our investigation we have carried out several
experiments with initial enantiomeric excesses of 20Á
/
80% and in the presence of excess 1. The results are
summarized in Scheme 4. In a typical procedure, two
equivalents of BH3×/SMe2 were added to a solution of six
equivalents of partially resolved 1 in dichloromethane at
0 8C. The mixture was allowed to warm to room
temperature and stirred for 6 h. Dichloromethane was
removed under reduced pressure and the residue was
dissolved in ether to precipitate 2. Filtered 2 was
redissolved in dichloromethane and treated with water
Scheme 5. Asymmetric reduction of acetophenone 13 with chiral
Scheme 4. Increase of the enantiomeric purity of b-binaphthol (R)-1.
hydroboraneÁamine complexes 12.
/

S. Thormeier et al. / Journal of Organometallic Chemistry 657 (2002) 136Á
/145
139
The interaction can be enhanced by attaching an
electron withdrawing group to the N-aryl ring.
2.4.3. Nickel(0)-catalyzed [3ꢀ
vinylboronates
/
2] cycloadditions with
The construction of cyclopentane systems is still
gaining much attention due to the biological significance
of many natural products possessing these structural
units [14].
Trimethylenemethane (TMM) is an excellent synthon
for preparing a wide range of methylenecyclopentanes
2.4. Binaphthyl based boronates
Starting material for all routes to binaphthyl boro-
nates 4Á6 was the easily available b-binaphthol 1.
/
Several synthetic pathways were tried; the optimized
ones are reported. When reacting 1 with triallylborane
the corresponding allylbinaphthyl boronate 4 was
formed in 78% yield. Preparation of the phenyl sub-
stituted derivative 5 was readily accomplished by treat-
ment of 1 with phenylboronic acid 16 in toluene at
reflux. Reaction of dichlorovinylborane and b-bi-
naphthol in dichloromethane afforded the vinylboronic
ester 6.
directly by [3ꢀ2] cycloadditions with suitable alkenes
/
[15]. The idea to modify the alkene by replacing one of
the olefinic hydrogens by an activating boronic ester
group is synthetically attractive, because, the cycload-
ducts can be transformed stereoselectively into alcohols,
amines and several other classes of compounds. Another
option includes the aspect of asymmetry by the use of an
optically active diol as a chiral auxiliary. Vinylboronic
esters are easily accessible. Especially those derived from
pinacol are very stable to oxidation and moisture and
can be even purified by column chromatography [16].
Our initial cycloaddition studies focused on the parent
methylenecyclopropane 24 as a TMM precursor and the
vinylboronates 6 or 28 derived from 1 or pinacol. The
binaphthyl vinylboronate (6) was prepared in good
2.4.1. Asymmetric allylboration
Allylboration of aldehydes is an important method
for the synthesis of chiral homoallylic alcohols [12]. The
reason for high levels of stereoselectivity observed in
additions of chiral allyl organometallics to carbonyl
compounds is a chair like six-membered transition state.
Carbonyl addition was carried out by reacting benz-
aldehyde 18 with the allyl reagent 4 at low temperature
in ether and working up with dilute hydrochloric acid,
followed by extraction with ether. The chiral auxiliary
was easily recycled by precipitation with hexane. Allyl-
boration of benzaldehyde with 4 produced the homo-
allylic alcohol 19 in high chemical yield and with an
enantioselectivity of 88%.
yields using the sequence outlined in Schemes 6Á
The reaction of 6 with 24 was carried out in the presence
of catalytic amounts (5 mol%) of Ni(COD)2 at ꢁ15 8C
in toluene.
/9.
/
Cycloadditions of methylenecyclopropane 24 cata-
lyzed with ‘naked’ Ni(COD)2 usually favour proximal
cleavage of the cyclopropane CÃ/C bond [17]. Accord-
ingly, the formation of the corresponding cycloadduct
25 was expected. However, this alkenylboronate did not
afford the desired [3ꢀ
able products from the reaction mixture were recovered
/
2] cycloadduct. The only identifi-
2.4.2. Asymmetric synthesis via an (a-
chloromethyl)boronic ester
The discovery of the class of (a-haloalkyl)boronic
esters in high enantiomeric purity has led to a novel
method of asymmetric synthesis of broad scope [13].
The asymmetric insertion of a CHCl group into a BÃ
/C
bond can be controlled precisely if the chiral ligand is
appropriately chosen. The chlorine is readily replaced by
the alkyl group of a Grignard reagent or by other
nucleophiles. The resulting boronic esters can be further
homologated by introducing a second carbon atom.
Optically pure 1 was used as the chiral directing group
and the starting boronic ester 5 was easily obtained.
(Dichloromethyl)lithium was prepared from butyl-
lithium and dichloromethane in THF at ꢁ100 8C and
/
then treated with 5. The resulting clear solution was
allowed to warm to ambient temperature in order to
rearrange the intermediate borate compas isolated by
filtering off the precipitated lithium chloride. The
solution was then cooled to ꢁ78 8C and treated with
/
methylmagnesium bromide and kept at 20 8C over-
night. Peroxidic oxidation of 23 gave 1-phenylethanol 14
in almost quantitative yield and with an ee of 92%.
Scheme 6. Synthesis of b-binaphthyl based boronate reagents 4Á6.
/

140
S. Thormeier et al. / Journal of Organometallic Chemistry 657 (2002) 136Á145
/
starting material 6 and the cyclodimerization product 26
of methylenecyclopropane itself.
Compared with the parent compound 24 double bond
substituted cyclopropanes often give better results in
cycloaddition reactions with a wider range of alkenes.
Mono- and di-substituted alkylidenecyclopropanes react
with nickel(0) catalysts exclusively by distal ring open-
ing. Moreover, they are also less sensitive to self-
oligomerization. Therefore, less reactive alkenes, which
do not undergo [3ꢀ2] cycloadditions with the parent
/
methylenecyclopropane do react in this manner with
double bond substituted species.
For our further investigation we selected diphenyl-
methylene-cyclopropane 27*
selectivity and giving
idenecyclopentanes without scrambling of the phenyl
groups*and vinylboronate 28. The reaction proceeded
/
showing excellent regio-
Scheme 7. Allylboration of benzaldehyde 18.
exclusively diphenyl-
/
at 60 8C, and without any phosphorous ligand present
only 5% of the desired cycloadduct 29 was formed.
The use of triphenylphosphine or triarylphosphite
modified nickel(0) catalysts permits higher reaction
temperatures and led to an increase of the yield up to
65%. All of the cycloaddition studies described in this
area utilized the same convenient catalyst system pre-
pared in situ from Ni(COD)2 by addition of either
triphenylphosphine or triphenylphosphite (Ni:P ratio
1:2). The cycloadditions were performed by simply
heating the substrates in toluene in the presence of 2
mol% of this catalyst mixture. The product 29 is stable
towards air and water and can be purified by column
chromatography.
The use of vinylboronate 28 as an acceptor was
unsatisfactory due to its lack of reactivity. Therefore,
we decided to increase the reactivity of the vinylbor-
onate by introducing an, electron withdrawing group b
Scheme 8. Asymmetric synthesis of phenylethanol 14 via an (a-
chloromethyl)boronic ester 22.
to the boryl group, such as Ã
/
CO2Me or Ã
/
SO2-p-Tol
[18]. Attempted cycloadditions of 27 to the vinylbor-
onates 31a/b were successful, in particular the
reactions with the sulfonylated vinylboronate derivate
31b. This vinylboronate was shown to react already at
room temperature with 27, thus showing the activating
effect of the arylsulfonyl group. By heating the reaction
mixture at 80 8C the yield of 32b raised up to 95%. The
cycloaddition reactions of the (E)-vinylboronic esters
31a/b were highly stereoselective and yielded exclusively
the corresponding trans-products.
The carbonÃ
/
boron bond of these cycloaddition
products can be further transformed stereoselectively
by oxidation to the corresponding cyclopentanols as it
has been illustrated exemplary by 29. This borylated
cyclopentane was easily oxidized by sodium perborate in
THF in the presence of sodium hydroxide (Scheme 10)
giving 30. Therefore, vinylboronates serve as synthetic
equivalents of enols.
Scheme 9. Attempted [3ꢀ
methylenecyclopropane 24.
/
2] cycloaddition of the vinyl boronate 6 with

S. Thormeier et al. / Journal of Organometallic Chemistry 657 (2002) 136Á
/145
141
Scheme 10. [3ꢀ
/
2] Cycloaddition of vinyl boronates 28 and 31 with diphenylmethyleneÁcyclopropane 27.
/
3. Conclusions
The NMR spectra were recorded on a Bruker AMX
400 and AC 200F spectrometer (1H: 400 and 200
We have described the synthesis of several new
boronates 3Á6 and 12 and borates 2, 9, and 11 with
MHz*13
/
C: 100 and 50 MHz*11
/
B: 128 MHz) with
Et2O as external
standard; d values are given in ppm, J values in Hz.
/
tetramethylsilane as internal and BF3×
/
an axially chiral backbone. They belong to the three
different structural types 2, 11 and X. As the bicyclic
borates 2 and 9 are homochiral propeller compounds,
their exclusive formation can be used to increase the
enantiomerical purity of biarylols like b-binaphthol 1.
Especially the borates can serve as efficient Lewis acidic
Multiplicities of 13C-NMR signals were determined by
the DEPT sequence and are reported as follows: ꢀ
/
, for
CH or CH3; ꢁ, for CH2 and o, for C. Mass spectra were
/
obtained with a Hewlett Packard 5898B (at 70 eV); high
resolution mass spectra were recorded with a Varian
MAT 311A spectrometer with pre-selected molecular
catalysts for stereoselective DielsÁAlder reactions.
/
We have shown that the new seven-membered boron
reagents 4, 5, 6, and 12 are easily available and may be
used for asymmetric reductions, allylborations, synth-
ion peak matching at R ꢀ
of the exact masses. Melting points (m.p.) are uncor-
rected.
/
10 000 to be within 92 ppm
/
esis of (a-chloromethyl)boronic esters, and [3ꢀ
/
2] cy-
cloadditions of vinylborates with methylenecyclo-
propanes. The use of twofold activated vinylboronates
31 opens an efficient and easy access to boryl substituted
cyclopentanes 32, interesting precursors for natural
product chemistry.
4.1.1. Hexanaphthohexaoxa-1,8-diborabicyclo[6.6.6]-
eicosa-3,5,10,12,16,18-hexaene (2)
BoraneÁdimethyl sulfide (0.2 ml, 2 mmol) is added
/
dropwise to a cooled (0 8C) solution of b-binaphthol
(858 mg, 3 mmol) 1 in 60 ml CH2Cl2. The solution is
allowed to warm up to room temperature (r.t.) and is
stirred for 14 h. After evaporation of all volatile
compounds the residue is washed with diethyl ether
(30 ml). The product is dried in vacuo; colorless crystals;
4. Experimental
4.1. General data
m.p.: 348 8C; yield: 855 mg (98%). 1H-NMR (400 MHz,
3
CDCl3): dꢂ
3Jꢂ
aromat), 7.06 (d, 3Jꢂ
System, 3Jꢂ8.8, 4H, Haromat). 13C-NMR (100 MHz,
CDCl3): dꢂ120.2 (ꢀ, 2C, Caromat), 121.7 (o, 2C,
aromat), 124.2 (ꢀ, 2C, Caromat), 125.4 (ꢀ, 2C, Caromat),
125.8 (ꢀ, 2C, Caromat), 127.6 (ꢀ, 2C, Caromat), 127.8 (ꢀ
2C, Caromat), 130.3 (o, 2C, Caromat), 133.3 (o, 2C,
/
7.74 (d, Jꢂ
/
8.0, 2H, Haromat), 7.47 (dd,
3
All manipulations were carried out under a dry
nitrogen atmosphere using standard vacuum techniques.
The solvents were purified by conventional means and
distilled under nitrogen prior to use. The elemental
analyses were performed by the Microanalytical La-
/
8.1, 6.7, 2H, Haromat), 7.22 (dd, Jꢂ
/8.3, 6.7, 2H,
H
/
8.3, 2H, Haromat), 6.64 (AB-
/
/
/
C
/
/
boratory of the Institut fur Pharmazeutische Chemie der
¨
Universitat Braunschweig.
/
/
/,
¨

142
S. Thormeier et al. / Journal of Organometallic Chemistry 657 (2002) 136Á145
/
Caromat), 147.7 (o, 2C, Caromat). 11B-NMR (128 MHz,
4.1.5. Catalyzed DielsÁAlder reactions
/
CDCl3): dꢂ15.6 (bs). MS (70 eV); m/z (%): 874 (38)
/
[Mꢀ], 680 (3), 606 (5), 562 (2), 437 (16) [M2ꢀ], 386 (4),
342 (47), 312 (76), 294 (33), 268 (100), 239 (87).
4.1.5.1. General procedure for the reaction of
cyclopentadiene with methacrolein and a-bromoacrolein.
A solution of the dienophile in CH2Cl2 is added to the
4.1.2. Bis-(3-trimethylsilylnaphtho)[2,1-a:1?,2?-c]-1-
chloro-1,3,2-dioxaborepin (3a)
Procedure see 2: 2,2?-Dihydroxy-3,3?-bis(trimethylsi-
solution of 3 mol% of the boron catalyst in CH2Cl2 (ꢁ
/
78 8C). After stirring for 15 min to form the dienophile-
catalyst complex the cyclopentadiene is added. The
lyl)binaphthyl (60 mg, 0.14 mmol); 8 ml CH2Cl2; BH2Cl×
SMe2 (0.14 mmol); crystallization from CH2Cl2Áhexane
(1:1); colorless crystals; m.p.: 193 8C; yield: 57 mg (86%);
1H-NMR (200 MHz, CDCl3): dꢂ
0.00 (s, 18H,
Si(CH3)3), 6.97 (d, 3Jꢂ
8.0, 2H, Haromat), 7.10 (ddd,
/
reaction mixture is stirred for 1 day at ꢁ78 8C, then
/
/
it is allowed to warm slowly to 0 8C and hydrolyzed with
a saturated NaHCO3-solution. The aqueous phase is
/
extracted 3ꢃ with CH2Cl2, then dried with Na2SO4.
/
/
Yield and exo/endo ratio are determined by GC (internal
standard 2-methylnaphthalene). The products are iden-
4
3
3Jꢂ
7.0, 4Jꢂ
7.97 (s, 2H, Haromat). 13C-NMR (50 MHz, CDCl3): dꢂ
1.8 (ꢀ, 6C, Si(CH3)3), 123.6 (ꢀ, 2C, Caromat), 124.8 (o,
2C, Caromat), 126.7, 127.3 und 127.9 (ꢀ, 6C, Caromat),
132.6, 132.9 und 133.9 (o, 6C, Caromat), 134.0 (ꢀ, 2C,
aromat), 152.3 (o, 2C, Caromat). 11B-NMR (128 MHz,
CDCl3): dꢂ
23.5 (s). MS (70 eV); m/z (%): 474 (62) [Mꢀ],
/
8.5, 6.8, Jꢂ
/
1.4, 2H, Haromat), 7.32 (ddd, Jꢂ
/
7.8,
/
1.0, 2H, Haromat), 7.81 (d, 3Jꢂ
/
8.0, 2H, Haromat),
tified by GCÁMS and compared with authentic materials.
/
/
/
/
4.1.6. Increase of the enantiomerical purity of b-binaph-
thol (1)
/
/
Fifty-two microliters (0.5 mmol) BH3×
dropwise to a solution of 430 mg (1.5 mmol) of
enantiomerically enriched (88% ee) (ꢀ)-b-binaphthol
/
SMe2 is added
C
/
/
425 (40), 417 (19), 413 (11), 381 (12), 367 (11), 351 (16),
323 (9), 309 (21), 291 (11), 281 (10), 279 (20), 277 (17), 265
(35), 263 (26), 250 (7), 167 (15), 93 (52), 73 (100). HRMS
(C26H28BClO2Si2): 474.1409 (calc. and found).
(1) in 15 ml CH2Cl2 at 0 8C. The solution is allowed to
warm to r.t. and kept at this temperature for 6 h. The
solvent is removed in vacuo, the residue treated with 15
ml diethyl ether and stirred for 15 min; during this time
the excess b-binaphthol is solved. The diborate propeller
molecule 2 is filtered and dried in vacuo. Before
hydrolysis the purity is checked by 1H-NMR. Com-
pound 2 is then hydrolyzed in a solution of CH2Cl2. The
phases are separated, the solvent is removed and the
4.1.3. Hexa(dibenzofuranyl)hexaoxa-1,8-diborabicyclo-
[6.6.6]eicosa-3,5,10,12,16,18-hexaene (9)
Procedure see 2: 2,2?-dihydroxy-1,1?-bisdibenzofura-
nyl (366 mg, 1 mmol) 8; 30 ml CH2Cl2; BH3×
ml, 0.67 mmol); crystallization from CH2Cl2Á
(1:1); colorless crystals; m.p.:ꢁ350 8C; yield: 370 mg
/SMe2 (67
/hexane
product dried in vacuo. Yield: 130 mg (60%) (ꢀ
/
)-1;
/
a2D0ꢂ )-1, a2D0ꢂ
/
348, 99% ee; 300 mg (ꢀ 23.48, 69% ee.
/
/
1
3
(quant). H-NMR (200 MHz, CDCl3): dꢂ
8.1, 6H, Haromat), 6.60 (bs, 12H, Haromat), 6.83 (t, Jꢂ
7.1, 6H, Haromat), 7.23 (t, 3Jꢂ
7.5, 6H, Haromat), 7.56 (d,
3Jꢂ8.1, 6H, Haromat). 11B-NMR (128 MHz, CDCl3):
dꢂ
18.6 (s). MS (70 eV); m/z (%): 1114 (4) [Mꢀ], 766
/
6.5 (d, Jꢂ
/
3
/
/
4.1.7. Asymmetric reduction of acetophenone (13) with
hydroboraneÁamine complexes
A solution of 1.56 g (5.46 mmol) (ꢀ
binaphthol 1 in 15 ml THF is dropwise added to a
solution of 0.56 ml (5.91 mmol) boraneÁdimethyl sulfide
/
/
/
/
)- or (ꢁ)-b-
/
(6), 558 (5), 456 (100), 410 (4), 347 (33), 263 (8), 228 (25).
/
4.1.4. 2,2?-Bis(dibenzo[a,c]-1,3,2-dioxaborepin-2-
yloxy)biphenyl (11a)
Procedure see 2: 2,2?-Dihydroxybiphenyl (279 mg, 1.5
in 2 ml THF at 0 8C. The mixture is stirred at 0 8C for
1 h, then a solution of 5.59 mmol of the amine in THF is
added and the mixture is stirred for another h at 0 8C.
Afterwards a solution of 0.29 ml (2.46 mmol) acetophe-
mmol) 10a; 30 ml CH2Cl2; BH3×
crystallization from CH2Cl2Áhexane (1:1); colorless
crystals; m.p.: 148 8C; yield: 280 mg (97%). H-NMR
/
SMe2 (50 ml, 0.5 mmol);
/
none und 0.3 ml (2.46 mmol) boron trifluorideÁethyl-
/
1
ether in 0.5 ml THF is added. The reaction mixture is
kept for 12 h at 0 8C, the conversion is checked by GC.
The reaction is worked up by adding 2 ml 6 N HCl. The
product is isolated by Kugelrohr-distillation and identi-
3
(200 MHz, CDCl3): dꢂ
6.98Á
7.18 (m, 12H, Haromat), 7.25 (d, 3Jꢂ
aromat). 13C-NMR (50 MHz, CDCl3): dꢂ
120.9 (ꢀ
6C, Caromat), 124.2 (ꢀ, 6C, Caromat), 127.4 (o, 6C,
aromat, C-1,1?), 129.5 (ꢀ, 6C, Caromat), 130.1 (ꢀ, 6C,
aromat), 151.5 (ꢀ, 6C, CÃ
Oaromat, C-2,2?). 11B-NMR
19.3 (bs). MS (70 eV); m/z (%):
574 (95) [Mꢀ], 406 (39), 380 (30), 287 (11, M2ꢀ
), 121
/
6.77 (d, Jꢂ
/
7.8, 6H, Haromat),
/
/7.5, 6H,
H
/
/,
/
fied by GCÁMS, the ee is determined by GC.
/
C
C
/
/
/
/
a) 799.37 mg (5.59 mmol) b-naphthylamine; yield:
279.1 mg (93%) 14, 35% ee.
b) 771.42 mg (5.59 mmol) p-nitroaniline; yield: 225.0
mg (75%) 14, 45% ee.
c) 771.42 mg (5.59 mmol) m-nitroaniline; yield: 228.1
mg (76%) 14, 54% ee.
(128 MHz, CDCl3): dꢂ
/
/
(31), 168 (100), 139 (51). Calculated elemental analysis
(Anal. Calc.) for C36H24B2O6 (574.18): C, 75.30; H,
4.21. Found: C, 75.21; H, 4.14%.

S. Thormeier et al. / Journal of Organometallic Chemistry 657 (2002) 136Á
/145
143
d) 0.83 ml (5.59 mmol) DBU; yield: 216.0 mg (72%) 14,
24% ee.
e) Without amine; yield: 270.1 mg (90%) 14, 5% ee.
4.1.10. Dinaphtho[2,1-a;1?,2?-c]-1-phenyl-1,3,2-dioxa-
borepin (5) [19]
A mixture of b-binaphthol (1.38 g, 4.8 mmol) 1 and
phenylboronic acid (588.0 mg, 4.8 mmol) 16 in 25 ml
toluene is refluxed with a water separator for 4 h. The
solvent is removed in vacuo; crystallization from
4.1.8. Dinaphtho[2,1-a;1?,2?-c]-1-allyl-1,3,2-
dioxaborepin (4)
A mixture of 0.19 ml (1 mmol) triallylborane 15 and
CH2Cl2Áhexane (1:1); colorless crystals; yield: 82.6 mg
/
1
(76%). H-NMR (200 MHz, CDCl3): dꢂ
4H, Haromat), 7.35Á7.44 (m, 3H, Haromat), 7.50 (d, Jꢂ
9.0, 4H, Haromat), 7.91 (t, Jꢂ
(dd, 3Jꢂ7.9, 4Jꢂ1.4, 2H, Haromat). 13C-NMR (50
MHz, CDCl3): dꢂ121.3 (o, 2C, Caromat), 124.6, 125.9,
127.0 (ꢀ, 6C, Caromat), 127.3 (ꢀ, 1C, Caromat), 127.9,
128.0, 130.1 (ꢀ, 6C, Caromat), 130.8 (o, 2C, Caromat),
132.6 (ꢀ, 2C, Caromat), 134.9 (o, 2C, Caromat), 135.8 (ꢀ
2C, Caromat), 152.1 (o, 2C, Caromat
O). 11B-NMR (128
26.4 (bs). MS (70 eV); m/z (%): 372
/
7.19Á
/
7.28 (m,
3
/
/
286 mg (1 mmol) (ꢀ
/
)- or (ꢁ)-b-binaphthol 1 in 8 ml
/
3
/
8.4, 4H, Haromat), 8.22
diethyl ether is stirred at r.t. After their gas evolution
has ceased the mixture is stirred for another 2 h. The
solvent is removed in vacuo and the product crystallized
/
/
/
/
/
from diethyl etherÁ
/
hexane; colorless oil, slowly solidify-
1
ing; yield: 262 mg (78%). H-NMR (200 MHz, CDCl3):
/
/
/
,
3
2
dꢂ
3Jꢂ
3Jꢂ
/
1.26 (d, Jꢂ
9.3, 2H, 1-Hallyl), 5.12 (m, 1H, 2-Hallyl), 6.99 (d,
8.0, 2H, Haromat), 7.18Á7.29 (m, 4H, Haromat), 7.34
/
7.5, 2H, 3-Hallyl), 4.41 (dd, Jꢂ
/
10.3,
Ã
/
/
MHz, CDCl3): dꢂ
/
/
/
(96) [Mꢀ], 357 (18), 294 (18), 268 (64), 239 (100), 120
(19), 104 (35), 78 (21). HRMS (C26H17BO3): 372.1322
(calc.) 372.1321 (found).
3
4
3
(ddd, Jꢂ
7.8, 2H, Haromat), 7.98 (d, Jꢂ
13C-NMR (50 MHz, CDCl3): dꢂ
allyl-3, CÃB), 120.9 (ꢀ, 2C, Caromat), 121.2 (o, 2C,
aromat), 125.5, 125.8, 127.5, 128.4 (ꢀ, 8C, Caromat),
, 2C, Caromat), 133.8 (ꢀ
1C, Callyl-2), 133.9 (2C, Caromat), 150.6 (o, 2C, Caromat).
/
7.9, 7.1, Jꢂ
/
1.0, 2H, Haromat), 7.83 (d, Jꢂ
/
3
/
9.0, 2H, Haromat).
/
23.0 (b, ꢀ, 1C,
/
C
C
/
/
4.1.11. (a-Chloromethyl)boronic ester
/
131.0 (o, 2C, Caromat), 131.1 (ꢀ
/
/,
4.1.11.1. Asymmetric synthesis of 1-phenylethanol (14).
4.1.11.1.1. Lithiodichloromethane. To a rapidly stirred
11B-NMR (128 MHz, CDCl3): dꢂ
28.2 (bs). MS (70
/
solution of 0.8 ml CH2Cl2 in 20 ml THF at ꢁ100 8C a
/
eV); m/z (%): 336 (100) [Mꢀ], 295 (37), 294 (41), 286
(66), 268 (27), 267 (43), 239 (50). HRMS (C23H17BO2):
336.1322 (calc.) 336.1321 (found).
precooled solution of 6.6 ml (9.25 mmol, 1.4 M solution
in hexane) n-BuLi is added in such a manner, that the
temperature does not rise. After the addition is com-
pleted the solution is kept at this low temperature for 30
min.
4.1.9. Allylboration of benzaldehyde: 1-phenyl-3-buten-1-
ol (20)
4.1.11.1.2. (a-Chloromethyl)boronic ester. Thirty
milliliters THF is now slowly added to the above
Twenty-four microliters (0.24 mmol) benzaldehyde 18
is added to a solution of 100 mg (0.30 mmol) of the allyl
solution, the temperature is kept at ꢁ100 8C. Com-
/
pound 5 (3.3 g, 8.85 mmol) is added in small portions.
The solution gets clear. The reaction mixture is allowed
to warm to r.t. overnight. The THF is removed in vacuo
and the residue is washed with CH2Cl2 to precipitate
LiCl. The CH2Cl2 is removed in vacuo and solved in 30
ml THF again.
4.1.11.1.3. Methylation. Methyl lithium (6.7 ml, 10.6
mmol, 1.6 M solution in diethyl ether) is added dropwise
to a solution of the chloromethylboronic ester 22 in
boronate 4 in 0.5 ml diethyl ether at ꢁ
/
78 8C. The
reaction mixture is stirred at ꢁ78 8C for 2 h, then
/
warmed to r.t. and poured into 1 ml of dil. HCl. The
product is extracted with 2 ml diethyl ether. The
combined ether extracts are treated with NaHCO3 and
saturated NaCl solution and dried with Na2SO4. The
solution is concentrated to a third of its original volume
and then diluted with hexane to precipitate the b-
binaphthol. The solution is separated, the solvent is
removed in vacuo and the product purified by chroma-
tography (SiO2, petrol ether:diethyl ether 5:1); colorless
oil; yield: 40 mg (94%) 88% ee (GC). 1H-NMR (200 MHz,
THF at ꢁ78 8C. The reaction mixture is allowed to
/
warm to r.t. and the solvent is removed in vacuo. The
residue is treated with diethyl ether. The lithium chloride
is filtered off and a solution of 0.79 g (9.73 mmol)
sodium perborate and 0.18 g (4.42 mmol) NaOH in 10
ml water is added dropwise. The reaction mixture is
rapidly stirred for 16 h. The phases are separated; the
ether is removed in vacuo and the product is purified by
Kugelrohr-distillation; colorless oil; yield: 1.06 g (99%)
CDCl3): dꢂ
/
2.28 (s, 1H, OH), 2.45Á2.51 (m, 2H, 2-H),
/
3
3
4.69 (t, Jꢂ
/
6.4, 1H, 1-H), 5.11 (d, Jꢂ10.0, 1H, 4-H),
/
3
3
5.13 (d, Jꢂ
1H, 3-H), 7.22Á
MHz, CDCl3): dꢂ
C-1), 118.3 (ꢁ, 1C, C-4), 125.8 (ꢀ
(ꢀ, 2C, Caromat), 128.3 (ꢀ, 2C, Caromat), 134.4 (ꢀ
/
7.1, 1H, 4-H), 5.78 (ddt, Jꢂ
7.37 (m, 5H, Haromat). 13C-NMR (50
43.7 (ꢁ, 1C, C-2), 73.2 (ꢀ, 1C,
, 1C, Caromat), 127.4
/
7.1, 10.0, 17,
/
/
/
/
/
/
13, 92% ee (GC). 1H-NMR (200 MHz, CDCl3): dꢂ
1.19
/
3
3
/
/
/,
(d, Jꢂ
6.4, 1H, CH), 7.21Á
MHz, CDCl3): dꢂ25.0 (ꢀ
/
6.4, 3H, CH3), 2.42 (s, 1H, OH), 4.81 (q, Jꢂ
7.33 (m, 5H, Haromat). 13C-NMR (50
, 1C, C-2), 70.3 (ꢀ, 1C, C-1),
/
1C, C-3), 143.8 (o, 1C, Caromat). MS (70 eV); m/z (%): 148
(3) [Mꢀ], 131 (4), 107 (96), 79 (100), 51 (46).
/
/
/
/

144
S. Thormeier et al. / Journal of Organometallic Chemistry 657 (2002) 136Á145
/
125.3 (ꢀ
2C, Caromat), 145.8 (o, 1C, Caromat).
/
, 1C, Caromat), 127.3 (ꢀ
/
, 2C, Caromat), 128.4 (ꢀ
/
,
(ꢁ
aromat, C-4,4?), 128.7 (ꢀ
(ꢀ, 4C, Caromat, C-3,3?,5,5?), 133.8 (o, 2C, Caromat, C-
1,1?), 144.3 (o, 1C, C-6), 144.6 (o, 1C, C-1). 11B-NMR
/
, 1C, C-5), 83.3 (o, 2C, C(CH3)2), 126.7 (ꢀ
/
, 2C,
C
/
, 4C, Caromat, C-2,2?,6,6?), 130.1
/
4.1.12. Dinaphtho[2,1-a:1?,2?-c]-1-vinyl-1,3,2-dioxa-
borepin (6) [20]
(128 MHz, C6D6): dꢂ
/
34.0 (bs). GCÁMS (70 eV); m/z
/
A solution of 112.40 mg (1.03 mmol) dichlorovinyl-
borane 17 in 5 ml CH2Cl2 is slowly added dropwise to a
solution of 295.2 mg (1.03 mmol) b-binaphthol 1 in 12
ml CH2Cl2 at 0 8C. The reaction mixture is warmed to
r.t. and stirred for 6 h. The solvent is removed in vacuo
and the residue crystallized from toluene; colorless solid;
(%): 360 (45) [Mꢀ], 275 (11), 260 (15), 232 (100), 193 (33),
167 (51), 129 (16), 115 (32), 101 (28), 91 (37), 85 (47).
HRMS (C24H19BO2): 360.2261 (calc.) 360.2260 (found).
4.1.15. Diphenylmethylene-cyclopentan-3-ol (30)
Two hundred milligram (0.55 mmol) 29 in 8 ml diethyl
1
yield: 265.3 mg (80%). H-NMR (200 MHz, CDCl3):
3
5.43 (dd, J(E)
ether; 324.6 mg (2.11 mmol) sodium perborate, 55 mgÁ
/
3
18.6, J(Z)
dꢂ
/
ꢂ
/
ꢂ
/
13.5, 1H, Ä
/
CH), 5.78
3.8, 2H,
1.38 mmol NaOH in 4 ml water; reaction time: 6 h. The
product was purified by chromatography (SiO2, petrol
ether:ethyl ether 10:1); colorless oil, slowly solidifying;
3
(ddd, J(E)
3
18.2, J(Z)
2
14.2, J(gem)
ꢂ
/
ꢂ
/
ꢂ
/
3
Ä
/
CH2), 6.99 (d, Jꢂ
/
8.6, 2H, Haromat), 7.10Á
/7.20 (m,
3
2H, Haromat), 7.23 (d, Jꢂ
/8.8, 2H, Haromat), 7.30 (ddd,
yield: 61 mg (95%). 1H-NMR (200 MHz, C6D6): dꢂ
1.52
/
3Jꢂ
2H, Haromat), 7.84 (d, Jꢂ
(50 MHz, CDCl3): dꢂ
2C, Caromat), 124.8, 126.0, 127.2, 128.1 (ꢀ
130.6 (o, 2C, Caromat), 131.0 (ꢀ, 2C, Caromat), 133.6 (2C,
aromat), 136.2 (ꢀ, 1C, ÄCH2), 152.3 (o, 2C, Caromat).
24.5 (bs). MS (70
/
8.0, 7.0, Jꢂ
/
1.2, 2H, Haromat), 7.78 (d, Jꢂ
/8.3,
(m, 2H, 4-H), 2.22 (m, 2H, 5-H), 2.46 (ddd, 3Jꢂ
/
17.3, 5.4,
4
3
3
3
/
9.0, 2H, Haromat). 13C-NMR
2.3, 1H, 2-H), 2.63 (ddd, Jꢂ
/
17.3, 8.5, 6.1, 1H, 2?-H),
/
119.8 (ꢀ
/
, 2C, Caromat), 121.4 (o,
3.94 (quintett, 3Jꢂ
/
4.4, 1H, 3-H), 7.02Á
7.18 (m, 4H, Haromat), 7.20Á
aromat). 13C-NMR (50 MHz, C6D6): dꢂ
31.0 (ꢁ
, 1C, C-4), 43.4 (ꢁ, 1C, C-2), 73.4 (ꢀ, 1C, C-
3), 127.2 (ꢀ, 2C, Caromat, C-4,4?), 128.6 (ꢀ, 4C, Caromat
C-3,3?,5,5?), 130.3 (ꢀ, 4C, Caromat, C-2,2?,6,6?), 135.7 (o,
/
7.10 (m, 2H,
2.24 (m, 4H,
, 1C, C-
/
, 8C, Caromat),
H
H
aromat), 7.12Á
/
/
/
/
/
C
/
/
5), 35.9 (ꢁ
/
/
/
11B-NMR (128 MHz, CDCl3): dꢂ
/
/
/
,
eV); m/z (%): 322 (37) [Mꢀ], 307 (6), 295 (8), 286 (30),
268 (22), 257 (9), 239 (36), 226 (4), 213 (4), 147 (8), 119
(14), 84 (100), 66 (89). HRMS (C22H15BO2): 322.1165
(calc.) 322.1164 (found).
/
2C, Caromat, C-1,1?), 141.3 (o, 1C, C-6), 144.1 (o, 1C, C-1).
MS (70 eV); m/z (%): 250 (19) [Mꢀ], 232 (100), 215 (42),
204 (96), 191 (49), 178 (12), 165 (21), 152 (23), 141 (16),
128 (32), 115 (34), 107 (22), 101 (57), 91 (40), 89 (25), 77
(29), 63 (14), 51 (19). HRMS (C18H18O): 250.1358 (calc.)
250.1357 (found).
4.1.13. Nickel(0)-catalyzed [3ꢀ
vinylboronates with methylenecyclopropanes
/2] cycloadditions of
4.1.13.1. General procedure. A mixture of 2Á
/
5 mol%
4.1.16. Diphenylidenecyclopentane-trans-3-carboxylic
acid methylester 4-boronic acid (2,3-dimethylbutan-2,3-
diyl)ester (32a)
Ni(COD)2, two equivalents arylphosphine or arylphos-
phite and the vinylboronate is stirred in toluene at r.t.
for 15 min, then the methylenecyclopropane is added.
The reaction mixture is warmed up and the conversion is
followed by GC or DC. After completion the solvent is
removed in vacuo and the product purified.
Compound 31a (45.4 mg, 0.31 mmol), 63.6 mg (0.31
10ꢁ5 mol,
5 mol%)
mmol) 27, 4.26 mg (1.55ꢃ
/
Ni(COD)2, 8.12 mg (3.1ꢃ
/
10ꢁ5 mol, two equivalents)
PPh3, 1.5 ml toluene, 12 h, 100 8C. The product was
purified by chromatography (SiO2, petrol ether:ethyl
ether 10:1); yellow oil, slowly solidifying; yield: 83 mg
(64%, conversion (GC): 87%). 1H-NMR (200 MHz,
4.1.14. Diphenylidenecyclopentane-3-boronic acid (2,3-
dimethylbutan-2,3-diyl)ester (29)
Six hundred milligrams (2.91 mmol) 27, 448.5 mg
C6D6): dꢂ
2.52 (m, 2H, H-5,5?), 2.73 (m, 2H, H-2,2?), 2.89 (m, 1H,
H-3), 3.65 (s, 3H, CO2CH3), 7.15Á7.35 (m, 10H,
aromat). 13C-NMR (50 MHz, C6D6): dꢂ
25.1 (ꢀ, 4C,
C(CH3)2), 35.4 (ꢁ, 1C, C-5), 37.4 (ꢁ, 1C, C-2), 47.5 (ꢀ
1C, C-3), 52.0 (ꢀ, 1C, CO2CH3), 83.8 (o, 2C, C(CH3)2),
126.6 (ꢀ, 2C, Caromat, C-4,4?), 128.5 (ꢀ, 4C, Caromat, C-
2,2?,6,6?), 129.5 (ꢀ, 4C, Caromat, C-3,3?,5,5?), 134.3 (o,
/1.23 (s, 12H, C(CH3)2, 1.56 (m, 1H, H-4),
(2.91 mmol) 28, 24.0 mg (8.74ꢃ
/
10ꢁ5 mol, 3 mol%)
Ni(COD)2, 54.1 mg (1.75ꢃ
/
10ꢁ4 mol, two equivalents)
/
P(OPh)3, 5 ml toluene, 1.5 d, 100 8C. The product is
purified by chromatography (SiO2, petrol ether:ethyl
H
/
/
/
/
/,
ether 10:1; colorless oil; yield: 562 mg (54%, conversion
1
(GC): 65%). H-NMR (200 MHz, CDCl3): dꢂ
/
/1.23 (s,
/
/
12H, C(CH3)2), 1.56 (m, 2H, 4,4?-H), 1.92 (quintett,
/
3Jꢂ
(m, 10H, Haromat). 1H-NMR (200 MHz, C6D6): dꢂ
(s, 12H, C(CH3)2), 1.63 (m, 1H, 3-H), 1.89 (m, 1H, 4-H),
/
8.3, 1H, 3-H), 2.44 (m, 4H, H-5,5?,2,2?), 7.16Á
/
7.27
2C, Caromat, C-1,1?), 141.4 (o, 1C, C-6), 143.4 (o, 1C, C-
/
1.16
1), 175.8 (o, 1C, CO2CH3). 11B-NMR (128 MHz, C6D6):
dꢂ
33.7 (bs). MS (70 eV); m/z (%): 418 (11) [Mꢀ], 358
/
2.09 (m, 1H, 4?-H), 2.60 (m, 2H, 5,5?-H), 2.88 (m, 2H,
(16), 318 (6), 219 (14), 258 (9), 323 (31), 230 (33), 215
(22), 204 (15), 191 (13), 167 (22), 152 (13), 100 (34), 67
(26), 57 (100). HRMS (C26H31BO4): 418.2316 (calc.)
418.2315 (found).
2,2?-H), 7.13Á
13C-NMR (50 MHz, C6D6): dꢂ
C(CH3)2), 30.1 (ꢁ, 1C, C-4), 35.1 (ꢁ, 1C, C-2), 36.3
/
7.46 (m, 10H, Haromat).
/
25.2 (ꢀ, 4C,
/
/
/

S. Thormeier et al. / Journal of Organometallic Chemistry 657 (2002) 136Á
/145
145
(b) H. Yamamoto, K. Ishihara, H. Kurihara, J. Org. Chem. 62
(1997) 3026;
4.1.17. Diphenylidenecyclopentane-trans-3-p-
toluolsulfonyl-4-boronic acid (2,3-dimethylbutan-2,3-
diyl)ester (32b)
(c) H. Yamamoto, K. Ishihara, Eur. J. Org. Chem. 64 (1999) 527.
[8] (a) G.P.Y. Sogah, D.J. Cram, J. Am. Chem. Soc. 101 (1979) 3035;
(b) J.M. Brunel, G. Buono, J. Org. Chem. 58 (1993) 7313.
[9] J. Brussee, A.C.A. Jansen, Tetrahedron Lett. 24 (1983) 3261.
[10] (a) F. Toda, K. Tanaka, L. Nassimbeni, M. Nivem, Chem. Lett.
(1988) 1371;
Compound 31b (67.7 mg, 0.22 mmol), 45.3 mg (0.22
10ꢁ5 mol, 5 mol%) Ni(COD)2,
mmol) 27, 3.0 mg (1.1ꢃ
/
5.8 mg (2.2ꢃ
/
10ꢁ5 mol, two equivalents) PPh3, 1.5 ml
toluene, 12 h, 80 8C. The solvent is removed in vacuo
and the residue washed with hexane to remove excess 27
and triphenylphosphine. When the product is treated
with ether the nickel precipitates. The solution is
decanted and the solvent removed. The residue is
(b) F. Toda, K. Tanaka, T. Okada, Angew. Chem. Int. Ed. Engl.
32 (1993) 1147;
(c) M. Periasamy, L. Vaukatraman, J. Thomas, J. Org. Chem. 62
(1997) 4302.
[11] (a) J.W.A. Simon, T.L. Collier, Tetrahedron 42 (1986) 5157;
(b) T. Mukaiyama, M. Asami, Topics on the Current Chemistry
and Organic Chemistry, vol. 127, Springer-Verlag, Berlin, 1985, p.
133;
crystallized from ethyl etherÁ
slowly solidifying; yield: 107 mg (95%). H-NMR (400
MHz, CDCl3): dꢂ1.11 (s, 6H, C(CH3)2), 1.13 (s, 6H,
/
hexane 1:1; colorless oil,
1
/
(c) H. Suda, S. Kanoh, N. Umeda, T. Nakajo, M. Motoi,
Tetrahedron Lett. 24 (1983) 1513.
3
C(CH3)2), 1.87 (q, Jꢂ
/
9.1, 1H, H-4), 2.36 (s, 3H, PhÃ
/
CH3 and m, 1H, H-5?), 2.68 (m, 2H, H-2,5?), 2.85 (ddd,
[12] (a) B.M. Mikhailov, N.Y. Bubnov, Izv. Ak. Nauk SSSR Ser.
Khim. (1964) 1874;
3
3
2Jꢂ
/
17.4, Jꢂ
/
7.9, 4.0, 1H, H-2), 3.74 (q, Jꢂ8.4, 1H,
8.1, 2H, Haromat), 7.26Á
/
H-3), 7.28 (3Jꢂ
/
/7.32 (m, 10H,
(b) S. Masamune, M. Hirama, Tetrahedron Lett. (1979) 2225;
(c) S. Masamune, M. Hirama, D.S. Garvey, L.D.L. Lu, Tetra-
hedron Lett. (1979) 3937;
3
H
aromat), 7.72 (d, Jꢂ
MHz, CDCl3): dꢂ
25.1 (ꢀ, 4C, C(CH3)2), 34.5 (ꢁ
C-2), 67.0 (ꢀ, 1C, C-3), 84.2 (o, 2C, C(CH3)2), 128.5 (ꢀ
, 3C, Caromat), 129.3 (ꢀ, 6C, Caromat), 130.1 (ꢀ, 6C,
aromat), 135.4 (o, 3C, Caromat), 142.5 (o, 1C, C-6), 144.6
(o, 1C, C-1). CIÁ
MS (CH4); m/z (%): 557 (11) [Mꢀꢀ
C3H7]ꢀ, 543 (9) [MꢀꢀC2H5]ꢀ, 515 (88) [Mꢀꢀ1]ꢀ,
/
8.3, 2H, Haromat). 13C-NMR (100
/
22.0 (ꢀ
/
, 1C, PhÃ
/
CH3), 25.0 und
(d) D.A. Evans, E. Vogel, J.V. Nelson, J. Am. Chem. Soc. 102
(1979) 6120;
/
/
, 1C, C-5), 34.8 (ꢁ
/, 1C,
/
/
(e) R.W. Hoffmann, Angew. Chem. 94 (1982) 569;
(f) R.W. Hoffmann, Angew. Chem. Int. Ed. Engl. 21 (1982) 555.
[13] (a) M.W. Rathke, E. Chao, G. Wu, J. Organomet. Chem. 122
(1976) 145;
/
/
C
/
/
(b) D.S. Matteson, D.J. Majumdar, J. Am. Chem. Soc. 102 (1980)
7588;
/
/
499 (3), 443 (8), 415 (36), 387 (11), 359 (100), 307 (22),
279 (98), 271 (5), 201 (4).
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