An electrophilic cleavage procedure for the asymmetric dihydroxylation: Direct enantioselective synthesis of cyclic boronic esters from olefins

Article abstract of DOI:10.1002/chem.200500095

A variation within the osmium-catalysed asymmetric dihydroxylation (AD) of olefins is described that yields cyclic boronic esters from olefins in a straight-forward manner. This process represents the first real product alteration in asymmetric dihydroxylation, since all previous protocols lead to free diols exclusively. A protocol based on the Sharpless AD conditions (for enantioselective oxidation of prochiral olefins) was developed that gives cyclic boronic esters with excellent enantiomeric excesses (ee's). Some of the ee's are higher than those reported for conventional AD. The unprecedented role of phenyl boronic acid on the course of the AD reaction was investigated in detail. PhB(OH)₂ does not interfere with the chiral ligand. leaving the enantioselective step of olefin oxidation intact. The main role of the boronic acids - apart from protecting the diol products against potential overoxidation-relies on removing the diol entity in an electrophilic cleavage, which is in contrast to the conventional hydrolylic cleavage of the AD protocols. Thus, a mechanistically new cleavage for enantioselective dihydroxylation reactions is introduced within the present work.

Full text of DOI:10.1002/chem.200500095

FULL PAPER
An Electrophilic Cleavage Procedure for the Asymmetric Dihydroxylation:
Direct Enantioselective Synthesis of Cyclic Boronic Esters from Olefins**
Claas H. Hçvelmann and Kilian MuÇiz*[a]
Dedicated to Professor Josꢀ Barluenga on the occasion of his 65th birthday.
Abstract:
A
variation within the
esters with excellent enantiomeric ex-
cesses (eeꢀs). Some of the eeꢀs are
higher than those reported for conven-
tional AD. The unprecedented role of
phenyl boronic acid on the course of
the AD reaction was investigated in
detail. PhB(OH)2 does not interfere
with the chiral ligand, leaving the enan-
tioselective step of olefin oxidation
intact. The main role of the boronic
acids—apart from protecting the diol
products against potential overoxida-
tion—relies on removing the diol entity
in an electrophilic cleavage, which is in
contrast to the conventional hydrolytic
cleavage of the AD protocols. Thus, a
mechanistically new cleavage for enan-
tioselective dihydroxylation reactions is
introduced within the present work.
osmium-catalysed asymmetric dihy-
droxylation (AD) of olefins is de-
scribed that yields cyclic boronic esters
from olefins in
a straight-forward
manner. This process represents the
first real product alteration in asym-
metric dihydroxylation, since all previ-
ous protocols lead to free diols exclu-
sively. A protocol based on the Sharp-
less AD conditions (for enantioselec-
tive oxidation of prochiral olefins) was
developed that gives cyclic boronic
Keywords: alkenes · boronic esters ·
dihydroxylation
oxidation
·
osmium
·
Introduction
The overall catalytic cycle is initiated by formation of the
catalyst upon complexation of osmium tetroxide to a Cin-
chona alkaloid ligand L*. This chiral complex then differen-
tiates the enantiotopic face of the olefinic substrate effi-
ciently to generate osma(vi) glycolates with high enantio-
meric excess. Reoxidation of the osmium centre is accom-
plished by hexacyanoferrate(iii), which gives an osmium(viii)
glycolate and, upon hydrolytic cleavage, the free diol and
the regenerated osmium tetroxide. This process represents
the so-called first AD cycle and is characterised by forma-
tion of diols with high enantiomeric excesses (Figure 1,
right). In principle, the reaction can take an alternative
course at the stage of the osma(viii) glycolate upon direct
oxidation of a second olefin. This pathway is denominated
the secondary cycle and proceeds through a bisglycolate
ester with usually low diastereoselectivity, because the
remote stereochemical information of the primary glycol
entity is largely uneffective. Subsequent hydrolysis leads to
liberation of a diol with lower enantiomeric excess than the
one from the primary cycle. Under the optimised biphasic
Sharpless AD conditions,[4] formation of a bisglycolate is
prevented and the hydrolytic cleavage occurs at the stage of
the monoglycolate osmium ester.
Since its original discovery in 1980, the osmium(viii)-cata-
lysed Sharpless asymmetric dihydroxylation (AD reaction),
which converts olefins into non-racemic vicinal diols, has de-
veloped into the most versatile oxidative catalytic process
available today.[1–3] Its optimised protocol is characterised by
a high substrate generality and broad functional group toler-
ance.[4]
[a] Dipl.-Chem. C. H. Hçvelmann, Dr. K. MuÇiz
Kekulꢁ-Institut fꢂr Organische Chemie und Biochemie
der Universitꢃt Bonn, Gerhard-Domagk-Str. 1
53121 Bonn (Germany)
Fax : (+49)228-735-813
E-mail: kilian.muniz@uni-bonn.de
[**] Abbreviations in this article: NMO: N-methyl morpholine-N-oxide;
AD: asymmetric dihydroxylation; (DHQD)2PHAL: dihydroquini-
dine-1,4-phthalazindiyl diether; (DHQ)2PHAL: dihydroquinine-1,4-
phthalazindiyl diether; (DHQD)2AQN: dihydroquinidineanthraqui-
none-1,4-diyl diether; DHQD-PCB (4-chlorobenzoyldihydroquini-
dine.
Supporting information for this article is available on the WWW
under http://www.chemeurj.org/ or from the author.
Chem. Eur. J. 2005, 11, 3951 – 3958
DOI: 10.1002/chem.200500095
ꢄ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3951

tion of chiral ligands in order to
render the overall process
enantioselective.
Diastereoselective dihydroxyla-
tion: Under Upjohn conditions,
dihydroxylation of enantiopure
olefins led to boronic esters
with complete diastereoselectiv-
ity. For example, oxidation of
2,3,4-triacetyl-O-glucal
and
2,3,4-tribenzyl-O-glucal provid-
ed the corresponding boronic
esters as single stereoisomers
each and in good isolated yields
(Scheme 1).
These
results
match with those from a con-
ventional dihydroxylation de-
scribed earlier[10] and rely on an
efficient stereochemical induc-
tion through the chiral glucal
motif of the substrate.
Figure 1. Current understanding of the catalytic asymmetric Sharpless dihydroxylation. L*=Cinchona alkaloid-
based ligand.
In the past, extensive investigation on the course of the
primary cycle have dealt with the question on the exact
mechanism for olefin oxidation with the osmium(viii) oxi-
dant. Here, different primary oxidation steps were debated
both in experimental[5] and theoretical[6] investigations.
Among rare changes on the established conditions for oxi-
dation of the osma(vi) glycolate, development of dihydroxy-
lation reactions under aerobic conditions or in the presence
of hydrogenperoxide as terminal oxidant have emerged re-
cently.[7] Apart from this intensive search for alternative re-
oxidation, further alteration in order to obtain chiral prod-
ucts other than free diols has remained uninvestigated.
Some years ago, Narasaka and Sharpless reported use of
phenyl boronic acid as turnover-generating reagent in achi-
ral dihydroxylations under strictly anhydrous conditions
(OsO4, CH2Cl2, NMO) to form racemic boronic esters.[8,9]
Herein, we describe the first development of an asymmet-
ric PhB(OH)2-promoted dihydroxylation that gives rise di-
rectly to enantiomerically pure boronic esters from olefins
and thereby establish a new cleavage concept for AD reac-
tions.
Scheme 1. Diastereoselective dihydroxylation of glucals under Upjohn
conditions.
This sequence represents a uniquely efficient approach
toward boronic ester protection of the anomeric centre in
carbohydrate chemistry. This type of ester has met with sig-
nificant interest over past years in the construction of sugar-
based sensors.[11]
Enantioselective dihydroxylation: To devise a highly enan-
tioselective version of the Narasaka/Sharpless process,[8,9] it
was decided to combine the standard Sharpless AD proce-
dure[1,4] with phenyl boronic acid. Upon addition of
1.2 equivalents of PhB(OH)2 to the otherwise unchanged
conditions for enantioselective AD reaction, completely se-
lective olefin oxidation and concomitant formation of cyclic
boronic esters 4 took place (Scheme 2). These were the only
detectable products at quantitative olefin conversion. Impor-
tantly, free diols were never observed.
Results and Discussion
Our experimentation started from the discovery that the
presence of phenyl boronic acid is compatible with the gen-
eral Upjohn conditions for olefin dihydroxylation and thus
does not demand anhydrous conditions at all. This process
was found to be general and provided quantitative transfor-
mation of alkenes such as (E)-stilbene, styrene, a- and b-
methyl styrene, 2-vinyl naphthalene, 1-decene, indene, and
methyl and benzyl cinnamate to their corresponding cyclic
boronic esters. It furthermore set the basis for the applica-
A series of ten different substrates, with different aromat-
ic, aliphatic and electron-demanding substitution patterns,
was submitted to dihydroxylation in the presence of phenyl
boronic acid and (DHQD)2PHAL as
a chiral ligand
(Table 1). All the corresponding cyclic boronic esters were
isolated in high to excellent yields, showing the catalytic
process to be general. In almost all cases, already the crude
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Chem. Eur. J. 2005, 11, 3951 – 3958

Asymmetric Dihydroxylation
FULL PAPER
diols, respectively. Their complete agreement demonstrates
the absence of any racemisation during boron removal. All
obtained ee values and absolute configurations are in excel-
lent agreement with those from the original Sharpless AD
reactions.[12] Identical values were obtained for reactions
which were carried out with commercially available AD-mix
samples. For oxidations of stilbene, styrene and indene, AD
mix-b gave identical values regarding yields (99, 95 and
96%, respectively) and enantiomeric excesses (99, 96 and
58%, respectively). The excel-
Scheme 2. Enantioselective catalytic synthesis of cyclic boronic esters
from olefins.
lent yields of boronic esters are
particularly noteworthy for sub-
Table 1. Boronic esters from PhB(OH)2-aided catalytic olefin oxidation.
Entry
Substrate 3
Product 4
Yield [%][a]
ee [%][b]
Config.[c]
strates such as styrene, b-
methyl styrene or 2-vinyl naph-
thalene, which tend to suffer
from overoxidation under cer-
tain aqueous conditions.[13] We
observed benzaldehyde and 2-
naphthaldehyde formation in
the range of 7–16% under stan-
dard AD reactions. This is not
the case in the present protocol,
which leads to protection of the
chiral diol entities as boronic
esters immediately after the pri-
mary oxidation step.
1
(E)-stilbene
99
99 (99)[d]
R,R
2[e]
(E)-stilbene
99
94
97
94
92
99
96
94
98
98
S,S
R
3
styrene
4
a-methyl styrene
b-methyl styrene
methyl cinnamate
R
5
R,R
S,R
As
(DHQ)2PHAL led to enantio-
complimentary induction
expected,
use
of
6
(Table 1, entry 2). Oxidations of
(E)-stilbene employing other li-
gands such as (DHQD)2AQN
and DHQD-PCB gave 99 and
95% ee, respectively, and isolat-
ed chemical yields of more than
95%. Apparently, the presence
of phenyl boronic acid does not
affect the crucial step of enan-
tioselective olefin functionalisa-
tion with the OsO4–Cinchona
alkaloid complex. In view of
the high ratio for phenyl boron-
ic acid:Cinchona alkaloid of
7
benzyl cinnamate
95
99
S,R
8
9
2-vinyl naphthalene
1-decene
93
88
98
98
R
82
R
10
indene
61 (61)[d]
R,S
[a] Isolated yield at quantitative conversion. [b] Determined by HPLC after deprotection to the free diol.
[c] Determined on the diol stage by comparison with literature values for optical rotation and HPLC retention
times. [d] Determined on the boronic ester stage. [e] With (DHQ)2PHAL as ligand.
products from aqueous work-up were analytically pure ac-
24:1, complete removal of the stereoinducing Lewis basic
ligand as the primary source of chiral information through
deleterious complexation to the Lewis acidic boron centre
was an evident possibility. Otherwise, even low concentra-
tions of free Cinchona alkaloid would still lead to a kineti-
cally favoured enantioselective pathway, since the AD reac-
tion benefits from a highly ligand-accelerated catalysis.[14]
Thus, already at the outset of the present investigation there
had been a reasonable chance to maintain asymmetric in-
duction under the given conditions. Even so, 1H and 11B
NMR spectroscopic control experiments included titration
of a solution of DHQD-PCB with phenyl boronic acid;
these experiments revealed no detectable complexation at
all of the basic quinuclidine unit of the chiral ligand to the
1
cording to H and 13C NMR. Complete enantioselection was
observed in oxidations of (E)-stilbene and benzyl cinnamate.
Other substrates such as styrene, a- and b-methyl styrene,
methyl cinnamate and 2-vinyl naphthalene gave boronic
esters with high to excellent enantiomeric excesses (eeꢀs) in
the range of 95–98%. In general, enantiomeric excesses of
the products were determined after deprotection of the
cyclic boronic esters under standard conditions (H2O2, H2O,
then NaOH). Epimerisation during course of deprotection
was never observed and the final vicinal diol products were
isolated in over 90% chemical yield. For (E)-stilbene and
indene oxidation, the enantiomeric excesses were deter-
mined both at the stage of the boronic esters and the free
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3953

K. MuÇiz and C. H. Hçvelmann
Lewis acidic boron reagent within NMR timescale. This
characterises the boron centre an oxophilic, but not azaphil-
ic Lewis acid.
tion of diols by means of circular dichroism spectroscopic
analysis.[17]
Asymmetric dihydroxylation of cyclopentadiene was car-
ried out under Upjohn conditions due to the problematic
base conditions of the original AD procedure (Scheme 3).
Mechanistic discussion: It has been a common feature in all
dihydroxylation protocols established so far[1,3] that removal
of the diol entity from the intermediate osma(vi) glycolate
represents the decisive step for catalyst regeneration. This is
usually accomplished through the hydrolytic cleavage of the
osmium–oxygen bonds (Figure 2, left). Regarding the aryl
boronic acid variants, already the earlier anhydrous condi-
tions in the racemic protocol[8,9] pose the underlying mecha-
nistic question on diol removal in the intermediary step
prior to catalyst regeneration. Surprisingly, the importance
of the exact working mode of diol removal by the phenyl
boronic acid had not been clarified in these earlier proto-
cols[5] and has remained largely unappreciated.
Scheme 3. Enantioselective dihydroxylation of cyclopentadiene. Assumed
absolute S,S,S,S configuration made on the basis of the regular face selec-
tivity of the AD.[1]
Given the inherent properties of phenyl boronic acid, it
appears reasonable to assume cleavage by the unique elec-
trophilic character of the boron centre (Figure 2, right). The
role of boronic acid in this cleavage does not rely on a
simple proton effect as revealed by control experiments
with Brønsted acids such as acetic acid or toluene sulfonic
acid. These additives gave significantly lower conversion.
This reaction gave a single compound (>96% purity) and
the potentially formed meso-derivative was not observed in
the 300 MHz H NMR spectrum. The only product was the
chiral bis-boronic ester which was isolated in >99% ee.
This result matches earlier elegant work from Sharpless on
per-dihydroxylation of polyalkenes.[15] In addition, the ster-
eochemistry of the second step of oxidation is consistent
with the Kishi rules on dihydroxylation of cyclic allylic
ethers and esters.[16]
1
Substituted aryl boronic acids are compatible with this
new AD protocol (Scheme 4, Table 2). For the case of (E)-
stilbene as standard AD substrate, no electronic effect re-
garding the substituent was detected and dihydroxylation
under the usual conditions consistently gave the respective
aryl boronic esters with essentially complete enantioselec-
tion (99% ee). The example of 4-biphenyl boronic acid
(entry 4) is particularly noteworthy, since it allows for direct
access to the respective chiral boronic esters, which are im-
portant derivatives for determination of absolute configura-
Figure 2. Hydrolytic cleavage versus electrophilic cleavage of osma glyco-
lates.
Scheme 4. Dihydroxylation in the presence of substituted aryl boronic
acids.
Table 2. Catalytic asymmetric synthesis of aryl boronic esters.
Entry
Ar
Product
Yield [%][a]
ee [%][b]
1
2
3
4
Ph
4a
7
8
99
97
95
98
99
99
99
99
4-F-Ph
4-MeO-Ph
4-Ph-Ph
9
[a] Isolated yield at quantitative conversion. [b] Determined by HPLC
after deprotection to free 1,2-diphenyl ethanediol.
Figure 3. Catalytic cycle for phenyl boronic acid-initiated turnover in
enantioselective olefin dihydroxylation.
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Asymmetric Dihydroxylation
FULL PAPER
The resulting overall catalytic cycle is depicted in
Figure 3. The stereochemically decisive initial stages are un-
changed with respect to the parent Sharpless process. Thus
ligation of the chiral Cinchona alkaloid ligand to osmium
tetroxide furnishes the asymmetric catalyst for differentia-
tion of the prochiral olefin faces. Asymmetric dihydroxyla-
tion and dissociation of the ligand then leads to the glyco-
late osmium(vi) ester, which is reoxidised to the correspond-
ing glycolate osmium(viii) ester. At this stage, the osmium–
diolate entity is cleaved by the above-mentioned electrophil-
ic cleavage (Figure 3). In such a scenario, initial interaction
between the electrophilic boron centre and the basic oxygen
atom of the glycol entity weakens the osmium–oxygen bond
and ultimately leads to transesterification from osmium to
boron. This releases boronic esters with high enantiomeric
excess and regenerates the osmium tetroxide catalyst.
The high enantiomeric excesses obtained by our proce-
dure are the consequences of a well-balanced electrophilic
character of the boronic acid. While it is completely cooper-
ative with the stereoinducing ligand, it renders the rate for
this cleavage process sufficiently fast in order to overcome
the competitive hydrolytic cleavage. This is further strength-
ened by the observation that the hydrolysis-aiding methyl
sulfonamide effect[1,4] is completely absent in the presence
of phenyl boronic acid. For example, a qualitative compari-
son on the respective rates (and enantiomeric excesses) for
boronic acid promoted asymmetric dihydroxylation of stil-
bene (Table 1, entry 7) are essentially identical for reactions
with and without methyl sulfonamide addition. Therefore,
product formation ocurrs exclusively through the electro-
philic cleavage pathway and boronic esters are the only
products from this new AD version.
Experimental Section
General: Potassium osmate K2[OsO2(OH)4] was purchased from Aldrich
and stored under argon. Methyl cinnamate, benzyl cinnamate, indene, 2-
formyl
naphthaldehyde,
(DHQD)2PHAL,
(DHQ)2PHAL,
(DHQD)2AQN and DHQ-PCB were purchased from Fluka. Phenyl bor-
onic acid, styrene, stilbene, a-methyl styrene and b-methyl styrene and 1-
decene were purchased from Aldrich. 2-Vinyl naphthalin was synthesised
following a literature Wittig procedure.[19]
All other solvents were reagent grade and used as received. Column
chromatography was performed with silica gel (Merck, type 60, 0.063–
0.2 mm and Machery Nagel, type 60, 0.015–0.025 mm). Optical rotations
were measured on a Perkin–Elmer 341 polarimeter. Concentrations are
given in g per 100 mL in dichloromethane. NMR spectra were recorded
on Bruker DPX 300 MHz and Bruker DRX 500 MHz spectrometers. All
chemical shifts in the NMR experiments are reported as ppm downfield
from TMS. The following calibrations were used: CDCl3 d=7.26 and
77.00 ppm, C6D6 d=7.16 and 128.00 ppm. Multiplicities are given by the
common abbreviations (s, singlet; d, doublet; t, triplet, q, quartet; m,
multiplet; ps for pseudo). IR spectra were recorded on a Nicolet Magna
550 FT-IR spectrometer. MS and HRMS experiments were performed on
a Kratos MS 50 within the service centres at the Kekulꢁ-Department,
Bonn. HPLC determinations were carried out on a Knauer Wellchrome
(injection valve A0258, pump K-100, solvent organizer K-1500, UV-de-
tector K-2600). The reported values refer to 254 nm detection wave-
length.
General synthetic procedure for dihydroxylation under Upjohn condi-
tions (Procedure A): A solution of K2[OsO2(OH)4] (3.2 mg, 0.01 mmol)
and phenyl boronic acid (146 mg, 1.2 mmol) in tert-butanol and water
(10 mL, 1:1, v/v) was stirred at room temperature. NMO was added as a
1.2m solution in water (1.0 mL) and the resulting solution was stirred.
The substrate (1.0 mmol) was added in one portion and the solution was
sealed and stirred for 12 h at room temperature. It was worked up by ad-
dition of an aqueous solution of sodium thiosulfate and extracted with di-
chloromethane. The organic phase was separated, dried over MgSO4 and
evaporated to dryness to leave the crude products.
Where appropriate, column chromatography (silica gel, hexane/ethyl ace-
tate, 4:1, v/v) gave the analytically pure products as described below.
Moreover, since the rate of the electrophilic cleavage
process at least equals the one from sulfonamide-based AD
protocols, any occurrence of secondary cycle catalysis is effi-
ciently surpressed. Thus, the highly enantioselective osmium
tetroxide Cinchona alkaloid catalyst from the Sharpless AD
process constantly dominates the catalysis.
General synthetic procedure for dihydroxylation under Sharpless AD
conditions (Procedure B):
A solution of K2[OsO2(OH)4] (3.2 mg,
0.01 mmol), potassium carbonate (410 mg), potassium hexacyanoferrate-
(iii) (980 mg), phenyl boronic acid (146 mg, 1.2 mmol) and the Cinchona
alkaloid ligand (0.05 mmol) in tert-butanol and water (10 mL, 1:1, v/v)
was stirred at room temperature. The substrate (1.0 mmol) was added in
one portion and the solution was sealed and stirred for 12 h at room tem-
perature. It was worked up by addition of an aqueous solution of sodium
thiosulfate and extracted with water and dichloromethane. The organic
phase was separated, dried over MgSO4 and evaporated to dryness to
leave the crude products.
Finally, formation of boronic esters does not proceed
through the alternative pathway of diol condensation with
ArB(OH)2.[18] A control experiment showed that reaction of
free stilbene diol with PhB(OH)2 in MeOD/D2O (1:1, v/v) is
comparably slow at room temperature and gives only an in-
complete yield, even after a prolonged reaction time of 24 h.
In summary, we have described a new electrophilic cleav-
age concept for the Sharpless asymmetric dihydroxylation
reaction. This has resulted in the development of a one-step
synthesis of enantiopure boronic esters through the asym-
metric dihydroxylation of olefins in the presence of phenyl-
boronic acid. This new procedure is noteworthy, since it is
more convenient than the previous racemic protocol
(osmate instead of OsO4 as osmium source, cheap re-oxi-
dant instead of anhydrous NMO) and combines the power
of the AD with the advantage of boronic ester protection.
Where appropriate, column chromatography (silica gel, hexane/ethyl ace-
tate, 4:1, v/v) gave the analytically pure products as described below.
General procedure for cleavage of boronic esters: The boronic ester
(1 mmol) was dissolved in ethyl acetate/acetone (10 mL 1:1, v/v) and a
solution of H2O2 (35% in H2O, 2 equiv, 0.17 mL) was added upon stir-
ring. The resulting solution was stirred for a period of 3–4 h at room tem-
perature. The remaining H2O2 was reduced upon addition of an aqueous
solution of Na2S2O3 at room temperature. The reaction mixture was ex-
tracted twice with ethyl acetate (2ꢅ20 mL), the organic layers were sepa-
rated, washed with an aqueous solution of NaOH (1m, 10 mL), dried
over MgSO4 and filtered. The solvents were removed under reduced
pressure. If required, the colourless solids were purified by column chro-
matography (silicagel, hexanes/ethyl acetate, 3:1, v/v) to give the analyti-
cally pure diols.
Dioxoborolane 2a from oxidation of triacetyl glucal: This compound was
synthesised according to the general procedure A from 2,3,4-tribenzyl-O-
glucal (272 mg, 1 mmol). After column chromatography (silica gel, ethyl
acetate), 2a was obtained as a white solid (302 mg, 0.77 mmol, 77%).
Chem. Eur. J. 2005, 11, 3951 – 3958
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K. MuÇiz and C. H. Hçvelmann
[a]2D0 =À 22.3 (c=0.2 in acetone); 1H NMR (300 MHz, CDCl3, 258C,
TMS): d=1.97 (s, 3H; C(O)CH3), 2.00 (s, 3H; C(O)CH3), 2.02 (s, 3H;
C(O)CH3), 4.14–4.20 (m, 2H; CH2OAc), 4.29–4.36 (m, 1H; CHOAc),
4.77 (dd, J=3.2, 6.2 Hz, 1H; CHOAc), 5.12–5.21 (m, 1H; CHOAc),
5.26–5.29 (m, 1H; CHOB), 6.39 (dd, J=1.2, 6.1 Hz, 1H; CHOB), 7.30–
7.38 (m, 3H; CHAr), 7.64–7.68 ppm (m, 2H; CHAr); 13C NMR (75 MHz,
CDCl3): d=20.58, 20.70, 20.82, 63.29, 67.45, 67.60, 70.51, 73.90, 97.90,
128.02, 132.35, 135.18, 162.32, 169.28, 169.59, 170.65 ppm; MS (70 eV):
m/z (%): 392 (100), [M+],346 (22), 276 (9); HRMS: calcd for
C18H2110BO9: 391.1313; found: 391.1312.
77 (10); HRMS: calcd for C15H1510BO2: 236.1121; found: 236.1121. Deter-
mination of enantiomeric excess was carried out at the stage of the bis-
benzoate of the free 2-phenylpropylenediol: CHIRALCEL OB-H, n-
hexane/2-propanol, 97:3 (v/v), 1.0 mLminÀ1, retention times: 25.6 min
[(S)], 27.2 min [(R)].
(R,R)-5-Methyl-2,4-diphenyl-1,3,2-dioxaborolane (4d): This compound
was synthesised according to the general procedure B from b-methyl
styrol (0.13 mL, 1 mmol). Yield: 224 mg (0.94 mmol, 94%). [a]2D0 =À75
1
(c=0.5 in acetone); H NMR (300 MHz, CDCl3, 258C, TMS): d=1.42 (d,
J=6.2 Hz, 3H; CH3), 4.34 (dq, J=6.2, 7.5 Hz, 1H; CH3CHOB), 4.91 (d,
J=7.5 Hz, 1H; PhCHOB), 7.12–7.43 (m, 8H; CHAr), 7.77–7.81 ppm (m,
2H; CHAr); 13C NMR (75 MHz, CDCl3, 258C): d=21.17, 81.72, 86.10,
125.63, 127.86, 128.23, 128.73, 131.58, 134.98, 140.60 ppm; IR (KBr): n˜ =
3450, 3050, 3015, 3025, 3015, 1760, 1730, 1600, 1500, 1440, 1400, 1380,
1360, 1290, 1205, 1100, 1020, 780, 695, 680, 650 cmÀ1; MS (70 eV): m/z
(%): 238 (100) [M+], 223 (12), 194 (55), 105 (33), 90 (100); HRMS: calcd
for C15H1511BO2: 238.1165; found: 238.1156. Determination of enantio-
meric excess was carried out at the stage of free 1-phenylpropylenediol:
CHIRALPAK AD, n-hexane/2-propanol, 90:10 (v/v), 0.5 mLminÀ1, re-
tention times: 18.1 min [(S,S)], 21.6 min [(R,R)].
Dioxoborolane 2b from oxidation of tribenzyl glucal: This compound
was synthesised according to the general procedure A from 2,3,4-triben-
zyl-O-glucal (416 mg, 1 mmol). After column chromatography (silica gel,
ethyl acetate), 2b was obtained as a white to light purple solid (450 mg,
0.84 mmol, 84%). [a]2D0 =À34.9 (c=0.1 in acetone); 1H NMR (300 MHz,
CDCl3, 258C, TMS): d=3.64 (d, J=2.4 Hz, 1H; CHOBn), 3.71–3.75 (m,
2H; OCHCH2OBn, OCHCHHOBn), 3.88 (dd, J=4.1, 4.9 Hz, 1H;
OCHCHHOBn), 4.39 (d, J=11.3 Hz, 1H; PhCHHO), 4.47 (d, J=
12.1 Hz, 1H; CHOBn), 4.50 (d, J=10.0 Hz, 1H; PhCHHO), 4.53 (d, J=
10.0 Hz, 1H; PhCHHO), 4.55 (d, J=12.1 Hz, 1H; PhCHHO), 4.56 (d,
J=11.3 Hz, 1H; PhCHHO)H), , 4.65 (d, J=12.1 Hz, 1H; PhCHHO),
4.77 (m, 1H; CHOB), 6.02 (d, J=6.2 Hz, 1H; CHOB), 7.77–7.83 (m,
17H; CHAr), 8.19 (d, J=1.5 Hz, 2H; CHAr), 8.22 ppm (d, J=1.4 Hz, 1H;
CHAr); 13C NMR (75 MHz, CDCl3, 258C): d=69.06, 70.29, 72.12, 72.78,
73.25, 74.45, 76.81, 79.86, 98.84, 127.48, 127.50, 127.63, 127.71, 127.88,
128.12, 128.19, 128.31, 131.83, 134.95, 135.47, 137.64, 137.81 ppm; MS
(70 eV): m/z (%): 536 (100), [M+],446 (12), 356 (14); HRMS: calcd for
C33H3310BO6: 535.2405; found: 535.2513.
(R,R)-2,4,5-Triphenyl-1,3,2-dioxaborolane (4a):[20] This compound was
synthesised according to the general procedure B from stilbene (180 mg,
1 mmol). Yield: 300 mg (1.00 mmol, 99%). [a]2D0 =À70 (c=0.5 in chloro-
form); 1H NMR (300 MHz, CDCl3, 258C, TMS): d=5.35 (s, 2H;
CHOB), 7.37–7.55 (m, 13H; CHAr), 8.00 ppm (m, 2H; CHAr); 13C NMR
(75 MHz, CDCl3, 258C): d=86.96, 125.85, 127.96, 128.39, 128.82, 131.84,
135.23, 140.39 ppm; IR (KBr): n˜ =3460, 3095, 3045, 2917, 2395, 2340,
1597, 1451, 1390, 1340, 1318, 1220, 1215, 1105, 1060, 1000, 780, 775, 695,
650, 640, 510 cmÀ1; MS (70 eV): m/z (%): 300 (100), [M+], 222 (20), 194
(40), 178 (5), 167 (18), 151 (10), 107 (22), 90 (45); HRMS: calcd for
C20H1710BO2: 299.1358; found: 299.1330; HPLC data for determination of
enantiomeric excess: CHIRALCEL OD-H, n-hexane/2-propanol, 95:5
(v/v), 0.3 mLminÀ1, retention times: 13.7 min [(R,R)], 15.5 min [(S,S)].
Determination of enantiomeric excess was carried out at the stage of the
free (R,R)- and (S,S)-1,2-diphenylethylenediol: CHIRALCEL OB-H, n-
hexane/2-propanol, 90:10 (v/v), 1.0 mLminÀ1, retention times: 13.0 min
[(R,R)], 17.6 min [(S,S)].
(S,R)-4-(Methoxycarbonyl)-2,5-diphenyl-1,3,2-dioxaborolane (4e): This
compound was synthesised according to the general procedure B from
methyl cinnamate (162 mg, 1 mmol). Yield: 260 mg (0.92 mmol, 92%).
[a]2D0 =À47.4 (c=0.5 in acetone); 1H NMR (400 MHz, CDCl3, 258C,
TMS): d=3.70 (s, 3H; CO2CH3), 4.69 (d, J=6.0 Hz, 1H; PhCHOB), 5.44
(d, J=6.0 Hz, 1H; MeO2CCHOB), 7.17–7.37 (m, 8H; CHAr), 7.77–
7.81 ppm (m, 2H; CHAr); 13C NMR (100 MHz, CDCl3, 258C): d=52.69,
81.82, 82.48, 125.30, 127.92, 128.50, 128.82, 132.04, 135.22, 140.31,
170.96 ppm; IR (KBr): n˜ =3475, 3051, 3022, 2950, 2895, 2397, 2362, 1752,
1740, 1600, 1502, 1425, 1403, 1205, 1100, 1020, 997, 782, 695, 652 cmÀ1
;
MS (70 eV): m/z (%): 282 (2) [M+], 223 (6), 205 (32), 176 (70), 105 (33),
59 (100); HRMS: calcd for C16H1510BO4: 281.1097; found: 281.1087. De-
termination of enantiomeric excess was carried out at the stage of free
methyl 3-phenyl-2,3-dihydroxy propionate: CHIRALCEL OB-H, n-
hexane/2-propanol, 95:5 (v/v), 0.7 mLminÀ1, retention times: 41.6 min
[(R,S)], 46.8 min [(S,R)].
(S,R)-4-(Benzyloxycarbonyl)-2,5-diphenyl-1,3,2-dioxaborolane (4 f): This
compound was synthesised according to the general procedure B from
benzyl cinnamate (238 mg, 1 mmol). Yield: 339 mg (0.95 mmol, 95%).
1
[a]2D0 =À32 (c=0.5 in acetone); H NMR (300 MHz, CDCl3, 258C, TMS):
d=4.73 (d, J=6.2 Hz, 1H; PhCHOB), 5.18 (dd, J=12.2, 29.8 Hz, 2H;
PhCH2O2C), 5.42 (d, J=6.2 Hz, 1H; BnO2CCHOB), 7.12–7.37 (m, 8H;
CHAr), 7.81–7.84 ppm (m, 2H; CHAr); 13C NMR (75 MHz, CDCl3, 258C):
d=31.06, 67.16, 81.71, 82.34, 125.24, 127.80, 128.21, 128.36, 128.44,
128.53, 128.67, 131.90, 135.13, 140.11, 170.09 ppm; IR (KBr): n˜ =3485,
3057, 3018, 2963, 2395, 2355, 1760, 1598, 1495, 1452, 1440, 1400, 1365,
1280, 1200, 1105, 1025, 1000, 770, 705, 680, 660, 525 cmÀ1; MS (70 eV):
m/z (%): 335 (7) [M+], 238 (21), 224 (81), 205 (15), 176 (100), 105 (38),
59 (96); HRMS: calcd for C22H1910BO4: 357.1413; found: 357.1401. Deter-
mination of enantiomeric excess was carried out at the stage of the
bisbenzoate from the free benzyl 3-phenyl-2,3-dihydroxy propionate:
CHIRALCEL OB-H, n-hexane/2-propanol, 97:3 (v/v), 0.8 mLminÀ1, re-
tention times: 21.0 min [(S,R)], 24.5 min [(R,S)].
(R)-2,4-Diphenyl-1,3,2-dioxaborolane (4b):[21] This compound was syn-
thesised according to the general procedure B from styrene (0.12 mL,
1 mmol). Yield: 211 mg (0.94 mmol, 94%). [a]2D0 =À43.1 (c=0.5 in ace-
tone); 1H NMR (400 MHz, CDCl3, 258C, TMS): d=4.09 (dd, J=7.5,
9.0 Hz, 1H; CHHOB), 4.62 (dd, J=8.3, 9.0 Hz, 1H; CHHOB), 5.47 (dd,
J=7.5, 8.3 Hz, 1H; CHOB), 7.19–7.43 (m, 8H; CHAr), 7.80–7.83 ppm (m,
2H; CHAr); 13C NMR (100 MHz, CDCl3, 258C): d=73.34, 78.89, 125.56,
127.86, 128.15, 128.72, 131.63, 135.00, 141.12 ppm; MS (70 eV): m/z (%):
224 (100) [M+], 151 (18), 147 (44),107 (9), 90 (48); HRMS: calcd for
C14H1310BO2: 223.1045; found: 223.1056. Determination of enantiomeric
excess was carried out at the stage of free 1-phenylethylenediol: CHIR-
ALCEL OB-H, n-hexane/2-propanol, 90:10 (v/v), 0.5 mLminÀ1, retention
times: 16.0 min [(R)], 20.2 min [(S)].
(R)-4-(2’-Naphthyl)-2-phenyl-1,3,2-dioxaborolane (4g): This compound
was synthesised according to the general procedure B from 2-vinyl naph-
thalene (154 mg, 1 mmol). Yield: 255 mg (0.93 mmol, 93%). [a]2D0 =À68.3
(c=0.5 in acetone); 1H NMR (400 MHz, CDCl3, 258C, TMS): d=4.32
(dd, J=7.7, 9.0 Hz, 1H; CHHOB), 4.83 (dd, J=8.2, 9.0 Hz, 1H;
CHHOB), 5.79 (dd, J=7.7, 8.2 Hz, 1H; CHOB), 7.44–7.60 (m, 6H;
CHAr), 7.84–7.93 (m, 4H; CHAr), 8.00–8.04 ppm (m, 2H; CHAr);
13C NMR (100 MHz, CDCl3, 258C): d=73.24, 79.07, 123.16, 124.70,
126.18, 126.40, 127.72, 127.94, 127.97, 128.82, 131.69, 133.19, 135.06,
135.61, 138.35 ppm; MS (70 eV): m/z (%): 274 (16) [M+], 156 (80), 127
(100), 77 (21); HRMS: calcd for C18H1511BO2: 274.1165; found: 274.1161.
Determination of enantiomeric excess was carried out at the stage of free
1-(2-naphthyl)ethylenediol: CHIRALCEL OD, n-hexane/2-propanol,
90:10 (v/v), 1.0 mLminÀ1, retention times: 12.6 min [(R)], 15.7 min [(S)].
(R)-4-Methyl-2,4-diphenyl-1,3,2-dioxaborolane (4c): This compound was
synthesised according to the general procedure B from a-methyl styrol
(0.13 mL, 1 mmol). Yield: 230 mg (0.97 mmol, 97%). [a]2D0 =À154 (c=0.5
in acetone); 1H NMR (400 MHz, CDCl3, 258C, TMS): d=1.66 (s, 3H;
CH3), 4.29 (s, 2H; CH2OB), 7.16–7.41 (m, 8H; CHAr), 7.87–7.90 ppm (m,
2H; CHAr); 13C NMR (100 MHz, CDCl3, 258C): d=29.58, 78.78, 83.39,
124.15, 127.17, 127.81, 128.40, 131.50, 134.91, 146.01 ppm; IR (KBr): n˜ =
3445, 3090, 3060, 3045, 2985, 2940, 2920, 2370, 2340, 1600, 1495, 1435,
1385, 1360, 1240, 1220, 1085, 1010, 750, 690, 640 cmÀ1; MS (70 eV): m/z
(%): 238 (5) [M+], 223 (100), 162 (5), 147 (5), 119 (11), 104 (26), 91 (16),
3956
ꢄ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2005, 11, 3951 – 3958

Asymmetric Dihydroxylation
FULL PAPER
(R)-4-n-Octyl-2-phenyl-1,3,2-dioxaborolane (4h): This compound was
synthesised according to the general procedure B from decene (0.2 mL,
1 mmol). Yield: 229 mg (0.88 mmol, 88%). [a]2D0 =À39 (c=0.5 in ace-
tone); 1H NMR (300 MHz, CDCl3, 258C, TMS): d=0.89 (t, J=6.9 Hz,
3H; CH3), 1.29–1.56 (m, 12H; CH2), 1.58–1.68 (m, 1H; CHH), 1.70–1.75
(m, 1H; CHH), 3.95 (dd, J=7.1, 8.8 Hz, 1H; CHHOB), 4.42 (dd, J=7.7,
8.8 Hz, 1H; CHHOB), 4.57 (ddd, J=6.0, 7.1, 7.7 Hz, 1H; CHOB), 7.35–
7.40 (m, 2H; CHAr), 7.45–7.50 (m, 1H; CHAr), 7.81–7.83 ppm (m, 2H;
CHAr); 13C NMR (75 MHz, CDCl3, 258C): d=14.06, 22.63, 24.95, 29.21,
29.47, 29.50, 31.84, 36.17, 71.20, 77.57, 127.76, 131.33, 134.80, 162.36 ppm;
IR (KBr): n˜ =3445, 3080, 3070, 3030, 2960, 2905, 2395, 2340, 1610, 1505,
1425, 1405, 1385, 1350, 1305, 1220, 1095, 1015, 980, 970, 860, 760, 700,
650, 640 cmÀ1; MS (70 eV): m/z (%): 260 (20) [M+], 231 (5), 203 (5), 175
(10), 147 (100), 118 (36), 105 (17), 91 (20), 69 (10), 55 (11); HRMS: calcd
for C16H2511BO2: 259.1984; found: 259.1985. Determination of enantio-
meric excess was carried out at the stage of the bisbenzoate from the
free decane-1,2-diol: CHIRALCEL OB-H, n-hexane/2-propanol, 95:5
(v/v), 0.7 mLminÀ1, retention times: 13.6 min [(S)], 17.1 min [(R)].
209 (32), 197 (30), 191 (15), 165 (10), 147 (11), 105 (45), 90 (26), 77 (26),
59 (100); HRMS: calcd for C21H1911BO3: 330.1427; found: 330.1422.
HPLC data for determination of enantiomeric excess at the stage of the
free (R,R)- and (S,S)-1,2-diphenylethylenediol: CHIRALCEL OB-H, n-
hexane/2-propanol, 90:10 (v/v), 1.0 mLminÀ1, retention times: 13.0 min
[(R,R)], 17.6 min [(S,S)].
(R,R)-2-(4’-Biphenylyl)-4,5-diphenyl-1,3,2-dioxaborolane (9): This com-
pound was synthesised according to the general procedure B from stil-
bene (180 mg, 1 mmol) with 4’-biphenylyl boronic acid (237 mg,
1.2 mmol) instead of phenyl boronic acid. Yield: 369 mg (0.98 mmol,
98%). [a]2D0 =À133 (c=0.7 in acetone); 1H NMR (300 MHz, CDCl3,
258C, TMS): d=4.65 (s, 2H; CHOB), 7.04–7.17 (m, 4H; CHAr), 7.27–
7.42 (m, 9H; CHAr), 7.53–7.87 ppm (m, 6H; CHAr); 13C NMR (75 MHz,
CDCl3, 258C): d=79.15, 125.89, 126.71, 126.96, 127.28, 127.71, 127.96,
128.17, 128.87, 135.30, 140.89, 143.79 ppm; MS (70 eV): m/z (%): 377
(100) [M++1], 222 (9), 178 (4), 167 (12), 151 (5), 107 (18), 90 (25);
HRMS: calcd for C26H2111BO2: 376.1635; found: 376.1632. HPLC data for
determination of enantiomeric excess at the stage of the free (R,R)- and
(S,S)-1,2-diphenylethylenediol: CHIRALCEL OB-H, n-hexane/2-propa-
nol, 90:10 (v/v), 1.0 mLminÀ1, retention times: 13.0 min [(R,R)], 17.6 min
[(S,S)].
(8R,4S)-2-(B-Phenyl)bora-1,3-dioxo-6,7-benzo-bicyclo[3.3.2]octane
(4i):[8] This compound was synthesised according to the general proce-
dure B from indene (0.12 mL, 1 mmol). Yield: 232 mg (0.98 mmol, 98%).
[a]2D0 =+3.2 (c=0.5 in acetone); 1H NMR (400 MHz, CDCl3, 258C,
TMS): d=3.21 (dd, J=0.5, 16.9 Hz, 1H; CHHCHOB), 3.36 (dd, J=0.5,
6.7 Hz, 1H; CHHCHOB), 5.28 (ddd, J=6.6, 6.7, 16.9 Hz, 1H;
CHHCHOB), 5.81 (d, J=6.6 Hz, 1H; CHOB), 7.15–7.28 (m, 5H; CHAr),
7.33–7.38 (m, 1H; CHAr), 7.47–7.50 (m, 1H; CHAr), 7.70–7.73 ppm (m,
2H; CHAr); 13C NMR (100 MHz, CDCl3, 258C): d=39.84, 80.91, 85.01,
125.41, 126.16, 127.43, 127.72, 129.58, 131.35, 134.82, 140.41, 140.74 ppm;
IR (KBr): n˜ =3515, 3420, 3095, 3060, 3035, 2940, 2920, 2830, 1597, 1415,
1390, 1370, 1290, 1195, 1090, 1085, 1005, 980, 755, 695, 620 cmÀ1. Deter-
mination of enantiomeric excess was carried out at the stage of free in-
denediol: CHIRALCEL OB-H, n-hexane/2-propanol, 90:10 (v/v),
0.7 mLminÀ1, retention times: 12.6 min [(R,S)], 15.8 min [(S,R)].
Cyclopentane-1,2:3,4-tetrayl-1,2:3,4-bis(phenylboronate) (6):[9] This com-
pound was synthesised from cyclopentadiene (66 mg, 1 mmol) according
to Procedure A with (DHQD)2PHAL as chiral ligand. Yield: 291 mg
(95 mmol, 95%). [a]2D0 =À25 (c=0.5 in dichloromethane); 1H NMR
(300 MHz, CDCl3, 258C, TMS): d=2.51 (pst, J=6.3 Hz, 2H; CH2), 5.03
(d, J=6.3 Hz, 2H; CHOB), 5.17 (psq, J=5.8 Hz, 2H; CH2CHOB), 7.36–
7.43 (m, 4H; CHAr), 7.50–7.56 (m, 2H; CHAr), 7.79–7.85 ppm (m, 4H;
CHAr); 13C NMR (75 MHz, CDCl3): d=40.17, 79.02, 86.09, 127.56, 130.16,
131.11, 132.92, 134.63, 157.81.
Acknowledgements
This work was generously supported by the Fonds der Chemischen Indus-
trie and the Deutsche Forschungsgemeinschaft. The authors are grateful
to Prof. Dr. K. H. Dçtz for his continuous support and interest.
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[3] Additional reviews: a) C. Bolm, J. P. Hildebrand, K. MuÇiz, in Cata-
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2000, p. 299; b) H. C. Kolb, K. B. Sharpless in Transition Metals For
Organic Chemistry: Building Blocks and Fine Chemicals, Vol. 2, 2nd
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Bennani, R. K. Chadha, G. A. Crispino, W. D. Davis, J. Hartung, K.-
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58, 844.
[5] a) A. J. DelMonte, J. Haller, K. N. Houk, K. B. Sharpless, D. A. Din-
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Soc. 1994, 116, 8470; f) H. Becker, P. T. Ho, H. C. Kolb, S. Loren, P.-
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(R,R)-2-(4’-Fluorophenyl)-4,5-diphenyl-1,3,2-dioxaborolane (7): This
compound was synthesised according to the general procedure B from
stilbene (180 mg, 1 mmol) with 4’-fluorophenyl boronic acid (168 mg,
1.2 mmol) instead of phenyl boronic acid. Yield: 302 mg (0.97 mmol,
97%). [a]2D0 =À61.7 (c=0.5 in acetone); 1H NMR (300 MHz, CDCl3,
258C, TMS): d=5.26 (s, 2H; CHOB), 7.02–7.18 (m, 2H; CHArF), 7.26–
7.36 (m, 10H; CHAr), 7.88–7.93 ppm (m, 2H; CHArF); 13C NMR (75 MHz,
CDCl3, 258C): d=87.01, 115.08, 115.28, 125.84, 128.45, 128.84, 137.51 (d,
2J(C,F)=8.4 Hz), 140.21, 166.73 ppm; 19F NMR (282 MHz, CDCl3, 258C):
d=À107.82; IR (KBr): n˜ =3425, 3055, 3015, 2930, 1600, 1505, 1470, 1400,
1380, 1360, 1300, 1215, 1195, 1145, 1090, 1080, 980, 825, 775, 695, 650,
580, 520 ppm; MS (70 eV): m/z (%): 318 (71) [M+], 240 (49), 311 (36),
180 (31), 165 (35), 135 (15),105 (42), 90 (100), 77 (28); HRMS: calcd for
C20H1611BFO2: 318.1227; found: 318.1234. HPLC data for determination
of enantiomeric excess at the stage of the free (R,R)- and (S,S)-1,2-diphe-
nylethylenediol: CHIRALCEL OB-H, n-hexane/2-propanol, 90:10 (v/v),
1.0 mLminÀ1, retention times: 13.0 min [(R,R)], 17.6 min [(S,S)].
(R,R)-2-(4’-Methoxyphenyl)-4,5-diphenyl-1,3,2-dioxaborolane (8): Syn-
thesised according to the general procedure B from stilbene (180 mg,
1 mmol) with 4’-methoxyphenyl boronic acid (182 mg, 1.2 mmol) instead
of phenyl boronic acid. Yield: 314 mg (0.95 mmol, 95%). [a]2D0 =À80.1
1
(c=0.5 in acetone); H NMR (300 MHz, CDCl3, 258C, TMS): d=3.70 (s,
3H, OCH3), 5.18 (s, 2H; CHOB), 6.85 (d, J=8.7 Hz, 2H; CHArOMe),
7.18–7.29 (m, 10H; CHAr), 7.84 ppm (d, J=8.7 Hz, 2H; CHArOMe);
13C NMR (75 MHz, CDCl3): d=55.03, 86.80, 113.58, 125.81, 128.26,
128.72, 136.99, 140.46, 162.61 ppm; MS (70 eV): m/z (%): 330 (33) [M+],
Chem. Eur. J. 2005, 11, 3951 – 3958
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ꢄ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3957

K. MuÇiz and C. H. Hçvelmann
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Received: January 27, 2005
Published online: April 21, 2005
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