A new highly stereoselective rearrangement of acyclic tertiary organoboranes: An example of highly stereoselective remote C - H activation [3]

Full text of DOI:10.1021/ja9843977

6940
J. Am. Chem. Soc. 1999, 121, 6940-6941
Scheme 1
A New Highly Stereoselective Rearrangement of
Acyclic Tertiary Organoboranes: An Example of
Highly Stereoselective Remote C-H Activation
Hamid Laaziri, Lars O. Bromm, Fre´de´ric Lhermitte,
Ruth M. Gschwind, and Paul Knochel*
Fachbereich Chemie der Philipps-UniVersita¨t Marburg
Hans-Meerwein Strasse, D-35032 Marburg, Germany
ReceiVed December 22, 1998
The activation of allylic C-H bonds is an important reaction,
which has attracted much attention. Most results have been
obtained with cyclic systems.1 Recently, we have shown that an
efficient allylic C-H activation can be formally realized by the
hydroboration of tetrasubstituted cycloalkenes with BH3 in THF
followed by a smooth thermal rearrangement.2,3 We are pleased
to report that this rearrangement can be performed with acyclic
tetrasubstituted olefins and that it is opening a new way for the
acyclic control of two adjacent carbon centers. In the course of
this study, we have also found a new remote C-H activation
allowing a unique functionalization at a carbon center in position
6.
Preliminary results have shown that the hydroboration of 1,1-
diphenyl-2-methylpropene (1) with BH3 in THF furnishes an
intermediate tertiary organoborane, which rearranges at 50 °C
within 60 h, providing the primary organoborane 2. After
oxidative workup (30% H2O2, NaOH), 3,3-diphenyl-2-methyl-
propanol (3) can be isolated in 92% yield showing that mild
thermic conditions are sufficient to induce a complete rearrange-
ment (Scheme 1).
Scheme 2
Next, we have examined the hydroboration of Z- and E-2,3-
dimethylstilbene (4).4 The treatment of E-4 and Z-4 with BH3‚
THF and subsequent heating at 70 °C for 12 h furnishes
stereoselectively the syn- and anti-organoboranes 5, which after
oxidative workup provide the corresponding alcohols syn-6 and
anti-6 in 90% yield and dr > 99.5% (Scheme 1). This high
diastereoselectivity can be explained by assuming a dehydrobo-
ration-rehydroboration mechanism, in which the intermediate
borane-olefin complex of type 7 never dissociates (Scheme 1).
The resulting organoboranes syn-5 and anti-5 can be converted
to various organic products (Scheme 2).
Thus, the reaction of syn-5 with BCl3 (4 equiv) in CH2Cl2
followed by the reaction with benzyl azide5 furnishes the amine
syn-8a in 80% yield.6 The organoborane syn-5 is converted to
the corresponding diethylborane derivative by bubbling ethylene
(excess) through the reaction mixture. This compound undergoes
a smooth transmetalation7 to the corresponding zinc derivative
by reaction with diethylzinc (10 equiv, 0 °C, 3 h). This mixed
diorganozinc can be further converted to the corresponding zinc-
copper derivative by the addition of CuCN‚2LiCl8 and reacted
with allyl bromide, leading to the desired allylated product syn-
8b in 72% yield.9 Its reaction with 2-bromo-1-phenylacetylene
(1) (a) Janowicz, A. H.; Bergman, R. G. J. Am. Chem. Soc. 1982, 104,
352. (b) Ryabov, A. D. Chem. ReV. 1990, 90, 403. (c) Adam, W.; Nestler, B.
Angew. Chem., Int. Ed. Engl. 1993, 32, 733. (d) Murai, S.; Kakiuchi, F.; Sekine,
S.; Tanaka, Y.; Kamatani, A.; Sonoda, M.; Chatani, N. Nature 1993, 366,
529. (e) Arndtsen, B. A.; Bergman, R. G. Science 1995, 270, 1970. (f) Crabtree,
R. H. Chem. ReV. 1995, 95, 987. (g) Rispens, M. T.; Zondervan, C.; Feringa,
B. L. Tetrahedron: Asymmetry 1995, 6, 661. (h) Sonoda, M.; Kakiuchi, F.;
Chatani, N.; Murai, S. J. Organomet. Chem. 1995, 504, 151. (i) Trost, B. M.;
Imi, K.; Davies, I. W. J. Am. Chem. Soc. 1995, 117, 5371. (j) Williams, N.
A.; Uchimaru, Y.; Tanaka, M. J. Chem. Soc., Chem. Commun. 1995, 1129.
(k) Alaimo, P. J.; Arndtsen, B. A.; Bergman, R. G. J. Am. Chem. Soc. 1997,
119, 5269. (l) Grigg, R.; Savic, V. Tetrahedron Lett. 1997, 38, 5737. (m)
Jun, C.-H.; Lee, D.-Y.; Hong, J.-B. Tetrahedron Lett. 1997, 38, 6673. (n)
Luecke, H. F.; Bergman, R. G. J. Am. Chem. Soc. 1997, 119, 11538.
(2) Lhermitte, F.; Knochel, P. Angew. Chem., Int. Ed. 1998, 37, 2460.
(3) (a) Wood, S. E.; Rickborn, B. J. Org. Chem. 1983, 48, 555. (b) Field,
L. D.; Gallagher, S. P. Tetrahedron Lett. 1985, 26, 6125. (c) Parks, D. J.;
Piers, W. E. Tetrahedron 1998, 54, 15469.
(6) Typical procedure for the amination. To a solution of (Z)-2,3-diphenyl-
2-butene (Z-4) (230 mg, 1.1 mmol) in THF (5 mL) at room temperature was
added BH3‚THF (2.2 mL, 2.2 mmol, 1 M). The resulting solution was heated
at reflux for 16 h. After cooling to room temperature, the solvent and excess
of borane were removed under vacuum (rt, 0.1 mmHg, 45 min). The residue
was dissolved in CH2Cl2 (5 mL). BCl3 (4.4 mL, 4.4 mmol, 1 M) was added
at 0 °C. The mixture was warmed to room temperature and was stirred for 2
h. The solvent and excess of BCl3 were removed under vacuum (rt, 0.1 mmHg,
45 min) The resulting residue was dissolved in CH2Cl2 (5 mL), and benzyl
azide (160 mg, 1.2 equiv) was added at 0 °C. The mixture was warmed to
room temperature and was stirred for 1 h. The resulting mixture was quenched
with an aqueous 3 M NaOH solution and was extracted with Et2O. The
combined organic layers were dried (MgSO4) and concentrated. Flash-
chromatographical purification of the residue (n-pentane: ether 7:3) afforded
the desired product syn-8a (280 mg, 80%) as a clear oil.
(4) Andersson, P. G. Tetrahedron Lett. 1994, 35, 2609.
(7) Langer, F.; Schwink, L.; Devasagayaraj, A.; Chavant, P.-Y.; Knochel,
P. J. Org. Chem. 1996, 61, 8229.
(8) Knochel, P.; Yeh, M. C. P.; Berk, S. C.; Talbert, J. J. Org. Chem. 1988,
53, 2390.
(5) (a) Suzuki, A.; Sono, S.; Itoh, M.; Brown, H. C.; Midland, M. M. J.
Am. Chem. Soc. 1971, 93, 4329. (b) Chavant, P.-Y.; Lhermitte, F.; Vaultier,
M. Synlett 1993, 519.
10.1021/ja9843977 CCC: $18.00 © 1999 American Chemical Society
Published on Web 07/09/1999

Communications to the Editor
J. Am. Chem. Soc., Vol. 121, No. 29, 1999 6941
Scheme 3
Scheme 4
provides the cross-coupling product syn-8c in 51% yield, and its
benzoylation with PhCOCl furnishes as sole product the diaste-
reomerically pure ketone syn-8d in 52% yield. Similarly, the
organoborane anti-5 furnished under the same reaction conditions
anti-8a (78%), anti-8b (68%), and anti-8d (52%).
By using exocyclic tetrasubstituted olefins such as the cyclo-
pentene derivative 9 the migration in the five-membered ring is
the only observed reaction pathway leading exclusively to the
trans-benzylamine 10 after treatment of the intermediate orga-
noborane 11 with BCl3 followed by benzyl azide (Scheme 3).5,10
Finally, we have observed a remarkable intramolecular C-H
activation,11 which occurred with the sterically hindered tetra-
substituted olefins 12 and 13. The initial hydroboration of 12 is
leading to 14. Then, a diastereoselective insertion into the ortho-
C-H bond of a phenyl ring occurs at 50 °C, affording the borane
15, which is oxidized with H2O2/NaOH providing the hydrox-
yphenol 16 as only one diastereoisomer.12
Similarly, the tert-butyl-substituted olefin 13 furnishes after
initial hydroboration the organoborane 17, which gives the six-
membered intermediate organoborane via regio- and stereoselec-
tive C-H insertion reaction (40 °C, 72 h). After oxidation, the
diol 19 is obtained in 90% yield as only one diastereoisomer
(Scheme 4).13
In summary, we have shown that the thermic rearrangement
of tertiary organoboranes readily obtained by the hydroboration
of tetrasubstituted olefins affords a variety of primary organobo-
ranes corresponding formally to an allylic functionalization of
the starting olefin. The high stereoselectivity of the migration
should make this reaction very useful for the stereoselective
synthesis of open-chain products. Applications of these orga-
noborane rearrangements are currently being actively investigated
in our laboratories.
(9) Typical procedure for a transmetalation to the zinc organometallic and
allylation. To a solution of (Z)-1,3-diphenyl-2-butene (Z-4) (416 mg, 2.0 mmol)
in THF (10 mL) at room temperature was added BH3‚THF (4 mL, 4 mmol,
1 M). The resulting solution was heated at reflux for 16 h. After cooling to
room temperature, the solvent and excess of borane were removed under
vacuum (rt, 0.1 mmHg, 1 h). The residue was taken up in THF (10 mL) and
treated with ethylene for 0.5 h. After the solvent was removed under vacuum,
Et2Zn (1 mL) was added at 0 °C, and stirring was continued for 3 h. The
excess of Et2Zn was removed under vacuum, and the residue was diluted
with THF (10 mL). The resulting mixture was cooled to -78 °C, and a solution
of CuCN‚2LiCl (0.4 mL, 0.2 equiv, 1 M) was slowly added. The mixture
was allowed to warm to -60 °C, and allyl bromide (2 mL) was added. The
resulting mixture was warmed to room temperature, stirred for 1 h, and
quenched with a 5% aqueous HCl solution. After extraction with Et2O, the
combined organic phases were dried (MgSO4), and the solvents were
evaporated. Flash-chromatographical purification of the residue (n-pentane)
afforded the desired product syn-8b (361 mg, 72%) as a clear oil.
Acknowledgment. This work was supported by the Deutsche
Forschungsgemeinschaft (SFB 260, Leibniz program). We thank the
BASF AG (Ludwigshafen), Chemetall (Frankfurt), and Degussa AG
(Hanau) for the generous gift of chemicals.
Supporting Information Available: Spectral data for compounds
3, syn-6, anti-6, 8, 10, 16, 19, and A12 (PDF). This material is available
free of charge via the Internet at http://pubs.acs.org.
JA9843977
(10) The relative stereochemistry of 11 and 10 has been proven by
performing an oxidation (H2O2/NaOH) of 11, leading to the corresponding
trans-2-isopropylcyclopentanol as shown by comparison with the literature
spectra: Schneider, H.-J.; Nguyen-Ba, N.; Thomas, F. Tetrahedron 1982, 38,
2327.
(13) The regioselectivity of the C-H activation has been determined by
NMR analysis. The complete proton and carbon assignment was done by a
combination of COSY, HMQC, and HMBC spectra (Croasmun, W. R.;
Carlson, R. M. K. Two-Dimensional NMR Spectroscopy; VCH Publishers
Inc.: New York, 1994). The HMBC experiment can be used to connect proton
spin systems that are interrupted by nonprotonated atoms. Owing to the
observed HMBC cross-peaks (e.g., H9/C4, H3/C1, H4/C9, and H3/C6) the linkage
positions of the substituents of 19 could be identified. Again, the relative
stereochemistry of 19 is obtained after conversion to the cyclic ether B (1.3
equiv DEAD, 1.0 equiv Ph3P, THF, 3 h, rt, 75%). The absence of an observable
coupling constant between Ha and Hb indicates a very rigid conformation in
the substituted part of B with an axial/equatorial combination of Ha/Hb.
(11) Some remote C-H activations of organoboranes have been de-
scribed: (a) Ko¨ster, R.; Larbig, W.; Rotermund, G. W. Liebigs Ann. 1965,
682, 21. (b) Ko¨ster, R.; Rotermund, G. Angew. Chem. 1960, 72, 563. (c)
Ko¨ster, R.; Benedikt, G.; Fenzl, W.; Reinert, K. Liebigs Ann. 1967, 702, 197.
(12) The relative stereochemistry of 16 is obtained by converting it to the
cyclic ether A (1.3 equiv DEAD, 1.0 equiv Ph3P, THF, 12 h, rt, 79%). The
observed long-range coupling constant 4J(Hb,Hd) ) 1.3 Hz shows a W
3
conformation of Hb and Hd, the large coupling constant J ) (Ha,Hc) ) 11.2
Hz, the diaxial combination of Ha and Hc.