A versatile synthesis of 9-BBN derivatives from organometallic reagents and 9-(triisopropylsilyl)thio-9-borabicyclo[3.3.1]nonane

Article abstract of DOI:10.1016/S0040-4039(00)00450-0

Representative B-substituted-9-BBNs (3) are efficiently prepared from either organolithium or Grignard reagents through their addition to (TIPS)S- 9-BBN (1) which is readily available from TIPSSH and 9-BBN-H. The thermally induced collapse of the intermediate 'ate' complexes (2) produces 3 which is easily isolated in good yield and high purity. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4039(00)00450-0

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 41 (2000) 3537–3539
A versatile synthesis of 9-BBN derivatives from organometallic
reagents and 9-(triisopropylsilyl)thio-9-borabicyclo[3.3.1]nonane
John A. Soderquist ∗ and Jorge C. Justo de Pomar †
Department of Chemistry, University of Puerto Rico, Rio Piedras, PR 00931-3346, USA
Received 8 March 2000; accepted 15 March 2000
Abstract
Representative B-substituted-9-BBNs (3) are efficiently prepared from either organolithium or Grignard reagents
through their addition to (TIPS)S-9-BBN (1) which is readily available from TIPSSH and 9-BBN-H. The thermally
induced collapse of the intermediate ‘ate’ complexes (2) produces 3 which is easily isolated in good yield and high
purity. © 2000 Elsevier Science Ltd. All rights reserved.
For many important organoborane conversions (e.g. Suzuki–Miyaura coupling),1 the greater Lewis
acidity of trialkylboranes compared to more oxygenated counterparts (e.g. RB(OR0)2) can be ad-
vantageous. Among these reagents, 9-BBN derivatives (3) are often the reagents of choice because
of the robust nature of the 9-BBN moiety which functions efficiently as spectator ligation in many
such transformations.2 Hydroboration provides many of these derivatives, but for those which cannot
be prepared by this method, several organometallic routes exist, the most straightforward being the
addition of organolithium reagents to B-MeO-9-BBN in hydrocarbon solvents.3a In some cases (e.g.
R=alkynyl), the intermediate ‘ate’ complex, Li[R(MeO)-9-BBN] is very stable and the addition of Lewis
acids is required to produce 3.4 Unfortunately, with the exception of MeMgX, the analogous Grignard
process is unworkable because the intermediate complex (M=MgX) decomposes too easily leading to
di-addition (e.g. M[R2-9-BBN]) and unreacted B-MeO-9-BBN.3a These complications and others3b–d
limit the generality of the method and for a number of applications of 3, it is preferable to either prepare
∗
†
Corresponding author.
Graduate student supported by DOE-EPSCoR (DE-FC02-91ER75674).
0040-4039/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(00)00450-0
tetl 16730

3538
3 from 9-BBN-H and organocuprate reagents, or to generate 3 in situ from the exchange of B-Cl-9-BBN
with RSnR0 .2,5
3
We wish to report that (TIPS)S-9-BBN (1), which is easily prepared from 9-BBN-H and (TIPS)SH
(1:1, 135–150°C (12 h), 85%, bp 143–146°C, 0.3 torr, 11B NMR 81.7 (C6D6)),7 provides a simple entry
to 3 through both organolithium and Grignard procedures (Table 1).8 With the exception of ViMgBr, the
1:1 adducts 2 are generally formed cleanly. Simply heating 2 under vacuum liberates 3, which distills in
pure form from the mixture (Table 1).8 Acidification of the residue (HCl (aq.)) gives (TIPS)SH with a
minor amount (∼3%) of its hydrolysis product, TIPSOH.
Table 1
Representative B-R-9-BBNs (3) from 1
In contrast to the behavior of 1, the addition of BuMgBr to B-(n-PrS)-9-BBN (76.7)6 at 0°C, from 11
B
NMR analysis, gives a 1:1 mixture of unreacted B-(n-PrS)-9-BBN and MgBr[Bu2-(9-BBN)] (−18.9).
This reagent with B-(TIPSO)-9-BBN (57.1) produces ∼1:1:1 mixture of this borate complex (−18.3),
starting borane, and an intermediate complex assigned to the adduct (MgBr[(TIPSO)(Bu)-(9-BBN)]
−17.9), which is converted to B-Bu-9-BBN (87.7) upon treatment with Me3SiCl. Thus, the unique ability
of the STIPS group to stabilize 2 is critical to the success of this new route to 3.
Acknowledgements
We thank DOE (DE-FC02-91ER75674) for the financial support of this work.
References
1. Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457. (b) Matos, K.; Soderquist, J. A. J. Org. Chem. 1998, 63, 461. (c)
Suzuki, A. J. Organomet. Chem. 1999, 576, 147.
2. Pelter, A.; Smith, K.; Brown, H. C. In Borane Reagents; Academic Press Inc.: San Diego, 1988. (b) Soderquist, J. A. In
Encyclopedia of Reagents for Organic Synthesis; Paquette, L. A., Ed.; J. Wiley & Sons Ltd: London, 1995; Vol. 1, pp.
622–630.
3. Kramer, G. W.; Brown, H. C. J. Organomet. Chem. 1974, 73, 1. See also: ibid, idem 1977, 132, 9. See also: (b) Hennion,
G. F.; McCusker, P. A.; Rutkowski, A. J. J. Am. Chem. Soc. 1958, 80, 617. (c) McCusker, P. A.; Marra, J. V.; Hennion, G.

3539
F. J. Am. Chem. Soc. 1961, 83, 1924. (d) Hennion, G. A.; McCusker, P. A.; Ashby, E. C.; Rutkowski, A. J. J. Am. Chem.
Soc. 1973, 93, 2802.
4. Brown, H. C.; Sinclair, J. A. J. Organomet. Chem. 1977, 131, 163. (b) Brown, H. C.; Bhat, N. G.; Rajagopalan, S.
Organometallics 1986, 5, 816. (c) However, B-SMe derivatives give alkynylboranes without added Lewis acids upon
warming to 25°C. Pelter, A.; Hughes, R. J.; Smith, K.; Tabata, M. Tetrahedron Lett. 1976, 4385.
5. Singleton, D. A.; Martinez, J. P. J. Am. Chem. Soc. 1990, 112, 7423. (b) Whiteley, C. G. S. Afr. J. Chem. 1982, 35, 9. (c)
Soderquist, J. A. In Encyclopedia of Inorganic Chemistry; King, R. B., Ed.; J. Wiley & Sons Ltd: London, 1994; Vol. 1,
pp. 401–433.
6. Köster, R.; Seidel, G.; Boese, R. Chem. Ber. 1988, 121, 1137.
7. Soderquist, J. A.; Negron, A. Org. Synth. 1991, 70, 169. (b) Miranda, E. I.; Díaz, M. J.; Rosado, I.; Soderquist, J. A.
Tetrahedron Lett. 1994, 35, 3221.
8. Representative procedures: (RLi) To a solution of 1 (1.24 g, 4.0 mmol) in dry ethyl ether (10 mL) at −78°C was added
t-BuLi (3.4 mL, 1.6 M). After 45 min, concentration and distillation (head temp. 52–55°C, 3 torr) gave 0.50 g (72%) of 1h.
(RMgX) To a solution of 1 (1.52 g, 4.8 mmol) in dry THF (10 mL) at 0°C was added n-BuMgBr (2.75 mL, 2.0 M in THF)
dropwise. After 45 min, the system was allowed to reach 25°C, the solvents were removed in vacuo, and heating as above
(92–95°C at 5 torr) gave 0.72 g (84%) of pure 1g.