Stereoselective 1,4-Silaboration of 1,3-Dienes Catalyzed by Nickel Complexes

Abstract

The silicon−boron bond of (dimethylphenylsilyl)pinacolborane was stereoselectively added to acyclic 1,3-dienes in a 1,4-fashion to give (Z)-4-boryl-1-silyl-2-alkene derivatives in the presence of a Ni(0) catalyst generated from Ni(acac) 2 and diisobutylaluminum hydride. 1,4-Silaboration of cyclic 1,3-dienes required the use of cyclohexyldiphenylphosphine with the Ni(0) catalyst to afford cis-4-boryl-1-silyl-2-cycloalkene derivatives in high yields with high stereoselectivities.Transition-metal catalyzed insertion reactions of carboncarbon multiple bonds to inter-element σ-bonds such as SiSi, 1 Si-Sn, 2 and B-B 3 have provided powerful methods for the preparation of organometallic compounds containing multiple metallic elements in regio-and stereodefined fashions. The synthetic applications of these organometallic compounds have been extensively explored. 4,5 We have reported regioselective additions of the siliconboron bond of silylboranes to alkynes 6 and alkenes, 7 which are catalyzed by palladium and platinum complexes. Moreover, silaboration of 1,3-dienes was found to be catalyzed by a platinum complex, giving 1,4-conjugate adducts as a 1:1 mixture of the corresponding Z-and E-isomers. 8 Re-(1) (a) Horn, K. A. Johann, T. R. F.; Marder, T. B.; Norman, N. C.; Orpen, A. G.; Peakman, T. M.; Quayle, M. J.; Rice, C. R.; Scott, A. J. J. Chem. Soc., Dalton Trans. 1998, 1431 and references therein. (4) For recent reviews on the synthetic utilization of organosilicon compounds, see: (a) Langkopf, E.; Schinzer, D. Chem. ReV. 1995, 95, 1375. (b) Fleming, I.; Barbero, A.; Walter, D. For examples of the use of bis-silylation for stereoselective organic synthesis, see: (a) Murakami, M.; Suginome, M.; Fujimoto, K.; Nakamura, H.; Andersson, P. G.; Ito, Y.

Enantioselective Platinum‐Catalyzed Silicon‐Boron Addition to 1,3‐Cyclohexadiene

“…Spectral data were in accordance with those published. [7] Figure 5. Reactions performed in toluene at 110 8C.…”

“…Ito and coworkers demonstrated that catalysts based on nickel require electron-rich phosphines for the addition reaction to be efficient. [7] Thus, while a catalyst prepared from cyclohexyldiphenylphosphine and Ni(acac) 2 /DIBALH resulted in 99% yield after 24 h at 80 8C, reactions using triphenylphosphine as ligand did not afford any product under the same conditions. We found that even at 110 8C merely 16% conversion was observed and that the more reactive catalyst, containing cyclohexyldiphe- nylphosphine, probably degraded at this higher temperature, as suggested by the low conversion observed (7%).…”

“…[6] In the presence of a Ni catalyst, regioselective 1,4-addition gave the pure Z-olefin. [7] The stereochemistry of the addition to 1,3-cyclohexadiene (1) was shown to be dependent on the nature of the catalyst. Additions to 1,3-cyclohexadiene and 1,3-cycloheptadiene afforded cisaddition products when Ni(acac) 2 /DIBALH/PCyPh 2 was used as catalyst precursor, whereas exchange of the ligand for dimethylphenylphosphine resulted in a 60/40 mixture of the cis-and trans-isomers in the addition to 1,3-cyclohexadiene.…”

“…[7] We next turned to exploring chiral ligands. In order to enable determination of the degree of enantioselectivity, the product 3 was oxidized with aqueous H 2 O 2 /NaOH in THF to yield 4, a process known to take place with retention of configuration.…”

Silylboranes as New Tools in Organic Synthesis

“…38 We finally found that nickel catalyst promoted stereoselective 1,4-silaboration of 22a. 39 In the presence of a nickel catalyst generated in situ from Ni(acac) 2 with DIBAH, the reaction proceeded at 80°C, giving (Z)-1-boryl-2,3-dimethyl-4-silyl-2-butene 23a in high yield with complete Z selectivity (Entry 3). The reaction of isoprene (22c) and 2-methyl-1,3-pentadiene (22d) afforded the corresponding 1,4-adducts as a mixture of regioisomers (Entries 5 and 6).…”