Allylation of Ketones with a Ferrocene‐Based Planar Chiral Lewis Acid

Abstract

-N-methyl pseudoephedrine, and (4S,5S)-(-)-4,5-dihydro-4-methoxymethyl-2-methyl-5-phenyloxazole) were purchased from Sigma Aldrich and dichlorophenylborane from Acros. All chemicals were used without further purification. (1R,2R)-(-)-N-methyl pseudoephedrine [1] , Me 3 SnAll [2] , and 1,2-Fc(SnMe 2 Cl)(BClMe) [3] were prepared according to literature procedures. Deuterated chloroform (CDCl 3 >99.7%) was obtained from Cambridge Isotope Laboratories (CIL). The solvent was stirred for several days over anhydrous CaH 2 , then degassed via several freeze pump thaw cycles and stored over 3Å molecular sieves. All reactions and manipulations were carried out under an atmosphere of prepurified nitrogen using either Schlenk techniques or an inert-atmosphere glove box (MBraun Glovebox Technology). Hydrocarbon and chlorinated solvents were purified using a solvent purification system (Innovative Technologies; alumina / copper columns for hydrocarbon solvents) and the chlorinated solvents were subsequently degassed via several freeze pump thaw cycles.All 499.9 MHz 1 H, 125.7 MHz 13 C, 186.4 MHz 119 Sn, and 160.3 11 B NMR spectra were recorded on a Varian INOVA NMR spectrometer (Varian Inc., Palo Alto, CA) equipped with a 5 mm dual broadband gradient probe (Nalorac, Varian Inc., Martinez, CA). Solution 1 H and 13 C NMR spectra were referenced internally to the solvent signals. 119 Sn and 11 B NMR spectra were referenced externally to SnMe 4 (δ = 0) and BF 3 . Et 2 O (δ = 0) in C 6 D 6 , respectively. Splittings of NMR signals are abbreviated as pst (pseudo-triplet), dpst (doublet of pseudo-triplet), nr (not resolved).Two-dimensional 1 H NOESY [4] measurements were obtained with the standard pulse sequence that was followed by a 90° pulse flanked by two 5 G/cm gradient for dephasing any residual transverse magnetization and suppressing potential artifacts, before the relaxation delay. Spectra were recorded in the phase sensitive mode by employing the TPPI improvement [5] of the States-Haberkorn-Ruben Hypercomplex method. [6] Typically, 256 t1 increments of 2K complex data points over 5.0 kHz spectral widths were collected with 32 scans per t1 increment, preceded by 16 or 32 dummy scans, and a relaxation delay of 2 s. Data sets were processed on a Sun Blade 100 workstation (Sun Microsystems Inc., Palo Alto, CA) using the VNMR software package (Varian Inc., Palo Alto, CA). In order to decrease t1 ridges arising from incorrect treatment of the first data point in the discreet Fourier transform (FT) algorithm, the spectrum corresponding to the first t1 value was divided by 2 prior to FT along t1. [7] Unshifted Sine Bell window functions were used in both dimensions. Data sets were zero-filled in the t1 dimension yielding 1K x 1K final matrices.Elemental analyses were performed by Quantitative Technologies Inc. Whitehouse, NJ. Optical rotation analysis was performed on an Autopol II polarimeter, Rudolph Research Analytical, using a tungsten-halogen light source operating at λ = 589 nm. GC analysis was performed on Hewlett Packard ...

Structure and reactivity of a planar chiral naphthylferrocenylcopper heteroaggregate

“…Rearrangements of this type with migration of protons from one Cp ring to another have been observed previously in the reaction of 1,1 0 -bis(trimethylstannyl)ferrocene with BCl 3 and other boron halides [15,20]. However, to our knowledge, they are unprecedented in the case of metalated ferrocene derivatives with more strongly polarized metal-carbon bonds.…”

“…In this regard, we are currently exploring heteronuclear bidentate Lewis acids, in which an organotin and an organoborane Lewis acid group are attached adjacent to one another at one of the Cp rings of ferrocene [15], as well as planar chiral 2-naphthylferrocenylborane species [10,16]. We describe here the preparation of a planar chiral 2-naphthylferrocenylcopper species and its reactivity toward boron halides.…”

Ferrocene-based Lewis acids and Lewis pairs: Synthesis and structural characterization

“…The 11 B NMR signal is considerably upfield shifted compared to other triorganyl boranes (in general they resonate at 60-70 ppm). [8][9][10][11][12][13] This may be due to the interaction between the boron in -BMes 2 unit and the oxygen of tolylsulphinate moiety. The absolute configuration of 2(S P , S S ) was assigned from the singlecrystal X-ray structure, which confirms diastereoselective ortho lithiation of 1 (figure 1a).…”

“…[1][2][3] Lewis acidic organoboranes play key role both as reagents and catalysts in asymmetric organic synthesis. [4][5][6][7][8][9] The rigid three-dimensional structure and inherent planar chirality of 1,2-disubstituted ferrocenes bearing non-identical atoms provide excellent chiral environment for enantioselective synthesis. 9,10 Several planar chiral ferrocene based phosphines and amines are known and their catalytic activity in the presence of transition metals is well documented.…”

“…9,10 Several planar chiral ferrocene based phosphines and amines are known and their catalytic activity in the presence of transition metals is well documented. 10 Piers, 8 Wagner 11 and Aldridge 12 have independently prepared various ferrocenylboranes and studied their applications in catalysis and as anion sensors. Jakle et al 9,13 have prepared verious ferrocenylboranes and studied their applications in anion binding as well as * For correspondence in chiral synthesis.…”