Palladium-Catalyzed, Enantioselective Formal Cycloaddition between Benzyltriflamides and Allenes: Straightforward Access to Enantioenriched Isoquinolines
General experimental procedures Reactions were conducted in dry solvents under argon atmosphere unless otherwise stated. Dry solvents were obtained from Aldrich and used without further purification. Toluene HPLC grade used for catalysis was obtained from Fisher Chemical. Pd(OAc)2 (98%) [3375-31-3] was obtained from Strem. All other chemicals were purchased in Aldrich and used without further purification. The abbreviation "rt" refers to reactions carried out at a temperature between 21-25 ºC.
... eaction mixtures were stirred using Teflon-coated magnetic stir bars. High reaction temperatures were maintained using Thermowatch-controlled heating blocks. Thin-layer chromatography (TLC) was performed on silica gel plates and components were visualized by observation under UV light, and/or by treating the plates with p-anisaldehyde, ninhydrin, phospomolybdic or potassium permanganate solutions, followed by heating. Flash chromatography was carried out on silica gel. Dryings were performed with anhydrous Na2SO4. Concentration refers to the removal of volatile solvents via distillation using a Büchi rotary evaporator followed by high vacuum. All palladium-catalyzed reactions were carried out without particular precautions to extrude moisture or oxygen. 1 H-NMR spectra were recorded at room temperature on a Varian 300 MHz or 500 MHz spectrometer in CDCl3 [using CDCl3 (for 1 H, δ = 7.26) as internal standard]. 19 F-NMR (282 MHz) spectra were recorded at room temperature on a Varian 300 MHz spectrometer in CDCl3. 13 C NMR spectra were recorded at room temperature on a Varian spectrometer in CDCl3 [using CDCl3 (for 13 C, δ = 77.160) as internal standard]. The following abbreviations were used to explain the multiplicities: s = singlet, d = doublet, t = triplet, q = quartet, m = multiplet, brs = broad singlet. Carbon types and structure assignments were determined from DEPT-NMR and two dimensional experiments (HSQC and HMBC, COSY and NOESY). NMR spectra were analyzed using MestReNova © NMR data processing software (www.mestrelab.com). Mass spectra were acquired using electrospray ionization (ESI, ion polarity positive) or atmospheric pressure chemical ionization (APCI) and were recorded at the CACTUS facility of the University of Santiago de Compostela on Bruker micrOTOF. Melting points were measured on a Büchi Melting Point B-560 apparatus. Enantiomeric ratios (er) were determined on an Agilent HPLC 1100 Series or on a Jasco SFC 4000 series using commercially available chiral colums. All racemic products were prepared under the same procedure than the chiral products but with the employment of a racemic amino acid. X-ray crystallographic analysis of 3ga and 3ba was performed at the CACTUS facility of the University of Santiago de Compostela. Amounts of isolated products are indicated independently of the scale used. S4 Allene 2a (vinylidenecyclohexane) and allene 2f (propa-1,2-dien-1-ylcyclohexane) were purchased from Aldrich. Allene 2b (5-vinylidenenonane), allene 2c ((4-methylpenta-1,2-dien-3-yl)benzene), allene 2d (1,3-diphenylpropa-1,2-diene), allene 2e (buta-1,2-dien-1-ylbenzene), allene 2g ((3-methylbuta-1,2-dien-1-yl)benzene) and allene 2h ((3-methylhepta-1,2-dien-1-yl)benzene) were prepared according procedures reported in the literature 1 . General procedure for the synthesis of benzylamines: Benzylamine, 1-phenylpropan-1-amine, diphenylmethanamine, bis(4-methoxyphenyl)methanamine, bis(3methoxyphenyl)methanamine and 2-(cyclohex-1-en-1-yl)ethan-1-amine were commercially available. All noncommercial benzylamines were synthesized with a method previously reported in literature. 2 All spectral data recorded for known compounds were in agreement with those in the corresponding literature 3 . Racemic sample Asymmetric sample (3fc, 95 : 5 e.r., 3fc', 94 : 6 e.r.) S17 (Z)-4-(cyclohexylmethylene)-1-phenyl-2-((trifluoromethyl)sulfonyl)-1,2,3,4-tetrahydroisoquinoline (3ff) Method A: (58.9 mg, 81% yield), obtained as a transparent oil. 1 H NMR (300 MHz, CDCl3) δ 7.65 (d, J = 8.0 Hz, 1H), 7.29 -7.09 (m, 7H), 6.98 (d, J = 7.1 Hz, 1H), 6.07 (s, 1H), 5.97 (d, J = 9.6 Hz, 1H), 4.60 (d, J = 16.6 Hz, 1H), 3.80 (d, J = 16.6 Hz, 1H), 2.23 -2.01 (m, 1H), 1.76 -0.89 (m, 10H). . HRMS [ESI]: m/z calculated for C23H25F3NO2S [M+H] + : 436.1553, found 436.1550. Assignment of stereochemistry based on the observed nOe between the Ha (5.97 ppm, 100%) with Hb (7.65 ppm, 11.8%). Enantioselectivity was determined by chiral SFC analysis on Phenomenex Cellulose-1 at 40 ºC (CO2 : MeOH = 98:02, 1 mL/min). Racemic sample Asymmetric sample (93 : 7 e.r.)