9-Borabicyclononane (9-BBN) has been utilized to protect functionalized amino acids for potential chemoselective side chain manipulation. The 9-BBN group imparts organic solubility to otherwise hydrophilic molecules and is tolerant of a wide range of reaction conditions. The high degree of solubility of these molecules in THF is particularly noteworthy. It is cleaved with either aqueous HCl or by exchange with ethylenediamine in methanol. [reaction: see text]
5431exchangeable), 1.8-2.1 (5 H, complex m), 2.1-2.6 (4 H, complex m), 3.15-3.3(4H,m),3.4(4H,t,J=1.5Hz),4.0(1H,t),4.58(1H,d, J = 3 Hz); MS, exact mass calcd for C,,H2,0S4 (M' + 1) 309.048, found 309.047.Keto Thiolactol 27. To a solution of oxa-tricyclic ketone 13 (50 mg, 0.36 mmol) and 1,2-ethanedithiol (30 kL, 0.36 mmol) in THF (1 mL) was added at -78 O C 1 M ZnCl, in THF (2% equiv). The mixture was slowly warmed to -10 O C , the reaction was quenched with 25% aqueous ammonium acetate, and the solution was extracted with Et20. The organic layer was dried and evaporated. The residue was flash chromatographed on silica gel, eluting with 20% EtOAc/hexane to afford 27 (53 mg, 64%) as an oil: 'H NMR (250 MHz, CDCI,) 6 1.65-1.8 (3 H, complex m), 2.1-2.25 (1 H, m), 2.3-2.42 (1 H, m), 2.6 (1 H, dd, J = 14, 2 Hz), 2.7-3.1 (8 H, complex m), 4.25 (1 H, s(b)), 5.4 (1 H, s(b)).Ketone 28. To a solution of 27 (23 mg, 0.10 mmol) in CH,CI, (1 mL) was added, at room temperature, boron trifluoride etherate (2% equiv) and the solution was stirred for 10 min. The mixture was quenched with 25% aqueous ammonium acetate, extracted with CH,C12, dried, and evaporated to afford 28 (20 mg, 87%): 'H NMR (250 MHz, CDCI,) 6 1.6 (1 H, s(b), exchangeable), 1.65-1.9 (4 H, complex m), 2.0-2.15 (1 H, m), 3.5 ( 1 H, dd, J = 12, 9 Hz), 3.65 (1 H, dd, J = 12, 3 Hz), 3.7-3.85 (2 H, m), 3.15 (4 H, s(b)), 4.2 (1 H, t), 4.52 (1 H, d, J = 4 Hz); MS, exact mass calcd for C,0H1702S2 (M' + 1) 233.067, found 233.067. Ketone 29a. A solution of oxa-tricyclic ketone 14 (358 mg, 2.18 mmol) and 1,2-ethanedithiol (0.21 mL, 2.18 mmol) in THF (6 mL) was cooled to -78 O C and TiCI4 (5 fiL, 0.044 mmol) added. The mixture was warmed to room temperature for 30 min and finally heated to 50 O C for 48 h. The reaction mixture was quenched with 25% aqueous ammonium acetate, extracted with ether, dried, and evaporated. The residue was flash chromatographed on silica gel, eluting with 40% EtOAc/hexane to afford 29a (460 mg, 82%) (substantial amount of hemiacetal 29b): 'H NMR (250 MHz, CDCI3) 6 1.35 (3 H, s), 1.4-2.3 (11 H, complex m), 3.0 (1 H, s, exchangeable), 3.15-3.25 (4 H, m), 4.52 (1 H, d, J = 4 Hz); MS, exact mass calcd for CI2Hl90SZ (M' + 1 -H,O) 243.088, found 243.088. Registry No. HS(CH2),SH, 540-63-6; methyl 3,4-dihydro-2H-pyran-2-acetate, 109390-70-7; sodium 3,4-dihydro-2H-pyran-2-acetate, 109390-71-8; ethyl frans-3-(3,4-dihydro-2H-pyran-2-yl)acrylate, 76919-60-3; ethyl cis-3-(3,4-dihydro-2H-pyran-2-yl)acrylate, 109390-73-0; 3-(3,4-dihydro-2H-pyran-2-yl)propanal, 109390-91-2; ethyl trans-5-(3,4-dihydro-2H-pyran-2-yl)-2-pentenoate, 109390-92-3; ethyl trans-5-(3,4-dihydro-2-methyl-2H-pyran-2-yl)-2-pentenoate, 109391-01-7; ethyl trans-3-(3,4-dihydro-2-methyl-2H-pyran-2-yl)acrylate, 109390-96-7; ethyl cis-3-(3,4-dihydro-2-methyl-2H-pyran-2-yl)acrylate, 109390-97-8; methyl 4-(3,4-dihydro-2-methyl-2H-pyran-2-yl)butanoate, 10939 1-00-6.Supplementary Material Available: X-ray crystal structure analysis of 25 and tables of functional coordinates and temperature factors, bon...
A series of -cyanoaminosilanes have been found to act as azomethine ylide equivalents. Treatment of these compounds with silver fluoride in the presence of electron-deficient alkynes and olefins gives substituted pyrroles and pyrrolidines in high yield. It was found that A-benzyl-TV-(cyanomethyl) -N-[ (trimethylsilyl)methyl] amine undergoes stereospecific cycloaddition with dimethyl fumarate and maléate. The stereospecificity of the reaction is consistent with a concerted cycloaddition reaction. The cycloaddition behavior of an unsymmetrically substituted -cyanosilylamine with methyl propicíate was also examined and found to react with high overall regioselectivity.The synthetic utility of cyanoaminosilanes as azomethine ylide equivalents was demonstrated by the preparation of a Reniera isoindole alkaloid. The key step in the synthesis involved the reaction of 2-methyl-3-methoxyquinone with iV-methyl-Ai-(cyanomethyl)-iV-[(trimethylsilyl)methyl]amine in the presence of silver fluoride to give 2,5dimethyl-6-methoxy-2H-isoindole-4,7-dione in good yield.
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