Reactions of (Arene) Tricarbonylchromium Complexes with Anions from Schiff Bases of α-Amino Esters: Synthesis of α-Aryl Amino Acids

References

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• General procedure: under nitrogen, at -78°C, the Schiff base 1 (10 mmol) dissolved in dry THF (15 ml) was slowly added to a suspension of LDA (10 mmo1) in dry THF (50 ml). The mixture was stirred during 30 min at this temperature and diluted with HMPA (15 ml, 10 eq). The complex 2 (10 mmo1) dissolved in THF (10 ml) was slowly added and the mixture was stirred 30 min at − 78°C and 40H at room temperature. After treatment with aqueous NH4C1, extraction with ether, the compound 3 was purified by flash chromatography (silicagel 60, eluant: ether/hexane 3/1)
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• RMN 1H (CDCl3/TMS, 100 MHz Varian, δ ppm). 3a: 3,73(s, CH3), 4,65 (s, CH), 5,35(m, 4H), 5,80(m, 1H), 7,43(AB, 2H), 7,83(AB, 2H), 8,38(s, CH). 3b: 1,83(s, CH3), 3,80(s, CH3), 5,33(m, 3H), 5,93(m, 2H), 7,50(AB, 2H), 7,86(AB, 2H), 8,38(s, CH). 3c: 1,67(s, CH3), 2,20(s, CH3), 3,76(s, CH3), 5,25(m, 3H), 5,76(m, 2H), 7,53(AB, 2H), 7,90(AB, 2H), 8,40(s, CH). 3d: 3,06(d, CH2, 1H), 3,63(d, CH2, 1H), 3,73(s, CH3), 5,26(m, 4H), 5,93(m, 1H), 6,83–7,85(m, 10H). 3e: 0,83(d, 6H), 1,66(m, CH), 2,13(br d, CH2), 3,85(s, CH3), 5,40(m, 4H), 6,00(m, 1H), 7,50(AB, 2H), 7,93(AB, 2H), 8,43(s, CH). 3f: 0,83(d, CH3), 0,96(d, CH3), 2,63(m, CH), 3,91(s, CH3), 5,33(m, 3H), 5,93(m, 2H), 7,43(AB, 2H), 7,90(AB, 2H), 8,56(s, CH)
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• The compound 3 was dissolved in ether (20 ml) and treated by a 1N HCl solution (10ml) during 12h under stirring. After extraction with ether, the aqueous layer was neutralized with a saturated solution of K2CO3 and extracted several times with ether. After drying and concentration 4 was obtained. b) After the reaction of arylation the mixture was cooled at − 78°C and iodine (10 mmol) in THF (40 ml) was added. The mixture was stirred 3h at ambient temperature, treated at 0°C with a 30% solution of K2CO3 and extracted with ether. The organic layers were washed 5 times in turn with a 5% solution of NaHSO3 and with water. After usual treatments 4 was obtained
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• RMN 1H (CDCl3/TMS, 100 MHz Varian, δ ppm). 4a: 1,86(br s, NH2), 3,70(s, CH3), 4,51(s, CH), 7,36(br s, 5H). 4b: 1,70(s, CH3), 2,08(br s, NH2), 3,71(s, CH3), 7,41(m, 5H). 4c: 1,60(s, CH3), 1,80(br s, NH2), 2,38(s, CH3), 3,70(s, CH3), 7,30(m, 5H). 4d: 1,91(br s NH2), 3,15(d, CH2, 1H), 3,65(d, CH2, 1H), 3,75(s, CH3), 7,38(m, 10H). 4e: 0,70(d, CH3), 0,83(d, CH3), 1,2–1,8(m, 3H, CH2, CH), 1,84(br s, NH2), 3,63(s, CH3), 7,33(m, 5H). 4f: 0,57(d, CH3), 0,90(d, CH3), 1,70(br s, NH2), 2,70(m, CH), 3,63(s, CH3), 7,30(m, 3H), 7,60(m, 2H)
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• However near 3d was obtained an arylated compound whose aromatic ring of the benzyl group was complexed, likely after a ligand exchange, with the initial complex. Hydrolysis of this compound led to 4d
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• RMN 1H (CDCl3/TMS, 100 MHz Varian, δ ppm) of the O arylation product: 0,77(d, CH3), 0,87(d, CH3), 1,73(m, CH), 2,30(m, CH2), 3,70(s, CH3), 4,00(m, CH), 5,40(m, 4H), 6,10(m, 1H), 7,30(AB, 2H), 7,63(AB, 2H)
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• RMN 1H (CDCl3/TMS, 100 MHz Varian, δ ppm) of the O arylation product: 0,87(d, CH3), 1,00(d, CH3), 2,40(m, CH), 3,73(s, CH3), 3,83(d, CH), 5,50(m, 4H), 6,16(m, 1H), 7,35(AB, 2H), 7,66(AB, 2H)
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