AN IMPROVED PREPARATION OF 3-(5-BENZOFURANYL)-L-ALANINE

REFERENCES

• Behrens , C. , Nielsen , J. N. , Fan , X.-J. , Doisy , X. , Kim , K.-H. , Praetorius-Ibba , M. , Nielsen , P. E. and Ibba , M. 2000 . Tetrahedron , 56 : 9443
   Google Scholar
• Morera , E. and Ortar , G. 2000 . Bioorg. Med. Chem. Lett. , 10 : 1815 and references cited therein.
   PubMed Web of Science ®Google Scholar
• Rossi , R. , Carpita , A. and Bellina , F. 1995 . Org. Prep. Proced Int. , 27 : 127
   Web of Science ®Google Scholar
• Crisp , G. T. and Gore , J. 1997 . Tetrahedron , 53 : 1523
   Web of Science ®Google Scholar
• Kundu , N. G. , Pal , M. , Mahanty , J. S. and De , M. 1997 . J. Chem. Soc. Perkin 1 , : 2815 (b) A. Arcadi, S. Cacchi, M. Del Rosario, G. Fabrizi and F. Marinelli, J. Org. Chem., 61, 9280(1996). (c) S. Torii, L. H. Xu and H. Okumoto, Synlett, 515(1992). (d) A. Arcadi, F. Marinelli and S. Cacchi, Synthesis, 749(1986)
   Google Scholar
• Morera , E. and Ortar , G. 2001 . Synth. Commun. , 31 : 2215
   Google Scholar
• Barton , T. J. and Groh , B. L. 1985 . J. Org. Chem. , 50 : 158 1 o-Alkynylphenols are known to cyclise under basic conditions (refs. 5a,b), but some authors have reported that the reaction does not proceed to an appreciable extent without transition metals catalysis (ref. 5c). Indeed, we found that lb could be converted into 2a in 44% yield by treatment with Et3N (2 equivalents) and a catalytic amount of Pd(OAc)2 (5 mol%) in MeOH at 45° for 4.5 h. 2a: oil; ‘α’D +38° (c 1.0, CHCl3); IR (CHCl3): 3437, 2953, 2927, 1740, 1707, 1498, 1368, 1252, 1164 crn−1; 1H NMR (CDCl3): δ 0.34 (9H, s, SiMe3), 1.41 (9H, s, t-Bu), 3.17 (2H, m, β-CH2), 3.71 (3H, s, CO2Me), 4.59 (1H, m, α-CH), 4.97 (1H, d, J = 5.6 Hz, NH), 6.90 (1H, d, J = 0.6 Hz, ArH), 7.02 (1H, dd, J = 8.5, 1.6 Hz, ArH), 7.31 (1H, br s, ArH), 7.41 (1H, d, J = 8.5 Hz, ArH); 13C NMR: δ 1.83, 30.12, 39.95, 53.99, 56.62, 81.72, 113.04, 117.68, 123.28, 127.44, 130.23, 131.71, 157.02, 159.23, 166.00, 174.28. Anal. Calcd for C20H29NO5Si: C, 61.35; H, 7.47; N, 3.58. Found: C, 61.25; H, 7.55; N, 3.65 2-(Trimethylsilyl)benzofurans have been previously obtained by flash vacuum pyrolysis of o-‘(trimethylsilyl)ethynyl’ phenols: and by metallation of benzofurans followed by quenching with Me3SiCl ‘M. Gill, Tetrahedron, 40, 621(1984)’
   Google Scholar