reduced pressure to give 3-tert-butoxycarbonyl-4-phenylpent-
2-en-2-yl trifluoromethanesulfonate (8.94 g, 85%); Rf [EtOAc–
light petroleum (bp 40–60 °C), 20:80] 0.77; nmax (film)/cm21
1721 (CNO) and 1602 (Ph); dH(250 MHz; CDCl3) 7.3–7.2 (5H,
m, Ph), 3.86 (1H, q, J 7.3, PhCH), 2.1 (3H, s, MeCNC), 1.57
(3H, d, J 7.2, MeCH) and 1.31 (9H, s, But). The triflate was
unstable and had to be used in the next step without further
characterisation. The triflate (8.94 g, 22.7 mmol) was stirred in
TFA (10 cm3) for 40 min at room temperature. The excess TFA
was removed under reduced pressure to give a light yellow–
brown solid, which was dissolved in acetone (50 cm3). K2CO3
(7.3 g, 53.4 mmol) was added and the reaction mixture refluxed
for 4 h, cooled, poured into water and extracted with Et2O. The
extract was washed with dilute HCl (50 cm3), water (50 cm3)
and brine (50 cm3), dried (MgSO4), and evaporated under
reduced pressure. The residue was chromatographed [SiO2,
light petroleum (bp 40–60 °C)] to give the 4-phenylpent-2-yne9
14c (2.97 g, 77% from the keto ester); Rf [EtOAc–light
petroleum (bp 40–60 °C), 10:90] 0.85; nmax(film)/cm21 1450
(Ph); dH(250 MHz; CDCl3) 7.4–7.2 (5H, m, Ph), 3.72 (1H, m,
PhCH), 1.88 (3 H, d, J 2.5, MeC·C) and 1.47 (3H, d, J 7.2,
MeCH); dC(250 MHz; CDCl3) 1442, 128.4+, 126.8+, 126.4+,
82, 77.52, 31.9+, 24.6+ and 3.6+ (+ indicates methyl or
methine and 2 indicates methylene or quaternary carbon).
We thank Avra Laboratories, Hyderabad, for a maintenance
grant (C. R.).
Notes and references
1 I. Fleming and J. Harley-Mason, J. Chem. Soc., 1963, 4771 and 4778;
E. J. D. Brown and J. Harley-Mason, J. Chem. Soc., 1966, 1390; I.
Fleming and C. R. Owen, J. Chem. Soc. (C), 1971, 2013.
2 I. Fleming and C. R. Owen, J. Chem. Soc. (B), 1971, 1293.
3 T. W. Bentley, in The Chemistry of Sulphonic Acids, Esters and their
Derivatives, ed. S. Patai and S. Rappoport, Wiley, Chichester, 1991, pp.
671–696.
Scheme 4 Reagents and conditions: i, Meldrum’s acid, Py, CH2Cl2, 0 °C ?
rt, 3 h; ii, ButOH, toluene, reflux, 4 h; iii, Ph(CH2)2CHO, TiCl4, Py, THF,
rt, 16 h; iv, H2, Pd/C, MeOH, rt, 12 h; v, NaH, Et2O, 0 °C, 1 h, then Tf2O,
0 °C ? rt, 2 h; vi, TFA, rt, 30 min; vii, K2CO3, Me2CO, reflux, 4–5 h; viii,
cyclohexanone, TiCl4, Py, CH2Cl2, rt, 16 h; ix, PhCHO, c-C5H10NH, EtOH,
5 °C, 14 h; x, Ph2CuLi, THF, 278 °C, 1 h; xi, Me2CuLi, THF, 278 °C, 1
h; xii, Tf2O and several other bases: KH, 2,6-di-tert-butylpyridine, etc.
4 K. Takeuchi, K. Ikai, T. Shibata and A. Tsugeno, J. Org. Chem., 1988, 53,
2852.
5 A. Streitwieser, Jr., C. L. Wilkins and E. Kiehlmann, J. Am. Chem. Soc.,
1968, 90, 1598. See also: M. G. Ahmed, R. W. Alder, G. H. James, M. L.
Sinnott and M. C. Whiting, J. Chem. Soc., Chem. Commun., 1968; 1533;
D. N. Kevill and G. M. Lin, Tetrahedron Lett., 1978, 949; J. F. Garrity
and J. W. Prodolliet, Tetrahedron Let., 1982, 23, 417.
6 D. N. Kevill, K. C. Kolwyck, D. M. Shold and C.-B. Kim, J. Am. Chem.
Soc., 1973, 95, 1065.
7 S. Benetti, R. Romagnoli, C. De Risi, G. Spalluto and V. Zanirato, Chem.
Rev., 1995, 95, 1065.
8 J. Boivin, L. ElKaim, P. G. Ferro and S. Z. Zard, Tetrahedron Lett., 1991,
32, 5321; J. Boivin, S. Huppe´ and S. Z. Zard, Tetrahedron Lett., 1995, 36,
5737; J. Boivin, S. Huppe´ and S. Z. Zard, Tetrahedron Let., 1996, 37,
8735.
Scheme 5
9 J. C. Gilbert, D. H. Giamalva and U. Weerasooriya, J. Org. Chem., 1983,
48, 5251.
and quenched carefully with water and extracted with Et2O (2 3
60 cm3). The extract was washed with saturated NaHCO3 (60
cm3) and brine (60 cm3), dried (MgSO4) and evaporated under
Communication 9/01921I
1114
Chem. Commun., 1999, 1113–1114