G. Smitha, Ch. S. Reddy / Tetrahedron 59 (2003) 9571–9576
9575
to internal TMS, and J values are quoted in Hz. IR spectra
were obtained neat, and only the most significant absorp-
tions in cm21 are indicated and the molecular ions and/or
base peaks in MS are given.
calcd for C21H34O5Si: C, 63.92; H, 8.69. Found: C, 63.84;
H, 8.62.
4.2.6. (4-Methyl phenyl)methylene bis(2,2-dimethyl pro-
panoate (14c). Colourless oil which upon standing at room
1
4.2. General procedure for the preparation of gem-
diacetates and dipivalates
temperature to give colourless crystals, mp 32–358C; H
NMR (CDCl3): 7.65 (s, 1H), 7.4 (d, J¼8 Hz, 2H), 7.22 (d,
J¼8 Hz, 2H), 2.4 (s, 3H), 1.24 (s, 18H); 13C NMR (CDCl3):
176.2, 133.9, 133.4, 128.1, 126.3, 88.8, 38.8, 26.8, 21.4; IR
(Neat): 2974, 1756, 1282, 1115, 928 cm21; MS (m/z): 306
(Mþ). Anal. calcd for C18H26O4: C, 70.56; H, 8.55. Found:
C, 70.52; H, 8.57.
To a stirred solution of aldehyde (1 mmol) in acetic
anhydride or pivalic anhydride (3 mmol) was added ZrCl4
(5 mol%) and the reaction mixture stirred at room
temperature for the given time. After completion of the
reaction (TLC), the mixture was diluted with EtOAc,
washed with 10% NaHCO3 solution, brine, dried over
Na2SO4, evaporated and the crude product purified by
column chromatography on silica gel to give the corre-
sponding gem-diacetates or dipivalates in excellent
yields.
4.2.7. (4-Bromo phenyl)methylene bis(2,2-dimethyl pro-
panoate (15c). White solid, mp 63–658C; 1H NMR
(CDCl3): 7.63 (s, 1H), 7.55 (d, J¼7.2 Hz, 2H), 7.38 (d,
J¼7.2 Hz, 2H), 1.23 (s, 18H); 13C NMR (CDCl3): 176.2,
134.9, 131.7, 128.1, 123.6, 88.9, 38.8, 26.8; IR (Neat): 2973,
1748, 1281, 1160, 934 cm21; MS (m/z): 370 (Mþ). Anal.
calcd for C17H23BrO4: C, 55.00; H, 6.24. Found: C, 54.94;
H, 6.18.
4.2.1. 1,1-Diacetoxy-1-(4-biphenyl)methane (1b). White
1
solid, mp 128–1308C; H NMR (CDCl3): 7.75 (s, 1H),
7.67–7.6 (m, 6H), 7.48–7.46 (m, 3H), 2.17 (s, 6H); 13C
NMR (CDCl3): 168.9, 142.8, 140.4, 134.4, 128.9, 127.8,
127.4, 127.2, 127.1, 89.7, 20.9; IR (Neat): 1756, 1233, 1192,
959 cm21; MS (m/z): 284 (Mþ). Anal. calcd for C17H16O4:
C, 71.82; H, 5.67. Found: C, 71.68; H, 5.68.
4.2.8. Methyl 4-[bis(2,2-dimethyl propionyloxy)-methyl]-
benzoate (16c). Colourless oil; 1H NMR (CDCl3): 8.09 (d,
J¼8.1 Hz, 2H), 7.72 (s, 1H), 7.57 (d, J¼8.1 Hz, 2H), 3.95
(s, 3H), 1.25 (s, 18H); 13C NMR (CDCl3): 176.2, 166.5,
140.4, 131.0, 129.8, 126.4, 88.7, 52.3, 38.8, 26.8; IR (Neat):
2978, 1752, 1723, 1278, 1106 cm21; MS (m/z): 350 (Mþ).
Anal. calcd for C19H26O6: C, 65.13; H, 7.48. Found: C,
65.08; H, 7.42.
4.2.2. 1,1-Diacetoxy-1-(2-methoxy naphthyl)methane
(3b). Pale yellow solid, mp 133–1358C; 1H NMR
(CDCl3): 8.66 (s, 1H), 7.88 (d, J¼9 Hz, 2H), 7.8–7.77
(m, 2H), 7.29–7.26 (m, 2H), 4.01 (s, 3H), 2.09 (s, 6H); 13C
NMR (CDCl3): 169.0, 156.0, 132.5, 132.0, 129.7, 128.7,
127.1, 125.5, 124.0, 116.3, 113.0, 86.7, 57.5, 21.2; IR
(Neat): 1752, 1206, 1008, 947 cm21; MS (m/z): 288 (Mþ).
Anal. calcd for C16H16O5: C, 66.66; H, 5.59. Found: C,
66.53; H, 5.42.
4.2.9. (1E)-1-Phenylprop-1-ene-3,3-diyl bis(2,2-dimethyl
1
propanoate (17c). White solid, mp 76–788C; H NMR
(CDCl3): 7.43–7.25 (m, 6H), 6.84 (d, J¼16 Hz, 1H), 6.23
(dd, J¼6, 16 Hz, 1H), 1.22 (s, 18H); 13C NMR (CDCl3):
176.2, 135.3, 135.0, 128.6, 127.0, 122.1, 89.6, 38.8, 26.9; IR
(Neat): 2967, 1762, 1122, 984 cm21; MS (m/z): 318 (Mþ).
Anal. calcd for C19H26O4: C, 71.67; H, 8.23. Found: C,
71.63; H, 8.19.
4.2.3. 1,1-Diacetoxy-1-[2-(acetyloxy)-5-chloro phenyl]
methane (4b). White solid, mp 63–658C; 1H NMR
(CDCl3): 7.83 (s, 1H), 7.74 (s, 1H), 7.51 (d, J¼8.6 Hz,
1H), 6.99 (d, J¼6 Hz, 1H), 2.31 (s, 3H), 2.09 (s, 6H); 13C
NMR (CDCl3): 169.7, 169.0, 150.1, 135.2, 130.9, 128.2,
128.1, 124.2, 92.1, 20.9, 20.8; IR (Neat): 1756, 1732, 1237,
4.2.10. Compounds 2b, 5b and 6b,5 8b,15j 9b,15m 11b,20
12b,17 13b,14 14b and 15b,5 16b,35 and 17b.15l 1H NMR,
IR and mass spectral data of these known compounds were
identical with the reported data.
;
923 cm21 MS (m/z): 300 (Mþ). Anal. calcd for
C13H13ClO6: C, 51.93; H, 4.36. Found: C, 51.89; H, 4.32.
4.3. General procedure for the cleavage of acylal
4.2.4. 1,1-Diacetoxy-1-[4-(benzyloxy)-3-methoxyphenyl]
1
methane (7b). Light yellow solid, mp 82–848C; H NMR
A solution of acylal (1 mmol) and ZrCl4 (5 mol%) in
CH3OH (5 mL) was stirred at room temperature (generally
10–20 min). After complete conversion (TLC), solvent was
evaporated in vacuo, extracted with EtOAc, washed with
10% NaHCO3 solution and brine solution. The combined
organic layers were dried (Na2SO4) and evaporated to give
the corresponding aldehydes in good yields.
(CDCl3): 7.63 (s, 1H), 7.46–7.36 (m, 5H), 7.08–7.07 (m,
2H), 6.92 (s, 1H), 5.19 (s, 2H), 3.94 (s, 3H), 2.14 (s, 6H); 13C
NMR (CDCl3): 169.3, 148.4, 146.3, 140.6, 134.1, 128.7,
127.3, 127.2, 120.5, 115.1, 114.4, 92.3, 78.2, 56.9, 20.9; IR
(Neat): 1754, 1228, 938, 830 cm21; MS (m/z): 344 (Mþ).
Anal. calcd for C19H20O6: C, 66.27; H, 5.85. Found: C,
66.24; H, 5.78.
4.3.1. 4-Chloro-2-formylphenyl acetate (4a0). White
crystalline needles, mp 52–548C; 1H NMR (CDCl3):
10.08 (s, 1H), 7.87 (s, 1H), 7.61 (d, J¼8.6 Hz, 1H), 7.18
(d, J¼8.6 Hz, 1H), 2.41 (s, 3H); 13C NMR (CDCl3): 187.3,
169.0, 150.1, 135.1, 132.3, 130.4, 129.0, 125.1, 20.8; IR
(Neat): 2965, 1712, 1670, 1234, 918 cm21; MS (m/z): 198
(Mþ). Anal. calcd for C9H7ClO3: C, 54.43; H, 3.55. Found:
C, 54.39; H, 3.53.
4.2.5. 2-(4-Triisopropylsilyloxy phenyl) ethane-1,1-diyl
diacetate (10b). Colourless oil; 1H NMR (CDCl3): 7.08 (d,
J¼8 Hz, 2H), 6.89 (d, J¼8 Hz, 2H), 6.7 (t, J¼6.4 Hz, 1H),
3.2 (d, J¼6 Hz, 2H), 2.15 (s, 6H), 1.29–1.22 (m, 3H), 1.12
(d, J¼7.2 Hz, 18H); 13C NMR (CDCl3): 168.9, 153.5,
134.1, 129.6, 120.1, 84.4, 39.9, 21.1, 17.9, 12.6; IR (Neat):
1736, 1218, 1106, 946 cm21; MS (m/z): 394 (Mþ). Anal.