CHEM01200604012 Dibakar Goswami - Homi Bhabha National ...

O
O
i
O
ii
O
CO 2 Et HO CO 2 Et
171 Bu 172
R 1 O H
O R 2
H
Bu
iii
173 R 1 = H, R 2 = CO 2 Et
174 R 1 = Me, R 2 = CH 2 OH
175 R 1 = R 2 = Me
O
O
Bu
H
CO 2 H
Me
176
iv
VII
(i) LDA, THF, HMPA, n-pentanal, -70 o C; (ii) (a) AcOH-H 2 O, NaIO 4 , 25 o C; (b) MeOH,
HCl, 25 o C; (c) LAH, Et 2 O, 25 o C; (d) TsCl, CH 2 Cl 2 , pyridine, DMAP, 0 o C; (e) LAH,
THF, 25 o C; (iii) (a) AcOH-H 2 O, 50 o C; (b) RuCl 3 .3H 2 O, NaIO 4 , CH 3 CN, H 2 O, CCl 4 , 25
o C.
Scheme IV.5.2
IV.5.3: Present work
In spite of their elegance, the earlier protocols were not conducive, since these used
reagents that are either expensive and/ or involved several steps. Hence using trans- oak
lactone (VII) as a model target, we developed its shorter and simpler synthesis than those
reported in literature.
For the synthesis (Scheme IV.5.4), the homoallylic alcohol 69c, obtained as the
major diastereomer via Ga-mediated crotylation of 1 in [bmim][Br] (discussed in the
previous chapter) appeared suitable for its elaboration to the target compound III. The
synthesis of VII started with the silyl derivative 128 of 69c. Hydroxylation of its terminal
olefin afforded the alcohol 177 in good yield. The formation of 177 was confirmed from
the absence of the olefinic peaks in both 1 H (Fig. IV.5.2) and 13 C NMR (Fig. IV.5.3)
spectra, as well as appearance of the IR hydroxyl peak at 3435 cm -1 . This was benzoylated
to get 178, which showed IR peak at 1719 cm -1 . The formation of 178 was also confirmed
179