CHEM01200604012 Dibakar Goswami - Homi Bhabha National ...

For the allylation, compound 1 was treated separately with 78a and 78b following
Luche’s procedure as well as our own protocol (Scheme III.1.6). The results of these
studies are summarised in Table III.1.3. The Co- and Fe-mediated reactions with both 78a
and 78b took place very efficiently with similar rates as that in Luche’s procedure (Table
III.1.3). Unfortunately, the Co-mediated reactions proved abortive (entries 4 and 8, Table
III.1.3) even after stirring the mixture up to 15 h. It was interesting to note that compared
to the earlier case, the reactivity of Cu was considerably higher with the bromides 78a and
78b. Interestingly, in all the successful cases three of the four possible diastereoisomers
79a-c were produced with good overall yields. The syn,syn-isomer was not formed with
either of the reagents. Moreover, all the successful additions took place with a similar type
of diastereoselectivity yielding 79b and 79c as the major products and a very minor
amount of 79a. Of these, both Zn- and Cu-mediated additions afforded better 3,4-syn
selectivity with 78b with slight preponderance of 79b (entries 5 and 6, Table III.1.3).
O
1
O
CHO
i
78a
or
78b
O
O C 6 H 13 O
+
O
C 6 H 13
+
OH
OH
79a
79b
O
O
OH
79c
C 6 H 13
O
O
C 6 H 13
ii, iii
O
O
C 6 H 13
OH
79b
OH
79a
92