CHEM01200604012 Dibakar Goswami - Homi Bhabha National ...

Allylation with (E) and (Z)-1-bromo-2-nonene (78a/78b): Next we explored the efficacy
of the bi-metallic strategy for the allylation of 1 with another γ-substituted allylic bromide
78, using all the three designated metals. 118 The reaction was also performed following
Luche’s procedure. Further the E- and Z- isomers of the allylic bromide 78a/78b were
prepared and used separately for the reaction to examine the role of olefin geometry of the
bromide in dictating the steric course of the reaction.
The bromides 78a and 78b were prepared (Scheme III.1.5) from commercially
available propargyl alcohol 75 in good overall yields via a) C-alkylation with
bromohexane in the presence of LiNH 2 to furnish the propargylic alcohol 76, b) E-
reduction 119 of 76 with LiAlH 4 for 77a, and partial hydrogenation of 76 in the presence of
P-2 Ni catalyst 120 for 77b and c) bromination of the resultant E- and Z-allylic alcohols (77a
and 77b respectively) in two steps via mesylation and subsequent reaction with NaBr.
iii
C 6 H 13 OH
i C 6 H 13 77a
OH
OH
iv
75 76
C 6 H 13 OH
iv
v
C 6 H 13
C 6 H 13
78a
Br
Br
77b
78b
i) LiNH 2 , 1-bromohexane, liquid NH 3 , -33 o C; ii) LiAlH 4 , THF, Δ; iii) P-2 Ni, H 2 , EtOH,
25 o C; iv) MsCl, Et 3 N, CH 2 Cl 2 , 0 o C; v) NaBr, acetone, 25 o C.
Scheme III.1.5
Compound 78a was characterized by IR peak at 964 cm -1 , olefinic resonances at δ
5.52-5.84 ppm in 1 H NMR spectra and at δ 125.9 and 135.9 ppm in 13 C NMR spectra. The
other isomer, 78b was likewise characterized by NMR spectroscopy [ 1 H NMR at δ 5.59-
5.73 and 13 C NMR peaks at δ 125.1 and 135.5 ppm].
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