CHEM01200604012 Dibakar Goswami - Homi Bhabha National ...

4 Zn/ CuCl 2 , 2H 2 O 1 : 3.0 : 2.5 : 2.0 15 h 78.7 4.2 : 29.5 : 66.3
5 Zn/ SnCl 2 , 2H 2 O 1 : 3.0 : 2.0 : 2.0 45 min 80.4 11 : 78.2 : 10.8
a The reactions were carried out at 5 mmol scale. b Combined yields of isolated pure
products. c Based on isolated yields.
The spectral data and optical data resonances of the crotylated products 69a-c
corroborated with those reported. 3b For example, the 1 H NMR resonances of the –CH 2 O
protons of 69a appeared as three multiplets in the ratio of 1:1:2 protons at δ ∼3.3-4.2, those
for the compound 69b (more polar) were seen as multiplets (1:2:1) at δ 3.6-4.1 and for
compound 69c it appeared as two multiplets (1:3) at δ ∼3.5-4.1. They also showed typical
hydroxyl bands at ~3400 cm -1
in their IR spectra, and also the presence of olefinic
resonances in their 1 H NMR and 13 C NMR spectra. The 1 H NMR and 13 C NMR spectra of
69b and 69c are shown in Fig. III.1.5 and Fig III.1.6 (for 69b), Fig III.1.7 and Fig. III.1.8
(for 69c). The stereochemical assignments of these diastereomers are separately presented.
It is worth noting that the reactions with low valent Co and Fe gave 69b and 69c in
~1:1 ratio, whereas the reaction with Cu gave preponderance of 69c (entries 2-4, Table
III.1.2). In contrast, the low valent Sn mediated reactions yielded 69b as the major
product. (entry 5, Table III.1.2) with a good diastereoselectivity. These results are very
important from preparative point of view, since both the diastereomers 69b and 69c could
be obtained individually as the major diastereomers using different metal salts.
84