60c
reacted while
60d
failed. Similary,
The coupling of (Z)-vinyl sulfide
60g
gave product while (
E
)-
isomer, remained inert. It led to the conclusion that chelation
of magnesium atom between the alcohol functionality and the
proximal sulfur atom is important for the reaction, and seems
to
Scheme 27. Synthesis towards Ticumicin B
activate the C-S bond, probably favoring the Pd
0
oxidative
addition. The reaction was extended to Csp
2
Grignard
reagents (Scheme 29). (
Z
)-Vinyl sulfides reacted with
phenylmagnesium
bromide
and
2-naphtylmagnesium
bromides. But, vinylmagnesium bromides degraded and even
aromatic sulfides were not reactive under reaction conditions.
The ethylmagnesium bromide
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