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38
39
40
41
Scheme 10 Photoaddition step of a lactoside glycodendron - a: i. hv, MeOH, 75%,
ii. NaOMe, MeOH, 97%, iii. TFA, quant.
For the reductive amination step, a N-methylamine was used: a pre-
liminary work had shown that reaction on a primary amine could not be
stopped at the mono alkylation level, but continues to a partial bis
amination.
Thus, hydroxyl groups at the 6-position of 38 were converted
into bromo leaving groups and the bis bromo derivative was reacted
with benzylmethylamine and deprotected by hydrogenolysis to give
the diamine 42. The reductive amination with 41 in the presence
of sodium cyanoborohydride as reducing agent led to the
formation of the dendrimer 43 in moderate yield (48%) (Scheme 11).
It is worth to mention the comparable thyol-yne coupling (TYC),
which is a double hydrothiolation of alkynes. This extension of TEC
may facilitate construction of dendrimer, a few examples have been
described.
39
4.2 Thiolysis of 1,2-epoxide
Epoxide ring opening reaction with thiol is known in the literature
especially for the synthesis of the b-hydroxy sulfide moiety.
40-42
Its
regioselectivity can be modulated with pH conditions, in basic medium
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