Chemistry Reference
In-Depth Information
Table 8.8
Enantioselective decarboxylative allylic amidation
O
[Ir(COD)Cl]
2
(2 mol %)
ligand (4 mol %)
Cbz
Cbz
HN
N
H
O
Proton Sponge™ (
1
)
(1 equiv)
R
R
DBU (1 equiv), THF, rt
ligand
R
yield (%)
ee (%)
OMe
Me
Me
92
94
O
P
N
O
Me
Me
80
92
OMe
80
> 99
catalyst, and both DBU and Proton Sponge (1) were found to be vital for high yield and
enantioselectivity (Table 8.8).
Reaction of an aniline derivative and ethyl methylthioacetate in the presence of sulfuryl
chloride and Proton Sponge (1) generated an azasulfonium salt, which showed [2,3]-
rearrangement under basic conditions to give oxindole (modified Gassman oxindole
synthesis [31]) [32]. In this reaction, Proton Sponge (1) plays a role as a hydrogen chloride
scavenger. When the reaction was carried out with tert-butyl methylthioacetate,
o-aminophenylacetic acid derivative was obtained [33] (Scheme 8.10).
8.5 Palladium Catalysed Reaction
Proton Sponge (1) sometimes drastically affects the enantiomeric excess and yield in the
asymmetric palladium catalysed Heck reaction.
Ozawa et al. reported the Pd(OAc)
2
-BINAP catalysed asymmetric intermolecular Heck
reaction of aryl triflate and 2,3-dihydrofuran in the presence of a base [34]. In this reaction,
the enantiomeric excess was significantly affected by the base, and Proton Sponge (1)gave
the best results among the various bases, such as triethylamine, diisopropylethylamine,
pyridine derivatives and inorganic bases (Table 8.9).
In the case of intermolecular Heck alkenylation of vinyl triflate and 2,2-disubstituted-
2,3-dihydrofuran, Proton Sponge (1) gave higher chemical yield and enantioselectivity
compared to the trialkylamines [35] (Table 8.10).
Kiely and Guiry reported an asymmetric version of the intramolecular Heck reaction of
aryl triflate [36]. In this reaction, Proton Sponge (1) also greatly improved the reactivity,
