Biomedical Engineering Reference
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AuCl (5 mol%), AgSbF
6
EtOH (10 equiv)
THF/CH
2
Cl
2
(1:1), rt, 30-60 min
CO
2
Et
OH
91%
OEt
(
E
/
Z
: 97/3)
SCHEME 8.34
Gold-catalyzed Meyer-Schuster rearrangement.
alkyne moiety by gold catalysts such as AuCl
3
has considerably expanded the interest
and scope of the Meyer-Schuster rearrangement by limiting side reactions [159,160]
(Scheme 8.34). After screening different Lewis acids [160a,b], the use of less
expensive catalysts such as InCl
3
[161] or Sc(OTf)
3
proved more convenient as a
lower catalyst loading was required (1 mol%) to perform the rearrangement [160c].
Moreover, it is worth pointing out that various oxo complexes of transition
metals such as vanadium(V) [162], molybdenum(VI) [163], ruthenium [164], or
rhenium(VII) [165] also promote the Meyer-Schuster rearrangement.
Similarly, the activation of propargylic alcohols as acetates or related carboxylic
esters has resulted in particularly interesting results as the Meyer-Schuster rearrange-
ment products could be obtained without any by-products. The basis of this approach
relies on the well-known [3,3]-sigmatropic rearrangement of propargylic acetates
promoted by indium [160c], palladium [166], mercury [167], copper catalysts, or
PtCl
2
[168], which affords acetoxy allenes that undergo hydrolysis to provide the
corresponding
a
,
b
-unsaturated ketones (Scheme 8.35). Again, gold complexes
appeared as the catalysts of choice, Au(PhP)NTf
2
leading to the best results [169].
Nolan and coworkers recently reported new conditions based on the use of
(NHC)Au(I) that allowed a larger substrate scope in the Meyer-Schuster rearrange-
ment (Scheme 8.36) [170].
In this context, acyloxylated divinyl ketones were conveniently formed
by a new gold(I)-catalyzed rearrangement of (3-acyloxyprop-1-ynyl)oxiranes
(Scheme 8.37) [171].
Unfortunately, due to various drawbacks, the Meyer-Schuster rearrangement
has rarely been used in total synthesis. However, several examples have been
reported showing the potential of this rearrangement for the preparation of various
InCl
3
(1 mol%)
CH
2
Cl
2
/EtOH (1:1), 24
h
70%
OH
CO
2
Et
C
5
H
11
C
5
H
11
OEt
(
E
/
Z
= 84:16)
Hg(OTf)
2
(1 mol%)
H
2
O (1 equiv)
COCH
3
PtCl
2
(5 mol%)
AcO
CO
2
Et
OEt
CH
2
Cl
2
Ph
CH
2
Cl
2
, 40 min
77%
Ph
Ph
CO
2
Et
81%
(
E/Z
: 1/1)
[Cu(CH
3
CN)
4
][BF
4
] (5 mol%)
CH
2
Cl
2
84%
COCH
3
Ph
(
E/Z
= 9:1)
CO
2
Et
SCHEME 8.35
Meyer-Schuster rearrangement of propargylic derivatives.
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