Suppression Of Racemization During The Scholarblogs Page 2

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cuprate. the use of higher order cqrrates. to-l*‘Lewls acid add&n to increase reaction rate or any other variants which
allow the desired reaction to proceed at tow temperatures. 13.14 Wtih butenolii
0, an addff
probfem could manifest
itself. The considerable increase in the acidity of the proton at C-4 upon introduction of both the C-2X-3 double bond and
the P-thiophenyl group could potentially lead to the racemization of the previously set C-4 stereocenter due to intermediate
dienolate formation.
’
Scheme 2:
The initial results of this study of the 1. rlorgenocuprate addftff (Tabta I) were in accord with this exp&ation.
Our introductory studies used lithium dknethyl cuprate, acoording to the method of House et al.‘* ( except that 1 .O4
Table I:
PO
1. Mf&CULU L.O.
2. Ma&ULU L.O.
3. Me&uLV L.O.
.__________________
4. R’RkuCNL~
I H.O.
5. R’RaCuCNLh I H.O.
___________-_____-.
s. (vhlyf)acklw L.O.
7. (vtnyl)~uLf/
L.O.
8. (Ph)2CuLU L.O.
8. (Ph)2CuLU L.O.
______________-___
10. “(I-Pr)Cu”/ Cat.
-78°C
I
24h
Ms
OOC
4h
Me
I I
. ..No R&n
28%c13%)
0-25=C
14h
Me
a456 VW
____________________________________
-78 -0X
0.5h
vlnyl
I
I
I
-78-0°C
0.6h
vfnyl
_____________________
-7&C
lh
vfnyl
-78°C
lh
vfnyl
-78°C
lh
Ph
-78-0X
4h
Ph
_____________________
-78°C
1
3.5h
1 I-Pr
1
8596 VW
1~w-w
____________.
1aoK (SS.7%)
tJg.8fj%Fx)
lw%
(t&I%)
lftg%cn%)
____________
lgg%(=%)
l
RI= Whknyl;
R* = vinyl; L.O. = Lowu om
H.O. = Higher ordq
“(f-Pr)Cu” = cuprats
formsd frwm i-PM,gCl and oat~fytfo wr
bmmids dfmothyl rufffdo compfsxi8
# all products wers fulfy characterked
by both proton and carbon 13 NMR,
combustion analysis.
IR., and low r.soMon
mass qzaotrosoo~y

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