Page 152 - Advanced Organic Chemistry Part B - Reactions & Synthesis

124 Scheme 2.7. Examples of Control of Stereoselectivity by Use of Additional Lewis Acid

CHAPTER 2
1 a O O O O OH
Reactions of Carbon 1) TiCl 4 or Ti(OiPr) 3
Nucleophiles with O N CH 3 (i-Pr 2 )NEt O N R R = i-Pr, Bu, Ph
Carbonyl Compounds 3 equiv
CH 3
2) RCH=O
CH(CH 3 ) 2
CH(CH 3 ) 2
2 b O O OH
O O
CH 3 1) Bu 2 BO 3 SCF 3 O N R
O N > 85% anti
2) RCH=O/Et 2 AlCl CH 3
CH(CH 3 ) 2
CH(CH 3 ) 2
R = Et, i -Pr, t -Bu, i -Bu, Ph
3 c S O OH
S O
1) 1 eq TiCl 4
CH 3 sparteine O N R
O N R = CH(CH 3 ) 2
–78°C CH 3
CH 2 Ph 2) RCH=O CH 2 Ph
70% yield, 97.6 ds
4 c S O OH
S O
1) 2 eq TiCl 4
CH 3 O N
O N i PrNEt 2 R R = CH(CH 3 ) 2
–78°C
CH 3
CH 2 Ph 2) RCH=O CH 2 Ph
87% yield, 94.9% ds
5 d S O S O OH
1) 2 eq TiCl 4
CH 3
O N 1.1. eqi Pr 2 NEt O N Ph
2) PhCH=CHCH=O CH 3
CH 2 Ph CH 2 Ph
6 e
O O OH
1) Et 2 BO 3 SCF 3
(i-Pr 2 )NEt
N N R R = Me, Et, i -Pr, Ph
2) RCH=O
CH 3
SO 2 SO 2
7 f
O O OH
1) Et 2 BO 3 SCF 3
(i -Pr 2 )NEt R = Me, Et, i -Pr, i -Bu, Ph
N N R
2) RCH=O/TiCl 4
CH 3
SO 2 SO 2
8 g OH OTBDPS
O O
OTBDPS 3 equiv Et 2 BOTf
+
N O=CH 2 equiv i Pr 2 NEt N
CH 3 83%
SO 2
SO 2
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