Page 240 - Advanced Organic Chemistry Part B - Reactions & Synthesis
P. 240
212 O 2 S
CH 3 CH 3
N
CHAPTER 2 CH 3
O
Reactions of Carbon O OTBS CH
Nucleophiles with 21A 3 H 3 C CH 3
Carbonyl Compounds N
2.5 eq TiCl 4 Ph
PhCH O
3.0 eq Bu N O O 86%
3
OH OTBS
3:1 syn
CH CH
CH 3 3 3 H C CH
1.1 eq TiCl 3 3
CH 4 CH N
3 3
CH O 1.1 eq i Pr NEt O 63%
2
O OTBS
OH 3:2 syn
CH 3 CH CH
3
2.2 eq TiCl 4
3 H 3 C CH
2.5 eq i Pr NEt 3 N
2
(CH ) CO C(CH ) CH O (CH ) CO C(CH )
2 3
2
3 3
2
2 3
3 3
O
HO O OTBS
84% yield
ds > 20:1
2.22. The facial selectivity of the aldehydes 22A and 22B is dependent on both the
configuration at the -center and the nature of the enolate as indicated by the
data below. Consider possible transition structures for these reactions and offer
a rationale for the observed facial selectivity.
TBDMSO OR 4 O TBDMSO OR 4 OH
CH O O
TBDPSO CH CH(CH )
+ 3 3 2 TBDPSO CH(CH )
3 2
CH
CH 3 CH 3 3
22A CH 3 CH CH 3
3
enolate R 4 3,4-syn:anti ratio enolate R 4 3,4-syn:anti ratio
Li MOM 97:3 Li TES 66:34
TiCl 4 MOM 84:16 TiCl 4 TES 60:40
Bu B MOM 63:38 Bu 2 B TES <5:95
2
(C H ) B MOM (C 5 H ) B TES 14:86
5 11 2 52:48 11 2
TBDMSO OR 4 O 4
TBDMSO
OR
OH O
CH O
TBDPSO CH 3 CH(CH )
)
+ 3 2 TBDPSO CH(CH 3 2
22B CH 3 CH 3 CH 3 CH CH
3 CH 3 3
enolate R 4 3,4-syn:anti ratio enolate R 4 3,4-syn:anti ratio
Li MOM 15:85 Li TES 7:93
TiCl 4 MOM 62:38 TiCl 4 TES 27:73
B Bu B
Bu 2 MOM 81:39 2 TES 45:55
(C H ) B MOM 50:50 (C H ) B TES 52:48
5
11 2
5
11 2
2.23. Predict the stereochemical outcome of the following aldol addition reactions
involving chiral auxiliaries.