Page 127 - Advanced Organic Chemistry Part B - Reactions & Synthesis

Scheme 2.3. (Continued) 99
C. Polar Control SECTION 2.1
11 i
O Aldol Addition and
O
CH O + BF 3 Condensation Reactions
N Ph N Ph
PMBO 75%
OTMS OH O
PMBO 90:10 3,5-anti:syn
12 j
TIPSO TBDMS CH TIPSO TBDMS
O OCH 3 3 OTMS BF O OCH 3
+ 3 OHO
CH O
CH 3 CH 3
CH 3 CH 3 –78°C CH 3
CH 3 CH 3 CH 3 CH 3
91%
13 k 8:1 3,5-anti:syn
TBDMSO TBDMSO OH
OTMS BF 3
CH O + C CO 2 C(CH )
3 3
(CH ) CH H 2 –78°C (CH ) CH 75%
3 2
)
14 l 3 2 OC(CH 3 3 CH > 95:5 dr
CH 3 3
CH 3 CH 3 CH CH 3 CH
CH 3 O 3 3 SC(CH )
CH O OTBDMS BF 3 CH 3 O 3 3
CH
PMBO 3 –78°C PMBO HO O 92%
+ SC(CH )
3 3
OCH 3 OCH 3 5:1 3,5-syn
CH Br
CH Br 2
15 m OTMS 2 OCH Ph
2
Ph OCH Ph O OH O
2
OCH 2 O BF 3
CH 3 2
CH 3 CH 3 + O CH CH 3 3 5 OCH 3
OCH 3
CH 3 CH 3 OCH 2 Ph
64% 2,3-anti-3,5-anti
21% 2,3-anti-3,5-syn
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PMBO CH 3 OPMB PMBO CH
+ 3
CH 3 O CH CH OPMB
TBSO OAr TBSO 3 OH
CH 3 CH 3
OLi
H CH CH 3 CH 3
R' OAr 3 CO Ar
2
Ar = 2,6-dimethylphenyl H O Li ds > 97%
R
O
CH3
H
Entries 3 and 8 show additions of a silyl thioketene acetal to -substituted
aldehydes. Entry 3 is under steric control and gives an 13:1 2,3-anti-syn ratio. The
reaction proceeds through an open TS with respect to the nucleophile and both the