CHEM01200604012 Dibakar Goswami - Homi Bhabha National ...

Scheme IV.1.1
The same group also developed a new chiral auxiliary 144f derived from (S)-(−)-1-
phenylethylamine to obtain crystalline intermediates with moderate diastereoselectivity,
50–69% de, which could be increased to 99% de after two recrystallizations (10% overall
yield).
Pelotier et al. 144g
reported the synthesis of V via diasetereoselective
photodeconjugation of diacetone-D-glucosyl α,β unsaturated ester 97 bearing a propyl
chain at the α-position. For this, the required acid 96 was synthesized by alkylation of
ethylphosphonoacetate 95, Wittig-Horner reaction and saponification. Diastereoselective
photoisomerisation of 97 proceeded with 72:28 enantiomeric ratio of E- and Z- isomers.
Quantitative hydrogenation followed by removal of auxiliary gave V in 88% ee (Scheme
IV.1.2).
OEt P O
O
P
OEt
i-iii
C 4 H 9
O
OH
iv
O
O
O
O
O
C 4 H v, vi 9
vii
O O C 6 H 13
O O
O
O
95 96 97 98
O
V
i) t-BuOK, C 3 H 7 Br, NaI, DMSO, 65 o C; (ii) NaH, hexanal, THF, 0 o C-25 o C; (iii) KOH,
H 2 O/EtOH, 80 o C; (iv) diacetone-D-glucose, DCC, DMAP, CH 2 Cl 2 , 0 o C-25 o C; (v) hν
(254 nm), N,N-dimethylaminoalcohol, CH 2 Cl 2 , -40 o C; (vi) H 2 , PtO 2 , Et 2 O, 25 o C; (vii)
LiOH.H 2 O, H 2 O 2 , 25 o C.
Scheme IV.1.2
140