Nitrile Oxides, Nitrones, and Nitronates in Organic Synthesis : Novel ...

326 NITRONES: NOVEL STRATEGIES IN SYNTHESIS
Bn
Bn
Bn
Bn
Bn
H
O N
O N
O N
O N
N
H
H H
H
H
H
H
H
O a
O
+
O
O
+ +
O
H O
H
OTs
O
H
H
O
H
OTs
OTs
O OTs
O
OBn
OBn
OBn
OBn
OBn
O
O
O
O
O
510 511 a syn 511 b anti 511 c syn
511 d anti
Re - face attack
Re - face attack Si - face attack Si - face attack
+
O
−
b
Cbz
N
R H
O
1
R
N
1
R2 R
c c N
1
R2 b
Cbz
N
H
R 1
R
O
H
R R
R
O
O
O
OH
H
R R
O
OH
R
R
512 c R = OH, R1 = H, 71%
512 d R = H, R1 = OH, 72%
512 a R = H, R1 = OH, 74%
512 b R = OH, R1 = H, 70%
513 c R = R2 = OH, R1 = H, 76%
513 d R = R1 = OH, R2 = H, 80%
514 c R = R2 = OAc, R1 = H, 80%
514 d R = R1 = OAc, R2 = H, 84%
513 a R = R1 = OH, R2 = H, 80%
513 b R = R2 = OH, R1 = H, 86%
514 a R = R1 = OAc, R2 = H, 80%
514 b R = R 2 = OAc, R 1 = H, 80%
Reaction conditions: a: (i) allyl alcohol, acetone, 70 ° C, 48 h, 95% (ii) TsCl, pyridine, 0 ° to 25 ° C, 2 h, 87% (syn:anti 76:24);
b: (i) HCOONH4, Pd/C, MeOH, 80 ° C, 1 h; (ii) CbzCl, NaHCO3, MeOH, 0 to 25 ° C, 2 h; c: (i) TFA-H2O (3:2), 25 ° C, 2 h; (ii) H2,
Pd/C, MeOH, 80 psi, 25 ° C, 12 h; d: Ac 2O, pyridine, DMAP, 0 ° to 25 ° C, 12 h.
Scheme 2.245