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

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236 NITRONES: NOVEL STRATEGIES IN SYNTHESIS<br />

O<br />

N(OH)Bn<br />

OH<br />

Scheme 2.130<br />

Bn<br />

N<br />

O− +<br />

RM<br />

OH Bn<br />

N<br />

R OH<br />

a high tendency toward complexation <strong>and</strong> protonation at the N -oxide group,<br />

lead<strong>in</strong>g to the <strong>in</strong>crease of im<strong>in</strong>o character, <strong>and</strong> consequently to <strong>in</strong>creas<strong>in</strong>g electrophilicity.<br />

Complexation can take place <strong>in</strong> the addition of organometalics <strong>and</strong><br />

pre-complexation with Lewis acids. The protonation methods <strong>and</strong> prelim<strong>in</strong>ary<br />

complexation raises the possibility of employ<strong>in</strong>g a large number of various nucleophilic<br />

agents <strong>in</strong> nucleophilic additions to nitrones. This opens up a high synthetic<br />

potential for nitrones as build<strong>in</strong>g blocks <strong>in</strong> various synthetic strategies, <strong>and</strong> <strong>in</strong> the<br />

synthesis of biomolecules. The complexation potential of nitrone groups, both at<br />

the α-carbon atom <strong>and</strong> nitrogen atom, determ<strong>in</strong>es frequently the stereochemistry<br />

of addition reactions.<br />

HO<br />

HO<br />

COOH<br />

COOH<br />

L-tartaric acid<br />

MOMO OMOM<br />

Et3N, DMF<br />

88%<br />

N<br />

H<br />

H<br />

N<br />

Ph 3P, CCl 4<br />

OMOM<br />

MOMO OMOM<br />

OMOM<br />

N<br />

O −<br />

312<br />

OH<br />

+<br />

HCl, MeOH<br />

Δ 91%<br />

+<br />

1. H 2, Ni-Raney<br />

BnO<br />

2. HCONH 4, Pd/C<br />

76%<br />

Scheme 2.131<br />

THF, r.t. 82%<br />

d.e. 90%<br />

N<br />

OH<br />

MgBr<br />

MOMO OMOM<br />

H<br />

N<br />

OH<br />

OH<br />

(1S, 2S, 8aS)- 313<br />

OBn<br />

[a] D 20 =+2.8

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